Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 261927
Area Forecast Discussion
National Weather Service Raleigh NC
325 PM EDT Wed Apr 26 2017
A high pressure ridge will build eastward over the Carolinas this
afternoon into tonight. A weakening cold front will approach the
mountains from the west on Thursday, then dissipate over the Mid-
Atlantic Thursday night.
.NEAR TERM /through tonight/...
As of 250 PM Wednesday...
Expect a quiet night as mid level ridging builds over the area from
the SW, and deep subsidence takes place in the wake of the deep low
now drifting off the Northeast coast. Flat scattered to broken
cumulus clouds over the area will dissipate with loss of heating
this evening, resulting in mostly clear skies overnight with a light
wind from the S or SW. Expect decent (although not ideal)
radiational cooling tonight, and with elevated dewpoints, lows will
be mild tonight, in the upper 50s to lower 60s. -GIH
.SHORT TERM /Thursday and Thursday Night/...
As of 345 AM EDT Wednesday...
A strong subsidence inversion /cap/ will remain over central NC on
Thu. As such, one would expect dry conditions to persist. A squall
line over MO/AR at 06Z this morning is expected to propagate
eastward into the TN valley by 12Z Thu as a potent (albeit
deamplifying) shortwave trough lifts NE from the lower Midwest
through the OH valley. Despite decreasing/departing forcing, the
ongoing squall line in the TN valley Thu morning is expected to
propagate eastward into the southern Appalachians during the
aft/eve. An increasingly hostile thermodynamic environment with
eastward extent over the Carolinas should result in rapid weakening
(and eventual dissipation) of the squall line as it progresses
over/east of the Appalachians, however, it is possible that
lingering convection could affect portions of the western Piedmont
between 21-00Z before dissipation occurs. Outflow assoc/w the
remnants of the squall line could result in gusty westerly winds and
a 10-15F temperature drop in the Foothills/western Piedmont late Thu
afternoon, complicating the temperature forecast. Will indicate a
chance for showers and thunderstorms in the western Piedmont during
the late afternoon, with dry conditions elsewhere and highs in the
80s, coolest west and warmest (mid/upper 80s along/east of Hwy 1).
Expect warmer low Thu night (mid 60s) in assoc/w low-level moisture
advection from the SW and likely development of low stratus during
the pre-dawn hours. -Vincent
.LONG TERM /Friday through Tuesday/...
-- Changed Discussion --As of 325 PM Wednesday...
A weak surface tough associated with dying overnight convection is
forecast to stall over the coastal plain and then retreat back to
the west on Friday as the subtropical ridge amplifies off the
Southeast coast. The ridge, and associated rising thicknesses will
peak on Saturday (thicknesses of 1410-1420m), with highs accordingly
peaking in the upper 80s to lower 90s, just short of record highs.
Convection each day should mainly be tied to the seabreeze and higher
terrain in southwesterly flow and no strong forcing. However, with
strong instability forecast, owing to a plume of steep mid-level
lapse rates off the Mexican Plateau, there could be a large hail and
damaging wind threat, more so on Saturday when models suggest a
shallow tropopause disturbance/jet moving lifting through the Deep
South that could aid in triggering storms. Confidence in this
feature and whether or not storms will be able to develop is still
low at this point.
The ridge will hold on Sunday and then give a little to a strong
upper low forecast to lift from the Southern Plains to the Great
Lake by Monday. POPs will increase on Monday as the associated cold
front advances east across the mountains. Shear looks favorable for
severe weather, but instability is questionable on Monday. Temps
will accordingly be knocked back toward normal for the middle of
-- End Changed Discussion --
.AVIATION /18Z Wednesday through Monday/...
As of 235 PM Wednesday...
High confidence in VFR conditions for the next 24 hours. Yesterday`s
deep low pressure system has moved well NE of the area, leaving
behind drier air beneath a ridge of high pressure aloft. Scattered
VFR clouds will largely dissipate this evening with loss of heating,
leaving mainly clear skies overnight, followed by a redevelopment of
flat daytime VFR cumulus clouds by late morning Thu. Surface winds
will be light from the S or SW through tonight, then increase from
the SW by 15z Thu to 12-15 kts gusting to around 20 kts late in the
TAF valid period.
Looking beyond 18z Thu, a line of showers and storms will approach
the southern Appalachians from the west during the afternoon, then
slowly weaken as it moves into central NC Thu afternoon through the
evening and early overnight hours. Best chance of showers/storms
will locally erratic winds/enhanced gusts and brief sub-VFR
conditions will be at INT/GSO late Thu into the early evening. Other
isolated storms are possible Sat and Sun afternoon/early evening,
especially at INT/GSO, with a better chance areawide Mon as a front
approaches. Sub-VFR fog and shallow stratus are possible each late-
night through early-morning. -GIH
As of 230 PM Wednesday...
High water in area creeks and drainage ditches continues to recede
today, with residual scattered road closures appearing to be more
infrastructure-related than hydrological. Main stem river flooding
will likely persist for several more days, particularly over north
central and northeast sections. See
water.weather.gov/ahps2/index.php?wfo=rah for the latest forecasts
and additional information.