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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KAKQ 210824
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
424 AM EDT Fri Jul 21 2017

.SYNOPSIS...
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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.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Early this morning, upper ridge axis was centered over the
Middle MS Valley and extended ewrd toward the Mid Atlc. These
higher heights will build ewrd into SW VA and wrn NC during
today. The core of the highest 850 temperatures today (21-22C)
will be over much of the local area, with dew pts expected to
be higher (only mixing out to near 70 F inland, and to the lower
to mid 70s near the coast). This will result in heat indices to
be more solidly into advisory criteria (105 to 109 F), and have
therefore issued a heat advisory for most of the CWA (left
coastal Worcester MD/NC Outer Banks out of it, with cooler
temperatures, as well as much of the far SW counties (Prince
Edward, Lunenburg, Mecklenburg) where it will be slightly
drier). Actual highs will be near 100 F metro Richmond to the
mid/upper 90s elsewhere (locally cooler/lower 90s immediate
coast). As far as precip chances, airmass appears too stable
overall for much in the way of pop-up storms during today. But,
with WNW flow aloft and some weak shortwave energy moving into
the area late this aftn, will have ~20% PoPs over the NW 1/2 of
the CWA.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
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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.
-- End Changed Discussion --

&&

.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 /08Z FRIDAY THROUGH TUESDAY/...
High pressure will prevail off the Southeast Coast tonight into
Friday, with a trough to the lee of the Appalachians. This will
promote light SW flow of 5-10kt. Thin high clouds tonight, with
sct aftn cu Friday. Mainly dry with only a minimal chc (15-20%)
of showers/tstms Friday aftn/evening. Similar conditions persist
into Saturday with a 20-40% chc (highest N) of late aftn/evening
showers tstms. A low probability of late aftn/evening
showers/tstms continues Sunday/Monday, but overall primarily
dry. A weak cold front approaches from the NW Tuesday.

&&

.MARINE...
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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.
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&&

.CLIMATE...
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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
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&&

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

&&

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