Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 210913
Area Forecast Discussion
National Weather Service Raleigh NC
513 AM EDT THU JUL 21 2016
A disturbance in northwest flow aloft will cross the Carolinas this
morning. Surface high pressure will follow and build across the
Middle Atlantic states today, then offshore tonight. A strong sub-
tropical ridge and associated hot conditions will otherwise expand
from the central U.S. to the Carolinas through the weekend.
.NEAR TERM /THROUGH TONIGHT/...
As of 355 AM Thursday...
WV imagery and model analysis PV fields depict a couple of
perturbations in NW flow aloft over the DelMarVA and Lower OH
Valley. The models indicate the former will amplify off the VA/NC
coast through 18Z, while the trailing one will dive across west-
central NC, to NERN SC, through the same time. The tail end of the lead
perturbation over the DelmarVA has already aided in the
development of a few showers over the Shenandoah Valley, amidst an
area of 6-9 thousand ft strato/alto-cumulus centered over central
and SRN VA; and the HRRR suggests a few additional showers may
develop over the NC Piedmont during the morning to midday hours,
presumably as the strongest QG-forcing for ascent accompanying
the trailing Lower OH valley wave moves SEWD.
Otherwise, 1025 mb surface high pressure now over WV will build
east across and offshore VA today, in the subsident wake of the
aforementioned perturbations aloft. The surface ridge axis and
associated NE low level flow around it, over the ERN half of NC,
will result in temperatures AOB those of Wed, with generally
upper 80s to around 90 degrees anticipated. To the west of the
ridge axis, a light SLY return flow will develop across WRN NC,
including the SRN and WRN Piedmont; and an associated 925-850 mb
theta-e ridge there warrants a continued slight chance of an
afternoon shower or storm.
Light return flow will envelop all of central NC tonight, once the
aforementioned surface ridge migrates offshore, with dry and
mainly clear conditions. Lows in the upper 60s to lower 70s.
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 410 AM Thursday...
A strong sub-tropical ridge centered over OK at 500 MB and AR at
700 mb, will gradually expand EWD this period, and more so this
weekend. Warmth beneath the ridge will likewise expand EWD, with
highs in central NC mainly in the lower 90s. Lows 70 t0 75. Associated
warm and dry mid levels will limit the chance of showers and
storms to differential heating boundaries in the mountains and
along the coast.
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 320 AM Thursday...
Period of hot and humid and conditions with heat index
values in excess of 100 expected for the weekend into Monday...
Central NC will be located in along the eastern periphery of an
eastward extending central Plains ridge at the beginning of the
long term period resulting in a weak, diffluent northwest flow aloft.
Over the weekend into early next week, the ridge will shift east
with rising heights across the Carolinas. At the surface, a Piedmont
trough will be present on Saturday and Sunday while a cold front
across the Mid Atlantic washes out as it stalls near the Mason-Dixon
line. A hot and humid air mass will be in place across the region
with surface dewpoints in the lower 70s only modestly abated to the
west of the Piedmont trough during day time mixing. PW values will
average between 1.75 and 2.0 inches throughout the period. Deep mixing
will likely generate some high-based afternoon cumulus most days but
warming mid levels with 500 hPa temps warming to -5 to -4C on Sun
and Monday in a generally subsident pattern should limit convective
coverage, only warranting slight chance PoPs during the afternoon
and evening. Morning thickness values in the 1420s will increase to
1435m on Sunday and Monday supporting highs in the mid to upper 90s
during the period. The hottest days appear to be Sunday and Monday
with heat index values climbing above 100 all three days and
exceeding 105 on Sunday and Monday.
The ridge relaxes a bit across the Carolinas on Tuesday into
Wednesday allowing the westerlies to drop southward. A cold front
will settle south across the Mid Atlantic on Tuesday, potentially
moving into NC on Wednesday. Not real confident the front will be
able to push that far south but its proximity, a more cyclonic flow
aloft and increasing shear along with weak to moderate instability
will result in an increase in the threat of convection. Increased
cloud cover and the retreat of the ridge will result in high
temperatures dropping back into the lower 90s with lows in the lower
to mid 70s. -blaes
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.AVIATION /09Z THURSDAY THROUGH MONDAY/...
As of 215 AM Thursday...
A disturbance in NNW flow aloft will dive SEWD across the Carolinas
early today. The passage of this feature and associated lift may
cause a few high-based (6-9 thousand ft) showers to develop and
spread across the Piedmont through midday. Otherwise, areas of fog
and stratus will probably expand across east-central NC this
morning, owing to the presence of a surface ridge axis over east-
central NC, and resultant good radiational cooling of a moist low
level air mass characterized by surface dewpoints in the lower 70s
there. VFR conditions and a light and variable surface wind will
follow, and continue through the end of the 06Z TAF period.
Outlook: Sub-tropical high pressure will expand across the SRN and
Central Appalachians, and Carolinas, and result in mostly dry/VFR,
and increasingly hot conditions, through the weekend. However, a
small chance of early morning fog/stratus, and isolated to widely
scattered afternoon and evening storms, will be possible each day,
but the probability of occurrence at any given TAF site will be
-- Changed Discussion --Record high temperatures and the year in which the record was most
recently set at Raleigh, Greensboro, and Fayetteville.
Sat Jul 23 Sun Jul 24 Sat Jul 23
RDU 105/1952 101/2011 102/2010
GSO 99/1952 99/1914 101/1914
FAY 103/2011 105/1952 103/1914
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