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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KAKQ 211756
AFDAKQ

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

.SYNOPSIS...
High pressure builds toward the Mid Atlantic today into Saturday,
bringing hot and humid conditions to the area. The hottest weather
can be expected from today through Sunday. A trough of low pressure
will slide across the area late Saturday into Saturday night.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Weak trough at the sfc and aloft over the region, with a
hot/humid airmass in place (though seeing some mixing
out.lowering of dew pts along and W of I-95. Dew pts may drop
enough to keep heat indices more marginal in central VA despite
actual air temperatures approaching/reaching 100 F for highs
later this aftn. Still hot though and made no changes to the
heat advisory even if the western portions of the advisory
don`t technically hit the 105 F heat index (have already seen a
few obs like at ECG with heat index of 105 F with dew pts at 80
F as of 11 am. Some high clouds persist over SE VA/NE NC with
MCS activity still ongoing over OH into WV. Most of this
expected to stay W of the Mtns and have minimal affect on the
local area through 20Z. With the high dew pts and light winds
overall, added a 15% PoP for isolated tstms after 18Z over NE
NC/SE VA invof the coast...and will maintain 20% PoPs NW 1/2 of
the CWA after 20Z. Actual highs will be near 100 F metro
Richmond to the mid/upper 90s elsewhere (locally cooler/lower
90s immediate coast).

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
Ramped PoPs up a bit more for tonight into Sat morning, esply
N/NE zones, closest to upper level shortwave energy tracking
through the WNW flow aloft. 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, it will be even more humid, so expect at least
southern portions of the CWA to need a heat advisory even with
highs on avg only in the mid to upper 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. The entire CWA is in a
marginal risk, where wind will be the primary threat. 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 Sun.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Long term period will feature near normal temps on avg and
occasional chances for rain. In general expect lwr temps than this
weekend as the broad upr-level ridge across the eastern CONUS breaks
down in response to an approaching upr-level trough. The trough and
associated low-level front will bring an increasing chance for rain
Mon, but will cap PoPs at 40% for now due to uncertainties regarding
timing and available moisture. Further model divergence occurs Tue
and Wed, with the 12Z ECMWF keeping the low-level boundary in the
vicinity and the 12Z GFS pushing things offshore, so will maintain
low end PoPs (20-40%) through midweek, with the best chance over far
SE areas. As for temps, after one more hot day Mon with highs up to
the mid 90s, expect mid/upr 80s for Tue through Thu.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
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 especailly from RIC north inclduing the MD
Eastern Shore as another wave move across in the NW flow aloft.
-- End Changed Discussion --

&&

.MARINE...
Latest obs/buoy reports reflect W-SW flow ~10-15 kt across the
waters this morning. Surface analysis features high pressure over
the western Atlantic with a pre-frontal surface trough persisting
inland from S NJ south into the VA/NC piedmont. No major changes to
rather stagnant sfc pattern today, with SW winds ~10 kt persisting
today, as Bermuda high remains the dominant wx feature through the
weekend. Winds again increase slightly late this afternoon and late
each day over the weekend into the overnight hours, and becoming
a bit gusty at times in the aftn/early evening w/developing
seabreeze. Seas generally 2-3 feet and waves 1-2 feet.

A weakening cold front approaches the region late Monday, dropping
across the region Monday night into Tuesday morning. Flow may briefly
increase with tightening pressure gradient Monday night, but have
held winds below SCA thresholds for now. Flow backs to the northwest to
the north Tuesday at or below 10 knots due to a lack of cold advection.
High pressure builds across the Northeast into Wednesday, resulting
in onshore flow Wednesday.

&&

.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.
NC...Heat Advisory until 8 PM EDT this evening 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.
MARINE...None.

&&

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