National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 172315
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
715 PM EDT Wed Apr 17 2024

.SYNOPSIS...
A warm and moist southwest flow will persist today. A weak front
will move east across the region tonight, then a stronger cold front
will cross the area late Friday into Saturday, before stalling out
just to our south.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 350 PM Wednesday...

A ribbon of weak, convectively-enhanced vorticity, accompanying a
weakening band of pre-frontal convection over the srn Appalachians
and TN Valley, will move east and across the Carolinas through this
evening, during which time it will move away from deeper/richer low-
level moisture advecting nwd across the lwr MS Valley and srn
Plains. As such, only mid/high-level ceilings and spotty light rain
should result across cntl NC through early this evening.

For late evening-overnight: Within a positive-tilted trough
stretching from the lwr Great Lakes to the Baja Peninsula, an
increasingly-sheared shortwave perturbation now over MO will move
east and across the srn Middle Atlantic early tonight and offshore
through Thu morning. 20-40 meter height falls and cooling of a
couple of degrees C at 500 mb will accompany this feature over cntl
NC late this evening (~03-06Z), during which time a slight chance of
a shower or storm will result, mainly over the ern half of cntl NC.
Late night clearing behind the shortwave perturbation, and calm to
light swly stirring around a lee surface trough, will then favor
radiational cooling centered in the upr 50s to lwr 60s.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 355 PM Wednesday...

Dry and unseasonably warm-mild.

In the wake of a shortwave perturbation that will shear east and
across the srn Middle Atlantic early Thu morning, progressive
shortwave ridging aloft will build across and offshore the South and
Middle Atlantic Thu-Thu night.

A surface frontal wave, accompanying the aforementioned shearing
shortwave perturbation noted above, will develop along a retreating
warm front across nrn VA/MD through Wed evening and offshore the
DelMarva Thu morning. While an attendant cold front will remain
draped in its wake across the Virginias and lwr OH Valley, a
trailing trough will move east and across the srn Middle Atlantic
Piedmont Thu morning and Coastal Plain through the afternoon. The
passage of the trough will be marked by a light wind shift to nwly
and marked low-level drying characterized by afternoon surface
dewpoints in the mid-upr 40s to lwr 50s. It will remain very warm
south the frontal zone, however, with high temperatures comparable
to those of Mon - 85-90 F. The dry air will also favor a large
diurnal temperature range, with Thu night low temperatures in the
50s, to around 60 in the ern Sandhills/srn Coastal Plain.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 210 PM Wednesday...

Shortwave ridging will move offshore on Friday and get replaced by
mostly zonal flow aloft, though a weak perturbation in the mean flow
looks to pass through in the afternoon. At the surface, a warm front
will lift north through central NC on Friday morning, while a much
stronger cold front begins to approach from the NW. The primary low
will lift from the OH Valley into SE Canada, while a secondary
surface low develops and slowly moves east across the Carolinas.
Decent heating and surface dew points in the upper-50s to lower-60s
will help CAPE reach 500-1000 J/kg, maybe even 1000-1500 J/kg
particularly across the south. All of this will bring a chance of
showers and storms during the afternoon and evening. So POPs are
still chance across the area, but think coverage should be fairly
limited given the weak upper forcing. 0-6 km shear around 25-35 kts
is borderline for any severe threat, and the SPC has our entire area
in a marginal (level 1 of 5) risk on Friday. Deep boundary layer
mixing could result in some damaging wind gusts, and isolated large
hail cannot be ruled out either. Forecast highs on Friday are a bit
cooler than Thursday in most places but still quite warm, ranging
from lower-80s in the far north to upper-80s in the far south. Lows
Friday night will again be mild, in the mid-50s to lower-60s, as
precipitation chances diminish but some cloud cover remains.

The cold front will slowly sink south into central NC Friday night
or Saturday morning. A shortwave trough will pass well to our north
across the OH Valley and northern Mid-Atlantic on Saturday afternoon
and evening, again leaving us with weak upper forcing. Ensemble
probabilities indicate most places should be dry, but there could
still be enough instability ahead of the front (wherever it sets up)
to result in more isolated to widely scattered showers and storms,
with the best chance across our far southern counties. Coverage
appears even more limited overall compared to Friday. The
temperature forecast is low confidence as it depends exactly where
the front sets up, but there could be a strong north-to-south
gradient across the area, and maybe some CAD across the north as a
weak high sets up over VA.

POPs then increase to likely on Sunday afternoon and evening,
highest SE, as the next wave of low pressure rides along the front.
With models showing the front well to our south by this point, we
would be on the cool and stable side which would preclude any chance
of storms and would result in just stratiform rain. Ensemble mean
guidance depicts around a third to two thirds of an inch (highest
SE), but deterministic ECMWF and GFS guidance indicates totals
around an inch can`t be ruled out. Leaned toward the cooler guidance
for temperatures on Sunday given potential for more CAD, and highs
in the 50s will be possible in some spots with 60s elsewhere, which
is well below normal.

Widespread rain from the low will end on Monday morning as it lifts
NE into the Atlantic. Yet another shortwave will move across the
region on Monday afternoon and evening, but the GFS is much stronger
with it and brings additional rain (even spawning surface
cyclogenesis off the coast), while on the ECMWF it is flatter and
mostly dry. Most GEFS are not as wet as the deterministic GFS, so it
appears to be an outlier and only have slight chance POPs at this
time. Regardless it will be quite cool once again, with raw guidance
indicating some highs in the 50s will again be possible. Tuesday
will finally turn mostly sunny and dry, before yet another cold
front approaches on Wednesday, though the best upper forcing again
looks to go to our north. Temperatures will warm back into the 70s
on Tuesday and especially Wednesday as the air mass modifies.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
As of 715 PM Wednesday...

24 hour TAF period: High confidence VFR conditions will prevail
through the 24-hr TAF period. A stray shower/sprinkle cannot be
ruled out this evening, mainly at the southern and eastern terminals
through about midnight. Overcast high clouds should begin to clear
from the NNW after midnight, with clear or mostly clear skies
expected at all terminals by 12Z Thu. Otherwise, mainly sly to swly
winds of 6-10 kts, with a few lingering intermittent gusts of 15-20
kts possible through midnight. Winds should generally remain in the
4-8 kt range through the remainder of the TAF period, gradually
veering around to nwly tonight through Thu morning. There could be a
brief period of borderline LLWS criteria at KRDU between 06Z and 09Z
Thu, but confidence was too low to include in this issuance. -KC

Outlook: VFR conditions are expected to dominate through early Fri
afternoon, although a period of sub-VFR cigs is expected 09z-13z Fri
morning in the northeast (mainly RWI, perhaps reaching RDU). We`ll
have a good chance of showers/storms late Fri through Sat morning,
with a risk of sub-VFR cigs/vsbys in fog Fri night. Rain chances and
the potential for sub-VFR conditions will linger Sun into Mon as the
front settles just to our S and cooler high pressure builds in from
the N, but uncertainty is high during this time frame. -GIH
-- End Changed Discussion --

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...Danco
AVIATION...KC/Hartfield