AWUS01 KWNH 171741
FFGMPD
ALZ000-MSZ000-172335-

Mesoscale Precipitation Discussion 0053
NWS Weather Prediction Center College Park MD
139 PM EDT Wed Mar 17 2021

Areas affected...East-Central TN into Southwest/Central AL

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

Valid 171735Z - 172335Z

SUMMARY...Severe supercell thunderstorms will be capable of
producing some flash flooding this afternoon with localized
repeating of cell activity and impacts on areas that have recently
seen heavy rainfall and have saturated soil conditions.

DISCUSSION...The latest GOES-16 satellite imagery shows convection
rapidly developing and expanding in coverage across the Deep South
with visible imagery showing a substantial amount of low-level
cloud street activity focusing across especially areas of southern
MS and southwest AL as thinning low clouds allows robust diurnal
heating to ensue and couples with a moist south-southwest
low-level jet of 40 to 45 kts for rapid boundary layer
destabilization.

The 17Z RAP mesoanalysis suggests a moderate to strongly unstable
airmass already pooled across the region with MLCAPE values as
high as 2000 to 2500 j/kg across much of central/southern MS and
west-central to southwest AL. Meanwhile, there is a significant
amount of shear in place which is being aided by the approach of a
strong upper low over the southern Plains. Already strong
kinematic profiles are favoring warm-sector effective bulk shear
values of 50 to 60 kts.

Overwhelmingly, the dominant hazard across the South this
afternoon and evening will be severe weather, as this highly
favorable thermodynamic environment couples with strong low to
mid-level shear profiles over the region for strong and locally
discrete supercell thunderstorms. Please see the latest SPC Day 1
Convective Outlook and Tornado Watch #0029 for more details.

However, there are portions of east-central MS and southwest to
central AL that will also have a somewhat elevated concern for
flash flooding if any of these supercell thunderstorms impact or
perhaps even locally repeat over the same area. Several areas in
east-central MS in between Hattiesburg and Meridian received as
much as 5 to 7 inches of rain since early yesterday morning, and
similar amounts have been noted in parts of southwest to
south-central AL from west-southwest of Montgomery to the MS/AL
border.

The latest HRRR guidance suggests some tracks of supercell
thunderstorms potentially repeating over the same area and
supporting as much as 3 to 4 inches of rain with isolate heavier
amounts going through the late-afternoon hours. This will drive
some concerns for flash flooding as a result, with a particular
emphasis on the areas that have seen heavy rainfall over the last
24 to 36 hours and thus have saturated and highly sensitive soil
conditions.

Orrison

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

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

LAT...LON 34008656 33238586 32258687 31558815 31258931
31558986 32118976 32858918 33648806
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AWUS01 KWNH 251258
FFGMPD
NCZ000-GAZ000-TNZ000-ALZ000-MSZ000-251856-

Mesoscale Precipitation Discussion 0065
NWS Weather Prediction Center College Park MD
856 AM EDT Thu Mar 25 2021

Areas affected...northern AL, southern TN, northwest GA

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

Valid 251256Z - 251856Z

Summary...A gradual increase in the flash flood risk is expected
across portions of northern AL, northwest GA and southern TN as
convection persists across the region through the morning.

Discussion...Convection is expanding in coverage/intensity this
morning across portions of northern AL into southern TN. This is
being driven by very strong low level moisture transport, with the
bulk of activity focusing on the northern instability/moisture
transport gradient. The southern extent of the moisture transport
axis over southern MS/AL will generally remained capped through
the morning hours...however continued convective development is
expected further north closer to the area of enhanced low level
convergence from northern AL into southern TN and far northwest GA.

The environment is not really conducive for true backbuilding
cells...however it is favorable for continued upstream convective development...given the persistence of moisture transport and
available instability...which will then likely track across the
same areas through the morning hours. It is this multiple rounds
of cells that will lead to some flash flood risk as the morning
progresses. Initially the flash flood risk will be isolated...but
as soils begin to saturate...and additional rounds of convection
continue...the flash flood risk is expected to increase as the
morning progresses. Recent HRRR runs seem to have a decent handle
on the current activity and expected evolution over the next
several hours. Generally looking at amounts as high as 2-3"
through 18z over the MPD area. Additional rain after 18z is
expected...with an uptick in the flash flood risk possible as
intense convection moves over saturated soils. We will continue to
monitor the area through the day.

Chenard

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

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

LAT...LON 35658564 35658432 35198397 34458483 33758670
33568748 33968801 34088808 34658823 35168814
35438709
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