Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 231843
Area Forecast Discussion
National Weather Service Raleigh NC
243 PM EDT FRI SEP 23 2016
An upper level low and the remnant low from Julia will linger and
weaken near the southern Carolina coast through Saturday. A cold
front will drop south into the area late Saturday and stall south
of the region on Sunday. A stronger cold front will push through the
region late Tuesday or early Wednesday.
.NEAR TERM /THROUGH TONIGHT/...
As of 145 PM Friday...
Quick update to account for a slightly faster erosion of clouds
across the northern tier than expected. Mainly clear skies are now
noted across Forsyth, Person, Granville, Vance and Warren
Counties. Some breaks in the overcast have developed across much
of the remainder of the area as well. Isolated to widely
scattered showers have developed across the far southern Coastal
Plain and Sandhills, these showers will continue to develop and
push south during the afternoon. Current PoP and temperature
trends looks good and need only minor adjustment. -Blaes
Previous discussion from 1045 AM Friday...Latest surface analysis
shows a the persistent remnant low from Julia located just south
of Cape Fear. A weakening mid level vortex that was located across
the eastern Carolinas was beginning to shear out and open up this
morning. The air mass across the eastern Carolinas remains very
moist with precipitable water values in excess of 1.9 inches in
the southern coastal region and Coastal Plain. Notably drier air
with PW values of 1.5 inches or less have reached the Richmond Va
area and the western Triad. The latest visible satellite imagery
shows a large region of almost exclusively low clouds across the
eastern two thirds of NC with some breaks and thin spots in the
overcast developing. Shower activity to the southeast of I-95
earlier this morning has diminished.
NWP guidance is in generally agreement that drier air over VA and
northwestern NC will push slowly south into central NC. Should
continue to gradually see a lifting of ceilings and brightening
of the sky this morning into this afternoon. Expect to see some
breaks develop in the overcast, especially in a slightly
divergent low level flow to the northwest of interstate 95 with
the clouds more stubborn to the southeast of I-95. Convection
allowing models develop scattered to widespread convection this
afternoon across the coastal region, with more widely scattered
convection in the RAH CWA across the southern Coastal Plain and
Sandhills region with little chance of rain elsewhere. A weakly
unstable air mass with thin CAPE should lead to a few
thunderstorms as well, but given the weak flow severe weather is
not expected but storms will be capable of producing locally heavy
rain as the move slowly.
Atypical highs are expected today with the warmest readings in the
northwest including the Triad where there will be the most sun
with the coolest conditions in the southeast with the more
persistent cloud cover and scattered showers. Highs will range
from the mid 80s northwest to lower 80s southeast.
Skies will continue to clear this evening with the loss of heating
and the arrival of drier air. With little forcing for ascent, no
rain is expected overnight. Some clouds may persist across the
southeast before areas of fog and perhaps some low stratus appear
increasingly likely, most widespread from the northern Coastal
Plain southwest across the remainder of the Coastal Plain into the
Sandhills and eastern Piedmont. Lows tonight will range in the
mid 60s northwest to near 780 southeast. -Blaes
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 255 AM Friday...
Dry and very warm weather expected. Mid level ridging aloft
continues to build in from the west, while at the surface, the weak
trough drifts further offshore as weak high pressure moves in from
the west, although lee troughing does form in the afternoon over the
western Piedmont. With low PW and a fairly stable column, will keep
pops under 15%, with mostly sunny skies. Thicknesses and statistical
guidance indicate highs in the mid-upper 80s, around 6-10 degrees
above normal. The anticipated backdoor front moving toward NC from
the NNE is poised to move into the NE CWA Sat night into early Sun
morning, driven by energy rotating around a large vortex centered
near the Newfoundland/Quebec border. But this low does not appear to
dig markedly down the East Coast, hinting that the front may not
work very far into NC despite being propelled by a cool dense
surface high to our north. The ECMWF tends to hold the front just
north of the VA/NC border through daybreak Sunday, while the NAM/GFS
dip the front into northern NC. Will lean toward the ECMWF solution
and hold onto mild temps overnight, with lows Sat night in the mid-
upper 60s and a minimal drop in dewpoints over the NE. Regardless of
frontal progression, we are likely to see increasing clouds from NNE
to SSW Sat night. While a few models generate shower activity ahead
of or along the front over north central and NE NC Sat night, the
presence of features to force ascent is uncertain, and will opt for
dry weather for now and monitor trends. -GIH
.LONG TERM /SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --As of 243 PM Friday...
The timing of the back-door cold front through the area on Sunday is
still in question. The GFS and NAM are much quicker to blow the
front south through the area late Saturday night/ear Sunday, while
the ECMWF suggest the frontal boundary will tend to "hang up" or
slow down across the forecast area on Sunday, which is very
plausible given weak sfc pressure rises from the transitory parent
high center retreating off the Northeast-Southern New England Coast.
These models discrepancies are leading to lower than average
forecaster confidence, making for a challenging temperature forecast
on Sunday and likely setup a sharp temperature gradient across the
area. For now will continue a "middle of the road approach" with
highs ranging from mid 70s northeast to mid 80s southwest.
Additionally, given the potential for the front invof the area, will
continue isolated to slight chance chance pops.
Mid/upper level ridge will build east over the area on Monday in
advance of a closed low and upper trough progressing eastward into
the Upper Great Lakes/Southern Canada. With the transitory parent
high quickly moving off the Southern New England Coast, south-
southeasterly return flow will quickly return to the area late
Monday with rain chances generally restricted to
upslope/differential heating over the higher terrain, while ridging
aloft should keep the remainder of NC dry. SELY moisture advection
and resultant weak isentropic upglide in advance of a cold front
approaching from the west could produce showers across the area as
early as Monday night/Tuesday morning with another round of showers
and storms expected to accompany the frontal passage Tuesday
afternoon/evening. Highs Monday and Tuesday slightly above normal
with mild overnight lows in the 60s.
In the wake of the cold front, high pressure will bring dry
seasonable weather for the later half of the work week. Highs 75-80.
Lows the 50s.
-- End Changed Discussion --
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
As of 155 PM Friday...
A much drier air mass that is pushing into central NC has resulted in
varying conditions across the area with VFR conditions near the VA
border and Triad area to MVFR conditions with low ceilings and
isolated showers to the southeast. The worst and most stubborn
conditions are located across the southern Coastal Plain and
Sandhills near the KFAY and KRWI terminals with ceilings around
1.5kft and widely scattered showers.
Aviation conditions will continue to generally improve
from north to south through the afternoon hours with most
locations becoming VFR by late in the afternoon. Showers across
the Southeast will decrease in coverage during the late afternoon.
An isolated thunderstorm is possible but coverage and confidence
precludes its mention in the TAF.
VFR conditions are expected this evening with a scattered low
cloud layer or two. Guidance suggests some fog will develop late
tonight toward daybreak from the Coastal Plain south and west to
the Sandhills. This will result in areas of MVFR to perhaps
briefly IFR fog, most prominently near the KFAY and KRWI terminals
perhaps extending to the KRDU terminal. Mainly clear skies with
little fog is expected overnight at the Triad terminals of KGSO
and KINT. Any fog or low cloudiness should quickly give way to VFR
conditions by mid morning Saturday with a light mainly northerly
Looking beyond 18z Saturday morning, VFR conditions are expected
on Saturday afternoon and evening before a cold front moves into
the region from the north Saturday night. A period of adverse
aviation conditions including reduced ceilings and visibilities in
showers is possible beginning late Saturday night/Sunday morning
and continuing through early Monday. Another period of
adverse aviation conditions is possible late Monday into Tuesday
as another cold front approaches the region. -Blaes