WPC Met Watch |
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Mesoscale Precipitation Discussion: #1053 (2018) |
(Issued at 919 PM EST Sat Dec 15 2018
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MPD Selection |
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Mesoscale Precipitation Discussion 1053
NWS Weather Prediction Center College Park MD
919 PM EST Sat Dec 15 2018
Areas affected...NRN VA...WASH DC...NRN MD...ERN WV...SRN PA
Concerning...Heavy rainfall...Flash flooding likely
Valid 160218Z - 160618Z
Summary...Reports of road closures, water flowing over roads, and
streams reaching bankful had escalated Saturday evening. Continued
moderate rainfall overnight will mean additional flooding and
isolated flash flooding.
Discussion...At 01Z WPC had upgraded portions of the mid Atlantic
to a Slight Risk of excessive rainfall overnight. Slight refers to
an increase in the neighborhood probability of exceeding flash
flood guidance. Certainly stronger wording could be used locally,
as singular impacts were already being felt, and are sure to
continue.
Twelve-hour NSSL precipitation estimates depicted 1 to 2 inches of
rain, locally greater than 2 inches, across Washington D.C. and
suburbs, extending north and west into VA/MD. Overnight this
region will remain amidst the greatest deep layer height falls
associated with the eastward migration of an upper low in the Ohio
Valley, as surface low pressure lifts along the mid-Atlantic
coast. The RAP lifts the surface low into southern Maryland,
tightening low level gradients, resulting in strengthened
frontogenesis along an arc from northern VA to southeast PA
through 06Z. The 00Z HRRR and 12Z NSSL WRF were handling the rain
distribution best of the hi-res models, and they paint additional
amounts up to 1 inch through 06Z along and west of I-95, with
rates generally near or under a half inch per hour at any given
location. This will include some extension of heavier rates into
some of the mountain upslope areas in western MD and eastern WV,
where FFG was also very low. Rates greater than half inch per hour
are possible near and east of I-95 where the environment appears
increasingly supportive of convective enhancement.
Of main concern is the increased number of reports of flooding,
and at least one report of a water rescue and deep water flowing
over a roadway in Maryland. Additional such events seem likely
given the wet soils and swollen river systems.
Burke
ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...
ATTN...RFC...MARFC...
LAT...LON 40467717 40417638 40097581 39787573 39057636
38467675 37967827 38867922 39627901 40307788
Last Updated: 919 PM EST Sat Dec 15 2018
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