AWUS01 KWNH 121209
FFGMPD
IAZ000-121658-

Mesoscale Precipitation Discussion 0706
NWS Weather Prediction Center College Park MD
809 AM EDT Wed Jul 12 2023

Areas affected...Iowa

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

Valid 121158Z - 121658Z

Summary...Intense rain rates up to 2"/hr will be possible this
morning with multiple rounds of thunderstorms. Localized totals
between 2-4" and flash flooding will be possible.

Discussion...Thunderstorms this morning continue to move west to
east along/north of a well defined stationary boundary that is
draped across central/southern Iowa into Illinois. Ahead of a fast
moving squall line now entering western Iowa, isolated to
scattered slower moving thunderstorms have developed across
central Iowa where IR imagery cloud tops continue to cool and area
radar imagery shows instantaneous rain rates exceeding
1.5-2.0"/hr. The latest mesoanalysis showed an axis of elevated
instability reaching 3000 J/kg across the outlook area with the
latest blended precipitable water product indicating upwards of
1.25" of available PW.

Multiple, repeating rounds of heavy rainfall appear most likely
this morning across portions of central Iowa where initial/leading
convection will remain slower than the advancing squall line.
Merging lines and clusters are also likely. The most recent runs
of the HRRR seem to be handling the current activity fairly well,
indicating streaks of 2-4" likely where those line mergers and
overlap occur. While the squall line is expected to be
increasingly progressive, helping to limit the duration, intense
rain rates near 2"/hr will be possible for a few more hours this
morning.

Antecedent conditions have been drier than normal over the last 7
days per the AHPS precipitation analysis, which may limit the
overall flash flood threat to the more sensitive and vulnerable
locations including urban areas.

Taylor

ATTN...WFO...ARX...DMX...DVN...FSD...OAX...

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

LAT...LON 43259319 43169270 42749153 42179100 41049129
40729237 40749333 40759435 40859480 41249527
41569539 42519519 43159455

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AWUS01 KWNH 141759
FFGMPD
FLZ000-ALZ000-MSZ000-142330-

Mesoscale Precipitation Discussion 0726
NWS Weather Prediction Center College Park MD
159 PM EDT Fri Jul 14 2023

Areas affected...Mississippi, Alabama, and Florida Panhandle

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

Valid 141751Z - 142330Z

Summary...An axis of slow moving and heavy thunderstorms will
continue to develop between a line of thunderstorms moving east
along the MS/TN line and persistent activity over the western FL
Panhandle. Under the axis between these features is the footprint
of the extreme (5-10") rainfall from yesterday over east-central
Mississippi into western Alabama. Given the sensitive nature of
these areas, there is likely to be further flash flooding this
afternoon there and localized elsewhere in the area of concern.

Discussion...Radar imagery depicts an MCS tracking east over
northern MS into western TN that is approaching northern AL at
1745Z. The south end of this line is rapidly developing with
rainfall rates likely 1" to 2"/hr. An axis of scattered
thunderstorms then extends south-southeast to the western FL
Panhandle which is where remnant MCS activity persists after the
extreme rainfall this morning that occurred along the Emerald
Coast of FL (and west of the associated MCV south of Panama City).

Along this axis is very moist air with PW of 2.0 to 2.2" (over +2
sigma), strong instability with MLCAPE 2000 to 3000 J/kg, and
light steering flow of 10kt or less from the north. A continued
expectation for a slow net westward propagation of the activity
over FL into higher instability and eastward progression of the
MCS along the TN border may further cause slow motion a pivoting
of the axis near the central MS/AL border where the extreme
rainfall fell yesterday.

All 12Z CAMs feature an axis of slow thunderstorms this afternoon
near the MS/AL border, though this is earlier than forecast.
Recent HRRRs also feature this activity, though only for a few
hours before dying off. The length of this event is uncertain
given how slow the flow is which may cause activity to rain out.
However, given the ample instability and robust moisture, there
should be plenty of outflow boundaries to reignite activity.
Therefore, there is a likely risk for further and possibly
considerable flash flooding over these sensitive areas along the
central MS/AL border and more localized flash flooding over far
western FL into southern AL and northeast MS into northwest AL
where 3hr FFG is generally 2.5 to 3".


Jackson

ATTN...WFO...BMX...HUN...JAN...MEG...MOB...

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

LAT...LON 34908843 34598790 33038688 31698642 30828648
30308660 30358737 30738811 32388897 33258935
33708952 33978951 34828907

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AWUS01 KWNH 141841
FFGMPD
MAZ000-NHZ000-VTZ000-CTZ000-NYZ000-NJZ000-PAZ000-150040-

Mesoscale Precipitation Discussion 0727
NWS Weather Prediction Center College Park MD
241 PM EDT Fri Jul 14 2023

Areas affected...Interior Northeast...New England

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

Valid 141840Z - 150040Z

Summary...Thunderstorms are beginning to erupt across portions of
the Interior Northeast and New England along a stationary front.
Bouts of high rainfall rates upwards of 2-2.5"/hr will lead to
some instances of flash flooding this afternoon given the
compromised soils across the Northeast and New England.

Discussion...Radar and day cloud phase imagery across the East
Coast depicts convective initiation is underway between KENX and
KBGM, in the vicinity of a stalled cold front. Thunderstorm
coverage is expected to increase over the next several hours as
convergence along the front interacts with several weak shortwaves
and some coupled jet forcing. Filtered insolation combined with
upper 60's-low 70's dewpoints supports 500-1500 J/Kg MLCAPE across
the region, albeit with some CIN in the wake of this morning's
storms. An abundance of tropical air remains across the region
with PWATs ranging from 1.2-1.9" (hovering in the 75th-90th
percentile range), and deep warm cloud layers hovering around
3-4000 meters. Meanwhile, enhanced southwesterly flow is forecast
to yield 25-30 kts of effective bulk shear which will encourage
some organized multi-cell clusters. In all, this environment
should support efficient warm rain production going into the
afternoon, with rates upwards of 2-2.5"/hr possible.

As storms build, bulk shear vectors oriented acutely to
quasi-parallel to the front and upper-forcing are expected to
support some repeat instances of thunderstorms, with rainfall
totals upwards of 2-4" possible through 0z tonight. This is
expected to lead to flash flooding given the degree of compromised
soils and FFGs (.25-1.25"/hr 1 HR FFGs) atop the region in light
of the very heavy rains over the last week. The 12Z HREF suggests
enhanced probabilities of 6 HR QPF exceeding the 5-10 year ARI
across the region (45-35%, respectively), with a signal for 100
year ARI exceedance also noted across portions of eastern PA
through NH (5-15%). Given the degree of the previous rainfall,
current signal from the HREF, and urban coverage, instances of
flash flooding are considered likely through tonight.

Asherman

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

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

LAT...LON 44857207 43827125 41997226 40277432 40527542
41267608 41817611 42537570 43297449 44107312


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AWUS01 KWNH 161344
FFGMPD
MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-161943-

Mesoscale Precipitation Discussion 0745
NWS Weather Prediction Center College Park MD
944 AM EDT Sun Jul 16 2023

Areas affected...New England

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

Valid 161343Z - 161943Z

SUMMARY...Areas of significant and locally life-threatening flash
flooding are expected going through the early to mid-afternoon
hours from extremely heavy showers and thunderstorms.

DISCUSSION...The latest GOES-16 IR satellite imagery in
conjunction with dual-pol radar shows an expansive area of
extremely heavy shower and thunderstorm activity lifting north up
across central and southern New England as shortwave energy pivots
across the region ahead of a stronger upper trough gradually
dropping southeast into the Great Lakes region.

This energy is interacting with a plume of deep tropical moisture
and instability surging up along the East Coast and inland across
the Northeast. In fact, the latest 12Z RAOB data and VWP data
shows the nose of confluent 40+ kt low-level jet nosing in off the
western Atlantic Ocean and up across Long Island and much of the
interior of New England which is helping to drive a 2.25+ inch PW
axis up across CT/MA and nosing into southern NH and southwest ME.
These PWs are near or at record levels relative to climatology for
this time of the year.

Coinciding this corridor of strong moisture transport is an axis
of moderately unstable air with MLCAPE values of as much as 1000
to 1500 J/kg. Vertical shear parameters are relatively steep as
well with as much as 30 to 40 kts of effective bulk shear in place
which is facilitating some notably strong and linear bands of
convection with some transient supercell type structures.

Going through midday and the early to mid-afternoon time frame,
the heaviest rainfall focus is expected to be over CT/MA and a
large portion of NH and southwest ME where the stronger convective
cells will be capable of producing rainfall rates of 2 to 4
inches/hour, with additional rainfall totals of as much as 5 to 7
inches possible given notable concerns for cell-training. The
stronger orographic ascent/upslope flow into higher terrain of the
Worcester Hills of central MA and up into the White Mountains of
NH will be areas most likely to see the heaviest totals.

Given the combination of extreme rainfall rates, cell-training,
locally wet antecedent conditions and areas of rugged terrain,
there is an elevated threat of significant and life-threatening
flash flooding over the next several hours.

Orrison

ATTN...WFO...ALY...BOX...BTV...CAR...GYX...OKX...

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

LAT...LON 45687070 45636982 45166939 44256964 43387020
42177090 40847223 40497303 40727382 41567368
42527302 44147211 45177139

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AWUS01 KWNH 171803
FFGMPD
PAZ000-MDZ000-VAZ000-WVZ000-OHZ000-KYZ000-INZ000-180000-

Mesoscale Precipitation Discussion 0753
NWS Weather Prediction Center College Park MD
202 PM EDT Mon Jul 17 2023

Areas affected...Central and Eastern Ohio Valley

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

Valid 171800Z - 180000Z

Summary...Showers and thunderstorms developing ahead of a cold
front will increase and coverage and train to the east through
this evening. Rainfall rates of 1-2"/hr are likely, resulting in
1-3" of rainfall. Flash flooding is possible.

Discussion...The regional radar mosaic this afternoon shows
rapidly expanding coverage of showers and thunderstorms from
eastern KY and southern OH through western PA and much of WV. This
convection is developing within modest height falls downstream of
a pronounced mid-level trough axis shifting eastward, aided by an
embedded shortwave noted in the RAP analysis and GOES-E WV
imagery. Additionally, a poleward arcing jet streak over New
England is leaving its diffluent RRQ atop the Ohio Valley,
providing an additional mechanism for ascent. This deep layer lift
is occurring within favorable thermodynamics for heavy rainfall
characterized by PWs of around 1.3 inches as measured by GPS,
around the 75th percentile for the date, and SBCAPE of 2000-3000
J/kg. Rainfall within this fresh convection is already reaching
radar-estimated rates of 1-1.5"/hr, with continued intensification
likely into the evening.

As the shortwave lifts northeast in tandem with increasing height
falls and continued upper diffluence, convection should become
more widespread as reflected by the available high-res guidance.
This is due not only to the increasing deep layer ascent, but more
robust thermodynamics as PWs surge above 1.5" in conjunction with
a ribbon of SBCAPE arcing from the SW to above 3000 J/kg. Within
this environment, convection will have the capability to produce
rainfall rates above 2"/hr as noted by modest HREF probabilities,
with 15-min rainfall from the HRR guidance possibly exceeding 0.5"
in some areas. General W/SW flow through the 0-6km layer noted in
regional 12Z U/A soundings will drive mean storm motions to 15-25
kts, but this speed will be somewhat offset by aligned Corfidi
vectors which will also be parallel to a pre-frontal trough. This
could result in short term training in many areas, with some
backbuilding into the greater instability also possible by this
evening. Where the longest duration of training can occur, or
along axes where multiple rounds of convection track, rainfall of
1-3" is likely.

7-day rainfall across this regio has been above normal noted by
pockets of 150-300% of normal according to AHPS. This has resulted
in more sensitive soils and lowered FFG to just 1.5"/3hrs in some
areas. Although HREF exceedance probabilities for this FFG peak
around 20%, it is possible training atop these vulnerable soils,
especially where within more sensitive terrain features, could
result in rapid runoff and instances of flash flooding.


Weiss

ATTN...WFO...CLE...CTP...ILN...JKL...LMK...LWX...PBZ...RLX...
RNK...

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

LAT...LON 41657941 41537872 41107824 40697827 39957843
39157904 38347987 37718119 37638234 37918337
38648434 39188489 39528478 39828392 40388265
41078146 41398075 41628010

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AWUS01 KWNH 171956
FFGMPD
MOZ000-ARZ000-180100-

Mesoscale Precipitation Discussion 0754
NWS Weather Prediction Center College Park MD
355 PM EDT Mon Jul 17 2023

Areas affected...South-Central Missouri into Arkansas

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

Valid 171953Z - 180100Z

Summary...Multi-cell cluster of supercells over central Missouri
will track southeast into Arkansas by this evening. Cell mergers
and repeating cells would cause rainfall rates of 2-3"/hr and
localized flash flooding.

Discussion...Supercells have developed in northwest flow over
central MO this afternoon. As these shift southeast cell mergers
and some repeating activity can be expected. Hourly rainfall
estimates from KSGF have already reached 2" with this activity
after accounting for hail contamination.

High instability (MLCAPE of 3000+ J/kg), wind shear (0-6km bulk
shear of 40-50kt), and lift from the left exit region of a NWly
jet streak centered over western IA will allow further
redevelopment. Moisture is only a little above normal with PWs
around 1.6", but the risk for activity to orient with the NWly (as
seen in recent scans from KSGF) leads to extended heavy rain which
should become excessive in at least localized areas into this
evening. Max hourly rainfall should be around 3".

This activity is not handled well in the CAM suite in terms of
timing and location. The area affected by this activity should be
bound on the west by outflow/cold pool from earlier activity over
eastern KS/OK, but the eastern bound is less certain. Upwind
propagation vectors do suggest a southward trend in the
southeastward motion from the mean flow, but the risk for this
activity extending over to the mid-MS river will be monitored
(though that area has higher FFG from being drier in recent days).

Recent rainfall, particularly over south-central MO and farther
west, along with terrain in the Ozarks, makes this area more
susceptible to flash flooding with FFG generally around 2"/hr.
Flash flooding should be limited to where cell mergers and
repeating cells are greatest and is considered possible into this
evening.


Jackson

ATTN...WFO...LSX...LZK...MEG...PAH...SGF...TSA...

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

LAT...LON 38009153 37919111 37619055 37019024 36429022
35829044 35529112 35669259 36429336 36919366
37559361 37889338 37929248

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AWUS01 KWNH 212055
FFGMPD
NCZ000-SCZ000-GAZ000-TNZ000-ALZ000-MSZ000-220230-

Mesoscale Precipitation Discussion 0782
NWS Weather Prediction Center College Park MD
454 PM EDT Fri Jul 21 2023

Areas affected...Southern TN...Northern AL...Far Northeast
MS...Northern GA...Western NC...Western Upstate SC...

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

Valid 212055Z - 220230Z

SUMMARY...Repeat/Training ahead of MCV with spots of 2-4" over
recently wetted grounds pose possible incidents of flash flooding.

DISCUSSION...Core of strong MCS is moving through western TN. At
the surface, the trailing end of the larger northern stream cold
front is positioned nearly splitting TN from west to east. South
and ahead of the MCV, a narrow ribbon of enhanced unstable air
with MLCAPE of 2500-3000 J/kg, while CIRA LPW shows core of very
deep layer moisture is along the southern TN boarder totaling from
1.75 over the E to nearly 2.25" in the core of the MCS. Moisture
convergence along the cold front with weak southerly WAA ahead of
the MCS has expanded convective coverage along and south of the
cold front in Middle TN. Visible and RADAR loops show storms are expanding/filling in with cold tops and strong updrafts to support
2-2.5"/hr rates. Effective cold front of MCS is oriented
perpendicular to the MCS motion maximizing moisture convergence
along/ahead, which may even reach up to 2.75-3"/hr or at least
2"/15-30 minutes as suggested by the 18z HRRR.

Deep layer flow, like the deep moisture axis, is fairly parallel
to the frontal boundary to support at least a short period
repeat/training environment. However, propagation vectors likely
supported by any weak cold pools over the next few hours may
deflect effective storm motions just south of due east. This
should limit most significant training, but even 1 to 1.5 hours of
training suggest spots of 3-4" are possible. These totals in a
sub-3hr period are above the 3hr FFG (generally below 3" within
the area of concern), with a few areas of fully-saturated soils
across N AL and SE TN due to recent rains. As such, scattered
incidents of flash flooding are considered likely over the next
few hours.

Gallina

ATTN...WFO...BMX...FFC...GSP...HUN...MEG...MRX...OHX...

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

LAT...LON 35768653 35718336 34848256 33978315 33798408
33808596 33808736 33978895 34808868 35398851
35628824

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AWUS01 KWNH 212142
FFGMPD
MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-220330-

Mesoscale Precipitation Discussion 0783
NWS Weather Prediction Center College Park MD
541 PM EDT Fri Jul 21 2023

Areas affected...New England...Northeast NY...

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

Valid 212145Z - 220330Z

SUMMARY...Multiple Bands of slow moving, strong thunderstorms with
up to 2"/hr rates. Continue to pose likely scattered incidents of
flash flooding through early overnight period.

DISCUSSION...GOES-E WV suite depicts a highly dynamic mid to upper
level pattern over SE Canada into New England. The main core of
the upper low is pivoting along the far eastern extent of Ontario
along the Quebec boarder with strong secondary trof digging
through the St. Lawrence Valley toward N VT by the end of the
forecast period. Moisture is a bit reduced relative to further
south-east across New England, but strong 850-700mb convergence
has increased overall values up to 1.5" due to slightly drier
mid-level. However, this does steepen lapse rates to strengthen
instability and updraft vigor and with moist low levels in strong
convergence, thunderstorms will be capable of intense rates up to
1.75"/hr. As such spots of 1.5-2.5" are possible mainly across
far NE NY into VT after 23-01z, before instability wanes with loss
of daytime heating.

Further southeast within the broader southwesterly flow of larger
scale cyclone, very strong thunderstorms with impressive anvils
and broader than normal updraft/downdraft cores for New England
continue to progress slowly across S NH, central MA with a few
trailing cells into E Long Island. A subtle shortwave is slipping
northeast through S VT, shearing along the way aiding vertical
ascent, while also strengthening confluent southwest to
south-southwest low level flow. The effective warm conveyor has
much deeper, rich moisture with 1.5 to 1.7" total Pwats and
slightly warmer lower profiles for similar stronger instability
signals to maintain these stronger cores. Rain rates of 1.5-2"
still remain, but as the wave shears and lifts north, the winds
should abate ever so slightly. This has a positive affect for
favorable upwind/flanking line redevelopment as well as slows
forward propagation; both increasing rainfall duration. As such,
scattered to numerous spots of 2-3" are possible across SE NH, MA
into CT, RI), with some suggestion of even spots to near 4" by
03z. All considered, both areas are likely to continuing seeing
incidents of flash flooding, while a spot or two of considerable
flash flooding are possible in S and SE New England, especially if
occurring in/near urban centers.

Gallina

ATTN...WFO...ALY...BOX...BTV...GYX...OKX...

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

LAT...LON 45417058 44237043 42617056 41867057 41207085
40957169 40947246 41477339 42617347 43177333
43637378 44067491 44417542 44837540 45137481
45107245 45167165

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AWUS01 KWNH 251747
FFGMPD
MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-252300-

Mesoscale Precipitation Discussion 0792
NWS Weather Prediction Center College Park MD
147 PM EDT Tue Jul 25 2023

Areas affected...Southeast NY...Southern New England...

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

Valid 251745Z - 252300Z

SUMMARY...Slow moving thunderstorms ahead of main shortwave likely
to be slow moving thunderstorms resulting in widely scattered
possible flash flooding. Additional upstream cells could further
exacerbate flooding conditions by repeating across already
saturated grounds.

DISCUSSION...GOES-E WV suite depicts base of large scale trough
marked by compact shortwave starting to press into NE PA.
Downstream, low level conditions were a bit drier aloft, but have
started to see a stead increase in southwesterly low to mid-level
flow increasing deep layer moisture. Strong surface heating has
increased temperatures into the low 80s, with mid to upper 60s Tds
providing buoyant environment for scattered thunderstorms.
Regional RADAR mosaic denote scattered development across SE NY
across S MA, this generally aligns with a low level
confluence/deformation zone extending from the shortwave toward
the northeast. It is proximity to the boundary with approaching
upstream height-falls that have resulted in stronger 850mb inflow
reducing forward propagation vectors, and so initial cells have
produced 1-1.5"/hr and have been and are likely to continue to be
fairly stationary for the next hour or so, before exhausting local
instability. Spots of 2-3" are possible in these widely scattered
cells.

As the shortwave approaches, stronger south-southwesterly flow
should increase and along with deeper moisture profile support
stronger flux convergence along the boundary. Additional cells
are probable to develop/track through this axis with a potential
of short-term training/repeating. Additional 2-3" totals (rates
up to 1.5-2"/hr) will be tracking through areas of high soil
saturation with AHPS 7 to 14 day anomalies above 200%. As such,
flash flooding is considered possible for ongoing convection as
well as further into the evening hours.

Gallina

ATTN...WFO...ALY...BOX...GYX...OKX...

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

LAT...LON 43157229 43037074 41687100 41367179 41267347
41797431 42447430 42937363

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AWUS01 KWNH 251939
FFGMPD
AZZ000-UTZ000-260130-

Mesoscale Precipitation Discussion 0793...Corrected
NWS Weather Prediction Center College Park MD
338 PM EDT Tue Jul 25 2023

Corrected for fixed typo in summary

Areas affected...Northern Arizona, Southern Utah

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

Valid 251930Z - 260130Z

Summary...Scattered showers and thunderstorms will increase in
coverage this afternoon and advect N/NE through the evening.
Rainfall rates may reach 0.5-1"/hr at times, producing locally
more than 1 inch of rain. Flash flooding is possible.

Discussion...The GOES-E visible imagery this afternoon is showing
rapid development of diurnal Cu across the Four Corners states,
with the most agitated activity currently setting up over terrain
features. The deepest Cu, and associated convective elements noted
by the onset of lightning, is occurring across northwest AZ west
of the Mogollon Rim, which is downstream of a shortwave lifting
northward out of the low deserts of AZ. Enhanced ascent through
subtle PVA/height falls will continue as this feature shifts
northward, rotating along the periphery of the monsoon ridge to
the east. PWs across the area are measured via GPS to be 0.7 to
1.1 inches, above the 75th percentile according to the SPC
sounding climatology, and are collocated with SBCAPE that has
eclipsed 1000 J/kg. The result of this overlap of ascent and
thermodynamics will be the continued expansion of thunderstorms
through the aftn.

The current convective coverage is outpacing all available
high-res models including the HRRR, UA WRF, and experimental RRFS,
suggesting the ascent is more intense than the models are
predicting. With this already the case, and forcing/thermodynamics
expected to remain favorable, anticipate coverage of storms will
continue to increase. The HRRR sub-hourly fields suggest rainfall
may reach as high as 0.25"/15 minutes, but this may also be
underdone in the most intense cells. While 0-6km mean winds are
progged at 10-15 kts indicating generally progressive storms,
enhanced ascent downstream of the northward moving shortwave
aligned with the greatest instability could result in some slowing
noted by Corfidi vectors falling to around 5 kts. This is also
observed in current radar with some near-zero storm motions
immediately downstream of the shortwave. While storms will
generally be progressive to limit rainfall accumulations, where
brief slowing can occur, rainfall totals may eclipse 1 inch.

This region has experienced pockets of heavy rain the last 7 days
noted by AHPS departures that are in places more than 150% of
normal, and FFG is as low as 0.5-0.75"/1hr. Although HREF
exceedance probabilities for this FFG are minimal, it is possible
that any slow moving cell could quickly lead to runoff and
isolated instances of flash flooding. This will be most likely
should a slow moving storm move across normally dry washes or
sensitive terrain like slot canyons or burn scars.


Weiss

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

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

LAT...LON 38991222 38911111 38371061 37571041 36451068
35341100 34771146 34481210 34521254 34681334
35061386 37001403 38771345

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AWUS01 KWNH 271842
FFGMPD
FLZ000-280000-

Mesoscale Precipitation Discussion 0797
NWS Weather Prediction Center College Park MD
241 PM EDT Thu Jul 27 2023

Areas affected...Eastern and Southeastern Peninsular Florida...

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

Valid 271840Z - 280000Z

SUMMARY...Very slow moving, highly efficient thunderstorms near
tropical wave. Rates up to 3"/hr possible and spots of 3-5" may
result in rapid inundation flooding in urban corridor.

DISCUSSION...GOES-E Visible loop denotes closing low to mid-level
circulation just north-east of Cape Canaveral at the apex of the
deeper tropical wave that drops south-southwest toward Everglades
City. This leaves much of the east and southeast urban corridor
under strong moisture flux with 2.3-2.5" total PWAT axis along the
coast. Weakening convergence convection over the Northwest
Bahamas has allow for increased southeasterly flow/fetch across
this moisture axis; while clearing skies as increase low level
heating for middle to upper 80s temps creating a highly unstable
environment. Given the placement of the axis, convergence is
fairly deep to support surface based convection with sufficient
flux for deep moisture loading to updrafts. Additionally,
proximity to the deeper tropical wave reduces mean cell motions
enough to be slow enough to maintain clearer updrafts before
becoming outflow dominant. Hourly rain rates of 3"/hr are
possible particularly across SE FL where inflow may be strongest
from the southeast. Spots of 3-5" are possible as the updrafts
continue to expand and potentially form broader updrafts on older
colliding outflows. Given upstream inflow is going to be enhanced
by frictional convergence, there is a higher probability for cells
to reside across the urban areas along the I-95 corridor,
particularly south of St.Lucie/Martin counties.


Further north, northeasterly return flow along the northwest edge
of the deeper mid-level cyclone is more confluent and may be more
persistent, with best convergence along the southern edge, perhaps
developing within clearer skies/increasingly more unstable area of
S Brevard/Indian River counties with even slower forward
propagation given closer proximity to the deep layer trof axis and
limited steering flow. All considered, rapid inundation flooding
is considered possible within the urban areas seeing these most
intense rainfall rates.

Gallina

ATTN...WFO...JAX...KEY...MFL...MLB...

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

LAT...LON 30098127 29528073 28438038 28098032 26627990
25588003 25208020 24848067 25348124 26348089
27058077 27778096 28288108 28988142 29588173
29958164

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AWUS01 KWNH 282034
FFGMPD
MIZ000-INZ000-WIZ000-ILZ000-IAZ000-290245-

Mesoscale Precipitation Discussion 0802
NWS Weather Prediction Center College Park MD
433 PM EDT Fri Jul 28 2023

Areas affected...near the IL/WI border into northern IN

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

Valid 282045Z - 290245Z

Summary...Shower and thunderstorm development will develop soon
near a front and returning outflow boundary. Hourly rain totals
to 2.5" with local amounts to 5" could lead to flash flooding.

Discussion...SPC mesoanalyses over the past several hours reveal
that CIN across the region is eroding in the wake of the
convective system heading across WV. An upper level shortwave
extending from WI and central IA is moving eastward, aiding upper
level divergence across the discussion area. Veggie band
satellite imagery reveals a cumulus field forming near the MN/IA
border east-southeast to the WI/IL border, supporting the SPC
mesoanalysis. This is near and to the northeast of a low pressure
area and a mesoscale warm front/returning outflow boundary. ML
CAPE is rising ~500 J/kg per hour, now over 4500 J/kg over
northern IL. Effective bulk shear of 25-45 kts lies across the
region. Precipitable water values per GPS data are 1.6-1.8".
Diffluence in the 1000-500 hPa thickness pattern is fairly
pronounced in this region. All of the above support the formation
or expectation of an organized convective complex in the near
future.

The expectation in the short term is for showers and thunderstorms
to develop from near the IA/WI/IL border east and east-southeast
into northern IN with time and eventually develop into an
organized convective complex. The mesoscale guidance has a varied
signal in this region which lowers confidence in details, hence
the Possible category. The GFS-based Galvez-Davison instability
Index implies an increase in thunderstorm development to at least
a scattered coverage between now and 03z. The ingredients
available support hourly rain totals to 2.5" with local amounts to
5". This would occur where cells train, merge, or mesocyclones
manage to form. This rainfall would be especially problematic in
urban areas and near the WI/IL border, which is a region that has
received 300% of their normal rainfall over the past week.
Isolated to widely scattered instances of flash flooding are
anticipated.

Roth

ATTN...WFO...ARX...DVN...GRR...IWX...LOT...MKX...

ATTN...RFC...NCRFC...OHRFC...NWC...

LAT...LON 43348945 42718718 41358500 40728534 40968732
41708941 42579099 43269104

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