AWUS01 KWNH 301933
FFGMPD
MAZ000-CTZ000-NYZ000-NJZ000-PAZ000-310125-

Mesoscale Precipitation Discussion 1220
NWS Weather Prediction Center College Park MD
332 PM EDT Thu Oct 30 2025

Areas affected...northern NJ into southern NY/Long Island and CT

Concerning...Heavy rainfall...Flash flooding possible

Valid 301931Z - 310125Z

Summary...Heavy rain across the Tri-State Area through this
evening may result in localized flooding/flash flooding. Localized
rainfall totals over 3 inches will be possible. Rainfall near 1
inch in 15-30 minutes can be expected.

Discussion...19Z radar imagery showed a low-topped squall-line,
oriented from south to north, edging east from 40 miles east of
ACY through NYC. This line was being aided by strong low level
convergence with 45-50 kt from the SSE/SE in the 925-850 mb layer,
located north of the triple point of an occluded cyclone over the
northern Mid-Atlantic region. The line of showers has been
accompanied by 0.50 to 1.00 inches of rain in 15 minutes across
northern NJ into the Five Boroughs.

Moisture from the Mid-Atlantic coast into southern New England was
already anomalous as sampled by area 12Z RAOBs, with PWAT values
of 1.2 to 1.5 inches. However, OSPO's ALPW has since shown an
increase stemming from Melissa's circulation, especially near and
below 700 mb, being drawn northward into NJ and southern NY. The
continued addition of this remnant tropical moisture should allow
for an increase in rainfall efficiency and locally higher rainfall
rate potential into the early evening hours.

While the line of showers has been progressive, there is some
concern for very brief slowing/stalling given the LEWP-like
appearance off the NJ coast, which could result in a quick 1-2
inches as this line continues to advance east through the
remainder of the afternoon. As a triple point low becomes better
organized south of Long Island this evening, low level flow will
maintain a southeasterly orientation, with possible backing.
Therefore, some orographic component to lift will be added into
the equation for the higher terrain north and west of I-95,
combining with increasing right-entrance jet ascent associated
with a forecast 130 kt jet streak on the east side of the parent
upper low to the west.

Farther south and west, instability is expected to remain weak
(briefly peaking in the 500-1000 J/kg range) but perhaps
sufficient to support a few additional heavy showers from eastern
PA and southern NJ, rotating northward into the Tri-State region.

Additional rainfall may result in isolated areas of rapid
inundation of water. Given below average rainfall over the past
few weeks and ongoing drought conditions across portions of the
region, any flooding that occurs is likely to remain constrained
to urban or other areas with poor drainage.

Otto

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9FIRi1NKBOaCg4MfFWriOWtP0K6LX9dCRMYV3e6rRPxWaiMPuzVhGNzgIyu1jio3gLQk= znq132MoWRgl8CwwSNIVZGE$ for graphic product...

ATTN...WFO...ALY...BGM...BOX...OKX...PHI...

ATTN...RFC...RHA...TAR...NWC...

LAT...LON 42367414 42157352 42087251 41907210 41397212=20
40707286 40387404 40737491 41357535 42037519=20
42327478=20

=3D =3D =3D
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AWUS01 KWNH 130959
FFGMPD
CAZ000-ORZ000-132158-

Mesoscale Precipitation Discussion 1221
NWS Weather Prediction Center College Park MD
458 AM EST Thu Nov 13 2025

Areas affected...much of central and northern California

Concerning...Heavy rainfall...Flash flooding likely

Valid 130958Z - 132158Z

Summary...Heavier downpours should result in instances of urban
flooding around San Francisco and vicinity during and after
morning commute. Heavier rainfall will also spread into more of
northern and central California from 13Z/6a PT through the
evening. Flash flooding is expected especially near burn scars,
urban areas, and other terrain-favored spots.

Discussion...As of 0955Z, a band of convection was beginning to
organize along a front extending from near 80 miles southwest of
Eureka to 180 miles southwest of Monterrey. Individual convection
along this band was streaming northward at a decent clip.=20
However, the band was only moving slowly eastward and already
favoring areas of repeating over open waters. 500 J/kg MUCAPE and
areas of 1.3+ PW values were supporting the convective band, and
MRMS data was already estimating 0.5-0.7 inch hourly rain rates
over land just southwest of Eureka.

The convective band and associated mid-level system are expected
to make only slow eastward progress toward more land areas of
California today. As the systems approach, low-level wind fields
will strengthen, colliding with terrain and locally enhancing rain
rates in many areas. Rates could reach 1 inch/hr on a localized
basis. These rates will overspread portions of the San Francisco
Metro beginning in the 12Z/5a PT hour and persist through the
afternoon, impacting morning rush with wet roads and areas of
excessive runoff. Portions of north-central through east-central
California will also experience terrain-enhanced heavy rainfall,
with some of the heavier rates (exceeding 0.75 inch/hr) falling on
sensitive ground conditions and burn scars. Flash flooding is
expected on at least an isolated basis. These areas could include
terrain near/north of Redding (beginning around 13Z/6a PT) and
upslope areas of the Sierra (near/east of Chico) beginning around
14Z/7a PT. Heavy rainfall could last for 8-12 hours in many of
the aforementioned areas, with totals of 3-5 inches likely through
00Z Fri Nov 14.

Again, at least a few instances of flash flooding are expected
given the scenario.

Cook

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5VKp-a7ebjiWmrdoxeWU409Xa9908ABb97wCJOe4OanaamOWmB6toVZM_1LbzpdVv3ry= Zvl45SPmtpirwxkshqXUjlM$ for graphic product...

ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...STO...

ATTN...RFC...PTR...RSA...NWC...

LAT...LON 42252315 42102191 41712116 41262098 40792092=20
40142070 38461980 37801954 36581993 35282051=20
35472124 37712319 40152469 41802483 42162420=20 =20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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AWUS01 KWNH 132136
FFGMPD
CAZ000-140900-

Mesoscale Precipitation Discussion 1222
NWS Weather Prediction Center College Park MD
435 PM EST Thu Nov 13 2025

Areas affected...western Transverse Ranges into central CA and
northern Sierra Nevada

Concerning...Heavy rainfall...Flash flooding possible

Valid 132133Z - 140900Z

Summary...Flash Flood potential will extend into the evening and
overnight hours from portions of the northern Sierra Nevada into
much of central CA and the western Transverse Ranges. Peak hourly
rainfall of 0.5 to near 1.0 inches is expected along with peak 12
hour rainfall values of 2 to 4 inches through 09Z.

Discussion...21Z radar imagery and GOES West infrared satellite
imagery showed a band of moderate to heavy rain extending from
Monterey Bay and the northern Santa Lucia Range into the eastern
Pacific, out ahead of a Pacific cold front. The cold front has
been steadily advancing east since this morning and was preceded
by an atmospheric river containing max PW values of 1.3 to 1.5
inches along the coast and just offshore. Within this plume were S
to SSW 850-700 mb winds of 40 to 50+ kt, supporting earlier hourly
rainfall of 0.7 to near 1 inch across the Santa Cruz Mountains. A
number of reports of flooding and debris flows have been observed
since earlier this morning, in and around the San Francisco Bay
region down to Monterey Bay.

As a closed low centered near 41N 128W and southward extending
trough/low, as seen on water vapor imagery, continues to advance
closer to the coast, some weakening of the mid-level low is
expected as the system continues to mature and evolve. The cold
front will maintain a slow but steady movement toward the east but
a ~10 kt weakening of the 850-700 mb winds is expected as the
moisture axis advances downstream ahead of the cold front. This
weakening will correspond to a lowering of IVT values over land,
maxing out in the 600-800 kg/m/s range through 09Z Friday.

Occasional peak hourly rainfall of 0.5 to ~1 inch is expected to
be focused within locations where low level winds will focus into
S to SW facing terrain. The most likely locations for these higher
rates will be within the Coastal Ranges and Sierra Nevada but any slowing/stalling of a band of weak convection across the San
Joaquin Valley will also have the potential to produce these
higher rates given the moisture already present and weak MLCAPE up
to 500 J/kg forecast by the RAP.

Most instances of flooding/flash flooding are expected to be
minor, but will be most probable across urban and other flood
prone locations. However, localized occurrences of more impactful
flash flooding will be possible where overlap of heavy rain occurs
with any sensitive burn scars and terrain with potential for
debris flows.

Otto

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6vhVfx5PrvXg1YFxrXbaLnPzE8TiC_lEuN1IOc2Kw_1rXYSFvDpdUCX5jP9z4cFbAig2= v04FN10JYa31QCEWqszhT5M$ for graphic product...

ATTN...WFO...HNX...LOX...MTR...REV...STO...

ATTN...RFC...RSA...NWC...

LAT...LON 40682176 40442144 39982074 39642050 39382033=20
39082023 38842014 38692005 38551994 38481986=20
38361970 38241972 38131973 38081971 37921946=20
37821936 37701937 37601929 37511915 37431904=20
37151884 36991877 36861884 36661952 36832010=20
36462052 35822041 35232021 34941972 34421932=20
34271951 34302044 34462098 35252146 35842184=20
36472222 37032175 38842141 40302192=20

=3D =3D =3D
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AWUS01 KWNH 140920
FFGMPD
CAZ000-141518-

Mesoscale Precipitation Discussion 1223
NWS Weather Prediction Center College Park MD
420 AM EST Fri Nov 14 2025

Areas affected...portions of southern California

Concerning...Heavy rainfall...Flash flooding likely

Valid 140918Z - 141518Z

Summary...Flash flood potential continues across portions of
southern California for at least another 4-6 hours. Areas of 2-3
inch rainfall totals are expected that could cause excessive
runoff and debris flows.

Discussion...Flash flood potential will continue through at least
15Z/7a Pacific Time this morning. A fetch of strong onshore flow
continues just ahead of a cold front along the coast extending
from near PRB near VBG. Just ahead of this front, mesoanalyses
indicate a focused area of 35 knot 850mb flow oriented
perpendicular to the western Transverse Ranges (Santa Barbara and
Ventura Counties). This orientation, ~1.5 inch PW, and modest
instability was supporting repeating heavy rainfall at times
across the discussion area. The repeating nature of the rain was
resulting in spots of 1 inch/hr rain rates in local areas from the
Santa Ynez mountains through the Sierra Madre mountains and
surrounding areas. Low spots were responding with runoff over
area roadways over the past few hours, and reports of flooding
have been received in the discussion area near Highway 101.

The ongoing scenario will continue for another 4-6 hours or so.=20
The mid-level system partially responsible for the ongoing heavy
rainfall hazard has stalled, and the attendant cold front will
also become stationary. Meanwhile, 35 knot 850mb flow will
continue to impinge on the Transverse Ranges and prompt several
hours of intermittent heavy rain. The very high PW values and
local burn scars yield concern that locally significant flash
flooding could occur. Rainfall totals of 2-3 inches are also
possible in a few spots through 15Z.

At some point around/after 15Z, 850mb wind fields should slacken
some and result in a gradual lessening of heavy rainfall potential
especially after 15Z.

Cook

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-YSANlPNsKgyhhxUH_7CB_jGnyTop2DRWsmPl_jtGQwo0EXHDv54zvvlmZJGVIBF9zjD= uJIxqChoHOgAm-IC_6FrKYQ$ for graphic product...

ATTN...WFO...HNX...LOX...

ATTN...RFC...RSA...NWC...

LAT...LON 35782038 35561882 34761781 34121776 33911846=20
34422009 34702073 35072071 35342098=20

=3D =3D =3D
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AWUS01 KWNH 140922
FFGMPD
CAZ000-141518-

Mesoscale Precipitation Discussion 1223
NWS Weather Prediction Center College Park MD
421 AM EST Fri Nov 14 2025

Areas affected...portions of southern California

Concerning...Heavy rainfall...Flash flooding likely

Valid 140918Z - 141518Z

Summary...Flash flood potential continues across portions of
southern California for at least another 4-6 hours. Areas of 2-3
inch rainfall totals are expected that could cause excessive
runoff and debris flows.

Discussion...Flash flood potential will continue through at least
15Z/7a Pacific Time this morning. A fetch of strong onshore flow
continues just ahead of a cold front along the coast extending
from near PRB near VBG. Just ahead of this front, mesoanalyses
indicate a focused area of 35 knot 850mb flow oriented
perpendicular to the western Transverse Ranges (Santa Barbara and
Ventura Counties). This orientation, ~1.5 inch PW, and modest
instability was supporting repeating heavy rainfall at times
across the discussion area. The repeating nature of the rain was
resulting in spots of 1 inch/hr rain rates in local areas from the
Santa Ynez mountains through the Sierra Madre mountains and
surrounding areas. Low spots were responding with runoff over
area roadways over the past few hours, and reports of flooding
have been received in the discussion area near Highway 101.

The ongoing scenario will continue for another 4-6 hours or so.=20
The mid-level system partially responsible for the ongoing heavy
rainfall hazard has stalled, and the attendant cold front will
also become stationary. Meanwhile, 35 knot 850mb flow will
continue to impinge on the Transverse Ranges and prompt several
hours of intermittent heavy rain. The very high PW values and
local burn scars yield concern that locally significant flash
flooding could occur. Rainfall totals of 2-3 inches are also
possible in a few spots through 15Z.

At some point around/after 15Z, 850mb wind fields should slacken
some and result in a gradual lessening of heavy rainfall potential.

Cook

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4kVz9ErDHVyIU0guZRGqc4RFSQxsXmSIXWegJ3Ytu8QbMk0sfY-OKaCW6SphBZsXzoCo= 9UcW436tz7Mjxjo7OEZcotY$ for graphic product...

ATTN...WFO...HNX...LOX...

ATTN...RFC...RSA...NWC...

LAT...LON 35782038 35561882 34761781 34121776 33911846=20
34422009 34702073 35072071 35342098=20

=3D =3D =3D
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AWUS01 KWNH 151010
FFGMPD
CAZ000-152209-

Mesoscale Precipitation Discussion 1224
NWS Weather Prediction Center College Park MD
510 AM EST Sat Nov 15 2025

Areas affected...portions of southern California

Concerning...Heavy rainfall...Flash flooding likely

Valid 151009Z - 152209Z

Summary...Heavy rainfall will become more likely - especially
beginning around the 14Z/6a Pacific timeframe. Rain rates
reaching 1 inch/hr are possible with this activity. Flash flood
potential will increase - especially across burn scars and other
low-lying, urban, and sensitive areas.

Discussion...Convection was beginning to deepen and move northward
across open waters adjacent to the southern California coastline
this morning. This convection was materializing in response to a
deep cutoff low centered near 32N, 124.5W that was beginning a
slow migration eastward toward the discussion area. On the
eastern periphery of this low, a very moist airmass was in place,
with PW values ranging from 1 inch near coastal areas to 1.6 inch
just offshore. Weak instability and modest forcing for ascent
over land areas are limiting factors for heavier rainfall
potential in the short-term and toward 14Z or so.

Later this morning, a belt of stronger southerly flow at 850mb
will develop toward coastal areas extending from the LA Basin
southward along the San Diego County coastline. Some of this flow
will interact favorably with coastal ranges (particularly the
Transverse) to promote an increasing risk of heavier rainfall.=20
Quick moistening is also expected to accompany this flow over
those areas. Rain rates should come up in tandem with approaching
ascent and orographic lift, and areas of 1 inch/hr rain rates
should occur on a more frequent basis. At least a few instances
of flash flooding/excessive runoff are expected. Furthermore,
these rain rates should occur over local burn scars, prompting
dangerous debris flows in some areas. Locally significant impacts
will become possible in this regime.

Heavy rain potential will persist through at least 2200Z/1p
Pacific Time today and beyond as the upstream mid-level wave makes
only slow/gradual progress toward land areas.

Cook

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7NmB96X_gKbvDQtUDkadiStzOtx5MFz8wPRwxfJkWWbtUL3__jOs9ytla2zeqyDQiJR4= -PFtCV8FgDw9DOF9htvwyZs$ for graphic product...

ATTN...WFO...HNX...LOX...PSR...SGX...VEF...

ATTN...RFC...RSA...NWC...

LAT...LON 35351981 35191853 34841736 34211654 33441614=20
32791601 32561639 32561714 33101753 33641831=20
34191949 34552052 35082065=20

=3D =3D =3D
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AWUS01 KWNH 151919
FFGMPD
AZZ000-NVZ000-CAZ000-160115-

Mesoscale Precipitation Discussion 1225
NWS Weather Prediction Center College Park MD
219 PM EST Sat Nov 15 2025

Areas affected...Desert regions of CA into southern NV and far
western AZ

Concerning...Heavy rainfall...Flash flooding possible

Valid 151917Z - 160115Z

Summary...Periods of heavy rain should become likely across the
desert regions of eastern/southern CA into southern NV and far
western AZ through 01Z. Peak hourly rainfall between 0.5 and 1.0
inches (locally higher) is expected which may result in isolated
to widely scattered instances of flash flooding.

Discussion...Radar mosaic imagery across southern CA into southern
NV at 19Z showed an arcing band of heavy showers continuing to
move inland, from the Peninsular Ranges toward the far southern
San Joaquin Valley. Observed hourly rainfall within this axis has
been in the 0.5 to 0.9 inch range over the past 2-3 hours.
Additional showers were noted from just west of the lower CO River
into western Clark County in southern NV with MRMS-derived hourly
rainfall in excess of 1 inch in eastern Imperial County. These
showers were forced in response to lift ahead of a negatively
tilted shortwave trough located ~100 miles off of the southern CA
coast, swinging toward interior southern CA. In addition,
divergence and diffluence were increasing across southern CA
within the left-exit region of a 90-110 kt upper level jet max
located just south of the shortwave trough axis. Moisture was
highly anomalous for mid-November with regional PW standardized
anomalies of 4 to 5+ throughout the area, with a source region
stemming from the tropical eastern Pacific as seen on OSPO ALPW
imagery.

As the closed low and negatively tilted shortwave trough continues
to advance east over the next 6 hours, low level moisture will
continue to advect into the deserts with a transient swath of 6.0
to 6.5 C/km 700-500 mb lapse rates (coincident with the shortwave)
which should help to briefly boost instability, despite the lack
of surface heating beneath clouds/rain. Also of note were the
850-700 mb winds oriented from the southeast at 30-35 kt over
south-central CA, forcing an upslope component along the eastern
slopes of the southern Sierra Nevada. With little change to the
low to mid-level wind fields anticipated over the next 3-6 hours,
steady upslope forced heavy rain is expected into the terrain.
Farther east, embedded higher rainfall rates are expected to
develop through the afternoon within the scattered
shower/stratiform rain regime. While CAPE values are generally
forecast to stay below 500 J/kg (outside of the lower CO Valley),
the anomalous moisture source should contribute to embedded higher
rainfall values with periods of brief training, allowing for
hourly rainfall in the 0.5 to 1.0 inch range (locally higher).
Peak total rainfall of 1 to 2 inches is expected (locally higher
near terrain) through 01Z which may result in areas of flash
flooding.

Otto

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9thXAR0MeAzY90w6Y5yt960fJNwMeBjCZqbAGy3VOG4ggdTCBbyCvWQaMI4GnO868aiI= 9KlPp1Z91dR8bBP6ueFEqGI$ for graphic product...

ATTN...WFO...HNX...LKN...LOX...PSR...REV...SGX...VEF...

ATTN...RFC...RSA...STR...NWC...

LAT...LON 38051725 37481583 36161447 35111412 33431409=20
32231432 32471532 32481594 33171615 33501626=20
33671637 33951653 34111664 34231678 34311702=20
34391729 34501763 34651808 34781841 34911860=20
35061867 35231863 35381859 35491856 35641849=20
35721842 35801837 35891833 35961828 36081823=20
36181815 36311810 36411813 36481817 36601822=20
36661826 36751829 36851834 36931837 37031839=20
37121843 37211847 37261852 37321860 37421865=20
37621866 37861848 38041808=20

=3D =3D =3D
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AWUS01 KWNH 152035
FFGMPD
CAZ000-160230-

Mesoscale Precipitation Discussion 1226
NWS Weather Prediction Center College Park MD
335 PM EST Sat Nov 15 2025

Areas affected...portions of southern CA

Concerning...Heavy rainfall...Flash flooding likely

Valid 152033Z - 160230Z

SUMMARY...The flash flood threat will continue for coastal CA into
the Transverse and Peninsular Ranges through 02Z. While the
main/widespread threat of flash flooding is expected to wane over
the next couple of hours, a lingering threat for more localized
but potentially significant flash flooding will remain.

DISCUSSION...Radar mosaic imagery at 20Z showed a band of moderate
to heavy rain that extended from the southern San Joaquin Valley
into some of the Valley/Desert regions east of the Peninsular
Ranges. This axis of heavier rain has been following a plume of
highly anomalous moisture translating eastward as seen on OSPO
ALPW imagery, out ahead of a negatively tilted mid to upper level
shortwave trough axis and vorticity max just west of the CA/MX
border. Additional heavy rainfall appeared in the waters just east
of Santa Catalina and San Clemente Islands, tied to the eastern
lobe of the mid/upper level shortwave. Rainfall over the past 6
hours has peaked near 1 inch for coastal locations into the
Peninsular Ranges while 1 to 2+ inch values have been observed
within portions of the Transverse Ranges, with hourly rainfall
between 0.5 and ~1.0 inches.

While relatively drier air was moving into southern CA as of 20Z,
the moisture remains anomalous with PW values of ~1.0 to 1.3
inches and despite continued drying of the layer, sufficient
moisture will remain through the evening to support localized high
rainfall rate potential. As the closed upper low center continues
to slowly edge closer to the coast, 700-500 mb lapse rates will
increase into the 6.5 to 7.0 C/km range and support localized
MLCAPE values in excess of 500 J/kg near the coast. Lift will also
be aided by left-exit region divergence/diffluence corresponding
to a 100 kt upper level jet max positioned south of the upper low
center. Hourly rainfall in the 0.5 to 1.0 inch range is expected,
though localized spot training could exceed these values and/or
support 0.5 to 1 inch of rain in about 30 minutes. The combination
of continued forcing and increased ground sensitivity due to
today's rainfall will likely support continued areas of flash
flooding over the next few hours. This will especially be true
where additional areas of heavy rain overlap with urban areas and
burn scars where localized higher impacts could occur. Within
sensitive burn scar regions, high rain rates are likely to result
in mudslides and debris flows.

Otto

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_j_67JJhFHvq_oLXeomayUqUVfoafWQU8SimSG6NwI_NxuB5p1MdyqdZT-jj6t1orl4x= bP4V2_PJ0kcdmAeJVjLQtOk$ for graphic product...

ATTN...WFO...HNX...LOX...SGX...VEF...

ATTN...RFC...RSA...NWC...

LAT...LON 35541966 35531858 35111811 34381686 33961642=20
33361612 32881611 32461613 32451668 32421710=20
32521739 32741783 33201827 33431858 33891947=20
34462098 35302118=20

=3D =3D =3D
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AWUS01 KWNH 171004
FFGMPD
CAZ000-171600-

Mesoscale Precipitation Discussion 1227
NWS Weather Prediction Center College Park MD
503 AM EST Mon Nov 17 2025

Areas affected...portions of northern and central California

Concerning...Heavy rainfall...Flash flooding possible

Valid 171001Z - 171600Z

Summary...A stout mid-level wave west of Eureka was prompting
scattered shower and thunderstorm activity across a broad part of
northern and central California. These trends will continue for
the next few hours, and areas of 0.5-0.75 inch/hr rain rates are
possible. A few instances of flash flooding could occur in
sensitive areas and near burn scars.

Discussion...A vigorous mid-level wave was providing ascent for
several areas of convection 1) just west of Eureka over open
Pacific waters and 2) along an axis from Redding south-southwest
to near Monterrey. Over the past hour, more robust convective
activity (with lightning) developed near/south of San Francisco
and moved inland. Both of these regimes were responsible for
areas of 0.5-0.75 inch/hr rain rates. The Redding/Monterrey
convective band was being forced by a strong front moving
southeastward across the region. PW values of 1 inch along and
ahead of the front near the coast was aiding in the heavier rain
rates.

Over time, as the aforementioned front shifts southward across the
state, strong upslope flow will aid in continued moderate to heavy
rainfall and a few instances of flash flooding especially along
upwind areas of the Sierra. The front will also aid in occasional
bursts of heavier rainfall along coastal areas from Monterrey
southward toward the Transverse Ranges/Santa Barbara County
through 16Z/8a Pacific time. Sensitive areas/burn scars could
experience another round of debris flows and excessive runoff.

Another more conditional risk for heavier rainfall will occur near
the center of the mid/upper trough near Eureka. Slow-moving
convection was being supported by ascent from the trough and very
cold temps aloft (-20 to -24C @ 500 mb). A conditional risk of
heavier rainfall occurring over land areas between Eureka and
Santa Rosa exists. Flash flooding is also possible with this
activity.

Cook

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!560lrQV056m3xGBG0stbT-bHIATx0Z9HQM1S20SgYEgnUXhKzyUrzp017a7UzT6gmk9-= EVim_853cWsvqz4dxWXL1b0$ for graphic product...

ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...STO...

ATTN...RFC...RSA...NWC...

LAT...LON 41372415 41372308 41312155 40062055 37211977=20
35161959 34441983 34832081 36762232 38532342=20
39742426 40652451=20

=3D =3D =3D
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AWUS01 KWNH 171014
FFGMPD
CAZ000-171600-

Mesoscale Precipitation Discussion 1227
NWS Weather Prediction Center College Park MD
514 AM EST Mon Nov 17 2025

Areas affected...portions of northern and central California

Concerning...Heavy rainfall...Flash flooding possible

Valid 171001Z - 171600Z

Summary...A stout mid-level wave west of Eureka was prompting
scattered shower and thunderstorm activity across a broad part of
northern and central California. These trends will continue for
the next few hours, and areas of 0.5-0.75 inch/hr rain rates are
possible. A few instances of flash flooding could occur in
sensitive areas and near burn scars.

Discussion...A vigorous mid-level wave was providing ascent for
several areas of convection 1) just west of Eureka over open
Pacific waters and 2) along an axis from Redding south-southwest
to near Monterrey. Over the past hour, more robust convective
activity (with lightning) developed near/south of San Francisco
and moved inland. Both of these regimes were responsible for
areas of 0.5-0.75 inch/hr rain rates. The Redding/Monterrey
convective band was being forced by a strong front moving
southeastward across the region. PW values of 1 inch along and
ahead of the front near the coast was aiding in the heavier rain
rates.

Over time, as the aforementioned front shifts southward across the
state, strong upslope flow will aid in continued moderate to heavy
rainfall and a few instances of flash flooding especially along
upwind areas of the Sierra. The front will also aid in occasional
bursts of heavier rainfall along coastal areas from Monterrey
southward toward the Transverse Ranges/Santa Barbara County
through 16Z/8a Pacific time. Sensitive areas/burn scars could
experience another round of debris flows and excessive runoff.

Another more conditional risk for heavier rainfall will occur near
the center of the mid/upper trough near Eureka. Slow-moving
convection was being supported by ascent from the trough and very
cold temps aloft (-20 to -24C @ 500 mb). Heavier rainfall could
occur between Eureka and Santa Rosa. Flash flooding is also
possible with this activity.

Cook

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8rzG_g6Z7dApF0i3lq4u5E6K6tP5BOaGy9fFex9v19JXKqseg8Owh9hveffNBlcDIn_G= wNucsI39g4QZODDfzDz9o8c$ for graphic product...

ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...STO...

ATTN...RFC...RSA...NWC...

LAT...LON 41372415 41372308 41312155 40062055 37211977=20
35161959 34441983 34832081 36762232 38532342=20
39742426 40652451=20

=3D =3D =3D
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AWUS01 KWNH 172145
FFGMPD
CAZ000-180345-

Mesoscale Precipitation Discussion 1229
NWS Weather Prediction Center College Park MD
445 PM EST Mon Nov 17 2025

Areas affected...Southern California...

Concerning...Heavy rainfall...Flash flooding possible

Valid 172145Z - 180345Z

SUMMARY...Heavy rainfall conditions improving, but still an
isolated potential for .5"/hr rates with max totals in the
Transverse Ranges near 1.5" through evening. Saturated grounds and
urban locations have possibility for isolated flooding concerns.

DISCUSSION...GOES-W Visible and Regional RADAR mosaic denotes a
broader shield of mid-level strato-cu across the western portions
of the Transverse Ranges across E Santa Barbara county indicative
of a subtle southwesterly shortwave lifting northeastward through
in proximity to the cold front. This is in some response to the
larger scale digging closed low orienting more NW to SE providing
deeper layer divergence above 500mb and overall DPVA through the
California Bight into Southern California this afternoon into
evening. However, the lower level pressure gradient is
broadening through the Bight and winds have diminished throughout
the afternoon. Still, 20-25kts of southerly flow coincident with
the vertically stacked moisture plume still advects .75 to 1"
total PWats (IVT values of 250-300 kg/m/s) fairly orthogonal to
the Transverse Ranges of Ventura and Los Angeles counties and will
spill over to the San Bernardino Ranges through evening.=20
Localized totals of 1-1.5" are possible in the highest elevations
but overall rates and ascent will be diminishing with the
weakening wind field.=20

Off the terrain, the environmental conditions are very limited
for flooding, but recent saturated grounds per NASA SPoRT suggest,
above average run-off could be expected. With that stated, some
modest surface to boundary layer heating has developed this
afternoon providing some weak but sufficient instability; MLCAPEs
of 150-250 J/kg are present and with 10-12 kg/m/s deep layer
moisture convergence along the front, some vertical development
and enhanced rainfall rates are possible through the evening
likely topping out around .5"/hr perhaps inducing some isolated to
widely scattered incident(s) of urban flooding concerns through
03z.=20=20

Gallina

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9unAJHAWFEgaYz1VRg6fwIkbpTRW82pvEbKw7sViPYiDcu1XKujuA8lj8kRTgFAw-F2X= DADRCR0SzZl4uVJLQ4Km9H4$ for graphic product...

ATTN...WFO...HNX...LOX...SGX...

ATTN...RFC...RSA...NWC...

LAT...LON 35061949 34961850 34191722 32761696 32611733=20
33011763 33531807 33761859 33831901 34401968=20
34741979=20

=3D =3D =3D
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AWUS01 KWNH 180354
FFGMPD
CAZ000-180753-

Mesoscale Precipitation Discussion 1230
NWS Weather Prediction Center College Park MD
1053 PM EST Mon Nov 17 2025

Areas affected...portions of southern California

Concerning...Heavy rainfall...Flash flooding possible

Valid 180353Z - 180753Z

Summary...Flash flood potential continues for at least 2-4 more
hours.

Discussion...A warm conveyor continues to spread moderate to heavy
rainfall into portions of southern California near the Los Angeles
basin and adjacent areas of the Transverse Ranges. Recent
observations suggest that 0.5 inch/hr rain rates were falling over
or very near burn scars just north of Los Angeles, suggesting
continued potential for excessive runoff and debris flows.=20
Mesoanalyses indicate a continued fetch of southwesterly 850mb
flow into the region oriented parallel to the coastal ranges,
supporting continued orographic enhancement of rain rates at
times. PW values near an inch and weak surface-based instability
also continue to support the convective nature of the activity and
locally heavy rain rates.=20

Models suggest that these rates will continue to impact burn scar
areas over the next 2-4 hours (through 07Z or so) while
translating slowly eastward. Flash flooding will remain a
possibility, though this risk should become more isolated with
time as rain rates are expected to gradually weaken.

Cook

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_Lg5brlhc3l8TD-QR5rcay76pvzFWwwYGIJQpPeKzNXG0xFgdiYBDr3pyuoXkzT3fOGP= k9Y_FcFrxoaKrLCXc2oRlZY$ for graphic product...

ATTN...WFO...HNX...LOX...PSR...SGX...VEF...

ATTN...RFC...RSA...NWC...

LAT...LON 34971836 34901737 34381647 33161635 32611652=20
32711701 33401774 34051865=20

=3D =3D =3D
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AWUS01 KWNH 181228
FFGMPD
AZZ000-CAZ000-181826-

Mesoscale Precipitation Discussion 1231
NWS Weather Prediction Center College Park MD
727 AM EST Tue Nov 18 2025

Areas affected...portions of western AZ

Concerning...Heavy rainfall...Flash flooding possible

Valid 181226Z - 181826Z

Summary...An area of heavy rain with embedded thunderstorms should
continue across portions of western AZ over the next several
hours. Hourly rain amounts to 1.5" and local 3" totals are
possible, which would continue isolated to widely scattered flash
flood concerns.

Discussion...An upper level low is sliding southeast down the CA
coast past Lompoc. It has led to a broad area of divergence aloft
across the Southwest. Precipitable water values of 1"+ are
indicated in RAP forecasts, with some GPS values across Las Vegas
and Phoenix in the 0.8-0.9" range. When combined with 1000-500
hPa thickness values of 5550 meters, the atmosphere is saturated
which has led to efficient heavy rainfall across portions of
southwest AZ this morning, with radar indications of 1"+ in an
hour at times. MU CAPE of 500-1000 J/kg exists downstream from
the Gulf of CA northward across southwest AZ. Effective bulk
shear of 25 kts is helping to organize the convective elements.

A shortwave noted on water vapor imagery across southern CA could
cause some backing of the low level flow in the short term,
potentially shifting the heavy rain area somewhat westward with
time. RAP guidance fields indicate expansion of the instability
pool northeast with time, which could lead to some northeast
shift. When taken together, the heavy rain footprint could
broaden with time. Hourly rain amounts to 1.5" and local totals
to 3" are possible where cells backbuild and train. Burn scar
locations, arroyos/dry washes, box canyons, and urban areas should
be most sensitive to this rainfall. Isolated to widely scattered
flash flood concerns should continue into the day today.=20

Roth

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7OSVbJv1SfLB2tqivOYQ7yd1rXTyeoYa0kBIta9AhWA5J57n9H8MSQQSYN4wASMHjc2P= 4BFi9vPa5od_YLPyG_1EGIk$ for graphic product...

ATTN...WFO...FGZ...PSR...VEF...

ATTN...RFC...STR...NWC...

LAT...LON 35721347 35591200 34471161 32961249 32731312=20
32951388 33841422 35121412=20

=3D =3D =3D
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AWUS01 KWNH 181904
FFGMPD
AZZ000-NVZ000-CAZ000-190103-

Mesoscale Precipitation Discussion 1232
NWS Weather Prediction Center College Park MD
203 PM EST Tue Nov 18 2025

Areas affected...Western Arizona, Southeast California and
Southern Nevada

Concerning...Heavy rainfall...Flash flooding likely

Valid 181903Z - 190103Z

SUMMARY...Flash flood risk increasing this afternoon into the
evening across the Colorado River basin between southeast
California, southern Nevada, and western Arizona. Heavy rainfall
potential existing through sunset leading to potential night time
flash flooding concerns.

DISCUSSION...Current radar/IR satellite composite indicates a
brief lull initiating over portions of southwest AZ and
southeastern CA. Meanwhile, a steady progression of a stronger
convective pulse over far northeast Baja will make headway to the
north as it migrates within the broad deep layer steering flow out
of the south-southwest. This is due to the proximity of the=20
persistent ULL presence off the southern CA coast with smaller
shortwave perturbations emanating around the southern and eastern
periphery of the upper-level circulation. Hi-res guidance,
especially the last several HRRR iterations have been manifesting
this very scenario of a brief lull, followed by the advection of
the next stronger mid-level perturbation exiting out of Baja and
shifting north along the adjacent Colorado River basin between
AZ/CA/NV. This will coincide within a field of relatively buoyant
air situated within the river basin, arcing back into southern NV
along the warm/cold conveyor belt transition along the northern
side of the surface low analyzed over the southern tip of NV.

SBCAPE between 1000-1500 J/kg is analyzed across much of southwest
AZ with an extension of 500-1000 J/kg located along the northern
extent of the Colorado River basin between the three-state
intersection. This setup is poised to advect further north with a
greater SBCAPE alignment focused over the southern tip of NV down
through far-southeast CA and much of western AZ. The combination
of suitable vorticity advection and modest instability over an
area of +2 to +3 sigma PWATs will assist in a re-invigoration of
area convection with cells capable of 0.5-1.25"/hr at peak
intensity, enough to favor some scattered flash flood prospects
within the confines of northern Yuma, La Paz, Mojave counties in
AZ, southern Clark county in NV, and far-eastern San Bernardino
county in CA. Some training could occur with cells materializing
on a north-south alignment for areas east of the Colorado River
given the deep layer flow remaining fairly uni-directional. This
could exacerbate flash flood concerns locally, leading to the
threat running closer to the flash flooding likely prospect,
especially within those western AZ counties.

Kleebauer

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9qZwoR-eYoOBPiD_vew7g_oNGgxGIH2VQ3sBHQQpMbB4o_gJuygnmXAcdPidULM-OuUA= grZKvmqIF-vCYVPBbaCFAgc$ for graphic product...

ATTN...WFO...FGZ...PSR...VEF...

ATTN...RFC...RSA...STR...NWC...

LAT...LON 35831459 35801375 35291312 34391280 33221314=20
33161409 33711453 34251494 34881526 35531530=20 =20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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