AWUS01 KWNH 052113
FFGMPD
FLZ000-ALZ000-MSZ000-LAZ000-060200-

Mesoscale Precipitation Discussion 0567
NWS Weather Prediction Center College Park MD
512 PM EDT Fri Jul 05 2024

Areas affected...Southern Mississippi & Alabama & Eastern
Louisiana

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

Valid 052111Z - 060200Z

SUMMARY...Storms that have developed ahead of a cold front are
nearly stationary, and have been producing rain rates over 3
inches per hour. Flash flooding possible.

DISCUSSION...Several areas of storms that have developed this
afternoon across the central Gulf Coast have been merging into
larger complexes. These storms have a history of producing
rainfall rates over 3 inches per hour, due to abundant atmospheric
moisture with PWATs over 2.5 inches from SPC mesoanalysis. SBCAPE
values are peaking near 5,000 J/kg over coastal Mississippi. These
very favorable atmospheric conditions suggest continued
maintenance of the ongoing convection. Since this main complex of
storms is well out ahead of a southward moving cold front
approaching the LA/AR border, they will have plenty of time to
remain in place and potentially cause flash flooding over the
impacted areas. FFGs in this area are very high, generally at or
above 3 inches per hour and 4 inches per 3-hours. Thus, only the
strongest and most stationary storms will be strong enough to
produce flash flooding. However, given the aforementioned near
record atmospheric moisture in place for these storms to feed
on...these rates of rainfall are possible. Thus, flash flooding is
possible.

CAMs guidance has been handling the convective evolution in this
area fairly well, and suggests that the storms generally along the
line that follows the east-west-oriented LA/MS border will
gradually creep southward, and may impact Mobile and New Orleans
over the coming hours. Significant flash flooding would be
possible should 3 inch per hour rates occur over those respective
metros. Additional storms associated with the cold front may form
in areas hit with the current convection north of the primary line
over south-central MS and northern LA, which may also result in an
isolated flash flooding threat. With loss of daytime heating this
evening, the convective coverage and intensity should wane,
resulting in a lessening threat for flash flooding.

Wegman

ATTN...WFO...JAN...LCH...LIX...MOB...SHV...

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

LAT...LON 32379243 32179014 32188880 31978810 31868751
31398731 30618759 30438854 29859005 29979140
30369272 31449277
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AWUS01 KWNH 191227
FFGMPD
FLZ000-ALZ000-MSZ000-LAZ000-191730-

Mesoscale Precipitation Discussion 0660
NWS Weather Prediction Center College Park MD
827 AM EDT Fri Jul 19 2024

Areas affected...Central Gulf Coast

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

Valid 191226Z - 191730Z

Summary...Efficient thunderstorms with rainfall rates upwards of
3"/hr at times are expected to persist this morning. Repeating of
these storms may lead to some flash flooding.

Discussion...Radar and IR imagery across the Central Gulf Coast
continue to track an axis of showers and thunderstorms lifting
northeastward at around 10-15 kts. A particularly efficient
cluster of thunderstorms southwest of Mobile, AL contained
estimated rainfall rates approaching 3"/hr earlier as individual
cells merged near the coastline recently.

This corridor of activity is likely forced by 1) an approaching
shortwave to the west and 2) a diffuse northeast to southwest
oriented offshore convergence axis, which is aligned with the mean
wind vector. Amid the forcing from this low-level boundary, the
RAP suggests a very moist and unstable airmass will continue to
push inland along a tight gradient to maintain efficient rainfall
rates, with 2.1-2.25" PWATS and 2000-2500 J/kg of MUCAPE expected
along the coastline over the next few hours.

While the rainfall footprint with this activity will be somewhat
"popcorn" owing to a lack of appreciable vertical shear, the very
efficient rainfall production will support some flash flooding
risk this morning as cells repeat along the lingering convergence
axis. CAM guidance is a bit all over the place with initializing
the ongoing storms, although several pieces of high-res guidance
(11Z HRRR, ARWs, FV3, and RRFS) are quite wet and suggest rainfall
amounts of 3-5" are possible through this morning. While 1-3 HR
FFGs are quite high in the area (2.5-4"), repeating instances of
these efficient storms could realize these higher end amounts on a
localized basis, indicating some flash flood threat through this
morning.

Asherman

ATTN...WFO...LIX...MOB...

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

LAT...LON 30978818 30878667 30148686 29398840 28818930
29049008 29509009 30308934
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AWUS01 KWNH 191344
FFGMPD
FLZ000-ALZ000-MSZ000-LAZ000-191900-

Mesoscale Precipitation Discussion 1158
NWS Weather Prediction Center College Park MD
843 AM EST Tue Nov 19 2024

Areas affected...Eastern LA...Southern MS...Southern AL...Far
Western FL Panhandle...

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

Valid 191345Z - 191900Z

SUMMARY...Highly anomalous deep moisture and strength of flux
allowing for efficient rainfall production with progressive
pre-frontal trough. Embedded slower moving rotating updrafts will
enhanced localized rainfall totals of 3-5" resulting in possible
flash flooding.

DISCUSSION...GOES-E WV suite depicts a large scale closed low
dominating the northern Plains with negative tilt lower scale wave
moving through the western Great Lakes, this is driving a very
strong mid to upper level jet across the Mississippi Valley which
in turn is spurring an very broad and strong low-level jet out of
the Tropics into the central Gulf of Mexico intersecting the
central Gulf Coast. CIRA LPW shows nose of 1-1.25" surface to
850mb starting to near the southern TN boarder while as broad as
central LA to western FL Panhandle. Combined with 40-45kts of
southerly 850mb winds and 60-90 degrees of directional
convergence; brings moisture flux values into the 99th and maximum
percentile rankings over a vast area of the Deep South.

An embedded shortwave/inflection can be analyzed through depth
across S MS at the broad left entrance of the 120kt polar jet
across AR/N MS, but also a weak diffluence region across S MS/AL
in the wake of an exiting sub-tropical jet streak that is rounding
the downstream large scale ridge into the Southern Appalachians.
So while the height-falls are driving the cold front forward,
there is weak surface to 850mb wave in S MS that is backing
low-level flow and increasing flux convergence in that region, as
well as further upstream in the coldest tops/highest unstable air
across the mouth of the MS River and northern Gulf of Mexico. The
instability gradient is along the Gulf Coast and as a result
strongest cells/tops to -83C have been measure and with moisture
values of 2.5-2.75", rates of 3"+/hr are possible across SE LA for
the next hour or so. Near the surface inflection, weaker
instability but solid flux convergence and increased bulk shear
will allow for short-term efficient rainfall production to 2"/hr;
with the vast majority falling in a sub-hourly manner given
forward progress. This should result in possible flash flooding
for urban and prone areas across E LA into S MS/S AL over the next
few hours as the pre-frontal convergence zone slides east.

As the morning progresses, bulk shear values increase over 40kts
along and east of the inflection as it slides slower to the east
in the further enhancing right entrance (increasing to 130-140kts)
300mb jet. This will slow the frontal zone as well, and allow for
some modest/weak instability to build back west to the boundary.
Embedded rotating updrafts have a higher probability of occurring
and with backed/increased directional moisture flux and reduced
forward speed/propagation... downdrafts with capability to produce
2.5-3"/hr rates may occur. Recent HRRR and 00z Hi-Res CAMs hint
at this solution across the lower 2-3 rows of counties in
MS/AL...combine this localized increase of 2-4" with the preceding
progressive but intense showers on the pre-frontal trough and
localized 3-5" totals become increasingly possible. Given the
bulk of unstable air remains offshore, there is some reduction in
confidence that updrafts will be strong enough to overcome the
increased bulk shear to support these increased rates. However,
the potential remains and would be the most likely driver to
potential flash flooding events even into rural areas where FFG
values of 3-4"/3hrs are more representative of soil conditions.
As such, flash flooding is considered possible through the morning
into early afternoon.

Gallina

ATTN...WFO...BMX...JAN...LIX...MOB...TAE...

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

LAT...LON 32648645 32208539 30938530 30128581 30188632
30098773 29628864 29068883 28878931 29139023
30578966 31758890 32518776

$$
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