Hydrologic Outlook
Hydrologic Outlook
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Hydrologic Outlook
National Weather Service Tallahassee FL
432 AM EDT Wed May 7 2025
...INCREASING THREAT OF HEAVY RAINFALL AND FLASH FLOODING THURSDAY
THROUGH EARLY NEXT WEEK...
Multiple waves of rain and storms, locally heavy, is expected across
the area beginning Thursday and lasting at least into the first part
of next week. This is all thanks to an area of low pressure that
will meander in the northern Gulf and central Gulf Coast region for
several days. While confidence is increasing in the threat of heavy
rain and flash flooding, the exact placement and rainfall totals are
still relatively low confidence.
The current most likely forecast calls for a widespread 4 to 8
inches across the forecast area from Thursday through Monday. This
does lie on the higher side of ensemble guidance, but still well
below the extreme high end. There is a 10% chance of exceeding 10
inches in localized spots during that time frame. The heaviest of
the rainfall and the period of greatest concern is Saturday through
Monday.
Conditions across the area have been fairly dry with abnormally dry
to moderate drought (D0 to D1) conditions observed on the US Drought
Monitor. Flash flood guidance is currently around 5-7 inches within
a 6 hour period or 6-8 inches within a 12 hour period. However, it
is important to note that as rain falls ahead of the main event,
these flash flood guidance values may come down. The waves of rain
over the next few days will help moisten the ground and prime us for
the potential of flash flooding this weekend.
Given low confidence in the exact placement of heavy rain, the
Weather Prediction Center (WPC) has outlined the entire forecast
area in a Marginal Risk of excessive rainfall (level 1 of 4) for
each day from Thursday through Saturday, which is as far out as the
outlooks go. This means there is a 5-14% chance of exceeding flash
flood guidance each day. As confidence increases, an increase in
risk level is likely closer to the event.
With the antecedent dry conditions, rivers are running low across
the area, and it will take a substantial amount of rain to result in
even minor riverine flooding. In most cases, the rivers can take 6
to 9 inches before minor flooding occurs. Chances for minor flooding
are rather low (generally less than 10%), but we will continue to
monitor. Remember the river forecasts locally only account for 48
hours worth of rainfall forecast.
If confidence increases in where the heaviest rainfall sets up and/or
if the rainfall forecast continues to the increase, a Flood Watch
may be needed for parts of the area in the coming days. Keep in mind
we are still about 2 to 3 days out from when the bulk of the
rainfall is expected, and the forecast can and probably will change
between now and then. Keep up to date with the latest forecasts over
the coming days.
Additional updates to this outlook will be issued if the forecast
changes significantly.
$$
73-YOUNG
