Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 271738
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
138 PM EDT Tue Sep 27 2016

.SYNOPSIS...
A cold front tracks across the region today, stalling along the
coast tonight. The front remains along the Mid-Atlantic coast
through the end of the work week, resulting in unsettled weather
conditions into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Updated the grids to reflect the 17Z radar sfc ob trends. Cold
front slowly moving east with main band of pcpn pushing east of
I95. BINOVC even showing up across NWRN zones. Cut back pops
behind fropa and dropped mentioned of thunder. Kept likely/cat
shwr/tstrm pops across SERN half of fa as the band continues to
move east. Highs in the 70s.


PVS DSCN:
The upper-level low centers over the Ohio Valley tonight as the
frontal boundary remains stalled along the Mid-Atlantic coast.
Shortwave energy pushes offshore as low pressure lifts offshore of
the Mid-Atlantic coast. Expect a generally downward trend in
precip tonight, but based on the air mass in place and the
dynamics provided by the deep upper low, will keep chance POP`s
through the overnight period. GFS/NAM isentropic surfaces also
indicate low level lift behind the front. Lows range from the
upper 50`s northwest to mid 60`s southeast.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
Anomalous/deep upper-level low settles over the Ohio Valley
Wednesday as today`s front aligns along the southeast coast. A
brief lull in precipitation is expected Wednesday morning as the
associated surface low lifts offshore. However, precipitation
returns in earnest Wednesday afternoon as diffluent flow upstream
of the upper low results in favorable upper vertical motion along
an area of deep moisture convergence over the Piedmont/central
Virginia. This represents a westward shift in the highest POP`s
compared to the previous forecast. Thermal profiles and cross
sections indicate the upper levels will begin to dry, with
precipitable waters dropping to around 1-1.25 inches. However, the
low levels remain quite moist with 1000-500mb relative humidity
values over 75%. Deep lift indicated in the models will be enough
to overrule limited moisture, resulting in widespread showers
Wednesday afternoon through Wednesday night. Showers may be heavy
at times. Went below guidance on temps Wednesday due to a cloudy
sky and precip, with highs forecast around 70 northwest to around
80 southeast. Few thunderstorms also possible Wednesday afternoon
due to elevated instability (dry air aloft). Lows Wednesday night
in the low to mid 60`s.

The upper low drops southward over the southern Appalachians
Thursday as a prevalent dry slot works into the forecast area.
Showers will lift northward through the day, with the best chances
confined north of Interstate 64 late Thursday. However, based on
the amount of forcing and lingering moisture, will keep chance
POPs across the remaining forecast area for light showers. Highs
Thursday range from the low to mid 70`s inland to upper 70`s
southeast. May begin to see the sun late Thursday afternoon across
the south as the sky begins to clear.

Per the latest GEFS standardized anomalies, best moisture
transport expected to remain north of the region through the short
term. However, even with limited moisture over the region, upper
level dynamics still expected to result in produce a widespread
1-2 inches inland. Less across the southeast.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Medium range period continues to feature the presence of a deep
anomalous upper level low centered over the TN/OH Valley Thu
night/Fri, gradually lifting N and slowly weakening/filling across
the Great Lakes by late Saturday-Sunday. At the surface, high
pressure centered over eastern Canada will also weaken/slide E
through the period as a surface low locates close to the upper
low, with a secondary area of low pressure over the Carolinas/VA
lifting N of the local area by Fri night/Sat. Fairly good
agreement exists among the operational GFS/GEFS mean and the ECMWF
with this overall scenario. Thus, precipitation chances will
initially begin high (especially across the N) Thu night where
50-70% chances have been added to the forecast. Fri will see
diminishing POPS (with southern 1/2 of the CWA only having about a
20% POP with at least partly sunny skies developing). Will
maintain 30-50% chances N closer to the retreating frontal
boundary. Will continue with a mainly dry forecast from fri night
through the weekend (except for a 20-30% POP across the NE).
Temperatures will be close to seasonal averages with highs
generally in the 70s and lows in the 50s W to the 60s along the
coast.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Cold front crossing the region as of 18Z. PCPN to end soon at
RIC/SBY but just getting started across SERN TAF sites. Given the
sporatic nature to the shower activity, decided to add a TEMPO
group for lower CIGS/VSBYS in showers as some mdt to lclly heavy
rainfall reported across the region. Kept thunder out attm given
no lightning strikes anywhere across the fa, but that could
quickly change over the next few hours as the front moves into
the warmer air near the coast.

Sct showers end this evening with the attention turning to fog
potential tonight given a wet ground and high dew point temps.
Have indicated MVFR conditions late tonight at all sites except
ORF, with some guidance taking progging locally dense fog towards
sunrise.

Next batch of pcpn advances norhward across the piedmont after 12Z
as low pressure along the front moves north. Thus, brought back
rain to RIC but kept coastal areas dry for now.

OUTLOOK...Unsettled weather conditions expected through the end
of the work week as waves of low pressure lift along the cold
front. Showers with late day tstms possible each day.

&&

.MARINE...
Have dropped SCA headlines across the remaining Bay zones, though
a few gusts to 20 KT will persist through daybreak (and an MWS may
be issued if showers to the west push over the Bay and enhance the
winds briefly). Otherwise, The approaching cold front drops into
the area and stalls near SE VA tonight and Wed. Waves of low
pressure forming along the front Wed night into Fri should
gradually lift the boundary back to the N Thu-Fri (though
confidence on exact timing is uncertain). Winds will become mainly
ENE across northern areas and S/SE over southern areas Wed-Fri.
SCA conditions are most likely over northern coastal waters Thu-
Fri as the gradient tightens between the High to the N/NE and the
front lifting back to the N. Still a fair amount of uncertainty
and if the front is slower to lift to the N, SCA conditions could
occur over most of the marine zones. Overall winds will avg 10-15
KT with mainly 1-2 ft waves over the Bay and 3-4 ft seas over
coastal waters through this period, with seas to 5-7 ft possible N
of Parramore Island.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.

&&

$$
SYNOPSIS...SAM
NEAR TERM...MPR
SHORT TERM...SAM
LONG TERM...LKB
AVIATION...MPR
MARINE...LKB


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