FOUS30 KWBC 110721
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Fri Oct 11 2024

Day 1
Valid 12Z Fri Oct 11 2024 - 12Z Sat Oct 12 2024

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

Easterly low level flow will bring showery conditions to the
central and southeast Atlantic coast of FL today into tonight. 
However with PWs below 2" and instability limited not currently 
expecting rainfall rates or totals to reach levels of concern for 
flash flooding. Thus we will continue to carry no risk area in the 
ERO.

Chenard


Day 2
Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

Moisture and instability return northward into southern FL Saturday
into Saturday night, with PWs increasing towards 2.25" and CAPE 
over 1000 j/kg. Meanwhile a weak wave moving into the eastern Gulf
of Mexico may result in an uptick in low level flow and
convergence. Thus expect we should gradually see an uptick in
convective coverage this weekend over the Keys into south FL.
 
Easterly low level flow and westerly upper level winds support the 
potential for slow moving convective cells near the coastal 
convergence axis. Timing remains a bit uncertain, and the better 
convective coverage may end up more over the Keys this period 
(where flash flooding is harder to come by), but given the 
increasing moisture and instability there is at least a conditional
threat of localized flash flooding Saturday into Saturday night 
into the more urban areas of southeast FL. If deep convection does
indeed develop then urban flash flooding is possible from the 
upper Keys into southeast FL.

Chenard


Day 3
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

The risk on day 3 is a continuation of the threat on day 2 over
Southeast FL. The overall thermodynamic ingredients remain the 
same, however there is a chance that forcing will be stronger by 
Sunday. Still some timing and positional differences amongst the 
guidance, but the general consensus is for a weak wave to move 
across FL Sunday, which should both result in a subtle uptick in 
mid/upper forcing and locally enhance lower level convergence. 

Thus currently expecting a greater chance of loosely organized 
convective clusters Sunday into Sunday night...and with wind fields
still supporting slow moving cells...this activity could tend to 
anchor along the coastal convergence axis for a while. Thus 
isolated urban flash flooding is considered possible. Certainly a 
chance that a Slight risk may be needed for one of these weekend 
days...but given some uncertainty with the synoptic evolution and 
convective coverage, think a good first step is just introducing 
Marginal risks for both days 2 and 3 (Sat and Sun) and continue to 
monitor trends.

Chenard
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