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000
FXUS62 KRAH 160817
AFDRAH

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
417 AM EDT Tue Jul 16 2019

.SYNOPSIS...
A hot, sub-tropical ridge aloft will remain over the southeastern US
through Wed. A trough, including the significantly weakened remnants
of Barry, will drift across the central Appalachians and southern
middle Atlantic states Wed night through Thu night. The sub-tropical
ridge will then redevelop northward across the central Appalachians
and Virgnias through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 345 AM Tuesday...

Another Heat Advisory has been issued for the NC Coastal Plain and
ern Sandhills for this afternoon. Note that in addition to the
Eastern Region Directive for Heat Advisory criteria of 105 degrees
for two consecutive hours or more, WFO RAH`s policy is also for
three or more consecutive days of 102 to 105 degrees. Today/Tuesday
will mark the sixth day of (at least) that criteria in the Advisory
area.

The forecast will be generally a persistence one, with perhaps a
slight increase in coverage of diurnal, pulse convection through
this evening.

A subtropical ridge --a strong one at 594 dm and 324 dm at 500 mb
and 700 mb, respectively-- will remain situated over the sern US
through tonight. A mid level shear axis that was draped across SC
and swrn NC during the past 36 hours left behind a relative maximum
in moisture around 700 mb; and this moist axis will drift around the
nrn periphery of the foregoing subtropical ridge and across cntl NC
and VA through this evening.

At the surface, a lee trough will sharpen over the Piedmont with
diurnal heating, while a another weak convergence axis/wind shift
may linger over nern NC/sern VA, in the vicinity of the weak frontal
zone that settled into that region early Monday, and since weakened.

A continued slight uptick in low level moisture/surface dewpoints
will occur today, owing to a more-sly/onshore component to the low
lvl flow across the Carolinas. With generally persistence high
temperatures, that uptick in low level moisture will favor higher
heat index values (than previous days) throughout cntl NC, with near
100 degree readings creeping wwd across all but the nrn and nw
Piedmont, and with another day of 102 to 107 degrees across the
Advisory area. That uptick in low lvl moisture, and the ewd drift of
the aforementioned mid level moist axis, will favor the development
of isolated to locally scattered pulse convection this afternoon,
some of which may linger over mainly the ne Piedmont and nrn Coastal
Plain through midnight. The presence of high DCAPE values, to as
much as 1200-1400 J/kg, may support a couple of episodes of severe
wind gusts.

Persistence lows in the 70s, coolest where earlier convection
occurs.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 410 AM Tuesday...

A mid and upr low over MO/AR this morning, and which includes the
remnants of Barry, will devolve into an open wave, positively-tilted
trough through early tonight, then drift ewd across the nrn middle
Atlantic and cntl Appalachians Wed through early Thu. Weak mid level
height falls of 10 to perhaps 20 meters, and the right entrance
region of a related weak swly upr jet streak, will consequently
overspread cntl NC late Wed afternoon and Wed night.

At the surface, the Appalachian-lee trough will again sharpen over
the Piedmont, with upr 60s to around 70 degrees surface dewpoints to
the west of that trough, and lwr to middle 70s ones to the east.

Low lvl thickness values are forecast to increase by about 5 meters
over those of Mon and forecast for Tue; and this should translate to
a degree or two hotter temperatures. When combined with slightly
higher surface dewpoints than those forecast for Tue, heat index
values will likely near 105 degrees over all but the nrn and nwrn NC
Piedmont, with 105-109 degree values common in the Coastal Plain and
ern Sandhills. Consequently, the Heat Advisory area will likely be
expanded wwd to include at least another tier of counties in cntl NC
for Wed.

Scattered showers and storms will again loosely focus in the
lee/Piedmont trough, and the sea breeze, with subsequent
development/outflow propagation throughout cntl NC through Wed
evening. Slightly greater coverage may occur over the nwrn and nrn
Piedmont after 6 PM, then continue through early Wed night, owing to
the best overlap there of the incoming weak forcing for ascent
accompanying the shortwave trough aloft with maximum diurnal
heating. The influence of the shortwave trough and jet streak will
also yield effective bulk shear values in the 20-30 kt range, which
may provide for multi-cell storm and cold pool organization, and
strong to marginally severe wind gusts.

Generally persistence lows in the 70s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 100 AM Tuesday...

Strong mid and upper level ridging will follow the weak, remnant
trough that was Barry late in the week through the weekend. Hot
temperatures will prevail Thursday through Sunday, with some cooling
with increased thunderstorm and associated cloudiness by Sunday and
Monday.

As the weak mid/upper trough (Barry remnants) pulls out to the NE
and off the northern mid-Atlantic coast/New England Thursday, the
heights again rise aloft Thu-Sat leading to a large upper ridge over
the region again. This will leave only a weak surface trough, strong
surface heating, and daily intense instability to focus isolated to
widely scattered PM thunderstorms.

Daily highs should reach the mid to upper 90s, with lows in the 70s.
Heat indices of 105-108 will be likely into the weekend.

The chances of much needed showers and thunderstorms are expected to
increase by Sunday into early next week as a pattern change to less
ridging and more troughing over the region occurs. A cold front or
two should stall over the region during this time frame acting as a
focus for convection.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 240 AM Tuesday...

Mainly VFR conditions are expected through the TAF period. However,
widely scattered showers and storms are expected to develop with
diurnal heating this afternoon, but given a lack of focusing
mechanisms, such development is apt to be random and with a
probability of occurrence at any given point only around 20 or so
percent.

Outlook: Increasing moisture ahead of the remnants of Barry will
provide a better chance of mainly diurnal (afternoon-evening)
convection Wed-Fri, and also a low to medium chance of
early morning stratus.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 7 PM EDT this evening for NCZ011-
027-028-042-043-078-088-089.

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...Badgett
AVIATION...MWS