Graphic for MPD #0108

Mesoscale Precipitation Discussion 0108
NWS Weather Prediction Center College Park MD
713 PM EDT Fri Mar 22 2024

Areas affected...southern FL Peninsula and the Keys

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

Valid 222312Z - 230500Z

Summary...Flash flooding will be possible across portions of
southern FL, including the FL Keys, through 05Z. Rainfall rates
with an approaching MCS may exceed 2 in/hr along with localized
totals of 3-5 inches (perhaps locally higher).

Discussion...GOES East infrared and regional radar imagery at
2230Z showed an MCS to the southwest of the southern FL Peninsula.
The coldest cloud tops and bulk of lightning strikes have been
advancing toward the southeast, missing Key West by 50-100 miles
to the west. However, ship observations showed a 1006 mb low was
located ~110 miles west of Key West and moderate to heavy rain
with embedded thunderstorms were occurring north of the low within
a low level warm advection regime...north of an estimated warm
front extending across the Keys (though ongoing convection was
making the exact frontal placement difficult). Farther east, a
supercell was observed over Biscayne Bay, tracking north near the
barrier island marking the eastern edge of the bay. Warm rain
processes were dominating this cell given the lack of recent
lightning data and relative warm tops on infrared imagery. Short
term trends indicate this cell may impact Key Biscayne and
portions of Miami/Miami Beach in the short term with rain rates of
1-2 in/hr if it is able to survive. According to the SPC
mesoanalysis, MLCAPE has not changed much since 18Z across
southern FL, with the northern extent of the 500 J/kg contour
reaching North Key Largo, coinciding with precipitable water
values of 1.7 to 2.0 inches.

As a mid-level closed low/trough over the Lower Mississippi Valley
continues to track east into the early overnight hours, large
scale lift will overspread FL, including increasing
divergence/diffluence aloft. 925-850 mb layer southerly flow will
likely increase at least another 10 kt from their present 25-30 kt
values across southern FL, ahead of the approaching surface low
west of Key West through 03-06Z. Widespread heavy rain will
translate into southern FL from the west but additional convective
development will be possible in advance as increasing moisture
transport and CAPE overspread southern FL over the next few hours.
Rainfall rates over 2 in/hr will be possible on a localized basis,
especially with organized cells given favorable shear profiles,
with storm totals of 3 to 5+ inches, perhaps focused near the Keys
or the southern Everglades. There will be localized potential for
higher rates along the urban southeastern corridor as well.

Otto

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

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

LAT...LON   26758023 26547979 26107953 25007990 24308110
            24178187 24438223 24848210 25428157 25918090
            26628050
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Last Updated: 713 PM EDT Fri Mar 22 2024