FOUS30 KWBC 100829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Mon Feb 10 2025

Day 1
Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Beginning Monday afternoon, an increase of convergence on the nose
of 850mb flow extending from Texas into Tennessee will support an
increase in light to moderate rain and a few rumbles of thunder
from eastern Oklahoma through Kentucky/Tennessee. Rain rates are
expected to be modest (around 0.25-0.5 inch/3-hour period),
although some of this rainfall will eventually reach areas of
southeastern Kentucky where soils are moist and sensitive from
antecedent rainfall. The relatively short duration of light to
moderate rainfall in this area precludes an introduction of
Marginal/5% risk probabilities, although one may be needed in later
outlook updates if a longer duration of rainfall (greater than 3-6
hours) becomes apparent across southeastern Kentucky.

Cook


Day 2
Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF 
THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

...ArkLaTex-ArkLaMis into the Mid-South and Tennessee Valley...
Increasing coverage of showers and thunderstorms along and ahead of
a well defined cold front trailing a developing area of low
pressure taking shape over the Tennessee Valley will lead to an
increasing threat of excessive rainfall Wednesday into early
Thursday from easter Texas and parts of Arkansas and Louisiana
into the west aspect of the Appalachians of Tennessee and southeast
Kentucky. At the synoptic scale, a broad trough over the western 
U.S. will amplify, thereby enhancing the deep-layer ascent and 
southwesterly flow/moisture transport over this part of the country
due to a increasing low level flow. 850-700 mb moisture flux 
anomalies still look to increase to 2-3 standard deviations above 
normal Tuesday/Tuesday night while Precipitable Water values climb
to 1.5-1.75" (around +2 standard deviation above normal). The 
strengthening dynamical and thermodynamical support will make for 
efficient rainfall rates despite the lack of deep- layer 
instability and the exit region of a 125 to 150 kt upper level jet
should aid deep layer vertical ascent. Much of the guidance
generally depicts a widespread swath of 1.5-3" of rain within the 
outlook areas, with the most aggressive model being the ECMWF with
maximum values exceeding 4 inches. Storm motions nearly parallel 
to the WSW-ENE oriented surface boundary will boost the potential 
for training despite meager deep- layer elevated instability 
(MUCAPEs generally 250-500 J/Kg). With 2.00"+/3hr rainfall rates 
still being anticipated where the cells do train, again most 
likely within the Slight Risk area, which could lead to localized- 
scattered instances of flash flooding.

Bann


Day 3
Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
TENNESSEE VALLEY INTO THE MID-SOUTH,,,

...Tennessee Valley into the Mid-South...
The threat of excessive rainfall will continue on Wednesday and
early Thursday ahead of the same system which brought the 
excessive rainfall potential on Tuesday into early Wednesday as a 
cold front makes its way eastward. Broad scale ascent will continue
to aided by the southern entrance region of a 135 to 155 kt upper 
level jet...while moisture convergence is maximized along a well 
defined surface cold front which intercepts a plume of moisture 
being pulled northward by a 40 to 50 knot low level jet. There is 
still spread in the guidance about placement of where the heaviest 
rainfall will occur but amounts generally in the 1 to 3 inch 
range...with locally higher amount where any enhanced rainfall 
rates set up due to banding/training. Given antecedent 
conditions...feel that a Slight risk should suffice.

...California Coast...
The plume of moisture from the Pacific Ocean towards the end of Day
2 will start to bring rain to the coastal areas during the Day 3
period...beginning in northern and central portions of California
on Wednesday that propagates southward during Wednesday night and
Thursday. Present indications are that the heaviest amounts remain
off shore...but a general uptick in amounts was noted over the past
24 hours in this area.  

Bann

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