Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 280800
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EDT Thu Jul 28 2016

.SYNOPSIS...A front will remain stationary along the Mason-Dixon
line through Friday morning. An area of low pressure will ride
along this front across the area Thursday night into Friday. The
front will move offshore during the weekend, then high pressure
will build in by early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...A mid-level trough over the mid-
south and TN valley will move ewd next 36 hrs crossing the area
around midday Fri. This will induce an area of low pressure to
form over srn VA that tracks northeast toward Long Island by Fri
afternoon. There will be ample moisture over the local area with
PWATs in excess of 2.0 inches, forcing and instability to fuel
widespread showers and thunderstorms later today into Fri morning.
There will be a severe wx and heavy rainfall threat with t-storms
this afternoon into early evening with heavy rainfall threat and
isolated flash flooding tonight into Fri morning. 0-6km bulk shear
of 35-40 kt and decent helicities will support a risk of isolated
discrete supercells with perhaps a tornado before activity
consolidates more during the evening. In terms of rainfall
potential, the 00Z GFS shifted the axis of heavy rainfall further
north into PA and NJ. The 00Z ECMWF shows two areas of significant
rainfall one over PA near stalled out front and one over the CHO
area. Lack of rainfall during the past 7 days especially in ern
WV, nrn VA and MD and northward shift of QPF axis from models make
me lean toward not issuing a flood watch at this time. Will wait a
few more hours for additional ensemble guidance and WPC excessive
rainfall outlook before issuing any flood watches. Based on RFC
flash flood guidance, the area of greatest concern is from
Winchester south to Augusta and Nelson counties and, of course the
urban areas of DC and Baltimore.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...Trough axis and low
pressure will be shifting east of the area by 18Z Fri with rain
largely ending, although a few showers could linger into the
afternoon. Another s/w trough is fcst to cross the area Sat and
aid in additional shower and t-storm development with pockets of
heavy rainfall Sat afternoon and night.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Broad upper level troughing
will gradually push across the area during the first part of next
week. A building ridge over the Plains will begin to spread
eastward on Wednesday. At the surface, the quasi-stationary front
which has been a persistent feature of the local weather may get a
shove south from low pressure moving across the area on Sunday.
Showers and storms will be likely during this time. There is some
question how far the south the front gets, but high pressure over
New England will be in a favorable position to push drier air down
the coast. There`s a better chance of dry weather for Tuesday-
Wednesday. Temperatures will remain closer to normal through the
first half of next week.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...Numerous to widespread
showers and thunderstorms expected this afternoon into Fri morning
with risk of strong gusty winds and heavy rainfall. MVFR/IFR
conditions possible in heavy rain. A lull in activity expected Fri
afternoon and night before more rain moves into the area Sat-Sat
night.

Showers and thunderstorms will likely be present across the area on
Sunday. A smaller risk of thunderstorms will linger into Monday.

&&

.MARINE...Winds generally 10 kt or less except higher in t-storms.
Small craft conditions possible Fri, will reassses fcst later.

Low pressure will cross the waters Sunday, helping to push a front
south of the area. At this time, gradient winds are forecast to stay
less than 15 kt. However, thunderstorms will be likely Sunday, with
the chance lingering into Monday, posing a threat of locally higher
winds.

&&

.CLIMATE...Record high minimums were set at DCA and IAD yesterday.
DCA tied the record of 81F set in 1930. IAD set a new record with
75F breaking the previous record of 73F in 2006.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...ADS
AVIATION...ADS/LFR
MARINE...ADS/LFR
CLIMATE...LFR


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