Flash Flood Guidance
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000
AWUS01 KWNH 221754
FFGMPD
FLZ000-222200-

Mesoscale Precipitation Discussion 0107
NWS Weather Prediction Center College Park MD
153 PM EDT Fri Mar 22 2024

Areas affected...FL Keys into southeastern FL

Concerning...Heavy rainfall...Flash flooding possible

Valid 221752Z - 222200Z

Summary...An increased risk of localized flash flooding will exist
across the FL Keys into southeastern FL over the next few hours.
Hourly rainfall totals of 1-2 inches will be possible, but cannot
rule out isolated rates over 2 in/hr where favorable
instability/forcing overlap.

Discussion...Regional radar and visible satellite imagery showed
an MCS extending from offshore of southwestern FL into the
southern Peninsula with an embedded circulation/low located over
the southern Everglades at 1730Z. An outflow enhanced effective
front extended southwestward from the low over the open water and
southeastward through the Upper Keys with surface dewpoints in the
upper 60s across the region near and south of the boundary.
Precipitable water values were 1.6 to 1.8 inches from the 12Z MFL
and KEY soundings which displayed high relative humidity
throughout the column and freezing levels of 12.5 to 14.0 kft.
Therefore, the environment was supportive of efficient rainfall
production despite relatively low instbility; the 500+ J/kg MLCAPE
contour only covering the Keys, with lower values to the north.
Rainfall over the past 3-4 hours has resulted in 0.5 to almost 2
inches of rain in the southern Miami suburbs with hourly totals
near 1 inch over the past 1-2 hours.

Moderate (~20-30 kt) low level warm advection ahead of the
meso-low will continue to allow for steady moderate to locally
heavy rain across the urban southeastern corridor over the next
few hours as it tracks southeastward, in addition to general
overrunning of the boundary in place just south of the region. The
greatest focus for higher rainfall intensities will exist just
ahead of the meso-low with possible training of heavy rain from
west to east mostly over the Everglades but the expected axis of
training may clip the the southeastern urban corridor as well,
with 1 to 2+ in/hr. Embedded convective elements will locally
increase hourly rainfall over 1 inch elsewhere across the region
with additional totals of 1-3 inches possible through 22Z. Farther
south where instability is a bit higher, greater potential will
exist for hourly rainfall of 1-2 inches, with locally higher rates
possible but the progressive southeastward movement of the MCS
should limit short term additional rainfall totals with this
initial round of storms across much of the Keys. However,
additional rounds of heavy rain are expected later this evening
with additional MPDs possible.

Otto

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...KEY...MFL...

ATTN...RFC...SERFC...NWC...

LAT...LON   26478041 26417988 25667990 24818047 24378135
            24448195 24698202 25128196 25558136


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