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302
FXUS61 KAKQ 212015
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
415 PM EDT Fri Jul 21 2017

.SYNOPSIS...
Hot and humid conditions will continue over the region through
Sunday. A weakening cold front will gradually push across the
area late Sunday through Monday, with temperatures cooling down
to near normal levels Monday through Thursday.

&&

.NEAR TERM /THROUGH SATURDAY/...
Weak sfc/lee trough in place across the local area this aftn,
with WNW flow prevailing aloft around the base of an upper
level trough centered over eastern Canada. Hot/humid airmass in
place, particularly humid over the E and SE zones with dew pts
still ranging from 75 to 80 F, with somewhat lower (though still
elevated) dew pts over central and S Central VA (mainly from
the mid/upper 60s to around 70 F). Heat advisory remains in
effect through 8 pm for most of the area (though areas that
receive rain will rapidly cool).

The WNW flow pattern appears to be allowing the ongoing
convection/MCS along the Mtns to hold together as it approaches
the NW flank of the CWA. Have ramped PoPs up to likely through
6pm for the NW, and high chance 30-50% for much of the northern
1/2 of the CWA through midnight, lingering into Sat morning for NE
zones.

Very warm/humid tonight with lows mainly 75 to 80 F. Not as hot
most areas for Sat, due to potential for more clouds and as
core of 850 mb heat shifts a bit S. However, with slightly
higher dew pts than Fri expect most of the area to reach heat
advisory criteria Sat aftn even with highs on avg only in the
mid 90s. As airmass destabilizes more by Sat aftn/early
evening, and as heights aloft drop, convection developing from
the NW will be more likely to hold together for at least 30-50%
PoPs across most areas (20% NE NC) from late Sat aftn through
Sat night. Deep layer shear will be higher as the upper trough
sharpens a bit and H5 to H7 flow increases. Most of the CWA is
in a marginal risk for severe wx, with a slight risk for the
far N/NE. Wind will be the primary threat with large hail also
possible.


&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Lows mainly in the mid to upper 70s Sat night, and continued
hot and humid with additional heat headlines likely needed for
some of the region on Sun. Highs mainly in the mid to upper 90s
Sunday. Slight risk in place for most of the CWA, but more
uncertainty exists depending on how long convective debris from
Sat night hangs around and potentially keeps more clouds around.
Cold front slated to pass through while weakening late Sun night
through Mon. Will maintain chc PoPs all zones Sun night, and
favor highest PoPs Mon across theS with 20% PoPs for the N.
Slightly less humid Monday, especially N. Highs Mon 90 to 95 F.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Cold front progged to push offshore Tuesday morning as the upper
trough slides over the Northeast into the Canadian Maritimes.
Deepest moisture pushes offshore late Monday night, but will keep
mention of slight chance to chance POPs near the coast. Southern
portion of the cold front expected to stall over the Carolinas
Tuesday as a baggy trough locates over the Southeast. Combination of
weak energy in the upper flow and a moist air mass near the
boundary, will keep mention of slight chance to chance POPs across
the far southeast local area Tuesday afternoon. Otherwise, cooler
Tuesday with a light north to northeast wind. Highs generally in the
upper 80`s to around 90 (near seasonable norms). High pressure at
the surface and aloft slides north of the region Tuesday night into
Wednesday as another trough tracks across Ontario. Meanwhile, a
broad upper ridge over the Southern Plains expands eastward, but the
baggy trough remains over the Southeast. Best chances for measurable
precip expected to be south of the region Wednesday, but will carry
slight chance to low end chance POPs across the southern portions of
the forecast area. Highs Wednesday generally in the mid 80`s.
Another trough tracks into the Great Lakes and Northeast Wednesday
night and Thursday, pushing another weakening cold front into the
Mid-Atlantic region Thursday afternoon. Will need to watch for
upstream convection Wednesday night in northwest flow aloft, so have
added chance POPs for the Maryland Eastern Shore. With the boundary
and cyclonic flow over the region Thursday, have chance POPs for
diurnally driven showers and thunderstorms. Highs Thursday generally
in the upper 80`s to low 90`s. Medium range guidance depicts
additional energy digging down the backside of the upper trough
Friday, with a wave of low pressure progged to develop along the Mid-
Atlantic front. Timing and spatial differences at that timeframe of
the forecast cause a great deal of uncertainty, so have only
mentioned 20-40% POPs at this time. Highs back around seasonal
norms, in the upper 80`s to low 90`s.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Mainly VFR conditions will prevail at the TAF sites this
afternoon...overnight and into Sat morning, as sfc high
pressure sits well off the SE Coast with a trough to the lee of
the Appalachians. Scattered CU around 5-6kft is developing
across the region in addition to a few isolated showers as of
18z. Convection moving into western VA will likely weaken some
as it crosses the mountains...however...some shower and storm
activity will make it into central VA and across the Eastern
Shore late this evening. Have VCSH at RIC from 21z-00z,
otherwise mainly dry most places this evening with a 20-30% of
showers/tstms late this aftn. Expect a little better chance
of storms late Sat especially from RIC north including the MD
Eastern Shore as another wave move across in the NW flow aloft.

&&

.MARINE...
Latest surface analysis depicts high pressure over the
western Atlantic with a trough of low pressure over central
Virginia. Obs indicate a light south to southeast winds at or below
10 knots. Waves are generally 1 foot and seas 2 feet. Diurnal
increase in the low level winds expected again tonight over the low
Bay and southern coastal waters. Hi-res guidance depicts winds
around 15 knots, with an occasional gust of 18 knots, mainly
centered a few hours either side of 11pm (03Z). Conditions expected
to remain sub-SCA. Wave kick up to 2 feet in the lower Bay and seas
2-3 feet. Stagnant surface pattern persists through the weekend.
Winds generally southwest at or below 15 knots, but near SCA
conditions possible late each day into the overnight period. Seas
generally 2-3 feet (upwards of 4 feet overnight) with waves of 1-2
feet.

A weakening cold front approaches the region late Monday, dropping
across the region Monday night into Tuesday morning. Flow backs to
the northwest to north Tuesday at or below 10-15 knots. High
pressure builds across the Northeast into Wednesday, resulting in
onshore flow Wednesday. Another weakening cold front approaches the
region Wednesday night and Thursday, stalling over the region into
next weekend.

&&

.CLIMATE...
Heat wave is expected to develop, mainly today through Sunday.
The 2nd half of July is climatologically the hottest few weeks
of the year, so we still may not set any daily records at our
main climate sites. For reference, record highs today through
Sunday are listed below:

* Date: Fri(7/21) Sat(7/22) Sun(7/23)

* RIC:  104/1930  103/1952  103/1952
* ORF:  101/1926  102/2011  103/2011
* SBY:  106/1930  104/1930  103/2011
* ECG:  102/1987  104/1952  104/1952

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...Heat Advisory until 8 PM EDT this evening for MDZ021>024.
     Heat Advisory from 10 AM to 8 PM EDT Saturday for MDZ021>024.
NC...Heat Advisory until 8 PM EDT this evening for NCZ012>017-
     030>032.
     Heat Advisory from 10 AM to 8 PM EDT Saturday for NCZ012>017-
     030>032.
VA...Heat Advisory until 8 PM EDT this evening for VAZ048-061-062-
     064-067>069-075>090-092-093-095>100-509>525.
     Heat Advisory from 10 AM to 8 PM EDT Saturday for VAZ060>062-
     064>069-075>090-092-093-095>100-511>525.
MARINE...None.

&&

$$
SYNOPSIS...LKB
NEAR TERM...LKB
SHORT TERM...LKB/TMG
LONG TERM...MAS
AVIATION...TMG/JAO
MARINE...MAM/SAM
CLIMATE...