Area Forecast Discussion
Issued by NWS Wakefield, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 211818
Area Forecast Discussion
National Weather Service Wakefield VA
118 PM EST Sat Jan 21 2017
High pressure over the area this morning will weaken and slide
offshore later today as a frontal boundary stays just off to
the south. 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 Tuesday.
.NEAR TERM /THROUGH TONIGHT/...
Per current conditions, added patchy fog for the next few hrs
across the fa although vsbys are quickly improving in some
areas. Local cams still showing low vsbys over the water so
maintained 1NM vsby with fog per marine dense fog advisory
criteria. Went ahead and lowered temps a few degrees (more in
line with the LAV numbers). Also slowed down the onset of pcpn
across the sw as the latest high res data doesn`t show much
until btwn 21Z-00Z.
Best timing for the approaching slug of moisture and forcing
will be this eveng across the area, and have increase PoPs to
likely-categorical southern half of area, with chance PoPs
remainder of area. With a break in the pcpn overnight and light
winds, could see another round of patchy DZ/FG so added this to
the forecast as well, through mid morning Sunday. Lows tonight
range from the mid 40s NE to lwr 50s SW.
.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Tricky forecast continues for the short term period. Following
any morning DZ/FG Sun, PoPs quickly ramp up through the day Sun
as strong sfc low pressure and shortwave energy aloft approach
from the west. Increasing PW`s will result in moderate to
locally heavy rainfall. Likely-categorical PoPs. Warm frontal
boundary progged to drift north to near the NC-VA border so will
have chc thunder across southern half of fa during the
afternoon with decent shear as well. High temps upr 50s north to
mid 60s south, but temps could easily end up higher or lower.
Models continue to have trouble with the stacked upr-level low
progged to slowly cross the region late Sunday night and Monday.
Categorical pops for shwrs Sunday night. Lows upr 40s/mid 50s.
At some point in time, a triple point low is forecasted to cross
Virginia. Current timing is Monday afternoon which will
continue to produce widespread shwrs across the north with a dry
slot potentially cutting off pcpn across parts of the area
Monday afternoon. However, enough instability is noted to keep
thunder mentioned across the SE in the warm sector. Highs mid
50s to lwr 60s. QPF through Monday should average one to two
inches with locally higher amounts possible.
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
-- Changed Discussion --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.
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.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Widespread IFR ceilings expected to persist through the entire
TAF period. with no mixing and the warm front well to south
expect IFR ceilings to persist through the afternoon and
overnight. A weak area of low pressure will move acrs NC and SE
VA later tngt thru Sun. This will bring a decent wave of rain to
spread from SW to NE across the entire region from 01z to 12Z.
Also expect some LLWS in areas across SE VA and NE NC overnight.
OUTLOOK...Periods of rain, moderate to heavy at times,
Sunday through Monday, will be accompanied by IFR conditions. As
low pressure moves off to the northeast...dry weather and a
clearing sky is indicated for Tuesday and Wednesday.
-- Changed Discussion --Weak high pressure right over the marine area will slide out
into the Atlantic this evening. winds will remain S to SE this
afternoon around 5 kt or less. an approaching low will turn
winds to the E or SE acrs most of the waters, except SW or S ovr
the NC waters during this time with speeds 5 to 15 kt. Waves 1
to 2 ft and seas 2 to 4 ft. Then Sun night into Tue morning,
stronger low pressure will move fm ern TN/wrn NC and SC east-
northeast acrs the CWA to just off the srn New England coast.
This will result in stronger E, SE and S winds over the waters
(10-20 kt with gusts to around 30 kt) Sun night thru most of
Mon, with the strongest ESE winds affecting the two nrn coastal
waters. SCA conditions will be likely there esply late Sun night
thru Mon. SCA may be needed acrs the remainder of the coastal
waters as seas could reach at least 5 ft out toward 20 NM. Seas
may build to 6 to 9 ft ovr the two nrn coastal waters. Winds
become NW all waters on Tue with SCA conditions probable, esply
for the coastal waters. Seas 4-6 ft.
-- End Changed Discussion --
MARINE...Dense Fog Advisory until 5 PM EST this afternoon for