Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 222005
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
405 PM EDT Mon May 22 2017

.SYNOPSIS...
Low pressure will track off the Mid Atlantic coast this evening
with a frontal boundary dropping into the Carolinas. This front
will lift back north into the region late tonight into Tuesday
and Tuesday night as a potent low pressure system tracks along
the boundary. Unsettled conditions continue Wednesday and
Thursday as an upper level trough approaches from the west.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Current surface observations, radar imagery, and satellite
imagery depict a compact low tracking newd across the Peninsula.
Periods of moderate to heavy rain are possible across the
Tidewater and Ern Shore late this aftn through early evening as
this system pushes through due to the combination of decent
forcing and pw values of +1-2 st dev. QPF of 0.5-1.00" is
possible through this evening, with some locally higher amounts.
Instability has climbed to 1000-2000 J/kg, but 0-6km bulk shear
is generally less than 25kt, so any severe threat has bee
localized, and should end by 5 pm along coastal SE VA/NE NC.
Temperatures this aftn are mainly in the low/mid 70s, with
low/mid 80s across NE NC.

The front associated with the low drop back into the Carolinas
this evening with some drying aloft as the shortwave aloft and
surface low push offshore. PoPs drop below 15% across the N with
some partial clearing possible, while mostly cloudy conditions
continue S. A chc of rain returns across srn VA/interior NE NC
overnight as moisture from the WSW begins to increase along the
frontal boundary. Likely to categorical PoPs arrive for the SW
corner of the area by daybreak Tuesday. Lows range from the
upper 50s to mid 60s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
The flow aloft remains SW Tuesday, with another wave lifting
newd across the Carolinas during the morning and the Mid-
Atlantic during the aftn and evening, with deep layer moisture
returning. Categorical PoPs overspread the entire area Tuesday.
Categorical PoPs overspread the entire area Tuesday after 12Z
for much of the area (and after 15-18Z across the NE). 22/12z
NAM/GFS/GEFS/ECMWF/CMC continue to show some differences in
timing and location and strength of this wave of low pressure,
but the general theme is for a potent system with deep anomalous
moisture transport per strong H925-H700 southerly flow and pw
values climbing to ~1.75" collocated with the favorable RRQ of a
potent 120-130kt jet over the Northeast Conus. The threat for
heavy rain and possible flooding will continue to be mentioned
in the HWO, and have opted against a flood watch at this time as
6hr FFG is generally 4-6" across much of the area, with some
values of 3-4" across the Piedmont and MD Ern Shore. QPF through
00z Wednesday averages 1-3" across the region, and higher
amounts are possible. Storm total QPF through Thursday ranges
from 1.5-3.5" (tonight through Thursday) The axis of heaviest
rain per 12z model consensus is generally in the I- 85/US 360
corridor. The current high temperature forecast shows generally
low/mid 70s SE to the upper 60s/around 70 F central and mid 60s
far NW.

This shortwave/surface low push offshore Tuesday evening.
However, 22/12z NAM/ECMWF depict a secondary wave lifting across
the srn half of the are 00-06z Wednesday, so have bumped PoPs
up to 40-70% S to account for this. Yet another wave approaches
from the SW Wednesday aftn as an upper low approaches from the
W. This wave tracks across the region Wednesday evening through
the early overnight hours bringing another round of likely PoPs
along with a chc of embedded thunderstorms. Current 12z guidance
suggests the best instability remains offshore. However, the
potential for some strong to severe storms will need to be
monitored with 500mb height falls and strengthening/veering flow
at the 500mb level. Unsettled conditions continue into Thursday
with chc to likely PoPs continuing along with a chc of thunder.
Mostly cloudy to overcast Tuesday night through Thursday with
lows Tuesday night/Wednesday night in the upper 50s to mid 60s,
followed by highs Wednesday/Thursday ranging through the 70s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The deep upper trough across the eastern U.S. will continue to
affect the Middle Atlantic into Thursday as there are some
indications that the trough may slow down and even become negatively
tilted as it moves off the east coast Thursday into Friday. This
should keep precipitable water values well above normal with an
upper jet axis nearby. As such, have raised PoPs to likely across
much of the area Wed night and maintained high chance PoPs on
Thursday before the upper trough axis moves east Thu night.
With weak high pressure building across the southeast and Middle
Atlantic for Friday and Friday night, will maintain a dry and
seasonable forecast with temperatures in the upper 70s/lower
80s. The upper trough finally moves northeast by Saturday,
leaving more zonal flow across the region with building heights.
The GFS and the Canadian suggest a weak upper disturbance
moving through the area in W-NW flow later Saturday into
Saturday Night, but the ECMWF keeps this further north as it
builds heights across the area faster than the GFS/Canadian.
With that being said, will Slight Chance of showers/storms
Saturday Afternoon for much of the area with the exception of SE
VA and NE NC. Better chances for showers and storms Sunday with
better agreement from the models of another upper disturbance
moving overhead.

In general, temperatures will stay seasonable for this time of year
with highs in the upper 70s and lower 80s with lows in the upper 50s
to mid 60s. No major warmth is expected through at least next
Sunday.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
Widespread IFR currently from RIC to SBY in a rain shield.
Meanwhile, over extreme SE VA and NE NC, a line of thunderstorms
have developed. These will reach ORF and ECG around 20z with
gusty winds and IFR conditions possible. This first batch of
rain will move through this afternoon, with conditions improving
MVFR or even VFR by late this afternoon before the next batch of
moderate rain moves into the area late tonight into Tuesday
mornign. Expect widespread IFR to redevelop later tonight and
continue through Tuesday morning. Could even see some brief LIFR
especially at SBY later tonight if fog develops, but will not
include in the terminal at this time.


OUTLOOK...Degraded aviation conditions will be likely into Tue
evening. Rain may become spotty for awhile Tue night through
midday Wed, though the potential for lingering low clouds will
still be present. Another slug of deeper moisture and
showers/tstms possible Wed night along with a breezy S to SE
flow. Dry weather not expected to return until late Thu/Fri.

&&

.MARINE...
Sfc high pressure off New England will continue to retreat to the NE
today. Meanwhile, a cold front approaches from the west during the
day and washes out over the local waters Tuesday morning. Potent low
pressure rides NE along this boundary during Tuesday, crossing
near/over the waters Tuesday aftn/eve. The low then pushes NE and
away from the area Tuesday night. Southeast winds 10-15 kt early
this morning will become SSE at similar speeds later this morning
into the afternoon. A complicated wind pattern develops tonight and
Tues with the frontal boundary washing out over the marine area.
Winds will eventually turn to the NNE around 10 kt all waters
tonight, except remaining southerly off the northern OBX thru
daybreak Tues. ENE winds increase on Tues to 15-20 kt, but may
become S-SW Tues aftn across the southern waters depending on the
eventual track of the sfc low. Winds the turn to the SW and diminish
to 10-15 kt all waters as the sfc low head NE. The wind forecast
remains tricky on Tues as there are still some timing differences in
the models. SCAs appear to be likely for a portion of the marine
area but confidence is still low at this time to issue. Quieter
marine weather expected for the end of the week as the flow becomes
offshore behind the low.

&&

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

&&

$$
SYNOPSIS...AJZ/LKB
NEAR TERM...AJZ
SHORT TERM...AJZ/LKB
LONG TERM...MRD
AVIATION...MRD
MARINE...JDM



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