Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 231528
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1128 AM EDT Sun Jul 23 2017

.SYNOPSIS...
A Piedmont trough will extend from Virginia into South Carolina
through Tuesday. A cold front will drop south into North Carolina on
Tuesday and then stall across the region on Wednesday and Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1100 AM Sunday...

...Dangerously hot conditions will continue across central NC
through this evening...

...Difficult forecast concerning the convective initiation and
development this afternoon and tonight...

The latest surface analysis shows a Piedmont trough extending
southwest across western VA into the western Carolinas. A
southwesterly flow at the surface is present across much of central
NC with surface dewpoints in the mid 70s and temperatures already in
the mid to upper 80s at 10am. Further aloft, the subtropical ridge
is well established across the subtropical Atlantic with other
ridging across the western US with troughiness in place across Great
Lakes and Mid Atlantic.  A notable short wave trough will drop
across the western Great Lakes this afternoon into the western OH
Valley this evening.

As noted above, the convective forecast for today is difficult. The
air mass across central NC is generally moderately unstable with
current MLCAPE values ranging from 1000-2000 J/Kg. A shallow
inversion is resulting in some CIN but this will be blown away when
the convective temp of 93 to 96 is reached. MLCAPE values will
likely climb to between 1500 and 3000 this afternoon, fueled by slow
to mix out dew points in the lower to mid 70s. Instability somewhat
inhibited by warm mid levels with 500 hPa temps of -6 t0 -7 deg. But
still, there`s plenty of juice out there.

Scattered showers across the Southern Coastal Plain have largely
fizzled out and convection that moved across southern VA and eastern
TN has failed to initiate any subsequent convection at this point
but the placement of an outflow boundary on the edge of a
differential heating axis would suggest convective redevelopment is
possible. Guidance from various convection allowing models are all
over the place with the 3 or 4 most recent runs of the HRRR bouncing
all over the place. In general they suggest that convection is apt
to move southeast out of the mountains early this afternoon and move
into NW Piedmont and VA border counties and then shift southeast
across central NC this afternoon and early evening. Another band of
convection/MCS may develop ahead of the OH Valley shortwave which
could move into the area from the northwest around and after
midnight. Much lower confidence on how that will play out given all
of the features that will evolve ahead of it but it`s one to watch.
The latest SPC outlook has expanded the slight risk slightly into
northern NC. Main risk today will be damaging downburst winds given
the profile and DCAPE values of 1200 J/kg and dangerous lightning
given the abundant CAPE and higher values of NCAPE and CAPE in the
-10 to -30C layer.

Low-level thickness values at KGSO are similar or just a bit warmer
than yesterday at this time, thickness values are 1m greater at
KGSO, 8m greater at KRNK and 3m greater at KMHX. Recent visible
satellite imagery shows a band of clouds across the southern Coastal
Plain associated with a low-level convergence axis, most clearly
noted at 925 hPa, and larger area of mainly debris clouds across the
northern Piedmont, especially near the VA border. Otherwise, there`s
a good deal of insolation through the haze ongoing across the area
but a tendency for there to be bit more cloudiness than yesterday.
See no reason to alter the current forecast highs in the 95-100
range which is supported by persistance, guidance and the morning
thickness values. The convective evolution today certainly will have
an impact on highs but given lower confidence on how things will
shake out, will leave the temperature forecast largely as is. The
combination of heat and humidity will result in heat index values
from around 100 to 105 in the Triad to 107-112 across the southeast.
Lows tonight will range from 73 in the Triad to 80 near
Fayetteville. -Blaes &&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 330 AM Sunday...

The upper level trough will remain over the region through Monday
night, as will the surface trough. The difference will be more cloud
cover expected over the region, resulting in high temps slightly
lower than previous days. Highs in the low to mid 90s expected,
resulting in heat indices of 95-102. Lows still expected to be in
the low to mid 70s. Expect more showers and thunderstorms Monday
aft/eve, better chances in the south and east, decreasing overnight.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As of 330 AM Sunday...

The upper level trough will remain over the region through Monday
night, as will the surface trough. The difference will be more cloud
cover expected over the region, resulting in high temps slightly
lower than previous days. Highs in the low to mid 90s expected,
resulting in heat indices of 95-102. Lows still expected to be in
the low to mid 70s. Expect more showers and thunderstorms Monday
aft/eve, better chances in the south and east, decreasing overnight.
&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 310 AM SUNDAY...

On Tuesday the upper trough begins to lift out to the northeast as
surface high pressure resides over the great lakes. The residual
frontal boundary will still remain over the southern part of the
state and the Piedmont trough will remain active through the week as
diurnal showers and thunderstorms will be prevalent through much if
not all of the period. Several weak disturbances will periodically
propagate along the frontal boundary providing some extra forcing
for ascent. The most notable of these will be Tuesday night into
Wednesday which could increase chances for rain overnight. Late in
the week a second frontal system will push down from the northwest
and will affect the area by next weekend. Expect high temperatures
in the upper 80s to lower 90s with lows in the low 70s.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
As of 740 AM Sunday...

24-Hour TAF period: Expect mainly VFR conditions through the TAF
period. The exception will be where storms develop late this
afternoon and evening. Best chances for convection and the
associated increase in winds and decrease in cigs and visbys may
begin around 18Z at KFAY, however the models have backed off a bit
and restrict most convective activity to the NC/VA border region
after 21Z. Have kept the PROB30 mention of such in at KINT, KGSO,
KRDU, and KRWI for this issuance. Some low stratus may develop
toward daybreak Monday, however chances and confidence in sub-vfr
cigs is low at this time.

Looking ahead: Mainly VFR conditions expected through Tuesday, with
the primary sub-VFR risk coming courtesy of showers and storms that
will grow in coverage each successive day through Tue. Chances for
early morning stratus increase Wednesday through Friday, but
otherwise expect VFR conditions to prevail.

&&

.CLIMATE...
RDU Records:
Date     | High   Year  |  High Min  Year
------------------------------------------
23 July  |  105   1952  |     78     2011
24 July  |  101   2011  |     79     2011

GSO Records:
Date     | High   Year  |  High Min  Year
------------------------------------------
23 July  |   99   1952  |     78     2010
24 July  |   99   1914  |     78     2010

FAY Records:
Date     |  High  Year  |  High Min  Year
-------------------------------------------
23 July  |  103   2011  |     79     1998
24 July  |  105   1952  |     79     1945

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 7 PM EDT this evening for NCZ010-
011-026>028-041>043-077-078-085-086-088-089.
Heat Advisory until 7 PM EDT this evening for NCZ007>009-
021>025-038>040-073>076-083-084.

&&

$$
SYNOPSIS...BLAES
NEAR TERM...BLAES
SHORT TERM...KCP
LONG TERM...RE
AVIATION...KCP
CLIMATE...RAH



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