AWUS01 KWNH 232206
FFGMPD
TNZ000-ALZ000-MSZ000-ARZ000-240400-

Mesoscale Precipitation Discussion 0079
NWS Weather Prediction Center College Park MD
605 PM EDT Sun Mar 23 2025

Areas affected...Western & Middle TN...Northern MS...Northwest
AL...

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

Valid 232205Z - 240400Z

SUMMARY...Multiple rounds of intense showers/thunderstorms with
rates of 1-1.5"/hr may allow for a few streets of repeating cells
and 2-3" localized totals nearing/exceeding FFG values resulting
in possible widely scattered incidents of low-end flash flooding,
particularly near urban centers.

DISCUSSION...GOES-E WV suite depicts a strong, compact short-wave
across N IL/S WI moving quickly east with a lower-scale
wave/mid-level trough accelerating eastward into the upper-Ohio
River Valley.  This is accompanied by a strong upper-level jet
streak that has rounded the base of the main trof with solid right
entrance ageostrophic response across the lower Ohio Valley
providing strong divergence along and south into the Tennessee
River Valley.=20

Surface and LLJ has responded with increasing Southwesterly flow
fluxing higher theta-E air northward with Tds into the upper 50s
and lower 60s.  Filtered insolation and mid-level steepening lapse
rates have made the area modestly unstable with MLCAPE nosing
across W KY into W TN over 1000-1250 J/kg, along and ahead of
solid cold front.  Additionally, GOES-E Vis and sfc to boundary
layer streamlines suggest a confluence axis between deeper Gulf
moisture from the Western Gulf and return from the central/eastern
Gulf becoming increasingly confluent across central MS to NE MS
into Middle TN.  With conditionally unstable air, this has been
sufficient to break out weaker but slowly increasing convective
activity across Middle TN... with some convection/flux convergence
supporting rates of .5-.75", which is expected to increase over
the next few hours.  Forward propagation is likely to limit
overall totals with any individual cell, but could be stage
setting for later development.

As the line expands, cells will have capability for
back-building/flanking line development that is probable to align
with strong/fast steering flow resulting in some accidental
training.  However, further upstream cold front is starting to
advance with solid 90 degree convergence along the leading edge
southwesterly LLJ/moisture plume.  Cells will expand in coverage
and width and should be capable of 1-1.5"/hr rates as they
advance, with similar very fast (40+ kt) forward speed, likely
limiting overall rainfall totals.  Hence, any flash flooding
potential will require these cells to traverse areas already
affected by 1-2" totals with earlier rounds.  If so, 2-4hr spot
totals of 2-3" are possible. This is in range of the lower FFG
values over the TN valley (1.5-2"/hr & 2-3"/3hr).  As such, a few
widely scattered instances of flash flooding are considered
possible particularly after 00z and in/near urban settings.

Gallina

ATTN...WFO...BMX...HUN...MEG...OHX...

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

LAT...LON   36488810 36478551 35158602 34288698 33908848=20
            34009006 34279071 34979061 35638953

AWUS01 KWNH 232256
FFGMPD
MSZ000-LAZ000-ARZ000-240430-

Mesoscale Precipitation Discussion 0080
NWS Weather Prediction Center College Park MD
656 PM EDT Sun Mar 23 2025

Areas affected...Northern LA...Southern AR...Central MS...

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

Valid 232300Z - 240430Z

SUMMARY...Strong moisture flux convergence with initial convective
development will allow for very quick moisture loading and strong
downdrafts capable of quick 2"/hr rates (15-minute totals of
1-1.5" psbl).  As cold front moves east, interaction with older
warm sector convection may allow for localized repeating/training
and spot totals of 2-3" in 1-2hrs resulting in possible flash
flooding.

DISCUSSION...GOES-E Visible/10.3um and RADAR mosaic denote
scattered destabilization occurring across the warm sector mainly
along the Lower Mississippi River Valley at the intersection of
the nose of instability axis (2500-3000 J/kg) of MLCAPE that
extends from the Heart of Texas into northeast LA and the nose of
the deepest sfc to 850mb moisture core (LPW of .8-.9" across
south-central LA into northeast LA.  This boundary layer moisture
is quickly advancing northward toward a southward pressing/well
defined (steep isentropes) that is bisecting AR from NE to SW.=20
These cells are expected to be slower moving but with steering
more northward toward the frontal zone before effective bulk shear
increases due to stronger flow aloft across the Delta Region into
the Bootheel of MO.  The collision of the air masses is likely to
result in rapid convective development along the front from NW MS
across S AR into N LA and eastern TX mainly in the 01-02z time
frame.  There has been solid signal throughout the day toward this
time frame, but trend in the HRRR is a bit earlier and more
focused resulting in very strong moisture flux loading to the
line. Stronger mid-level dry air will likely aid stronger
downdrafts due to mixing but given loading is expected to have
heavy rainfall totals in quick sub-hourly amounts.=20=20

Experimental HRRR 15-min estimates 1-1.25" at onset around 0130z
become near 1.75" by 02-03z across N LA.  Hourly totals of 2-2.5"
seem plausible given weaker overall steering before cold
front/outflow boundaries begin to organize and advance eastward.=20
While soil moisture is about 45-55% (in all but the braided
portions of the MS River...65+% there), this is running in the
10-15th percentile, suggesting upper-soils may initially not allow
much infiltration).  Still, the spotty/smaller areal coverage may
limit the overall magnitude of flash flooding suggesting highly
focused/localized at least initially across S AR/N LA for spotty
possible flash flooding.   It is only later toward 04-06z with
some organization and potential west to east training that
localized totals may reach 2-4" through 06z.  18z HREF and recent
HRRR runs support the best probability to be in proximity to the
AR/LA/MS intersection and points east-northeastward.   Confidence
is increasing toward possible scattered incidents of flash
flooding through this time period before cells become too
scattered/progressive generally after 06z, but will continue to
monitor trends closely.

Gallina

ATTN...WFO...JAN...LZK...MEG...SHV...

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

LAT...LON   34389006 34318925 34248863 33868836 33378837=20
            32958857 32398922 32039070 31829179 31709325=20
            31989383 32779367 33569269 34099146=20

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