Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 241808
AFDAKQ

Area Forecast Discussion
National Weather Service WAKEFIELD VA
208 PM EDT Fri Mar 24 2017

.SYNOPSIS...
High pressure remains offshore the Mid-Atlantic coast through
Saturday. An upper level disturbance lifts over the region
Sunday. A cold front crosses the region Tuesday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
Radar shows an area of light showers that is dropping ESE around
the upper ridge in the SERN US. The models do not have a great
handle on this feature as it is faster and further south than
the models indicated. So have adjusted the forecast for some
chance pops moving across NRN portions of the CWA and went about
3 hrs faster than the models would indicate, which should allow
the pcpn to exit the Delmarva coast by early to mid afternoon.
The QPF with the showers should be light, mainly less than .10".
Have left the temperature forecast in place, but may need to
adjust the nrn tier down a few decrease as a result of the
rain/clouds. Will take a look at that for the next update for
early this afternoon.

prev discussion...
Latest GOES water vapor imagery depicts an
active pattern across the CONUS. Upper trough that brought
cooler weather of the past few days is pushing off the Canadian
Maritime, with the next upper low over the Desert Southwest. The
next upper low is just off the Pacific Northwest coast. Ahead
of the desert southwest low, an upper level ridge axis is
located over the Ohio Valley. At the surface, strong ~1036mb
high pressure has centered just offshore. Not as cold this
morning as modest return flow and warming dewpoints have kept
temperatures generally in the low to mid 30`s.

Upper ridge builds east over the eastern US today as the upper
low tracks into the Southern Plains. A shortwave tracks across
the northern Mid Atlantic region this morning, with some
showers observed this morning over western Pennsylvania. Showers
stay north of the local area with only an increase in cloud
cover across the northeast local area. Return flow on the
backside of the departing surface high increases as the gradient
between the departing high and approaching low strengthens.
Southwest winds gust to 25 to 30 mph this afternoon. Dewpoints
continue to recover, warming into the 30`s to low 40`s this
afternoon, resulting in minimum relative humidity values in the
upper 20`s to low 30`s inland. While 850mb temps warm to +6 to
+8C, a large subsidence inversion will prevent temperatures from
reaching their full potential, even with a breezy southwest
wind. Highs generally in the mid 60`s. Cooler Eastern Shore and
along the coast. Temperatures expected to be warmer than
yesterdays high by late morning. Westerly flow will send some
mid to high level clouds over the region this afternoon, with
generally partly cloudy conditions.

Upper/surface low pressure locate over the Midwest today as the
ridge axis pushes offshore. A southwest wind and partly cloudy
sky results in a mild night tonight, with lows generally in the
upper 40`s to low 50`s. Continued dry.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
Stacked low pressure weakens/fills Saturday, tracking into the
lower Missouri River Valley late. A warm front extends eastward
over the northern Mid-Atlantic region as the cold front tracks
into the lower Mississippi River Valley. The result will be
ongoing return flow over the local area. 850Mb high pressure
slides offshore, with better moisture return expected, but
conditions remain dry thanks to ridging aloft (warm temperatures
and a lack of forcing). Warm, with highs in the mid to possibly
upper 70`s under a generally partly cloudy sky. Mild again
Saturday night with lows generally in the low 50`s thanks to
southerly winds and increasing clouds ahead of the approaching
low.

The upper low continues to weaken into Sunday, lifting over the
Great Lakes Sunday afternoon. A lead shortwave lifts into the
Mid-Atlantic region Sunday afternoon, but the cold front remains
well west of the local area. Moisture also remains limited with
precipitable waters only rising to around 1 inch over the
Piedmont. Dewpoints progged only in the low to mid 50`s. Have
pulled back POPs Sunday afternoon given the limited instability
due to warm air aloft and a general lack of dynamics, keeping
only a slight chance to low end chance POP Sunday afternoon from
the Piedmont into central Virginia. Dry elsewhere. Given the
lack of instability, especially in the mixed phase layer, have
removed any chance of thunder. Not quite as warm Sunday as
Saturday given the extra cloud cover. Highs generally in the low
to mid 70`s. Cooler Eastern Shore and along the coast. Lows
Sunday morning start in the low to mid 50`s with some patchy fog
possible.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Medium range period features a mild period, courtesy of surface
high pressure oriented just off the Mid-Atlantic/southeast
coast. Main weather features of note a couple of mid/upper level
lows, which will bring scattered light precipitation late in the
weekend and again by Tuesday. The first of these disturbances
traverses across the central/southern Plains on Saturday,
dampening as it crosses E- NE into the Ohio Valley and Eastern
Great Lakes on Sunday and into the northeast on Monday. This
feature will allow for some isolated to scattered showers Sunday
night into early on Monday. QPF will be limited with this
feature. Despite increasing PW values, minimal instability and
steadily weakening dynamics/forcing remain maximized well off
to our N-NW. Therefore, high end chc to likely pop is in place
for Sunday night over our western/NW tier of the area for
sct/numerous showers. Region remains mild in the warm sector
with southerly flow bringing highs in the upper 50s to 60s
Northern Neck and MD Lower Eastern Shore...with upper 60s to
low 70s inland for early next week.

For the middle of next week...attention turns to a second
southern stream disturbance, which is expected to track
east/northeastward from the CA coast...across the Plains and
Mid-South Late Sat-early Monday. There remains some significant
disagreement with the GFS/ECMWF, with the ECMWF and its member
ensembles remaining more progressive and flatter. Will lean in
the ECMWF direction with the GFS Parallel and GEFS seemingly
trending in this quicker direction as well. Still, this system
will be a bit stronger than the weekend system but it too will
weaken as it pushes across the eastern third of the conus Monday
through early Tuesday. So while would translate to another
period of showers late Monday night into Tuesday afternoon,
system will again be progressive. Given the timing, will mention
slight chance of thunder Tuesday afternoon west of the Bay.
Remaining mild, with highs in the 60s to near 70 Eastern
Shore...mid 70s to near 80 South central VA/Interior NE NC.

Shortwave ridging rebuilds behind this system for Wednesday.
Highs remain mild through the period, with 50s and 60s over the
northern neck of VA into MD, with highs well into the 60s to Mid
70s inland. Early morning lows mainly in the 40s to low 50s
southern sections.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR conditions are expected to continue through the forecast
period. Mid level clouds have worked into portions of the
region this afternoon with bases at or above 9000 feet.
Satellite imagery has shown a decreasing trend in cloud cover
with clouds expected to continue to dissipate through the
afternoon and evening. Winds have turned to the southwest and
increased to 10-15 knots with gusts to around 20 knots at times
this afternoon. Winds are forecast to diminish later this
evening and overnight. High clouds work into the area late
tonight and into Saturday.

Outlook: Periods of sub-VFR ceilings/visbilities due to fog will
be possible on both Sunday and Monday morning. Scattered showers
are expected to develop late in the day on Sunday. Unsettled
conditions are forecast to continue through early next week with
the highest potential of showers on Tuesday.

&&

.MARINE...
Sfc hi pres remains just off the mid-Atlantic coast through the
weekend. SSE winds starting off the today...mainly averaging
10-15 kt. SSW winds averaging 15 kt or less...lingering through
Sat. Pressure gradient tightens by this afternoon as low pres
develops invof central/srn Plains. While nearshore winds will
become elevated/gusty this afternoon...and (to a lesser extent)
Sat afternoon...cooler waters likely to cut down speeds and will
undercut guidance slightly/keep waters below any SCA thresholds
(though there may be a brief period of gusty/a bit higher speeds
over the waters from the eve into the overnight hours).

The next front crosses the waters early next week...w/
relatively benign marine conditions expected over the weekend in
SSW winds mainly aob 15 kt. Seas averaging 2-3 ft...waves 1-2
ft.

&&

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

&&

$$
SYNOPSIS...SAM
NEAR TERM...ESS/SAM
SHORT TERM...SAM
LONG TERM...MAM
AVIATION...AJB
MARINE...ALB/MAM


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