Area Forecast Discussion
Issued by NWS Wakefield, VA

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000
FXUS61 KAKQ 200835
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
435 AM EDT Thu Jul 20 2017

.SYNOPSIS...
High pressure builds toward the Mid Atlantic today into the
weekend, bringing increasingly hot and humid conditions to the
area. The hottest weather can be expected from Friday through
Sunday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The trough of low pressure (aloft) will continue to weaken along
the SE coast during today, as the upper ridge centered over the
central/southern Plains begins to build east. With rising
heights today, and increasing 850 mb temperatures, expect highs
today to be about 2 to 5 degrees warmer than Wed, ranging from
the mid to upper 90s well inland to 90-95 closer to the coast
(locally upper 80s immediate coast). To a varying degree, the
models once again depict enough mixing of dew pts in the aftn on
Thu for the WNW 2/3 of the CWA (into the 60s). While dew pts
will tend to remain in the 70-75 F range across the ern 1/3,
temperatures will be a little cooler there, so resultant heat
indices look to peak in the upper 90s to 104 F at reputable
sites. This will fall shy of heat advisory criteria (105 to 109
F), so will not be issuing any heat advisory headlines for
today, but will mention heat indices in the HWO. Except for
isolated sea breeze boundary induced showers or tstms this aftn,
expect mainly dry conditions and will keep PoPs of 14% or less
except near the coast (15-20% there).

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
Model consensus has the upper ridge axis centered from the TN
Valley to the Carolinas Fri into early Sat, with an upper trough
over the Great Lakes and NE states on Sat. The core of the
highest 850 temperatures on Fri (22-24C) will be over the NW
portion of the CWA, shifting to the southern zones on Sat
(22-23C). Fri may be the hottest day across the N, with high
temps ranging fm the mid 90s to around 100 degrees. A heat
advisory will be likely on Fri, as heat index values will be 103
to 108 degrees over most of the region. Sat may be slightly
cooler and a bit more unstable, as heights aloft drop, but
should once again see highs of 95 to 100 F. Dew pts may be a
little higher, so heat indices should be at least as high if
not higher. At least a heat advisory will likely be needed,
possibly even excessive heat warning (especially for SE VA/NE
NC). This is certainly not unprecedented heat for this part of
the country during this time of year (see climate section), but
it will be very hot nonetheless, and potentially dangerous for
those not prepared for it.

There will be isolated storms across the NW or nrn counties Fri
aftn into Fri night, and isolated to sctd storms across the nrn
half of the region Sat aftn into Sat night.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
An upper level trough tracks across the Great Lakes and Northeast
through the extended period, pushing a weakening cold front into the
region during the Monday night to Tuesday morning time frame.
Another hot day is forecast Sunday, but modest height falls and
lower thickness values will knock a few degrees off. Highs in the
mid to upper 90`s with heat indices back in the 105 to 108 range.
Pressure falls ahead of the approaching from will sharpen the
thermal gradient over the Piedmont, but a general lack of
appreciable forcing, warm temperatures aloft, and westerly flow will
result in only a slight chance POP over the Piedmont into central
Virginia. Better chances (albeit 30-40% at this time) for diurnally
driven showers/thunderstorms expected Monday as deep layer moisture
increases ahead of the front and the upper trough tracks into the
Northeast. Few degrees colder again, with highs generally in the mid
90`s and heat indices 100 to 105. Chance POPs continue into Monday
evening as general model consensus drops the front over the local
area Monday night.  Strongest height falls progged north of the
region, which result in cyclogenesis off the Northeast coast. The
front likely stalls along the coast Tuesday, with chance POPs
continuing across the southeast forecast area. Cooler, with highs in
the upper 80`s to low 90`s. Thereafter, medium range guidance is at
odds with handling the upper trough over southeast Canada. Prefer
the more progressive ECMWF solution, which builds high pressure
across the Northeast Tuesday, resulting in onshore flow and
unsettled conditions over the local area. However, confidence is not
high at this time, so have trended toward model consensus. Highs
Wednesday in the mid to upper 80`s. Overnight lows through the
period will generally be in the 70`s.

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
VFR conditions expected today into Fri morning, with just sctd
CU developing this aftn. Any fog tonight will be patchy at best
and left out of forecast for now. S-SW winds below 10 kts.

OUTLOOK...Mainly VFR conditions expected Fri and Sat. But, isolated
storms Fri aftn into Fri night acrs NW or nrn counties, and isolated
to sctd storms Sat aftn into Sat night could produce MVFR
conditions.

&&

.MARINE...
Latest obs/buoy reports reflect W-SW flow ~10-15 kt across the
waters this morning. Early morning surface analysis depicts high
pressure over the western Atlantic with a surface trough persisting
inland over the piedmont of central Virginia. Little change in the
surface pattern expected today and through the weekend as high
pressure remains entrenched over the western Atlantic and the storm
track remains well north of the region. Thus, given a weak pressure
gradient, resultant south to southwest wind will persist at or below
15 knots is expected through Monday. Winds increase slightly late
each day 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.

NWPS showing SE Swell developing Friday, which could result in a
moderate rip current risk for Fri/Sat. Forecast will remain low for
today.

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 knots due to a lack of
cold advection. High pressure builds across the Northeast into
Wednesday, resulting in onshore flow Wednesday.

&&

.CLIMATE...
Heatwave is expected to develop, mainly Friday 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 Thursday
through Sunday are listed below:

* Date: Thu(7/20) Fri(7/21) Sat(7/22) Sun(7/23)

* RIC:  103/1930  104/1930  103/1952  103/1952
* ORF:  102/1942  101/1926  102/2011  103/2011
* SBY:  104/1930  106/1930  104/1930  103/2011
* ECG:  104/1942  102/1987  104/1952  104/1952

&&

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

&&

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



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