Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 261825

Area Forecast Discussion
National Weather Service Raleigh NC
225 PM EDT TUE JUL 26 2016

Strong high pressure aloft will extend across the region through
Wednesday, bringing continued hot and humid conditions to central
NC. The chance for afternoon storms will increase toward the end of
the work week.


As of 1030 AM Tuesday...

Late today into this evening may bring our best chance for rain in
several days, with good chances for scattered showers and storms
across the northern half of the forecast area. Latest surface
analysis shows the offshore-centered ridge extending across the
Southeast states with weak lee troughing over our west and the
synoptic front to our N/NW along the OH valley. While the mid and
upper level ridge will hold across the region, the axis will shift a
bit southeastward later today as shortwave energy over the lower
Midwest tracks eastward across the OH valley and mid-Atlantic,
nudging the westerlies slightly to the south and inducing sufficient
acceleration aloft to boost deep layer bulk shear to around 20 kts
across northern NC. This, along with a corresponding slight increase
in previously-meager mid level lapse rates along and north of the
NC/VA border, will create an environment that will be more conducive
for convection to initiate and grow upscale. MUCAPE is expected to
peak at 1000-2000 J/kg today, highest near the border and over NE
NC, and this is where the convection-allowing models (CAMs) show the
most long-lived activity today. But the HRRR/HRRRX/RAP, WRF-NMM/ARW,
SSEO, NSSL WRF, and NCAR ensemble neighborhood probabilities all
indicate at least some convection over the remainder of the western
Piedmont as well, warranting at least isolated coverage there, with
warmer/drier air aloft limiting coverage. Scattered coverage is
anticipated over northern NC, and this activity may congeal into
clusters over our NE sections this evening -- fueled by better deep
layer bulk shear and slightly greater instability in this area -
- before gradually diminishing overnight. The only notable changes
to the existing forecast will be to delay convection onset a couple
of hours over all but the NW, raise pops a tad over all of the
western Piedmont, and retain pops in our eastern sections later into
the night as suggested by the NSSL WRF, HRRRX, and others. High-res
guidance still supports highs in the mid-upper 90s, and with a
mixing/lowering of dewpoints with heating likely to follow a pattern
similar to yesterday, we should reach dewpoints from the upper 60s
NW to lower 70s SE this afternoon, equating to heat index values
easily peaking at or above 105 over the advisory area. -GIH

Previous discussion as of 305 AM Tuesday: Today: Mid/upper level
ridging continues over the area this morning with the mid level high
centered across the Carolinas. Weak disturbances aloft continue to
track around the mid/upper level ridge to the west and north of
central NC. The center of the mid/upper level ridge is forecast to
shift slightly to the southeast today, which will allow for a better
chance of weak disturbances tracking around the ridge to affect
northern portions of central NC this afternoon/evening. Once such
disturbance is helping to support and area of showers drifting
northward across northern GA/AL. This weak energy coupled with
another weak disturbance located over the lower OH/TN valley region
this morning will combine along with a weak surface trough across
the area to produce isolated to widely scattered showers and storms
this afternoon/evening (with better coverage likely to the north of
our area). Given strong heating during the morning into the early
afternoon hours we will likely see at least 2000 to 2500 J/KG of
MLCAPE across the area today. Deep shear however looks fairly weak,
with maybe 15 to 20 kts of westerly flow at 500 MB. This environment
will be supportive of wet downbursts, with perhaps a few clusters of
storms possible. Thus, the latest day one convective outlook from
SPC has our far northern counties in a marginal risk for severe
storms with possibly a few damaging wet downbursts.

The main story today though will again be the relentless heat, with
high temps expected to again range from the mid to upper 90s and
heat index values ranging from near 100 NW to 104-107 elsewhere.
Thus, will continue the heat advisory today from noon to 8 PM for
all but the far Western Piedmont.

Tonight: Most convection will generally die off by late evening with
another warm night expected. Expect lows temps tonight to generally
be in the mid to upper 70s. Can`t completely rule out additional
weak disturbance tracking across northern portions of the area
overnight, possibly sparking a shower or storm, though think any
activity will be quite isolated as we should still be under the
general influence from the nearby mid/upper level ridge.-BSD


As of 325 AM TUESDAY...

Persistent mid/upper level ridge located just to the south/southeast
of central NC will continue to provide the region with hot and humid
conditions with another day of highs in the mid to upper 90s and
heat index values in the 100-107 degree range (highest east and
south again). Thus, another heat advisory will likely be needed
again on Wednesday afternoon/evening. With a similar pattern to
today, we will again see the best chance of scattered showers and
storms across the northern half of the area, with less across the
south (closer to the center of the ridge). Deep layer shear is a bit
stronger with around 20-25 KTS of 500 MB westerly flow. Thus, think
we could see a few more clusters of storms across northern portions
of the area. In addition a weak cold front will stall across
southern VA on Wednesday afternoon, helping to increase coverage near
the VA/NC border as well.

More of the same is expected on Wednesday night, with warm lows in
the mid to upper 70s and generally dry conditions. However, as will
be the case tonight, we can`t completely rule out isolated
showers/storms associated with possible weak disturbance(s) tracking
across northern portions of the area. Confidence is too low to
include any mention of precip in the forecast at this time though.


.LONG TERM /Thursday through Tuesday/...
As of 230 PM Tuesday...

Beginning Thursday, the high pressure system gets suppressed ever so
slightly to the southeast and allows the remnants of the frontal
boundary over VA to creep southward, increasing pops a bit for the
northern tier of the CWA but otherwise points south should remain
fairly dry but afternoon showers and thunderstorms will be favorable
east of the Piedmont trough. Thursday night a wave is expected to
develop just north of the area and move northeastward leaving Friday
fairly dry. Afternoon convection will be possible again Friday and
Saturday afternoons as the upper level flow turns more
southwesterly. By Sunday, central NC becomes increasingly squeezed
between a surface high to our southeast and another to our
northwest. This will set up a more active pattern over the area
which will funnel moisture into the area. This should help keep
skies cloudier and bring temps down a few degrees for the beginning
of next week. Early next week an upper trough develops to help push
the frontal boundary through the area and hopefully provide some
relief to temperatures. Until then expect continued highs in the mid
90s with heat index values approaching 105 degrees.


As of 100 PM Tuesday...

VFR conditions are likely to dominate through Wed afternoon,
although scattered storms may produce localized enhanced wind gusts
and brief sub-VFR conditions late today through this evening, mainly
at INT/GSO/RDU/RWI. Strong, dry, and deep ridge of high pressure in
the middle and upper levels of the atmosphere will hold overhead for
the 24 hours and beyond. Any cloudiness will be VFR, mostly
scattered except for a period of broken clouds late today into
tonight at INT/GSO/RDU/RWI, as well as in/near any storms. Light fog
(MVFR) is possible late tonight into Wed morning, mainly at RWI/FAY,
and isolated banks of shallow, more dense fog may occur, mainly near
RWI. The overall threat of sub-VFR fog is low, but places that see a
shower or storm later today will have a better chance of seeing fog
late tonight into Wed morning. Surface winds will be light from the
southwest at 6-10 kts through Wed.

Looking beyond 18z Wed: Mostly VFR conditions are anticipated,
although late night and early morning MVFR fog is possible each day
through Fri, with a better chance of sub-VFR fog/stratus Sat/Sun.
Scattered showers/storms are again expected Wed afternoon, mainly at
the northern TAF sites. Storm chances will drop once again for Thu
and Fri, before rising again over the weekend. -GIH


Heat Advisory from noon today to 8 PM EDT this evening for



NEAR TERM...Hartfield/BSD
AVIATION...Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.