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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 191806
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
206 PM EDT Wed Jul 19 2017

.SYNOPSIS...
A weak upper level low over will drift slowly over eastern NC
through tonight. A hot and dry upper level ridge will build east
from the Plains to the Carolinas through Saturday, before
breaking down Sunday and Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1100 AM Wednesday...

The latest data analysis indicated a broad and weak upper low
centered over the region, with the mid level low centered around or
just south of Rocky Mount. Lower pressure at the surface was hard to
find, but a weak surface trough was noted near the Blue Ridge and
another over the Coastal Plain. Latest satellite data indicated the
small spin of the mid/upper level circulation as noted above, with
the best moisture located along the coast - just ahead of the trough
axis. Dew points are down a few degrees today over the Piedmont
where some 60s were evident at mid-morning. There were plenty of
lower to mid 70s dew points down east. Soundings from the area
indicated some drying in the mid/upper levels over the Mountains
with the more northerly flow on the back side of the trough axis.

It appears that convection today will be much more isolated in the
western zones than what occurred on Tuesday afternoon. Still, widely
scattered thunderstorms will have plenty of instability to work with
as highs in that region reach the upper 80s to around 90, with dew
points in the upper 60s.

In the central and eastern zones, scattered thunderstorms are still
expected to develop near the mid/upper low over the eastern
Piedmont and Coastal Plain with continued heating. The areas south
and east of the Triangle appear to have the best chance of storms,
with the convection expected to be highly pulse and outflow driven.
MLCapes on the order of 1500 to 2000 J/KG suggest fairly intense
cores capable of gusty winds that may again produce some isolated
wind damage. Some hail may also occur, but it is favored to be just
below severe criteria in most cases. Highs in lower 90s are favored
in these areas.

Ongoing convection will diminish rapidly by mid evening, with
mostly clear skies overnight. Lows generally in the mid 60s over the
rural Piedmont, ranging into the lower 70s elsewhere.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 345 AM Wednesday...

The mid-upper level low now over NC is forecast to drift or reform
off the SC coast by 12Z Thu, before drifting swwd along the sern
U.S. coast, to nrn FL by 12Z Fri. This will tend to delay the ewd
expansion of the sub-tropical ridge from the MS Valley. Thu will
consequently be the transition day of warming temperatures, into the
middle 90s on average, that will then probably peak early in the
medium range (Fri-Sat). Heat indices around 100 degrees will result
Thu, except for over the nrn and wrn Piedmont where a mixing out of
surface dewpoints into the middle to upper 60s, behind a lee/
Piedmont surface trough, will yield a relatively "drier" heat. The
departure of the mid-upper level low and associated cold pool aloft
will result in minimal diurnal convective coverage that should be
limited to an isolated storm or two along the sea breeze/in the srn
Coastal Plain and ern Sandhills. Mild overnight, and rain-free, with
lows in the lower to middle 70s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 205 PM Wednesday...

An upstream ridge (over the lower MS river valley) and a downstream
ridge (offshore the SE coast) extending into the Carolinas Fri/Sat
will de-amplify Sun-Mon as an upper level ridge amplifies over the
Intermountain West, cyclonic flow aloft strengthens across the OH/TN
valley and Mid-Atlantic, and a closed low retrogrades westward along
the Gulf coast.

Fri-Sat: Expect temperatures several degrees above normal Fri/Sat,
with heat indices ~105F (primarily Triangle south/east), depending
on surface moisture/dewpoints. Heat advisories may be needed for
portions of the area Fri/Sat. With westerly flow aloft over the
central Appalachians and a lee trough extending southward through
central VA/NC in the midst of moderate diurnal destabilization,
expect a potential for scattered convection during the afternoon and
evening hours Fri-Sat, though activity could be suppressed over
eastern portions of the state depending on the strength/orientation
of the offshore ridge.

Sun-Wed: Above normal temps/humidity may persist into Sunday, though
chances for convection will also increase as cyclonic flow aloft
strengthens over/upstream of the Mid-Atlantic. With an unseasonably
complex synoptic pattern over the mid-latitudes, uncertainty
increases significantly by early/mid next week. At this time, will
indicate near normal temperatures and near climatological chances
for convection Mon-Wed, in assoc/w a synoptic pattern generally
characterized by ridging over the western CONUS and troughing over
the eastern CONUS. -Vincent
-- End Changed Discussion --

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 200 AM Wednesday...

24 hour TAF period...Drier airmass in place over the western 2/3rds
of the area will help limit coverage of early morning stratus/light
fog, with VFR conditions except for a 3-4 hour predawn window at
RWI, FAY, and possibly RDU. Upper low parked over central NC will
produce scattered convection in the east this afternoon into
evening, with only isolated showers west. Winds will be light, less
than 6 knots, through the period.

Looking further ahead...VFR conditions are expected with building
high pressure aloft mid week through Friday. The will be a low
probability of fog/low stratus in the predawn across the east.

&&

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

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
------------------------------------------

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
-------------------------------------------

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...MWS
NEAR TERM...Badgett/mlm
SHORT TERM...MWS
LONG TERM...Vincent
AVIATION...mlm
CLIMATE...RAH