Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 231357
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
957 AM EDT Tue Aug 23 2016

.SYNOPSIS...
High pressure remains over the region through much of the week
with a cold front moving through on Friday. High pressure returns
for the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure is centered over the central Appalachians this
morning. Overall the weather is quiet and non-impactful. Patch of
mid-level clouds, mainly across Virginia, beginning to transition
into a cu field; this should be areawide by afternoon, with
scattered to perhaps broken coverage. (Aside from the subsidence
inversion, the morning sounding is dry.) Thermal fields are
similar to yesterday, which will result in another day of lower to
mid 80s with dew points in the mid 50s to around 60.

The high will begin to move offshore tonight, but the pressure
gradient will remain weak. While some cirrus is possible,
temperatures should otherwise be able to drop close to the dew
points in the upper 50s and lower 60s away from the urban centers
and waters (upper 60s in these locales). Patchy valley fog will be
possible.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
The center of high pressure will move offshore for Wednesday and
Thursday, while mid/upper ridging expands over the SE CONUS. While
there will be an uptick for dew points on Wednesday, the more
noticeable change will come Thursday, when temperatures will near
90F and dew points will rise into the mid and upper 60s.

There is some model variation on how strong the SE ridge is. In
general the NAM is the weakest and allows some shortwave troughs
to more directly cross the area. Think Wednesday will be dry for
most, although there is a slim chance of a shower on the spine of
the Appalachians. Thursday will provide a better chance of
mountain convection as instability will be greater. While most of
this should be confined west of I-81, some of it could spill
eastward during the evening depending on shortwave trough
trajectory. A cold front will also be pushing south across PA late
at night, but convection should be at a diurnal minimum as it
nears the CWA.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Guidance remains in overall decent agreement through the long term
with the cold front crossing the region Friday and high pressure
passing to the north Saturday and exiting stage right slowly
Sunday and Monday. Pops spike Friday with instability associated
with the cold front then drop to sub-chance on Saturday. They
start ramping up especially in the west again Sunday and Monday as
upslope flow on southwest side of the high brings more moisture
into the mountains where terrain influences may allow storms to
pop. Probability looks low though without a larger forcing
mechanism. Temperatures will spike Friday ahead of the front into
the lower 90s then drop closer to normal through the weekend. They
may start to rise again Monday.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Stratocumulus near FL070 beginning to scatter into a cu field.
Scattered to perhaps broken coverage by afternoon. Little
aviation concern through Wednesday as high pressure moves
offshore. Could be some morning BR at MRB, but not a strong enough
signal to put in TAF yet. Scattered storms are expected to develop
over the mountains on Thursday, perhaps reaching MRB, but unlikely
in the metros at this point.

VFR overall Friday through the weekend. Main issue will be if any
thunderstorms impact the terminals on Friday.

&&

.MARINE...
Easterly flow on the waters this morning, generally around 10 kt.
Flow will become SE today and S by Wednesday and Thursday as high
pressure moves offshore. Sub- SCA expected through most of the
period. The best chance for southerly channeling appears to be
Thursday evening, but forecast is less than SCA criteria at this
time.

Front crossing the region Friday is a window for SCA conditions as
well as thunderstorms, but confidence is low on both. High
pressure likely keeps winds just below SCA over the weekend with
easterly flow.

&&

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

&&

$$
SYNOPSIS...RCM
NEAR TERM...ADS/HTS
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...ADS/RCM/HTS
MARINE...ADS/RCM/HTS



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