Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 250028

Area Forecast Discussion
National Weather Service Raleigh NC
728 PM EST Sat Feb 24 2024

A cold front will approach from the northwest and move across NC
through this evening. Following high pressure will move across and
offshore the Southeast tonight through Monday.


As of 255 PM Saturday...

Areas of (Trace to light measurable) rain have cooled surface
temperatures by a few degrees on average, and in some locations by
as much as 6-8 F, over much of the ne NC Piedmont and Coastal Plain
since 17Z. That cooling may limit the coverage of what was already
expected to be isolated thunder potential through the evening. While
an isolated storm cannot be entirely ruled out anywhere in cntl NC
given lingering pockets of scant instability, it appears the
relative best chance of thunder will be along a surface frontal
segment and maximized mass convergence and moisture pooling (ie.
surface dewpoints in the upr 30s to around 40F) extending from the
nrn Pamlico Sound nwwd along the Roanoke River and into a frontal
low over near FVX in w-cntl VA. The forecast otherwise remains
unchanged from this morning.

.PREV DISCUSSION... /ISSUED 1150 AM EST Sat Feb 24 2024/

A shortwave trough and accompanying pocket of anomalously cold 500
mb temperatures, minus 30-32 C evident in 12Z upr air charts over
the OH through TN Valleys, will pivot east and across the srn
Appalachians and Carolinas through early tonight. Beneath the
associated forcing for ascent, a developing lee low over w-cntl VA
and accompanying frontal zone will move generally sewd and across
cntl NC this afternoon-early evening. A trailing inverted trough,
perhaps the occluding remnants of a weakening frontal low now over
WV, will then move swd across cntl NC late this evening-early Sun

A band of mid/high-level ceilings and associated stratiform
precipitation/virga has developed immediately ahead of the
aforementioned shortwave trough, in a corridor of maximized DCVA,
and overspread the wrn NC Piedmont during the past several hours.
While most of this precipitation will sublimate/evaporate before
reaching the ground, associated radar reflectivity values from both
KRAX and KFCX have doubled from 5-15 dbz to 15-30 dbz since 15Z, and
also lowered to around 2500-3000 ft ARL. As such, a few sprinkles
may reach the surface from this regime of leading precipitation, as
it moves east across the ne Piedmont and Sandhills through 19Z.
Through the same time, shallow convection will develop and become
scattered to numerous, as the mid-level cold pool overspreads a
diurnally-heated surface layer through the 50s, to lwr 60s over srn
NC. Steep tropospheric-deep lapse rates of 7-8 C/km, with associated
weak MLCAPE of up to a couple of hundred J/kg, will result through
peak afternoon heating. Despite the weak and shallow CAPE profiles,
they may extend through the lightning production layer given the
presence of the anomalously cold temperatures aloft and low freezing
levels of 3000 ft observed at GSO this morning. As such, isolated
storms may accompany the otherwise scattered to numerous showers
that are expected to develop and overspread cntl NC through late
this afternoon-early evening, with the deepest cells capable of
producing small/pea-sized hail. Wind gusts to around 40 mph will
also be possible owing to the presence of a dry sub-cloud layer that
will be characterized by nearly dry adiabatic lapse rates and large
surface dewpoint depressions of 25-30 F.

Nly to nely flow, and a band of 925-850 mb saturation/clouds, will
develop along and behind the inverted trough tonight. Some may
extend deep enough to produce patchy light precipitation from the ne
Piedmont to Sandhills overnight. Precipitation intensity, should any
develop at all, should not be great enough to overcome and
diabatically cool an otherwise above freezing and dry sub-cloud
layer; and as such, precipitation should be all liquid. Low
temperatures will range from upr 20s over the nw Piedmont, on the
wrn edge of that cloud band, to 30s elsewhere beneath it.


As of 145 PM Saturday...

Dry conditions will develop Sunday, with WNW flow aloft and a weak,
decaying trough moving east across the Mid-Atlantic early in the
day. The trough may develop some mid-level clouds in the morning,
with mostly sunny skies in the afternoon as broad upper ridging
remains across the lower Rockies. Surface high pressure across the
region in the morning will quickly build east off the coast
throughout the day. This will switch flow from northerly to
southerly by the afternoon. Warm air advection will hold off until
Monday, with highs remaining around 5 degrees below seasonal
normals. A weak perturbation in the mean flow may develop some mid-
level clouds late overnight. These clouds, and increasing
thicknesses, will limit lows to the mid to upper 30s. A few of the
colder spots could dip into the low 30s.


As of 300 PM Saturday...

...Steady warmup to spring-like temperatures by midweek with a
chance for windy conditions and rain showers with a cold frontal
passage Wednesday into Thursday...

Mon through Tues night: Surface high pressure just off the Southeast
coast will slip towards Bermuda and then into the Canadian maritimes
by Wed morning. At the same time, a deepening area of low pressure
will develop in the central Plains on Tue and quickly pivot along a
front into northern Quebec by Wed afternoon. Increasing
southwesterly flow at the surface and steady mid-level height rises,
will bring spring-like temperatures to much of the Southeast and Mid-
Atlantic. Conditions will predominantly remain dry with increasing
cloud cover and passing chances for virga and sprinkles,
particularly on Tues on the leading edge of deeper layer moisture
beginning to advect into the region. Temperatures will steadily rise
during this time reaching into the mid 60s to mid 70s by Tues.

Wed/Wed night: The better chance for rain comes with the
amplification of a trough axis swinging through the central CONUS
and Ohio Valley and associated area of low pressure and cold frontal
passage. This time frame continues to suffer from a high degree of
uncertainty, mainly in timing with the above mentioned features.
Deterministic guidance suggests a quickly moving relatively narrow
band of showers, primarily forced by the deep and sharp cold front
as it swings through the area within a 6 to 10 hr timeframe. The
roughly 30 hours of slight chance (15-25%) to chance (25-55%) PoPs
within the current forecast is associated with wide ranging model
guidance spread on when the front will move through the region.
Cluster analysis even show the potential for a less likely solution
for an even slower frontal passage not until Thur afternoon
(primarily driven by GEPS members). Southwest surface winds ahead of
front will steadily increase to 15-20 mph with gusts up to 35 mph by
Wed with the sharp cold front and rapid pressure rises behind the
front capable of similarly strong northwest winds into early Thurs.
Forecast confidence is low to medium for the surface winds ahead of
the front on Wed as southwesterly wind gusts tend to underperform as
the event approaches and are difficult to nail down 5 days out. Wed
will be the warmest day in the extended with highs rising well into
the 70s for most locations and lows in the 50s to 60s early Wed

Thur through Sat: Post frontal northwesterly flow behind the cold
front and rapidly dropping surface dewpoints will continue into
Thurs as surface high pressure continues to build into the Mid-
Atlantic. Temperatures will return to below normal behind the cold
front with highs in the 50s and lows in the upper 20s to low 30s.
Surface high pressure shifts offshore Fri with 15 to 30% chance of
rain moving into the Piedmont Fri into Sat and may promote an in-
situ damming regime within lingering influence from the dry post-
frontal airmass.

As of 725 PM Saturday...

24-hour TAF period: An area of scattered showers with brief gusty
winds to 15-25 kts will continue to push east and affect the Coastal
Plain (including RWI) for the next hour. NW winds may also gust to
15-20 kts for a few more hours around INT and GSO before
diminishing. The rest of the period will be dry, but an area of MVFR
ceilings currently over central and northern VA will push south
through eastern portions of central NC tonight. Guidance is in
pretty good agreement that it will reach RDU and RWI around 04-05z,
then FAY around 06-08z. Confidence in IFR ceilings is lower but
can`t be entirely ruled out. The highest chance of IFR is at RWI,
followed by RDU, then FAY. INT and GSO should be far enough west to
remain VFR. MVFR ceilings will begin to lift and scatter out
tomorrow morning, but there is disagreement among the guidance on
how long they will stick around. Best guess is until early morning
at RDU and RWI and late morning at FAY, but periods of MVFR could
linger a bit beyond that. Skies will become mostly clear everywhere
after 18z, as winds shift to SW but remain light.

Outlook: While patchy light rain will be possible over the Piedmont
early Mon and again Tue, the next good chance of rain and flight
restrictions will accompany a passing cold front during the middle
of next week. It will also become windy both ahead of and behind
that cold front Tue through Thu.




LONG TERM...Swiggett
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