Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 221118
Area Forecast Discussion
National Weather Service Raleigh NC
719 AM EDT FRI JUL 22 2016
A positive tilt mid-level trough in NNW flow will move into the SRN
Appalachians and Carolinas this afternoon. An Appalachian-lee
surface trough will strengthen beneath a strong sub-tropical ridge
that will expand from the central U.S. to the Middle Atlantic states
.NEAR TERM /THROUGH TONIGHT/...
As of 345 AM Friday...
Central NC will remain on the ERN periphery of a strong sub-
tropical ridge centered over OK, while a surface trough will
sharpen in the of the Appalachians. Within the associated N to NNW
flow aloft around the ridge, a low amplitude, positive tilt mid-
level trough, now extending from the Lower Great lakes to the OH
Valley, will drift into NC this afternoon. An MCV evident in
model analysis 700-500 mb vorticity fields and earlier satellite
imagery is embedded within the broader mid-level trough, over ERN
KY; and this feature is forecast to drift focus forcing for ascent
as it drifts into the SRN Appalachians through the same time.
While the relative highest chance of showers and storms will be
along the track of the MCV and aided by differential heating -in
the mountains- a shower or storm will also be possible in the
vicinity of the lee trough, centered over the WRN Piedmont,
despite rather dry mid levels.
Return flow around high pressure centered near Bermuda will
support slightly higher temperatures and dewpoints versus those of
Thu, with highs generally 90 to 95 degrees.
Light SSW stirring overnight should hold temperatures in the
(lower) 70s, and also preclude the development of anything more
than patchy fog, particularly given the presence of cirrus
related to the MCS upstream/over IL.
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 400 AM Friday...
Generally a persistence forecast, with a slight chance of an
afternoon storm, and higher temperatures yet, owing to a slowly
increasing influence of the sub-tropical ridge --and associated
heat beneath it-- as it builds E. Highs 93 to 97 and lows in the
middle 70s. Heat indices are expected to range from around 100
over the NW Piedmont to 105 over the ERN Sandhills and Coastal
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 335 AM Friday...
...Hot and humid and conditions with heat index values in excess of
100 expected to continue into Sunday and Monday...
Central NC will be located along the eastern periphery of a west to
east extending upper level ridge at the beginning of the long term
period. A portion of the ridge strengthens across NC and VA late
Sunday and then shift offshore on Monday into Tuesday as weak
troughiness develops across the Great Lakes and OH Valley and a
westward pushing upper low moves from the Bahamas on Sunday to the
northern Gulf of Mexico on Tuesday. At the surface, a Piedmont
trough present on Sunday will weaken on Monday and be replaced by
the southerly flow associated with the circulation about a Bermuda
high pressure system. A hot and humid air mass will be in place
across the region with surface dewpoints in the lower to mid 70s
contributing to a weak to moderately unstable air mass during the
afternoon each day. Limited forcing for ascent in a generally
subsident environment with some capping will keep convective chances
limited on Sunday and Monday and increase slightly on Tuesday as a
short wave trough approaches the region from the OH Valley. Guidance
has cooled off a bit from previous runs with morning thickness
values ranging in the 1420-1430m range during the period, perhaps as
high as 1435m on Sunday which support highs in the mid to possibly
upper 90s during the period. The hottest days will be Sunday and
Monday with temperatures approaching 98 to 99 degrees in a few
spots. The west-east oriented low and mid level ridge axis often
support hot periods with higher boundary layer moisture and higher
heat index values than north-south ridges which often result in hot
and drier setups. Heat index values will climb above 100 and likely
exceed 105 in most areas on Sunday and Monday.
The ridge relaxes across the region On Wednesday and Thursday
allowing the westerlies to drop southward and mean troughiness to
develop across the Great Lakes and OH Valley. A cold front will
settle south across the Mid Atlantic on Wednesday and potentially
moving into NC on Thursday. The approaching trough aloft and the
cold front will result in an increase in the threat of convection.
Increased cloud cover and the retreat of the ridge will result in
high temperatures dropping back into the lower 90s with lows in the
lower to mid 70s. -blaes
.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
As of 715 AM Friday...
Light SSW flow and VFR conditions are anticipated through the TAF
period, aside from a very small chance of morning fog and an
afternoon shower or storm.
Outlook: Hot and subsident sub-tropical high pressure will expand
across NC and result in mostly dry/VFR conditions through early next
week. Exceptions to predominantly VFR conditions will be a small
chance of early morning fog/stratus and isolated to widely scattered
afternoon and evening storms, whose chances will gradually increase
Record high temperatures and the year in which the record was most
recently set at Raleigh, Greensboro, and Fayetteville.
Sat Jul 23 Sun Jul 24 Sat Jul 23
RDU 105/1952 101/2011 102/2010
GSO 99/1952 99/1914 101/1914
FAY 103/2011 105/1952 103/1914