Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
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FXUS61 KAKQ 220303
Area Forecast Discussion
National Weather Service Wakefield VA
1003 PM EST Sat Jan 21 2017
Low pressure will track across the Carolinas tonight. A second
area of low pressure over the nations mid section will intensify
as it slowly tracks east across the Mid Atlantic region Sunday
and Monday. The intense low will move off the New England coast
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
-- Changed Discussion --Widespread low level clouds remain over the FA in weak CAD
situation. Weak sfc low pressure expected to track NE invof
coastal plain NE NC-SE VA overnight...then off the coast late.
VSBYs down to 1/2SM or less at times...especially inland and
over the waters. Area of RA now moving through the FA...will
shift ENE/off the coast by late tonight leaving DZ in its wake.
Temperatures holding w/ a couple/few degrees F of where they are
late this evening...from the u40s-l50s.
-- End Changed Discussion --
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
First s/w exits to the ne Sunday morning with the fa in between
systems ahead of the stronger system approaching from the sw late.
Plenty of low level moisture in the tsctns should result in another
morning with areas of drizzle/fog and possible low vsbys. Moisture
quickly returns/overspreads the fa after 18Z as strong sfc low
pressure and shortwave energy aloft approach from the west.
Increasing PW`s will result in moderate to locally heavy rainfall.
Categorical PoPs all areas after 18Z. Warm frontal boundary progged
to drift north to near the NC-VA border so kept chc thunder across
southern half of fa during the afternoon with decent shear as well.
SPC has SLGHT risk of severe up to the Albemarle sound with a MRGNL
risk across srn VA. Appears damaging winds are the main threat.
Threat will be later in the day into the evening hours. Highs in the
mid-upr 50s north to mid-upr 60s south.
NAM a bit faster than the GFS and much faster than the ECMWF
with the movement of the stacked low, but the model trends are
now more progressive than before. Deep Atlantic moisture feed
results in mdt to locally downpours Sunday night tracking south
to north along with thunder chcs during the evening. Categorical
pops all areas with lows in the upr 40s to lwr 50s. QPF averages
between 1 to 2 inches with locally higher amounts in any banded
convection that may occur.
Sfc triple point progged to move north of the area Monday morning
with the trailing upr level low crossing the region during the
afternoon. Significant dry slot progged to cut off the deep moisture
feed. Main change to Mondays forecast was to lower pops to chc most
areas except low end likely across the west. Tstcns also show that
some BINOVC are possible leading to some instab after 18Z. Have
added chc thunder Monday afternoon to account for this. Well above
normal temps continue with highs ranging from the mid-upr 50s nwrn
most zones to the upr 60s across the se.
System continues to track ne Monday night but GFS has yet another
vort lobe spoke rotating arnd the main low. Will keep low chc pops
in the grids for now with this feature. Lows in the 40s.
Finally get a break Tuesday as winds become NW and dry out the
column. Expect skies to become pt to mstly sunny. Temps remain above
normal with highs in the 50s.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Overall, the models are in good agreement in the extended period
with only a few minor differences on the timing of the frontal
passage on Wed night into Thursday. But those differences are
minor and the 12z GFS has moved closer to the 00z ECMWF.
In the wake of the storm that will move through by Tuesday, a
shortwave ridge builds in Tues night into Wednesday. This will
allow for W to SW flow and should be a mild dry period. However,
the upper level pattern will begin to flip with a broad trough
developing over the eastern half of the country for the second
half of the week. This trough will enter the region Wed night
into Thursday as a sfc cold front slides into the area. This
front will be lacking moisture so have limited the pops to
slight chance to chance range. The best opportunity for rain
looks to be in the southeastern part of the area where a little
additional Atlantic moisture may be available. The timing on the
front is still a little up in the air. The ECMWF moves the
boundary through more quickly, while the GFS develops a wave and
is slower. But the trend has been toward the ECMWF timing so
focused the highest chance on Thursday. Will also need to watch
the timing on the cold air arrival as well as this could impact
the pcpn type, but for now don`t think the cold air will arrive
until after any pcpn is gone.
For Thursday night into Saturday, the region will be dominated
by strong NW flow which will drop temperatures back down into
the 40s for highs and lows in the upper 20s to low 30s. Have
kept the fcst dry too, but will have to monitor shortwaves
rotating through the upper trough as with this polar airmass, if
one of these waves amplifies a bit, some snow showers would not
be out of the realm of possibility.
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
A light onshore flow and overrunning north of a weak warm front over
the Carolinas were producing low ceilings over much of the area.
Some locations especially ECG had improved as of 23z but these were
expected to deteriorate again shortly. Some visibilities will be
down to a half mile or less this evening especially RIC. A band of
rain moving through in the evening through early morning will
affect the TAF sites and visibilities may improve during the
precipitation. Overall...expect IFR/LIFR Sunday morning which
may improve slightly during the day but generally IFR conditions
continue. More showers are expected Sunday afternoon.
OUTLOOK...A well organized low pressure system moves from Oklahoma
across the Tennessee Valley Sunday night and to Virginia late
Monday. Periods of rain continue through Monday with continued
IFR. The weather improves as high pressure builds in Tuesday and
Wednesday. There will be a chance for showers especially
southeast portions on Thursday as a cold front moves through.
7 PM update...A dense fog advisory is in effect for all the
marine area until 4 AM EST. Reports indicate that a few
locations near the mouth of the Bay have visibility down to a
few hundred feet or less and with air temperatures a few degrees
warmer than the water... expect dense fog to become more
widespread. The dense fog advisory may need to be extended
beyond 4 AM.
Weak high pressure still is lingering over the waters this
afternoon and with southerly flow aloft pushing moisture
northward, seeing lots of low clouds and fog. This pattern will
persist for a few more hours, before an area of low pressure
move northward off the North Carolina coast. This will help to
increase the winds and also with some rain showers will probably
lead to visibilities increasing a little more between 1 - 3 SM.
This low will track off the coast on Sunday as more showers
enter the region ahead of warm front and a much stronger area of
low pressure that will be moving into the Tennessee River
Valley by Sunday afternoon. Expect easterly winds to increase
during the day, but to remain below sca levels.
The strong low will slide over the Central Appalachians Sunday
night while a new areas of high pressure, centered over Eastern
Canada builds down the coast. The pressure gradient will tighten
off the NJ/DE coast and will extend southward into the coastal
waters off the Delmarva. This will allow winds to increase to
sca and possibly some gust to gale in the northern coastal zone.
At this time have just raised the sca flags as the gale
conditions are not a certainty and it is still about 36 hours
The center of the low pressure system slides over the Mid-
Atlantic states on Monday and the gradient relaxes so expect the
winds to diminish quickly Monday afternoon. But the seas will
remain up in the coastal zones for some time longer. The SCA
will probably need to be extended further in time, probably into
Tuesday for the coastal waters. The bay and inland waters will
remain below sca conditions through the event, only getting
close to sca conditions Sunday night into early Monday with
winds between 15 to 17 kt.
The low pressure area will slide north of the region on Tuesday
and high pressure over the southeastern US will build into the
area bringing a period of dry and tranquil weather to the area.
The next cold front will arrive on Early Thursday. With the
colder air and stronger winds slower to arrive on Friday.
MARINE...Dense Fog Advisory until 4 AM EST Sunday for ANZ630>638-650-
Small Craft Advisory from 1 AM to 4 PM EST Monday for ANZ652-
Small Craft Advisory from 7 PM Sunday to 4 PM EST Monday for