Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 270717 RRA

Area Forecast Discussion
National Weather Service Raleigh NC
217 AM EST Tue Feb 27 2024

High pressure will drift to near and north of Bermuda through mid-
week. A strong cold front will move across the Carolinas Wednesday


As of 215 AM Tuesday...

A mid-level s/w, moving into the mid/upper MS Valley as of 06Z,
should amplify slightly as it moves quickly through the OH Valley,
central Appalachians, and mid-Atlantic today. The disturbance should
lift through the mid-Atlantic and Northeast US tonight, with the sub-
tropical ridge building northward along the Southeast US coast. A
mid-level vort max associated with this disturbance is forecast to
progress eastward through central NC this morning through early this
evening, shifting NE and off the mid-Atlantic coast thereafter.

Precipitation: The lift associated with the disturbance aloft,
coincident with mid-upper level saturation should be enough to
generate some precipitation (light rain/virga) as it moves through
central NC. Additionally, some low-level saturation associated with
isentropic lift, mainly over the NC piedmont this afternoon, further
increases the chance for measurable rain. While rain is possible
area-wide, the best chances and highest amounts will likely be over
the northern Piedmont.

Temperatures: The overcast skies and rain expected over the area
should somewhat limit daytime heating, especially over the northwest
Piedmont where highs may only reach the low 60s today. A gradual
increase in highs is expected farther southeast, but will depend on
the extent/timing of the cloud cover and rain. For now expect mid
60s to around 70 degrees. Lows tonight expected to be quite mild,
mainly in the mid to upper 50s.

Winds: Perhaps the greatest uncertainty today, at least over the
Piedmont, will be how gusty the winds will be. With the tightening
surface pressure gradient over central NC, gradient winds are
expected to be fairly strong, 10-15 kts. The LLJ is expected to
strengthen to 35-50 kts between 925mb and 850mb this afternoon, so
the question is how much mixing will be realized. While gusts MAY be
limited over the northwest Piedmont, elsewhere expect gusts of 25 to
30 mph, with locally higher gusts to 40 mph possible. Gusts may
abate some between sunset and midnight, but are still expected to
increase again thereafter.


As of 330 PM Monday...

...Gusty winds ahead of the cold front Wednesday afternoon...

Tue: The models suggest a low amplitude disturbance now over sern
WY/nrn CO will amplify slightly while progressing quickly across the
mid MS Valley tonight and the OH Valley and cntl Appalachians on
Tue. An accompanying 700-850 mb trough and maximum of WAA, amid an
otherwise continued broad WAA regime, will overspread the Carolinas
and VA through the day. Associated lift and mostly mid/high-level
saturation/ceilings will overspread cntl NC and be accompanied by
another round of virga or patchy, very light rain. The best chance
for several hundredths of an inch will be over the wrn Piedmont,
where low-level moisture transport may support lower-level
saturation and warm-rain processes. The presence of that multi-
layered overcast and light precipitation will tend to limit mixing
and diurnal heating, with temperatures likely to range from lwr 60s
over the nw Piedmont to upr 60s-lwr 70s in the Coastal Plain. With
that overcast and limited mixing, there remains uncertainty
regarding how strong swly surface winds will become. While gusts
should be limited to between 20-30 mph in most areas, point forecast
soundings at RWI depict brief momentum transport potential for 30-40
mph gusts during the afternoon.

Tue night through Wed night: As the mid/upper level disturbance
moves across the region Tuesday night a mid/upper level trough over
the northern Central Plains will continue to shift east across the
Ohio valley Wednesday. At the surface, Tuesday night expect isolated
showers to continue along and north of US64. Latest model data is
still showing limited to none instability, therefore no significant
thunderstorms are expected with this round of showers. As the first
system lifts to the northeast early Wednesday morning, the cold
front associated with the trough to the north will begin to move
across the region Wednesday early afternoon. Ahead of the main
frontal passage, expect winds to pick up early Wednesday morning
with gusts through out the day of 35 to 45 mph. Latest model runs
for Wednesday are showing the timing of precipitation moving across
central NC beginning as early as mid afternoon in the NW Piedmont
and quickly shifting east across the region. QPF associated with the
cold front Wed/Thurs will be limited. Less than a quarter inch is
expected in the NW with nearly a tenth inch expected along the
southeast region.  The cold front is then expected to clear the
region before sunrise, with clearing skies by morning. Temperatures
Tuesday night will be relatively warm compared to tonight`s
temperatures with lows generally in the mid/upper 50s. Warm
southerly flow will continue ahead of the cold front helping highs
to potentially be in the low 70s NW to mid/upper 70s elsewhere.
Finally after the cold front passes by, cold air will filter in
behind with low Wednesday night in the low/mid 30s north to
mid/upper 30s south.


As of 315 PM Monday...

A sharp cold front will have pushed well offshore with a +1035mb
surface high pressure building into the lower OH Valley and cooler
and much drier air spilling east into the Mid-Atlantic. Forecast
confidence is increasing that the maximum pressure rises and surface
wind gusts will be well offshore and a relaxing pressure gradient
over central NC by early Thurs morning. Conditions will be dry with
strong mid to low-level subsidence overspreading the area behind the
front, but a continued stream of moisture in the upper levels will
keep cirrus clouds streaming overhead through the day on Thursday.
Highs will be in the low/mid 50s with lows generally in the low 30s.

A southern stream wave will approach from the central Plains and
increase warm-air advection into the area on Fri, first in western
NC and spreading SW to NE through the afternoon and evening hours.
There remains some uncertainty on how quickly increasing clouds and
stratiform rain move into the region with the GEFS members the
quickest, early Fri morning, while the EPS and GEPS notably slower
and closer to Fri afternoon/evening. Current forecast has trended
towards the slower, most likely, solution with best chances
occurring late Fri night into early Sat morning. If the forecast
trends towards a quicker solution, high temperatures will be
drastically cooler with precipitation locking-in in-situ wedging due
to diabatic cooling into a dry antecedent airmass.

Above normal forecast uncertainty exists heading into the weekend
and into early next week with the evolution of the southern stream
wave in a weakens in the mid/upper stream flow as the northern
stream ridge builds over the Northeast and an equatorward
suppression of the subtropical jet through the Southeast. The
forecast trends towards a diurnal slight rain chances and a general
warming trend due to the amplification of northern stream ridge.
Highs in the 60s to near 70 and lows mid/upper 40s to low 50s.


As of 1255 AM Tuesday...

24 hour TAF period: High confidence VFR conditions will prevail
through daybreak, with the primary aviation concern through 15Z
being some LLWS. Winds should pick up around 15Z, with gusts in the
20-30 kt range through the aft/eve. MVFR cigs should develop in the
Triad as showers move in from the west around 15Z as well, moving
eastward through central NC during the aft/eve. Cigs should lower to
IFR for a period of time coincident with the heaviest rain. Cigs
should return to VFR around 00Z at most sites, although MVFR cigs
could hold on a bit longer at KINT and KGSO. Another period of LLWS
is possible after midnight Wed as a 50-60 kt LLJ develops, however
it may depend on how well mixed/strong the surface winds are.

Outlook: Expect swly winds to become strong and gusty on Wed ahead
of an approaching cold front. A band of rain/showers and adverse
aviation conditions will are expected with the passage of a strong
cold front late Wed aft through early Wed night. In the wake of the
front, winds should become nwly, but remain windy/gusty through Thu
morning. There will be another chance for light rain and sub-VFR
conditions with the next frontal system Fri/Sat.




LONG TERM...Swiggett
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