National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 181817
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
217 PM EDT Tue Jul 18 2017

.SYNOPSIS...
-- Changed Discussion --
An upper level low across the Piedmont of North Carolina will drift
east and then southeast across the Carolinas through Thursday. A
strong ridge of high pressure across the Central Plains will expand
into our region for Friday through the weekend.
-- End Changed Discussion --
&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 215 PM Tuesday...

A well defined upper trough axis that extended southwest from
KDCA to just west of KCLT to near KATL at midday will shift
slightly east through tonight and will be the primary player in
convective evolution during the next 12 hours. The trough will
close off this afternoon as a couple of waves of vorticity
rotate about the center. Deeper moisture is present east of the
trough axis and the widespread area of morning stratus has
largely cleared out from U.S. 1 westward while a good deal of
cloud cover holds on to the east in the Coastal Plain and the
eastern Piedmont. Should seek an increase in the number of
breaks of sunshine as the afternoon wears on. Mid-level temperatures
near the trough axis at 500 hPa are relatively cool and range
between -11 and -12C resulting in mid level lapse rates
exceeding 6 deg C/km. In addition, the exit region of a 60+kt
jet across northeastern NC at 250 hPa will contribute to some
broader forcing for ascent. The air mass across central NC has
become moderately unstable with MLCAPE values ranging between
1000 and 2000 J/KG this afternoon with the instability axis
extending near the U.S. 1 gradient in the sweet spot where some
sunshine expanding from the west overlaps the deeper moisture
across the east.

Isolated convection is developing this afternoon resulting from
low-level convergence in a couple of locations: in a region of
differential heating near the instability axis from Roxboro
southwest through Asheboro to Charlotte, across the I-95
corridor and across the eastern slopes of the Appalachians. The
greatest coverage should be located across the east and
southeast ahead of the upper trough and in a region of deeper
moisture and greater instability. The wind field today is very
weak with the flow below 500 hPa generally less than 12 kts,
with stronger flow above that across the east in proximity to
the upper jet. Organized severe convection is not expected with
the weak shear and pulse or  convective mode although the
strongest storms could produce a localized strong wind gust or
even some small hail.

The convection should wane this evening with the loss of heating
and limited forcing for ascent. Overnight lows will range within
a few degrees of 70. -Blaes
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
As of 215 PM EDT Tuesday...

The upper trough will have become closed by Wednesday morning
and will be centered near Goldsboro with a northeast-southwest
trough axis. Convective coverage on Wednesday afternoon and
evening will be more limited than previous days as the deep
moisture axis will have shifted offshore and much of the area
will be located on the subsident side of the trough. Will
include slight chance PoPs for much of the area with slightly
higher Pops across the Coastal Plain, east of the trough axis.
The convection should dissipate early Wednesday evening. High
temperatures on Wednesday will be a few degrees higher as
morning low-level thickness values increase to 1410m or greater,
supporting highs in the 89 to 94 range. Lows on thursday
morning will range in the lower 70s. -Blaes
-- End Changed Discussion --
&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 355 AM Tuesday...

A mid-upper level evolving now over the middle Atlantic states will
move slowly east, to just off the sern NC coast by 12Z Thu, before
drifting swwd along the sern U.S. coast and to near the FL panhandle
by Sat. This is a change in model run-to-run continuity from
previous days, which indicated the low would move off DelMarVa and
out to sea through the end of the week. The retrogression of this
feature would occur in a break, or weakness, in a pair of sub-
tropical ridges that will otherwise span from the central Plains/mid
MS Valley to the wrn N. Atlantic, and may result in slightly less
hot conditions than earlier forecast, particularly along the sern
U.S. coast where a relative minimum in heights/thicknesses would
result.

At the surface, a trough will become established in the lee of the
srn and central Appalachians, on the wrn periphery of high pressure
over the central and wrn N. Atlantic. The presence and influence of
the sub-tropical ridge will likely restrict diurnal convection to
differential heating zones over the mountains and along the sea
breeze.

Despite the possibility of the slightly less hot temperatures noted
above, heat and high heat indices may yet become hazardous, as
temperatures beneath the ridge climb into the middle 90s to around
100 degrees - hottest Fri-Sat. When combined with surface dewpoints
ranging from the middle to upper 60s west of the Appalachian-lee
trough (over the nw NC piedmont) to lower to middle 70s to the east
of that feature (over the Coastal Plain), heat index values between
100 and 110 degrees are expected to result.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
As of 140 PM Tuesday...

24 hour TAF period... Areas of stratus this morning with widespread
IFR/MVFR restrictions has given way to a mix of VFR and MVFR
conditions in stratocumulus early this afternoon. Isolated to
scattered convection will develop during the afternoon, especially
from interstate 85 south and especially eastward. Coverage will be
more limited than a typical summer day but across the east we will
include temporary restriction of an MVFR shower and a mention of a
vicinity shower with VFR conditions across the west. Will hold off
mention of thunder at this point given low predictability. Mainly
VFR conditions are expected this evening and overnight. Another
period of stratus is expected to redevelop late tonight although the
coverage will be more limited and generally confined to the eastern
Piedmont and especially the Coastal Plain.

Looking further ahead... Mainly afternoon and evening showers and
isolated storms are expected again on Wednesday with a possibility
for fog/low stratus in the morning across the east. Chances of
diurnal showers and storms decrease a great deal by Thursday into
the weekend with hot weather and generally VFR conditions expected.
-Blaes

&&

.CLIMATE...
RDU Records:
Date     | High   Year  |  High Min  Year
------------------------------------------
18 July  |  103   1887  |     79     1887
19 July  |  101   1902  |     80     1942
20 July  |  102   1942  |     76     1981
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
------------------------------------------
18 July  |   97   1986  |     76     1986
19 July  |   98   1977  |     75     2016
20 July  |  100   1977  |     75     1986
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
-------------------------------------------
18 July  |  103   1942  |     76     2013
19 July  |  101   2002  |     77     1988
20 July  |  104   1932  |     80     1996
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...
None.

&&

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