Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 211937
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
337 PM EDT Fri Jul 21 2017

.SYNOPSIS...
A hot upper level high pressure will remain in place from the Plains
eastward over our region into the weekend. A cold front will
approach from the northwest late in the weekend into early next week
as the high pressure breaks down over the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 335 PM Friday...

...Heat advisory in effect for the eastern Piedmont, Sandhills,
and Coastal Plain through 800 PM...

A chance of a few strong thunderstorms this afternoon at 20-30
percent.

Heat indices of 110 already reached around Fayetteville and
Raleigh, with 100+ in all areas. Caution is advised, even late
tonight with temperatures slow to fall through the 80s.

The latest data analysis indicated a well defined surface trough
stretching SW to NE across the Piedmont, or roughly from near
Charlotte to Raleigh. It is along this boundary were isolated
thunderstorms are favored to develop this afternoon. MLCapes of
2000+ J/KG and high freezing levels support mainly a gusty wind
threat with any storm. Even within this favored zone near the
trough, POP is no higher than 20-30 percent for any one given spot
for a thunderstorm.

The MCS tracking over the central Appalachians is helping
initiate or even enhance diurnally driven thunderstorms over SW
VA and NW NC Mountains this afternoon. Some of the CAMS
indicate the probability (30-40 percent) that the NW Piedmont
may get in to some action soon. We are not currently in any
outlook by SPC; however, any storms that form or move into the
NW have the chance to be locally strong to severe given the
available energy to work with.

Convection chances are expected to drop off by mid-evening, but we
will have to watch the development of upstream MCS activity later
tonight. Lows will be in the 70s (80 around KFAY).

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 335 PM Friday...

...Excessive Heat Watch for the cities
of Raleigh and Fayetteville (counties of Wake and Cumberland)
1100 AM Saturday through 700 PM Sunday...

Heat advisory in effect for the rest of our region including all
the Piedmont, Sandhills, and Coastal Plain 11 AM Saturday
through 700 PM Saturday.

The big story will be the heat and humidity, but there will be a
slight chance of thunderstorms as well.

The Excessive Heat Watch is for the Fayetteville/Cumberland and
Raleigh/Wake urban areas. The Heat Advisory is in effect for the
rest of the counties in our region. The Watch is driven by the
potential for excessive heat with heat indices of 108 to 113 for
several hours both Saturday and Sunday in the Watch area. Highs
near 100 with dew points in the mid 70s are expected. Just as
importantly, the night time temperatures tonight through
Saturday night will remain in the 80s for all but an hour or so.
This will not give time for those outdoors to cool down without
fans or air conditioning. The accumulative affects of 3 or more
days with heat index values near or above 110 in the cities of
Fayetteville and Raleigh combined with the failure of
temperatures to fall below 80 at night will create excessive
stress. If these readings are still expected in later forecasts,
these two counties/cities will be upgraded to an Excessive Heat
Warning.

The Heat Advisory is in effect elsewhere for heat indices of
105+ for several hours time Saturday afternoon. Highs should top
out in the mid to upper 90s again Saturday. In the NW and W
Piedmont, heat indices may not reach 105; however criteria
allows for the issuance of advisories if the heat index values
are 100+ for several days in a row. The urban areas in the Triad
cities will also have nighttime temperatures slow to fall below
80, making the advisory needed as well when combined with the
consecutive days of high heat.

Convective chances should improve late Saturday from the north.
However, not all models are in agreement. Several CAMS runs do
have MCS activity rapidly moving ESE from the Ohio Valley to VA
late Saturday and Saturday night. Some of the MCS activity or
associated outflows may drive thunderstorms into the northern
Piedmont, yet this will have to be watched closely due to the
high variability in the current forecasts. Some severe storms
will also be possible, mainly after 500 PM Saturday into
Saturday night. Lows 70s to near 80 Saturday night, with some
potential for cooling north if storms make the run into that
region.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 225 PM Friday...

...Excessive Heat Watch for Raleigh and Fayetteville through
Sunday at 700 PM...

Hot and humid airmass will remain over central North Carolina
Sunday as a ridges remain centered near Bermuda and in the lower
Mississippi Valley. Meanwhile a shortwave moving across Great
Lakes Sunday into Tuesday will deepen a trough over the
Northeast and mid Atlantic states allowing a cold front to move
south into the North Carolina area. Temperatures will lower to
near seasonal averages by mid week with additional cloud cover
and convection. Another shortwave will move across the Great
Lakes Thursday and Friday keeping the eastern trough in place.

Maximum temperatures on Sunday are expected in the mid to upper 90s
with heat indices approaching or exceeding 105F to 110 in many locations.
However there is a possibility that some MCS related
clouds/rain may affect portions of the region, which would help
out and lower temps a bit. Chances appear to increase late
Sunday with the potential for strong to severe storms in the
north late day.


&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
As of 125 PM Friday...

24 hour TAF period: Generally VFR conditions under high pressure
will persist through the TAF period. There is a low probability (20-
30) for MVFR thunderstorm conditions between 20z and 00z/this
evening.

Outlook: Generally VFR conditions are expected Saturday. Scattered
mainly diurnally driven convection is possible Saturday and Sunday,
with MVFR to IFR conditions. An even better chance of storms are
expected by early next week as a cold front moves into the area,
along with morning stratus and/or fog.

&&

.CLIMATE...
RDU Records:
Date     | High   Year  |  High Min  Year
------------------------------------------

21 July  |  102   2011  |     78     1932
22 July  |  103   2011  |     78     2011
23 July  |  105   1952  |     78     2011
24 July  |  101   2011  |     79     2011

GSO Records:
Date     | High   Year  |  High Min  Year
------------------------------------------

21 July  |  102   1926  |     76     2011
22 July  |  101   1926  |     77     2011
23 July  |   99   1952  |     78     2010
24 July  |   99   1914  |     78     2010

FAY Records:
Date     |  High  Year  |  High Min  Year
-------------------------------------------

21 July  |  105   1932  |     79     1977
22 July  |  107   1932  |     79     2011
23 July  |  103   2011  |     79     1998
24 July  |  105   1952  |     79     1945

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT this evening for NCZ010-011-
025>028-040>043-075>078-084>086-088-089.
Heat Advisory from 11 AM to 7 PM EDT Saturday for NCZ007>011-
021>028-038>040-042-043-073>078-083>086-089.
Excessive Heat Watch from Saturday morning through Sunday
evening for NCZ041-088.

&&

$$
SYNOPSIS...BADGETT
NEAR TERM...BADGETT
SHORT TERM...BADGETT
LONG TERM...JF
AVIATION...BADGETT
CLIMATE...RAH


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