Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 210534

Area Forecast Discussion
National Weather Service Raleigh NC
135 AM EDT Fri Jul 21 2017

An upper level ridge will build east over the region through
Saturday. A cold front will approach late in the weekend and early
next week.


As of 915 PM Thursday...

Isolated pulse convection across the SW Piedmont will continue to
fade, leaving the remainder of the evening and overnight dry with
mostly clear skies with only a few cirrus expected overnight. Lows


As of 915 PM Thursday...

With the exception of my NW Piedmont counties, most of the CWA will
have heat indices of 104 to 107 for several hours tomorrow
afternoon. Even if the piedmont counties fall just short(potentially
due to dewpoints mixing out into the upper 60s), when considering
the cumulative effects of a 3 day heat episode that will begin
tomorrow, the stress/impacts will be significant to the area. Thus,
will issue Heat Advisory for the Sandhills, eastern Piedmont
counties, including the Triangle, and the coastal plain counties,
beginning at noon tomorrow and going through 8 pm.

Previous discussion: The upper ridge is forecast to peak Friday. The
issue will be the heat. After coordinating with surrounding NWS
offices, it was decided to hold off on a Heat Advisory for Friday.
However, it will be further analyzed tonight as the advisory can be
issued in the first or second period of the forecast. Forecast highs
of 95 NW to near 100 in the Sandhills still is on target. Dew point
forecasts are generally in the lower 70s in the Coastal Plain, and
this may be too low. There has been mixing this afternoon over the
Piedmont yielding surface dew points in the mid to upper 60s, yet
the southern and eastern zones in the Southern Piedmont and Coastal
Plain have not mixed out as much with dew points as high as 74 at
FAY and 75 at Clinton. FAY had a heat index of 107 at 200 PM today.
So, a heat advisory will most likely be needed for a portion of the
Coastal Plain and Southern Piedmont on Friday.

POP should continue 10 percent or less with strong upper ridging and
the MCS activity expected to stay northwest of the region. However,
models do point toward increasing chance of mountain storms
potentially drifting into the Piedmont late Friday and Friday night.
Lows Friday night should stay in the 70s all areas.


As of 245 PM Thursday...

Overview: At the beginning of the weekend central NC will be
situated in a weakness between a de-amplifying ridge over the
central/lower MS river valley and a downstream ridge offshore the SE
Coast, along the southern fringe of the westerlies. Cyclonic flow
aloft is progged to strengthen over the region late this
weekend/early next week, transitioning to NW flow aloft mid-week as
an amplifying ridge over the Rockies shifts east into the Central
Plains. Long range guidance is in relative good agreement on the
overall synoptic pattern, though significant uncertainty persists
with regard to the evolution of upstream convection in addition to
whether or not shortwave energy may cut-off over the Southeast US
early/mid next week.

Sat/Sun: Above normal temperatures in the mid/upper 90s are expected
over the majority of central NC this weekend, though maximum heat
indices are difficult to ascertain at this time. 12Z GFS/NAM
forecast soundings both suggest surface dewpoints will mix out into
the 60s along/west of a pronounced sfc trough in the lee of the
Appalachians on Sat, and uncertainty persists w/regard to the
evolution of convection (upstream or otherwise) and associated
mid/upper level ceilings. A heat advisory will likely be needed for
portions of central NC this weekend, particularly south and east of
the Triangle.

Mon-Thu: Near or slightly above normal temps and above normal
chances for convection are expected early next week as cyclonic flow
aloft strengthens over the region. Confidence in sensible weather
decreases significantly by mid-week as outlined above. At this time
will indicate climo temps/precip chances. -Vincent


As of 135 AM Friday...

24 hour TAF period: VFR conditions under high pressure will
generally persist through the TAF period. However, a brief period of
sub-VFR visbys at KRWI will be possible, mainly at RWI...from 08-12Z
this morning. Isolated convection is expected this afternoon/early
evening...too random to include in the TAFs. An outflow boundary
will be crossing the mountains towards evening and may make it into
the northwest Piedmont after sunset...will reevaluate this scenario
for increased confidence in its convective potential for the 12Z

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


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


Heat Advisory from noon to 8 PM EDT Friday for NCZ010-011-025>028-



LONG TERM...Vincent
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