FOUS30 KWBC 290739
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
339 AM EDT Tue Apr 29 2025

Day 1
Valid 12Z Tue Apr 29 2025 - 12Z Wed Apr 30 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...

...Southern Plains...

A repetitive scheme of successive convective outputs across
portions of West TX through Oklahoma will result in significant
flash flooding for a large portion of the above areas. The 
combination of several mid-level impulses ejecting northeast within
a large scale diffluent pattern will interact with a quasi-
stationary front aligned from the Western Rolling Plains of TX up
towards the Red River Basin mainly west of I-35. Favorable mid- 
level ascent will allow for waves of convective initiation
beginning late-morning and afternoon Tuesday with a secondary pulse
around 00z Wednesday with a final pulse forecast after 06z as the
mean trough finally starts pivoting east out of the Southwestern
CONUS. Instability within the confines of West TX up to the Red
River will allow for rapid development of convective clusters with
some supercellular modes plausible prior to nightfall, eventually
merging into a more multi-cellular scheme with backbuilding favored
within the confines of the front denoted pretty well within the
theta_E gradient output in each deterministic. All CAMs are well
supportive of the 3-wave convective evolution with heavy rainfall
situated across the Southern High Plains near the eastern Permian
Basin with a general QPF maxima aligned southwest to northeast
across the northern extension of the Rolling Plains in TX, up
through the Red River and into the southern portion of the OKC
Metro. This area has been the benefactor of multiple convective
episodes already, leading to flash flooding within the corridor
extending from Lawton down to the Red River. This area will be the
most primed location for not only widespread flash flooding, but
significant life-threatening flash flood prospects due to the well
above normal soil moisture anomalies likely curbing any potential
for rainfall to soak into the top soil layer. 

Latest 00z HREF probability fields are overwhelmingly indicative of
the threat with one of the more robust indications occurring
within the 6-hr FFG exceedance probability marker running between 
70-90% across the area extending from Foard County in TX up to
western Cleveland County in OK. Neighborhood probabilities of >5"
total rainfall are running between 50-80% in the same location with
>8" between 20-30% across Southwest OK between Lawton to the Red
River. Neighborhood probs for >3" are significant across much of OK
back into North TX with the southwest extension back into the
southeast corner of the LUB CWA. Considering the NASA SPoRT soil
moisture percentiles running between 70-99% for the 0-40cm layer
across the entire area above, the propensity for flooding, even in
rural zones will be higher than normal. Given expected rates
between 1-2"/hr during peak storm cycles and the expectation for
>3" of rainfall...the threat will be of the higher magnitude in
terms of impact prospects. The previous MDT risk inherited was not
only maintained, but expanded a bit further southwest to align with
the higher probabilities with the neighborhood >5" potential and 
the elevated HREF EAS >2" probabilities that have been depicted. A 
high-end MDT risk is forecast across the Red River Basin west of 
Wichita Falls up into the southern fringes of the OKC metro, 
including the town of Norman. Lower end probabilities for flash 
flooding will exist across areas of the eastern Permian Basin out 
through the Concho Valley as well as across much of Oklahoma not 
included in the MDT. 

...Mississippi and Ohio Valleys...

Mid-level impulses that eject out of the Southern Plains will
continue to press northeast towards the Mississippi and Ohio
Valleys with a progressive cold front moving southeast out of the
Midwest during the same time frame. Afternoon destabilization
coupled with the favorable addition of mid-level forcing and surface
frontogenesis will lead to scattered convective pulses across the
region with some organized elements focused within the confines of
the front and under the shortwave propagation. Soils remain moist
across much of the region extending from MO through the Ohio River
Basin with an eastern extension to the Central Appalachians and
Western PA Highlands. PWAT anomalies on the order of +1 to as high
as +2.5 deviations cements a favorable deep moist environment
conducive for heavy rainfall prospects within any convective
scheme. The greatest concentration of heavy rain will likely be
back over Southern and Central MO towards the 3 river confluence
zone near KY/MO/IN/IL. HREF probs for >1" are very high (70-90+%)
across much of the Mississippi and Ohio Valley areas with >2" probs
relatively high (50-70%) in-of the Ohio River Basin over Southern
IL through much of Eastern KY. The combination of convection over
areas that are still in recovery from previous rainfall episodes
and complex terrain will create a threat for isolated to perhaps 
scattered flash flood instances over a large area during the
afternoon and evening hours Tuesday. A SLGT risk remains firmly in
place across much of MO along and south of I-70 until the 3 river
confluence zone referenced above. A MRGL risk encompasses all other
areas east through Western PA and even the southwest corner of NY state.

Kleebauer


Day 2
Valid 12Z Wed Apr 30 2025 - 12Z Thu May 01 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE ARKLATEX, EASTERN OKLAHOMA, AND WESTERN OZARKS...

The pattern remains very active as we move into Wednesday as the
mean trough slowly slips eastward with ample mid-level energy
accompanying, creating an environment favorable for organized
convective clusters through the entire D2 time frame. Rich Gulf air
will be pulled poleward ahead of the advancing trough with several
mid-level perturbations ejecting out of the ahead of the primary
shortwave trough. This in combination with sufficient buoyancy
across Central and East TX through the Mississippi Valley will
maintain a widespread convective zone of impact with strong, heavy
thunderstorm cores and clusters capable of producing prolific
rainfall totals. 

Two primary periods of interest have become fairly well documented
within the recent deterministic cycles. The first is the 
continuation of the convective complex that will develop overnight 
Tuesday into Wednesday morning over the western Red River Basin and
slowly trudge eastward as it maneuvers in tandem with the primary 
shortwave energy, and across the remaining theta_E gradient running
parallel to the river. 00z HREF on the back end of its run is 
signaling some very impressive rainfall totals (2-5" within the 
first 12 hr. period in the forecast cycle (12z Wed to 00z Thu) 
across places along the Red River up through Central and Eastern OK
as the multi-cell cluster advances. Prob fields for >3" within 
that first 12 hrs. are between 50-90% across south-central OK, 
along and east of the I-35 corridor with 25-40% probs for even >5".
Considering this is only for the first 12 hrs., the probs are 
pretty impressive and really highlight the threat on the initial 
heavy QPF core. 

The second period of interest will occur in the afternoon and
evening hrs. as diurnally driven convection will flare up over
Eastern TX within a broad moisture rich environment as NAEFS
anomalies continue to point to +2 to +3 deviations for PWATs
(1.5-2" situated over the area. LLJ introduction by early evening
will only exacerbate the potential with increasing low-level shear
capable of persisting updrafts and eventual cell clusters that will
originate from cells moving northeast within the mean flow. Several
mid-level perturbations will be in the vicinity across Northeast TX
to truly enhance and maintain convective cores such that it becomes
a fairly favorable prospect for heavy rainfall extending into the
Lower Mississippi Valley. Totals between 2-4" within an areal
expanse are forecast across the ArkLaTex up through Western AR to
just before the MO Ozarks. Locally higher totals will be possible
across that entire area given the favorable rates between 1-2.5"/hr
forecast currently within global deterministic. Pending outflow 
propagation within the setup, heavier totals could advance further 
east towards Central AR, but at this juncture, the primary area of 
focus aligns over East TX up through Eastern OK and Western AR. 
This correlates well with the theta_E ridge extension up through 
the area where convective threats will be highest during peak 
diurnal destabilization and beyond. 

The previous MDT risk was maintained with a westward extension back
over portions of south-central OK down across the Red River into
TX. The MDT risk is NOT within the DFW metro, however it does lie
just north, so will have to monitor trends closely over the next
24-36 hrs. A broad SLGT risk extends south into East TX but well
north of the TX Gulf Coast. 

Kleebauer
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