Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 251837
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
237 PM EDT Thu Aug 25 2016

.SYNOPSIS...
High pressure remains off the coast today. A cold front will
cross the region early Friday. High pressure will return for the
weekend. Another front may slowly slide southward into the area by
the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Debris clouds from the overnight convective complex remain across
the forecast area this afternoon, which has inhibited new
convective development today. A composite of mesoscale guidance
suggests that any development likely to be in/near the central
foothills of the Blue Ridge before the end of the day. Based on
current trends and recent HRRR runs, suspect that coverage may be
widely scattered at best. Am still holding out hope for a limited
area 30 PoP for a couple hours near the end of the day in the
aforementioned area. Clouds may end up being the most noticible
sensible weather feature this afternoon.

Additional thunderstorms will be developing in northeast
Ohio/northwest Pennsylvania late today. Some of that may slip into
the Potomac Highalnds before dissipating tonight, somewhere near
midnight.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Timing of the surface boundary continues to inch earlier.
Consensus timing looking like daybreak-mid morning from northwest
to southeast. Based on this timing, believe the passage will be
dry. Not only is the timing out of synch with favored diurnal
trends, but west/northwest winds will promote subsidence, and at
all levels above the surface ridging will reinforce that
subsidence. The downslope flow may take the edge off the humidity
but compressional warming may add to the temperature instead. Will
await the 12z ECMWF before deciding tomorrow`s temperature.

Ridging will keep muggy but rain-free conditions in place Friday
night through Saturday night. Temperatures won`t stray far from an
ensemble blend.


&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Ridge of high pressure aloft sits over our region Sunday while a
frontal boundary slowly approaches Sunday night into Monday. This
boundary will remain near or over our CWA Monday into Tuesday
bringing a chance of showers and thunderstorms. Shortwave energy
moves near our CWA Tuesday night and forecast becomes uncertain
after this. Moisture advection will be affecting our area but
depends on which guidance is used, the source/wind direction
varies. But in general... showers and thunderstorms are possible
Wednesday and Thursday. The forecast will be refined as confidence
increases. Temperatures will be in the mid 80s and low 90s and
heat indexes in the mid 90s.
&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR conditions will prevail for the current TAF period. Plenty of
mid-high level moisture from convective debris providing the
ceiling, but lower cumulus forming near FL050. The mix of clouds
should carry through much of the night, inhibiting clouds. There
are small chances of thunderstorms, especially near CHO late today
and MRB late this evening. Odds of a direct impact of any storm
remain slim.

A weak boundary will slip across the terminals Friday morning,
veering winds west (around 10 kt). These winds will eventually be
northwest by the end of the day. Most moisture will mix out and
any additional clouds will be surpressed.

High pressure will return for the weekend. VFR should prevail.

&&

.MARINE...
Status quo on the waters. We`re in a marginal Small Craft Advisory
environment on the waters. Will keep the SCA in place through the
evening.

A weak front will slide through on Friday. Flow will veer west
Friday morning, northwest Firday evening, and eventually becoming
east by late Saturday, as high pressure moves to the north. At
this time, sub- SCA conditions expected.

&&

.TIDES/COASTAL FLOODING...
Water levels about a half-foot above astronomical norms. ESTOFS
depicting its typical water piling in the northern extent of the
Bay. Some of this is a model bias. Believe that caution stages
will be reached. Have low confidence in Annapolis reaching minor
flood (if it does, it will be a threshold Advisory for a couple of
hours), so have opted to not raise Advisory at this time.

Winds will become west Friday and north by early Saturday. There
should not be any concerns beyond tonight`s cycle.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ531>533-
     539>541.
     Small Craft Advisory until 6 AM EDT Friday for ANZ534-543.

&&

$$
SYNOPSIS...RCM/HTS
NEAR TERM...HTS
SHORT TERM...HTS
LONG TERM...IMR
AVIATION...HTS
MARINE...HTS
TIDES/COASTAL FLOODING...HTS



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