FOUS30 KWBC 130800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Thu Mar 13 2025

Day 1
Valid 12Z Thu Mar 13 2025 - 12Z Fri Mar 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN CALIFORNIA...

A strong Pacific cold front associated with an amplified upper
trough will continue to drop southeastward along the southern
California coast this morning. Hi-res guidance indicates that
moisture advection and modest instability ahead of the front will
be sufficient to maintain rainfall rates of 0.5+ in/hr along the
coast into the upslope areas of the Peninsular Ranges early in the
period. Rates are expected to diminish as the front moves south 
and east into the Colorado Basin and the Baja Peninsula by late 
morning, but not before an additional 1-2 inches of rain falls 
across portions of the highlighted area. Neighborhood probabilities
indicate the greatest threat for heavier amounts is centered along 
along the orographically favored regions of the Peninsular Ranges.
A Slight Risk was maintained for areas at or below 3500 ft, where
precipitation is expected to fall as mostly or all rain.

Pereira


Day 2
Valid 12Z Fri Mar 14 2025 - 12Z Sat Mar 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER TO MID MISSISSIPPI VALLEY INTO PARTS OF THE OHIO AND 
TENNESSEE VALLEYS...

A strong mid-to-upper level shortwave crossing the Southwest on Day
1 is expected to move east of the Rockies, with a negatively-tilted
low developing over the central Plains early in the period.
Powerful forcing is forecast to interact with what is expected to
be a relatively modest plume of moisture advecting north ahead of
the system. Storms are forecast to develop initially over the 
lower to mid Mississippi Valley Friday afternoon before moving 
east into the Tennessee and Ohio valleys during the evening and 
overnight. Cell motions will likely be quite progressive given the 
very strong wind fields in place. Therefore, this convection will 
likely pose more of a severe risk than a flash flood threat. 
However, given the strong dynamics, along with sufficient 
instability for deep convection, expect that rainfall rates will be
briefly intense enough to produce localized amounts that exceed 
current model forecasts (maybe locally over 2 inches). 
Still, this appears to be a lower-end flood threat, and probably 
confined to localized impacts over more sensitive urban or low 
lying areas that are impacted by a quick burst of intense rainfall.

Pereira


Day 3
Valid 12Z Sat Mar 15 2025 - 12Z Sun Mar 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
TENNESSEE AND OHIO VALLEYS...

Even as the previously noted low lifts to the north through the
Great Lakes into Ontario, the upper pattern will remain amplified
across the central U.S. as an upstream shortwave dives southeast
into the southern Plains on Saturday. A surface wave developing
along the leading system's trailing cold front will help focus
deeper moisture tapped by strengthening southerly winds. While
differences in the details remain, the general consensus of the 00Z
guidance indicates that widespread accumulations of 2-4 inches
centered over parts of the Tennessee and lower Ohio Valleys are 
likely. A large Slight Risk was maintained across the region,
reflecting the higher probabilities for 2 inches or more shown by
by the GEFS/ECENS and where deeper moisture, interacting with
strong forcing, along a relatively slow moving front, is expected 
to raise the potential for heavy amounts late Saturday
into early Sunday. This remains a higher-end Slight Risk for parts
of the area, with an upgrade to a Moderate Risk possibly
forthcoming, especially once the period moves within the hi-res
window and details concerning rainfall rates and the placement of
the heaviest amounts become more clear. 

Pereira

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