Quantitative Precipitation Forecast
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FXUS04 KWBC 270657

Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Sun May 27 2018

Prelim Day 1 QPF Discussion
Valid May 27/1200 UTC thru May 28/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr

Day 1

...Southeast / Alberto...
The forecast track for Alberto trended east with the 03Z Advisory.
The core of the system will track up through the eastern Gulf
today. Generally difluent upper flow and deep layer ascent will
support generous rainfall coverage over much of Florida / drying
out a bit over southwest Florida. The coneyor belt out to the east
of the parent synoptic trough may set up convergence right over
southeast Florida. Much of the guidance is not especially well
focused in the QPF fields, but the pattern is a little concerning
as cells dropping tropical style rainfall could train over the
urban areas / Miami. Some models are just offshore to the east
with the heaviest...but based on the NAM mass fields we painted
healthy areal average rainfall over Miami and more generally the
southeast coast of Florida to the tune of 2-3 inches. Expect
embedded heavier amounts. Meanwhile the difluent region farther
north and east will migrate up through southeast Georgia and into
the Carolinas with time. Expect again heavy areal average rainfall
and embedded totals exceeding 3 inches through Monday morning. WPC
QPF was derived from the UKMET, WRF-ARW2, and continuity.

...Mid Atlantic...
A shortwave trough is expected to ignite a convective event early
this morning from PA to the NJ coast, with other scattered
activity in the moist plume over Virginia to southern Maryland. In
the wake of this wave, convergent 850-700-mb flow is forecast to
set up during peak heating from central Virginia to southern
Maryland. The hi-res models, on average, light up this axis with
organized afternoon thunderstorms and locally heavy rainfall. The
global models, however - ECMWF and GEFS ensemble 6-hour
probabilities - have shown a slight trend to the north which could
place more heavy rain into the Washington D.C. vicinity. WPC QPF
was centered toward the HREF mean and ECMWF.

...Western/Northern U.S...
There will be another round of widely scattered diurnal convection
to the rear of the upper trough where low level moisture and mid
level lapse rates are sufficient. Farther east height falls and
upper difluence will overspread the high plains, and despite warm
mid level temperatures it does appear the low level moisture will
improve to the extent needed to support clusters of thunderstorms
from MT/WY down through western KS and into the OK/TX panhandles.
An early morning MCS will also drift downstream through
ND/MN...with additional afternoon activity expected to form there
along a front. All these things in the west and north were best
described by the WRF-ARW2 and HREF Mean, blended with WPC



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