Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 281430
Area Forecast Discussion
National Weather Service Raleigh NC
1030 AM EDT Fri Apr 27 2017
A warm moist southerly flow will continue through the weekend, as a
deep high pressure ridge strengthens off the Southeast coast.
.NEAR TERM /Today and Tonight/...
As of 1030 AM Friday...
Forecast is on track. 12z GSO sounding reveals a cap in the 850-750
mb layer which has helped to trap moisture beneath it within a weak
wind regime, resulting in stubborn stratus in the Triad and stratocu
elsewhere. As surface winds strengthen across the area in the next
few hours, horizontal dispersion should help mix out and lift the
remaining low clouds, resulting in partly cloudy skies for much of
the day areawide. Convection chances still appear slim, given the
cap and falling PW values in the wake of the early-morning
showers/storms now moving off the NE NC coast. But lapse rates aloft
are fairly steep and projected to top out over 7 C/km this afternoon
over the Coastal Plain, which could spur development of isolated
storms in our far SE, although deep layer shear will be less
favorable there (just 25 kts) compared to further west, thanks to
the building ridge just off the coast. Recent runs of convection-
allowing models support limited to no convection over central NC
today. Will maintain a dry forecast, although an isolated cell or
two remain possible where local effects can prompt sufficient mass
convergence and forced ascent. Expect highs today in the mid 80s to
lower 90s, except for lower 80s in the immediate Triad region where
insolated will be reduced. -GIH
Earlier discussion from 300 am: Extreme destabilization (3000-3500
J/Kg MLCAPE) is expected today as rich low-level moisture advects
poleward beneath a modified elevated mixed layer /steep mid-level
lapse rates/ in the presence of unimpeded insolation. Despite
atypically favorable thermodynamics, a strong cap at the base of the
EML combined with the absence of any discernible forcing is expected
to preclude convective development.
Convective inhibition will be greatest over western portions of the
state where afternoon temps will top out in the mid 80s (versus ~90F
in eastern NC). Unless a well-timed shortwave/MCV in SW flow aloft
progresses across western NC or upstream convection propagates
downstream into western NC (neither are likely based on the latest
mesoanalysis/observational data and short term model guidance),
convective development is highly unlikely. Erosion of CINH will be
greatest in eastern NC this afternoon where weak low-level
convergence will be present in assoc/w the seabreeze (assuming it
penetrates inland). However, such weak/shallow forcing is unlikely
to break the cap nor sustain updrafts in the presence of such a dry
mid-level airmass. It is fortunate that deep convection is unlikely
to develop considering that thermodynamic/kinematic profiles would
strongly support robust supercells capable of producing destructive
hail/microbursts. With a moist low-level return flow and expected
development of stratus, expect overnight lows in the mid 60s to
lower 70s. -Vincent
.SHORT TERM /Saturday and Saturday Night/...
As of 300 AM EDT Friday...
Thermodynamic conditions on Saturday will be very similar to today,
though kinematic profiles are progged to be weaker. Regardless, a
strong cap and lack of forcing is once again expected to preclude
convective development. Expect above normal highs in the lower 90s
with lows Sat night in the mid/upper 60s to lower 70s. -Vincent
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 325 AM EDT Friday...
Sunday and Sunday night: Bermuda high shifts ever so slightly
eastward on Sunday, with heights lowering a bit, especially across
western NC. While not as hot as Saturday, highs Sunday will still be
a good 7 to 10 degrees above normal. Highs in the lower 80s west to
mid 80s east. The slight eastward shift of the ridge could also
result in slightly higher pops in Ring of Fire fashion across the NC
mtns and fthls. Will retain a slight/small chance pop across the
western Piedmont, otherwise it will remain dry for much of central
NC. Strengthening moisture advection with the approach of the front
from the west Sunday night/early Monday morning will keep the chance
of showers in the west overnight. Mild overnight lows in the mid to
Monday and Monday night: A closed upper level low and associated
deepening sfc low lifting through the Upper Midwest/Great Lakes will
push a cold front into the area Monday evening/night. Attendant cold
front will bring increasing chance of showers and storms to areas
west of US 1 between 18 to 00z, delayed until after 00z across the
east. With regards to severe potential, despite being well removed
from the upper trough dynamics lifting off to the north and with
models continuing to show limited/weak instability across central
NC, impressive vertical shear anchored by a 50-60kt low to mid-level
jet moving through the region warrants close monitoring of the
system as we get closer in time. Breezy conditions are expected
ahead of the front, with gusts of 30-35 mph possible. Thickening
cloud cover and increasing pops from west to east during the
afternoon will result in cooler temps. Highs ranging from mid/upper
70s west to mid 80s east.
Tuesday through Thursday: Cooler/near normal temps will follow
Tuesday and Wednesday in the wake of the cold frontal passage Monday
night. By late next week, medium range models are actually in good
agreement in showing the development of a highly amplified trough
digging into the Deep South/SE US. This vigorous system has the
potential to bring multiple weather hazards to the area, including
heavy rain and severe storms to central NC.
.AVIATION /12Z Friday through Tuesday/...
As of 640 AM EDT Friday...
24 Hour TAF Period: Sub-VFR ceilings and fog will gradually improve
to VFR by mid/late morning in association with diurnal heating/
mixing. VFR conditions are expected to prevail through midnight,
with SCT/BKN diurnal Cu based at 3-4 KFT this afternoon. IFR/LIFR
stratus is anticipated to develop by the end of the TAF period at
all terminals, between midnight and sunrise Sat.
Looking Ahead: VFR conditions are expected to prevail through the
weekend, aside from early morning stratus (IFR/LIFR ceilings).
Convection appears unlikely until a cold front progresses eastward
into the Carolinas late Monday into Monday night. -Vincent