AWUS01 KWNH 021150
FFGMPD
KYZ000-ILZ000-MOZ000-IAZ000-KSZ000-NEZ000-021700-

Mesoscale Precipitation Discussion 0835
NWS Weather Prediction Center College Park MD
749 AM EDT Wed Aug 02 2023

Areas affected...Portions of the Mid-Mississippi Valley

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

Valid 021200Z - 021700Z

Summary...An impressive MCS will persist this morning before
gradually decaying into the early afternoon. Rainfall rates of
2"/hr will train along this MCS, producing an additional 2-4" of
rain with locally higher amounts possible. Flash flooding is
likely.

Discussion...A linear MCS draped from eastern NE through southeast
MO continues this morning as noted on the regional radar mosaic.
This MCS is continuing to strengthen along its upwind side noted
by cooling cloud tops in the GOES-E IR imagery reaching below
-70C. This convection is being fueled by weak height falls
downstream of a shortwave moving across NE/IA, traversing the
periphery of a mid-level ridge to the south. An impressive 850mb
LLJ of 35-45kts measured via regional VWPs is locally backing in
response, to surge northward intense moisture flux of +2 to +2.5
sigma according to the SREF. The accompanying WAA is helping to
drive additional convective development as thermodynamic advection
occurs beneath 2000-3000 J/kg of MUCAPE and PWs of 1.9-2.1 inches.
This event has already resulted in MRMS measured rainfall of 6-8"
in some areas overnight, and rainfall rates are still 2-2.5"/hr in
deeper convection as estimated by KLSX WSR-88D.

The LLJ which is responsible for most of this activity is likely
to begin to veer to the east and weaken in the next few hours.
However, the upstream shortwave and downstream thickness
diffluence should allow the intensity to maintain through the late
morning. While there is some uncertainty into the placement of the
axis of heaviest rainfall, HREF EAS probabilities for more than 1"
in the next 6 hours are quite high along the nose of this LLJ
where moisture transport vector convergence is maximized. As the
LLJ veers, Corfidi vectors are likely to respond by backing more
to the SW and weakening, suggesting continued backbuilding, with
training from the NW to SE along the MCS also expected. With rain
rates progged by the HREF to exceed 2"/hr at times, this could
result in an axis of 2-4" of rain, with locally higher amounts
possible as reflected by some low end HREF probabilities for 5".

This region has already experienced a corridor of of 2-5" of rain
with local amounts above 6" overnight. This has primed the soils
and compromised FFG to as low as 0.75"/1hr which will likely be
exceeded in the most intense cores as the HRRR shows locally up to
1"/15 minutes. As the LLJ veers the entire system should begin to
weaken and push a bit farther east before decaying, but for the
next several hours flash flooding is likely, especially where
heavy rain returns atop already saturated soils.

Weiss

ATTN...WFO...DMX...DVN...EAX...FSD...GID...ILX...LSX...OAX... PAH...SGF...TOP...

ATTN...RFC...LMRFC...MBRFC...NCRFC...NWC...

LAT...LON 42269642 42079409 41249183 39869037 38378952
37478924 36898920 36588936 36768987 36899012
37589136 38819338 39369528 40269714 41389783
41979762

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AWUS01 KWNH 141201
FFGMPD
TNZ000-KYZ000-141700-

Mesoscale Precipitation Discussion 0923
NWS Weather Prediction Center College Park MD
800 AM EDT Mon Aug 14 2023

Areas affected...Northern Tennessee into Southeastern Kentucky

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

Valid 141200Z - 141700Z

SUMMARY...Training thunderstorms to cause localized flash flooding
over northern Tennessee into southeastern Kentucky. Rainfall 1-3"
possible through noon.

DISCUSSION...Regional RADAR mosaic depict a developing line
thunderstorms over northwestern TN which are south of a surface
low/MCV over northern KY. This activity is oriented WSW-ENE which
is parallel to the 35kt WSWly mean layer flow. Sufficient
instability is present along ahead of this activity with MUCAPE of
1000-1500 J/kg over western KY/TN. Instability does decrease to
the east, though instability is advecting with the mean flow. A
strong moisture gradient is noted through this activity with PWs
of 2.0-2.2" along the activity and this is also advecting ENE with
the mean flow. Also, upper level divergence will will increase as
the upper low over Iowa approaches with the right entrance region
of the SWly jet.

Scattered 1.5-2" hourly rainfall estimates recently from KPAH and
KHPX will continue given the environment. This area has been wet
lately with FFG generally 1.5-2"/hrs with the more sensitive
Nashville metro downstream of the activity.

More progressive activity is over central KY, but conceptually
speaking, the activity farther south over south-central KY may
also join the TN activity in orienting with the deep layer mean
flow with southeast KY having lower FFG.

Outflow is noted from this activity on regional NEXRAD which may
disrupt the heavy rain threat. Recent CAMs are struggling with
this activity, but the environment should allow redevelopment with
recent 10.3 micron IR imagery continuing to show cooling cloud
tops. Flash flooding is considered possible.

Jackson

ATTN...WFO...JKL...LMK...MEG...MRX...OHX...PAH...

ATTN...RFC...LMRFC...OHRFC...NWC...

LAT...LON 37528399 35988480 35368727 35348917 35598962
36118927 36348812 37398631

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AWUS01 KWNH 271003
FFGMPD
TNZ000-KYZ000-ALZ000-ILZ000-MSZ000-MOZ000-ARZ000-271600-

Mesoscale Precipitation Discussion 0988
NWS Weather Prediction Center College Park MD
601 AM EDT Sun Aug 27 2023

Areas affected...Portions of the Lower OH Valley and Mid-South

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

Valid 271000Z - 271600Z

SUMMARY...A threat for some flash flooding will continue through
the morning hours across portions of the Lower OH Valley and
potentially extending down across the Mid-South from heavy showers
and thunderstorms.

DISCUSSION...The latest GOES-E Proxy Visible satellite imagery
continues to show a very well-defined and slow-moving MCV over
southeast MO. This energy is expected to continue drifting
generally off to the southeast through the morning hours with the
MCV tracking into western KY by midday. This energy should
continue to interact with a very moist and modestly unstable
airmass for some bands of heavy shower and thunderstorm activity.

MLCAPE values are generally on the order of 500 to 1000 J/kg
across areas of eastern AR, central and western TN and also
western KY. PWs remain very high with values of 2.0 to 2.25 inches
and characteristic of an airmass that is deeply tropical in nature.

The latest radar imagery does show an axis of convection becoming
a bit more focused across areas of southern IL around the eastern
flank of the MCV, and this band of convection should tend to
gradually advance or refocus farther down to the southeast into
western KY going through the morning hours.

Meanwhile, farther down to the south, there is a broken band of
convection impacting areas of eastern AR, northwest MS and western
TN. This activity is generally more progressive and should
continue to advance off to the east or east-southeast this morning.

The latest HRRR guidance supports areas of western KY seeing the
heaviest rainfall potential this morning, with the 06Z HREF
displaced a bit farther south into areas of northwest TN. However,
the latest radar trends would support portions of southern IL and
eventually western KY. The guidance throughout much of the night
has been notably overdone with its QPF, but the latest satellite
and radar trends do suggest heavier rainfall potential beginning
to materialize.

Expect rainfall rates to potentially reach 2.5 to 3 inches/hour
with the stronger storms, and some small-scale storm total amounts
of 3 to 5 inches going through the late morning hours. This will
maintain a threat for flash flooding as a result.

Orrison

ATTN...WFO...HUN...JAN...LSX...LZK...MEG...OHX...PAH...

ATTN...RFC...LMRFC...NCRFC...OHRFC...SERFC...NWC...

LAT...LON 38118981 38068851 37348735 36298723 34988766
33998882 34029061 34619127 35009115 35369017
36008971 36568982 37009019 37659036

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AWUS01 KWNH 292159
FFGMPD
PAZ000-MDZ000-VAZ000-WVZ000-300400-

Mesoscale Precipitation Discussion 1005
NWS Weather Prediction Center College Park MD
558 PM EDT Tue Aug 29 2023

Areas affected...much of WV...far northern VA and western
MD...southeast and central PA

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

Valid 292200Z - 300400Z

Summary...Occasional rainfall rates of 1-2"/hr to lead to
additional localized totals of 2-4" through late evening. Isolated
to scattered instances of flash flooding are likely.

Discussion...Disorganized clusters of showers and thunderstorms
are steadily progressing northeastward across portions of northern
WV late this afternoon, along and ahead of a quasi-stationary
front. Rainfall rates in association with percolating updrafts
have been as high as 1-2"/hr, owing to relatively efficient warm
rain processes. The mesoscale environment is characterized by SB
CAPE of 1000-1500 J/kg, PWATs of 1.4-1.7 inches (near the 90th
percentile, per nearby PBZ/IAD sounding climatology), and
effective bulk shear of 20-30 kts. While low-level moisture
transport values are fairly meager, the nearly stationary front
should continue to provide enough focus for additional development
and proliferation of convection (across more of northern and
eastern WV and into adjacent portions of VA/MD and southeast and
central PA). In addition, broad uplift and longevity of updrafts
should also be provided by increasing upper-level diffluence via
the right-entrance region of a strengthening jet streak over the
Northeast.

12z HREF and more recent HRRR runs are both in fairly good
agreement in depicting localized totals of 2-4" through the late
evening hours. HREF 40-km neighborhood probabilities for 2" and 3"
exceedance are as high as 40-80% and 20-40%, respectively. The
bulk of these totals are expected in a 3-hr period or less, where
associated flash flood guidance (FFG) ranges widely from 1.0-4.0",
but generally ranges from 1.0-3.0" (with a good amount of the
western outlooked area across the more vulnerable Appalachians
ranging from only 1.0-2.0"). Given the vulnerability across much
of the area and already ongoing convective activity, isolated to
scattered instances of flash flooding are considered likely.

Churchill


ATTN...WFO...CTP...LWX...PBZ...RLX...RNK...

ATTN...RFC...MARFC...OHRFC...NWC...

LAT...LON 41447761 41367723 40947705 40677724 40347740
39847774 39217752 38897743 38617806 38267888
37947957 37678103 38028139 38868070 39568052
39967998 40317938 40727883 41057845 41257812

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AWUS01 KWNH 122239
FFGMPD
AZZ000-UTZ000-NVZ000-CAZ000-130345-

Mesoscale Precipitation Discussion 1060
NWS Weather Prediction Center College Park MD
638 PM EDT Tue Sep 12 2023

Areas affected...southern NV into southwestern UT/northwestern AZ

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

Valid 122236Z - 130345Z

Summary...Thunderstorms may produce areas of localized flash
flooding from southern NV into southwestern UT and northwestern AZ
over the next 3-5 hours. Rainfall rates of 1-3 in/hr are expected
from some of the stronger/slower moving cells.

Discussion...22Z visible imagery from GOES West and area radars
showed widely scattered thunderstorms ongoing across portions of
southern NV into southwestern UT. A small convective cluster was
observed in southwestern UT, dropping south and preceded by an
outflow boundary. This region of the Southwest has seen favorable
solar insolation for much of the day, resulting in a small pocket
of MLCAPE with 500 to 1000 J/kg on the 22Z SPC mesoanalysis
centered over Lincoln and Clark counties. 21Z GPS measurements of
precipitable water were 1.0 to 1.1 inches at Las Vegas, slightly
lower than the 12Z VEF RAOB of 1.25 inches, but still lying above
the 90th percentile for early/mid-September. These anomalous
moisture values are likely representative for the general
tri-state region.

Cell motions across southern NV into southwestern UT have averaged
5-15 kt, owing to a weakness in the low to mid-level flow over the
region and further weakening of the mean flow is forecast by the
RAP through 03Z. The region lies beneath a broad and low amplitude
upper level trough, just ahead of a subtle mid-level vorticity max
crossing the Sierra Nevada on water vapor imagery.

While surface temperatures are likely at peak and no further
increases in instability are expected over the next few hours,
lingering instability will continue thunderstorm development over
the next 3-5 hours before remaining instability is exhausted.
Outflow boundary interactions and short term training may generate
a few areas with 1-2 in/hr rainfall rates, but isolated rates near
3 cannot be ruled out. Across southwestern UT, should the ongoing
convection survive as it heads south toward some of the sensitive
slot canyons of the region, a localized flash flood threat could
set up there as well with 1 inch of rain in 15-30 minutes, but
weaker instability was estimated to be present in UT. Overall, the
flash flood threat through 04Z should remain localized.

Otto

ATTN...WFO...FGZ...LKN...SLC...VEF...

ATTN...RFC...CBRFC...CNRFC...NWC...

LAT...LON 38531361 38491266 38131202 37581177 36911197
36641310 36061348 35481370 35241385 35011459
35321525 35961593 37021619 37711606 38111568
38391461

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* SLMR 2.1a * Arnold Layne, don't do it again!
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AWUS01 KWNH 122351
FFGMPD
NMZ000-AZZ000-130550-

Mesoscale Precipitation Discussion 1061
NWS Weather Prediction Center College Park MD
750 PM EDT Tue Sep 12 2023

Areas affected...central/southern AZ into NM

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

Valid 122350Z - 130550Z

Summary...Thunderstorms are expected to increase in coverage
across central/southern AZ into NM through 06Z. A few areas of
flash flooding are considered likely with repeating cells/cell
training and rates of 1 to 2+ in/hr.

Discussion...At 23Z, scattered thunderstorms were noted across
central and southeastern AZ into western NM. The region was
characterized by 500 to 1500 J/kg MLCAPE (via 23Z SPC mesoanalysis
data) and +1.5 to +2.5 standardized anomalies of precipitable
water (12Z NAM/GFS). Deeper layer mean flow was oriented from the
west at ~20-25 kt along with a zone of stronger 700 mb flow at
10-20 kt, also from the west. The Desert Southwest was located
downstream of a longwave and low amplitude mid-upper level trough
axis over NV/CA and just ahead of a shortwave impulse and related
jet streak moving through southern CA on 6.9 micron imagery from
GOES West.

Expectations are that thunderstorm coverage will increase over the
next 1-3 hours as the upstream shortwave impulse over southern CA
approaches, working with the available instability across the
region which is expected to maintain for at least another 3-6
hours. Even after the onset of nocturnal cooling and boundary
layer stabilization, elevated instability should remain given
steep lapse rates in the 850-500 mb layer forecast to hover near
7.5 C/km. While individual cell motions should tend to be
progressive toward the east, there will be potential for multiple
rounds of thunderstorms as well as localized areas of training
where west-east cell alignment occurs or where cells become
temporarily anchored on local topography. These situations should
support rainfall rates of 1-2 in/hr, but locally above 2 in/hr
cannot be ruled out. The high moisture and sufficient CAPE
environment may also support localized sub-hourly totals of 1-2
inches in 15-30 minutes. While flash flood coverage is not
expected to be widespread, a few areas of flash flooding appear
likely heading into the overnight with storm totals of 2-3 inches
through 06Z.

Otto

ATTN...WFO...ABQ...EPZ...FGZ...PSR...TWC...

ATTN...RFC...CBRFC...WGRFC...NWC...

LAT...LON 34670975 34440684 33710634 33210653 32840650
32370656 32040731 31740783 31290813 31100973
31241119 31891260 32741334 34371316

= = =
---
* SLMR 2.1a * Float on a river, forever and ever, Emily...Emily...
* Origin: Ilink: CCO - capitolcityonline.net (454:1/105)

It is storming in Holbrook, AZ, as I type. :)

AWUS01 KWNH 132122
FFGMPD
AZZ000-UTZ000-NVZ000-140315-

Mesoscale Precipitation Discussion 1067
NWS Weather Prediction Center College Park MD
522 PM EDT Wed Sep 13 2023

Areas affected...central/northern AZ, southeastern NV,
southwestern UT

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

Valid 132119Z - 140315Z

Summary...A couple of isolated areas of flash flooding will be
possible over the next 3-6 hours from central to northern AZ into
southeastern NV and southwestern UT. Rainfall rates between 1 and
2 inches in 15-30 minutes can be expected with the strongest cells.

Discussion...21Z regional radar imagery across the Desert
Southwest showed scattered thunderstorms stretching from
central/northern AZ into southeastern NV and southern UT. The
region was characterized by MLCAPE of 500 to 1000+ J/kg and
anomalous precipitable water values ranging from 0.8 to 1.1 inches
via 21Z SPC mesoanalysis data. 700 mb VAD wind plots helped
identify a low just west of the AZ border in eastern CA, and a
weak ridge over northwestern AZ. A downstream confluence axis
located near or just below 700 mb was noted over the southern
Colorado Plateau, roughly parallel to mean westerly flow present
in the 850-300 mb layer. Farther back to the west, slow moving and
training cells were observed from northwestern AZ into
southeastern NV where 850-300 mb mean winds were less than 10 kt,
supporting slow movement.

Thunderstorms will continue for at least another few hours within
the available pool of instability with elements of training where
outflow boundaries and/or cells line up with the mean steering
flow. One area where a short term flash flood threat will continue
is near an outflow boundary located in southern Navajo and
southeastern Coconino counties. Additional slow moving cells with
new development will also be possible from northwestern AZ into
southern NV until instability drops off after sunset with the loss
of heating. Repeating and training of heavy rain will have the
potential to produce high rainfall rates with 1-2 inches in 15-30
minutes. These rains may produce localized areas of flash flooding
with a focus on typical narrow canyons, normally dry washes and
any burn scars.

Otto

ATTN...WFO...FGZ...SLC...VEF...

ATTN...RFC...CBRFC...CNRFC...NWC...

LAT...LON 37941319 37921262 37531202 36841175 36181127
35631020 35010964 34050995 33931113 34391297
34921453 35891566 36551601 37101599 37681532
37911421

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---
* SLMR 2.1a * May The Force be with you...
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AWUS01 KWNH 140116
FFGMPD
MEZ000-140630-

Mesoscale Precipitation Discussion 1068
NWS Weather Prediction Center College Park MD
915 PM EDT Wed Sep 13 2023

Areas affected...Maine

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

Valid 140111Z - 140630Z

Summary...Showers with embedded thunderstorms will continue a
threat for flash flooding across portions of ME through 06Z with
rainfall rates up to 1.5 in/hr. The threat is expected to
translate northeastward with time but there's a low end chance of
the flash flood threat building southward toward the coast.

Discussion...Local radar imagery from KGYX showed an axis of heavy
rain over west-central ME at 01Z, oriented from SSW to NNE near
the Kennebec River Valley. Peak MRMS-derived hourly totals have
ranged between 1 to 1.5 inches within this axis, confirmed by
local automated gauge reports near Farmington recently reporting
1.3 in/hr rainfall rates. An axis of low level moisture
convergence was supporting the region of heavy rain, situated just
ahead of a weak 925-850 mb low estimated to be over northwestern
ME at 01Z per area VAD wind plots, and a related surface trough
axis. 20-30 kt of low level flow was focused just ahead of the
low/trough, co-located with an area of weak MLCAPE that ranged
between 100 and ~500 J/kg per SPC mesoanalysis data and the 00Z
GYX RAOB.

While instability is expected to slowly weaken overnight,
anomalous precipitable water values (1.5" at GYX, above 90th
percentile for this date) will continue to advect northward into
central ME, continuing to support areas of training along the low
level convergence axis as it translates northeastward. Farther
south, while there isn't a good signal in recent hires guidance,
there is a low chance that heavy rain develops and focuses near
the coast within the moisture plume as the entire state will be
situated beneath the favorable right-entrance region of a 90-100
kt jet max located east of a parent upper trough over western
Quebec. Peak rainfall rates of 0.5 to 1.5 in/hr are expected which
would exceed area FFG of 1 to 2 inches in 1 hour.

Otto

ATTN...WFO...CAR...GYX...

ATTN...RFC...NERFC...NWC...

LAT...LON 47056878 47026828 46546792 45856777 44316846
43296964 43487058 44397039 45627009 46266972
46806925

= = =
---
* SLMR 2.1a * Gone crazy, be back later, please leave message.
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AWUS01 KWNH 280957
FFGMPD
TNZ000-KYZ000-ILZ000-281555-

Mesoscale Precipitation Discussion 1109
NWS Weather Prediction Center College Park MD
556 AM EDT Thu Sep 28 2023

Areas affected...Far Southern IL...Western/South-Central
KY...Northern TN

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

Valid 280955Z - 281555Z

SUMMARY...Some additional concerns for flash flooding will exist
through the morning hours from locally repeating/training rounds
of heavy showers and thunderstorms.

DISCUSSION...An upper-level trough and associated closed low
continues to impact areas of the Great Lakes and portions of the
OH Valley early this morning. Surface data shows a well-defined
frontal zone situated very close to the OH River, and shortwave
energy rounding the base of the upper trough has been facilitating
the advance of a wave of low pressure off to the east along the
front.

An axis of relatively stronger low-level convergence near and east
of the low center continues to work in tandem with as much as 500
to 1000 J/kg of MUCAPE for some broken bands of showers and
thunderstorms. Some of the stronger forcing aloft associated with
the vort energy and broader height falls continues to be a player
as well in seeing pockets of sustainable convection.

Dual-pol radar more recently has been tending to redevelop and
focus convection back across areas of far southern IL and into
western KY, and this is where there is the nose of greatest
instability and close proximity of an outflow boundary resulting
from the earlier convection overnight farther to the north.

The general expectation is that there will be a broken axis of
additional convection going through the morning hours that will
impact areas of western to south-central KY, and possibly sneaking
into areas of northern TN as shortwave energy continues to
traverse the OH Valley. Some of the 00Z/06Z HREF guidance suggests
potential for repeating/training convective cells across these
areas.

Rainfall rates will be capable of reaching 1.5+ inches/hour, and
locally an additional 2 to 4 inches of rain may be possible by mid
to late morning.

Some additional concerns for some flash flooding will exist this
morning as a result from these additional rounds of heavy showers
and thunderstorms.

Orrison

ATTN...WFO...JKL...LMK...MEG...MRX...OHX...PAH...

ATTN...RFC...LMRFC...OHRFC...NWC...

LAT...LON 37728792 37358690 37138559 36908471 36478432
35968490 35798655 36158820 36838908 37348905
37668863

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AWUS01 KWNH 290906
FFGMPD
MAZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-291505-

Mesoscale Precipitation Discussion 1111
NWS Weather Prediction Center College Park MD
505 AM EDT Fri Sep 29 2023

Areas affected...Far Eastern PA...Much of NJ...Southeast NY and
Long Island...Western CT

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

Valid 290905Z - 291505Z

SUMMARY...Heavy rainfall and numerous instances of flash flooding
can be expected this morning across portions of the I-95 corridor
from central and northern NJ through far southeast NY and into
western CT. This will include the New York City metropolitan area
where locally significant runoff problems and urban flooding
generally appears likely.

DISCUSSION...Heavy shower and occasional thunderstorm activity
continues to generally expand in coverage along the I-95 corridor
from areas of central and northern NJ up through far southeast NY
and southwest CT. Recent radar trends have actually shown some
uptick in convection also across areas farther down to the
southwest involving southern NJ near the Atlantic City area, and
into a little bit of eastern PA.

The convection continues to develop and organize in response to a
upper-level trough approaching from the OH Valley and interacting
with a strengthening coastal front just offshore of the northern
Mid-Atlantic and southern New England coasts. A well-defined
low-level southeasterly fetch of moisture and warm air advection
continues to overrun this boundary, and this is favoring broad
isentropic ascent and areas of upright convection given a gradual
increase in instability in close proximity to the front. In fact,
the latest RAP analysis shows MUCAPE values of as much as 500 to
1000 J/kg, with some of the greatest positive 3-hour CAPE
differentials occurring over eastern PA and into NJ given arrival
of slightly steeper mid-level lapse rates with the upper trough.

The latest experimental CIRA-LVT data shows a notable surge of
southeasterly moisture transport in the SFC/850 mb layer advancing
toward coastal areas of central and northern NJ, far southeast NY
and Long Island which should help yield greater rainfall
efficiency and heavier rainfall rates closer to 12Z (8AM EDT) and
extending through 15Z (11AM EDT) with convection likely becoming
more concentrated and focused along the I-95 urban corridor.

Rainfall rates should easily reach into the 1 to 2 inch/hour range
this morning with the stronger convective cores, and the 00Z/06Z
HREF guidance favors this along with additional rainfall totals
locally of 3 to 5 inches by late this morning.

The additional heavy rainfall is likely to result in numerous
instances of flash flooding this morning, and this will include
the I-95 corridor from generally central and northern NJ through
far southeast NY, and into western CT. This will include the
entire New York City metropolitan area where locally significant
runoff problems and urban flooding appears likely.

Orrison

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

ATTN...RFC...MARFC...NERFC...NWC...

LAT...LON 42147334 41907260 41527241 40917252 40487343
39957401 39227464 39327525 39837545 40967540
41597509 42047434

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AWUS01 KWNH 011423
FFGMPD
FLZ000-012022-

Mesoscale Precipitation Discussion 1120
NWS Weather Prediction Center College Park MD
1023 AM EDT Sun Oct 01 2023

Areas affected...Eastern Florida Peninsula

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

Valid 011422Z - 012022Z

Summary...Flash flooding will be possible across portions of the
eastern Florida Peninsula through this afternoon due to
slow-moving thunderstorms producing intense rain rates. Localized
rain totals of 3 to 6 inches will be possible through
mid-afternoon.

Discussion...Showers and thunderstorms continue this morning
across portions of the eastern Florida Peninsula, focused in
primarily two different areas, one near Daytona Beach southward
through the Space Coast while another area forming just offshore
southeast Florida near Fort Lauderdale. This activity is aligned
with the persistent onshore flow regime and aided by the
stationary front positioned just to the north.

The environment through the afternoon is expected to remain
conducive for heavy rain. Precipitable water values of 2-2.5" have
been analyzed this morning (12Z MFL PW was 2.46", near the daily
max from the SPC sounding climatology). Meanwhile, the latest
mesoanalysis showed favorable amounts of instability through the
region, characterized by 1500-2000 J/kg of SBCAPE right along the
coast. Favorable low level convergence right along the coast is
helping to focus the deepest cores this morning.

The latest model guidance, including recent HRRR runs and the 06Z
HREF probabilities, all point toward isolated/localized intense
rain rates and totals near/on the coast through this afternoon.
The initial greater threat will be across east-central Florida but
up and down the coast pockets of heavy rainfall will be possible
until the frontal boundary sags southward through the area. HREF
2" hourly total probabilities are above 50-60 percent this morning
and remain elevated (20-30 percent) through this afternoon.
Isolated 3"+ hourly totals will be possible (10-20 percent HREF
probabilities). Through mid-afternoon, isolated totals of 3-6"
will be possible.

These rainfall amounts and intensity (high rain rates) over the
more urbanized corridor could result in isolated/localized flash
flooding, particularly given the wet antecedent conditions in
place for parts of the area.

Taylor

ATTN...WFO...MFL...MLB...

ATTN...RFC...SERFC...NWC...

LAT...LON 28918092 28888064 28158039 27638019 27127996
26587983 26137981 25798001 25418034 25888044
26568029 26998035 27318051 27898079 28288099
28698111

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