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WPC Met Watch

Mesoscale Precipitation Discussion: #0141
(Issued at 157 AM EDT Fri Apr 19 2019 )

MPD Selection

Graphic for MPD #0141

Mesoscale Precipitation Discussion 0141
NWS Weather Prediction Center College Park MD
157 AM EDT Fri Apr 19 2019

Areas affected...Florida Panhandle, Eastern Alabama, Western

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

Valid 190556Z - 191150Z

Summary...Thunderstorms were increasing around Midnight local time
from central Alabama into the western tip of the Florida
Panhandle. These storms should move to the northeast and may
repeatedly affect some locations, leading to localized heavy
rainfall and the potential for some flash flooding. Rain rates
around 1 in/hr will be common in most of the storms, but could
peak as high as 2 in/hr in some cases.

Discussion...Regional radars showed an increasingly organized band
of convection at 0530Z extending from ASN-MGM-PNS, or just east of
the I-65 corridor in Alabama. This renewed development was
occurring in the wake of an initial MCS that has since decayed;
GOES-16 IR satellite showed cold cloud tops in a similar location
around 03Z, but that MCS has all but vanished at this point.
Surface winds backed over eastern Alabama in the subsequent two
hours (03-05Z), likely in response to a slight surface ridge
developing in west-central Georgia, and an approaching cold front
from the west. This has increased low-level convergence and helped
focus the renewed development of thunderstorms. The initial MCS
likely outpaced the eastward progression of the instability and PW
axis closer to the cold front, but a corridor of MUCAPE in excess
of 1000 j/kg and PWs in excess of 1.7 inches exists across central
and eastern Alabama and the Florida Panhandle. This will support
vigorous convection through the early morning hours that may be
sustained as it lifts northeast into western Georgia in the 09-12Z
time frame as the cold front continues to progress. The
aforementioned orientation of the convective band is oriented
within about 20 degrees of the 850-300mb mean wind vectors, and
this favors at least some training convection and cell mergers in
the Florida Panhandle and eastern Alabama in the next several
hours. Therefore, localized maxima of heavy rainfall appear
likely. Many hi-res models indicate at least some swaths of 3+
inches of rainfall in the 06-12Z period, with rain rates peaking
in the 1-2 in/hr range.

Whether the training convection and localized opportunities for
several hours of heavy rain translate into flash flooding is still
uncertain. Flash flood guidance is relatively high (4+ inches in 6
hours or 3-4 inches in 3 hours) across the region and most
locations have seen rainfall close to average over the past few
weeks. USGS streamflow climatology indicates most regional rivers
and streams within the interquartile range, or reasonably close to
normal levels. Therefore, antecedent conditions don't especially
favor flash flooding, all other things being held equal.
Nevertheless, mesoscale conditions favor several hours of training
convection and if this intersects with vulnerable basins or urban
areas, some flooding issues may develop.




LAT...LON   34128517 34008413 32918378 31338453 29938538
            30258644 30198747 30688770 31918700 33338617

Last Updated: 157 AM EDT Fri Apr 19 2019

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Page last modified: Wednesday, 13-May-2015 19:29:02 GMT