FXUS61 KAKQ 210135
Area Forecast Discussion
National Weather Service Wakefield VA
935 PM EDT Thu Jul 20 2017
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
.NEAR TERM /THROUGH FRIDAY/...
Current analysis indicates a weak sfc/lee trough of low
pressure located from NJ...SSW to south central VA and central
NC. The trough of low pressure aloft is now situated south of
the CWA and centered along the SC/GA coast. The sky is partly
cloudy this evening under thin cirrus with some patches of
8-12kft altocu. Very warm and humid this evening with
temperatures ranging from the upper 70s to mid 80s. A few
isolated showers/tstms from earlier have now dissipated. Mainly
dry overnight. Earlier convection over OH/IN has weakened and
seems unlikely to hold together as a weak wave aloft crosses N
of the area overnight in the WNW aloft. Warmer than last night
with lows staying 70-75 F or higher tonight.
Model consensus has the upper ridge axis centered from the TN
Valley to NC on Fri into early Sat, with an upper trough over
the eastern Great Lakes and NE states. The core of the highest
850 temperatures on Fri (21-22C) will be over much of the local
area of fri and with dew pts expected to be higher (only mixing
out to around 70 F inland and to the lower-mid 70s near the
coast). Expect 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/NC Outer
Banks out for now with cooler temperatures as well as much of
the far SW where it will be slightly drier). Actual highs will
be around 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 the day, but with WNW flow aloft and
some weak shortwave energy moving into the area by late aftn,
will have ~20% PoPs by mid/late aftn over the NW 1/2 of the CWA.
Enough shear moves into the far NW for a marginal risk for
severe with wind being the main threat is any type of convective
complex can hold together upon crossing the Mtns.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
Ramped PoPs up a bit more for Fri night/especially N/NE zones
closest to upper level shortwave energy tracking through the WNW
flow aloft. Very warm/humid Fri night with lows mainly 75 to 80
F. Slightly cooler 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 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. Far N/NE portions of the CWA are in a slight risk
where higher shear will reside with marginal risk for the
remainder of the CWA. Again wind will be the primary threat.
Lows mainly in the mid to upper 70s Sat night and continued hot
an humid with additional heat headlines likely needed for some
of the region on Sunday. Highs mainly in the mid to upper 90s
.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 /02Z 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.
Extended period of sub-SCA conditions continues this week into the
weekend. Pattern is stagnant with Bermuda high pres centered well
offshore and typical summertime late day thermal troughs with S/SW
winds averaging 5-10 kt, occasionally up to 15 kt especially tonight
due to a slight increase in the pressure gradient. Waves over the
Bay 1-2 ft with seas over coastal wtrs 2-3 ft. The next (weakening)
cold front approaches the region late Mon, dropping into the area
Mon night/Tue. Mainly sub-SCA conditions expected to continue
however with weak CAA behind the front, and just some 4-5 ft seas
psbl out 20 nm. Flow becomes N/NEly then Tue through Thu as the frnt
slides offshore and dissipates.
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 today through
Sunday are listed below:
* Date: Today(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
MD...Heat Advisory from 10 AM to 8 PM EDT Friday for MDZ021>024.
NC...Heat Advisory from 10 AM to 8 PM EDT Friday for NCZ012>017-
VA...Heat Advisory from 10 AM to 8 PM EDT Friday for VAZ048-061-062-
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