Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201852

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
252 PM EDT Sat Aug 20 2016

Weak high pressure will continue to drift east from the Mid-
Atlantic coast through tonight. A cold front over northern
Illinois will move through the central Mid-Atlantic Sunday
afternoon into the evening. High pressure then builds over the
area into Tuesday before persisting offshore through the rest of
the week.


As of 2pm, 1020mb surface high is over the Canadian Maritimes
with a surface ridge stretching SW to the northern Mid-Atlantic
coast. South winds up to 10 mph have developed over the area with
dewpoints holding in the mid 60s over the Balt-Wash metro and
around 70F in the SWrn zones. Cu field clearly marks where the
higher dewpoints and scattered shower/isolated thunderstorm risk
persists rest of the afternoon - much denser cu central VA Blue
Ridge and W/NW.

Diurnal showers end this evening, but the warm/moist sector ahead
of the cold front over the Midwest will enter from the west
overnight. T-storm chances increase west to east late tonight.
Activity looks to extend as far east as central MD by sunrise
Sunday. Increased moisture may allow for patchy radiation fog
Piedmont and west tonight, though increased clouds will limit such
development. Min temps generally low 70s as dewpoints increase.

Sunday, cold frontal passage looks to enter the CWA from the west
around midday and clear the Bay by 9pm. Scattered showers/t-storms
spread in advance of line(s) of thunderstorms associated with the
front. Pwats increase to 2.2 inches, indicating heavy rain rates.
However, 25 kt bulk shear will keep the storms progressing,
limiting the flash flood risk to sensitive locations that have
repeating cells. 09Z SREF indicates MLCAPE struggles to exceed
1000 j/kg. Marginal shear and instability results in a marginal
risk for damaging wind. Max temps to hit 90F east of I-95 where
heating is longest ahead of the precip. Otherwise, max temps mid


The cold front clears the Bay late Sunday evening with the bulk of
upper trough energy PA and north. Sharp end to precip clears the
Bay before midnight with NWly flow (gusting to 25 mph) and a
truly dry air mass spreading across the area for the first time
since late June.

High pressure builds through Monday night. Sunday night min temps
low to mid 60s inland, Monday max temps low to mid 80s, and Monday
night min temps 50s west to low 60s east. Water temperatures are
in the low to mid 80s, so near shore locations will remain warm.


High pressure of Canadian origins will position itself over the area
leading to cooler and much less humid conditions Tuesday into
Wednesday. As the high moves off shore, southwesterly flow will
bring a return to warm and humid weather by late in the week. A cold
front will approach from the west and likely stall near the area
late in the week into next weekend increasing chances for showers
and thunderstorms.


VFR conds persist into tonight as high pressure shifts east from
the coast. Light sly flow slowly increases moisture with overnight
clouds increasing in coverage. Scattered showers and isolated
thunderstorms spread east from the Allegheny Mountains to the DC
metros overnight. Thunderstorm coverage increases until the cold
front crosses the DC metros from the west in the late
afternoon/early evening.

High pressure then builds overhead through Monday night with VFR
conds expected. NWly flow Sunday night around 20 kt.

Mainly VFR expected Tuesday-Wednesday as high pressure shifts east
and flow turns southerly.


High pressure drifts from the coast through tonight with continued
light southerly flow. Cold front approaches Sunday morning and
crosses Sunday evening. Gusty showers and thunderstorms ahead of
the front likely to warrant special marine warnings.

High pressure then builds overhead through Monday night with clear
and dry conditions expected. NWly flow Sunday night gusts 20 to 25
kt, so an SCA will be issued.

High pressure over the waters and light winds below Small Craft
Advisory levels during the middle of the week.




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