314
FXUS62 KRAH 220216
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
915 PM EST Thu Nov 21 2024

.SYNOPSIS...
A cold front tonight will bring a reinforcing shot of cold air to
central North Carolina. After a chilly day Friday, high pressure
will build in and bring gradually warming temperatures through early
next week. A cold front will appproach from the northwest on Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 915 PM Thursday...

Just minor forecast tweaks. The shortwave which brought a band of
sprinkles/virga over the last several hours is pushing to our east,
taking most clouds with it. But we`ll still see some clouds spilling
over the mountains into our NW overnight, and passage of yet another
mid level vorticity max between 04z and 08z should bring a band of
clouds sweeping through the area. Chances are still very good that
temps will dip to freezing or lower areawide outside of the urban
centers, as we decouple and surface winds generally drop off to
under 6 mph. But we have been running a degree or two warmer than
forecast pace so far this evening, and any lengthy period of
cloudiness and/or a continued stirring through the night could
sabotage our expected sub-freezing temps. Given the low dewpoints
pouring in, however, and the 00z GSO low level thickness already
down to 1316 m with at least some period of fair skies, will not
dramatically change forecast temps tonight, still bottoming out in
the 28-33 range everywhere. -GIH

Earlier discussion from 300 PM: A cold front has just entered the
northwestern reaches of the forecast area, as INT/GSO have shifted
to a westerly wind while the rest of the forecast area generally has
southwesterly winds. A large area of overcast clouds have developed
upstream over VA/NC, and this area of clouds should overtake the
area through the rest of the afternoon and evening before clouds
scatter out again. A secondary wave should produce another round of
clouds later tonight. With the reinforcing push of cold air behind
the front, the cloud cover will be key to determining what locations
may or may not drop below freezing tonight. The wind is expected to
remain around 5 mph overnight, which is not ideal for radiational
cooling. DESI NBM probabilities for below freezing temperatures are
quite high for most of the forecast area, although urban areas are
less likely to drop below freezing. For example, outlying areas of
Wake County will likely have below freezing temperatures even if
temperatures in downtown Raleigh remain above freezing. Have high
confidence in Freeze Warning criteria being reached in most
counties, although there is less confidence in criteria being
reached in southeastern counties such as Cumberland, Sampson, and
Wayne counties. Nevertheless, have upgraded the Freeze Watch to a
Freeze Warning everywhere. Overnight lows are forecast to range from
the upper 20s to the mid 30s.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 300 PM Thursday...

Cannot rule out a stray sprinkle or flurry reaching the ground
Friday morning out of the clouds that remain over the Triad, but
considering how dry the lowest mile of the atmosphere will be, virga
is a more likely result. Another mostly sunny day is expected
tomorrow, with another round of gusts between 20-25 mph. Friday
should be the coldest day of the next seven, with highs ranging from
the mid 40s to the mid 50s.

Similar to the midnight shift forecast, the GFS suggests boundary
layer mixing will continue through much of Friday night while the
NAM shows the development of a low-level inversion and brings an end
to the mixing. As the cloud cover is a key factor in tonight`s low
temperature forecast, the wind will be a key factor in Friday
night`s low temperature forecast. A more windy night would likely
keep the temperatures a bit higher. The current forecast ranges from
the mid 30s to the low 40s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 210 PM Thursday...

* Dry conditions prevail through Tuesday night with only a low
  chance for sprinkles on Tuesday.
* Forecast confidence is low late next week.

An area of low pressure is expected to rapidly deepen to 980mb to
985mb as it shifts near Nova Scotia Sat morning. This deepening
cyclone combining with weak high pressure sliding into the northern
GOM states will keep a tight pressure gradient over the region
through Sat morning before gradually weakening through the
afternoon. Gusts should increase a few hours after sunrise as the
shallow surface inversion breaks and stronger winds aloft translate
down to the surface. Point soundings suggest momentum transfer would
result in wind gusts predominantly 15 to 25 mph. Gusts will subside
shortly after sunset as high pressure begins to nose into the
southern Piedmont. Clear skies and conditions going calm over the
western/southern Piedmont should prompt a period of radiational
cooling and support lows dipping into the low 30s with mid/upper 30s
expected elsewhere.

Conditions are expected to remain dry as temperatures slowly
moderate as the surface high slips over the western Atlantic and
brings a return to southwesterly flow to the area by Mon. A low
amplitude wave aloft and associated area of low pressure is expected
to develop over the Middle Mississippi Valley Mon morning and lift
northeast into southern Ontario and Quebec by Tues evening. Lack of
overall synoptic forcing over the area should prevent much
appreciable rain from spreading east of the mountains, but some
sprinkles may fall out of a mid-level cloud layer.

Model guidance begins to vastly diverge beyond Tues but the most
likely scenario from cluster analysis suggest a more amplified and
slowly evolving pattern with a trough developing over the southern
Plains and ridge building over the eastern CONUS mid to late week.
This amplification would keep conditions dry over central NC behind
the fropa through Wed night before beginning to spread precipitation
into the Piedmont through the day on Thursday.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
As of 910 PM Thursday...

Minor tweaks where made to the TAFs due to wind gusts ceasing
earlier than expected. Regional VWP data around 2,000 feet and local
tower wind data suggest a more northerly component and stronger the
winds aloft around 35 kts. This results in the development of LLWS
with greatest confidence at GSO, INT, and RDU. Although it is
certainly still possible at RWI and FAY, VWP in eastern NC and SC
suggest winds aloft are about 10 kts weaker and have decided to
leave it out for now. Previous discussion as of 640 PM Thursday
follows.

Periods of wind gusts and subtle changes in wind direction will
drive the 00z TAFs across the area. An area of virga and a
reinforcing cold front moving across the region has brought brief
but strong wind gusts to the Triad terminals and RDU earlier this
evening with the possibility of occurring at RWI and FAY in the next
couple hours. Winds are expected to back towards westerly and cease
gusting overnight but will once again veer to WNW and begin gusting
up to 25 kts at all TAF sites by around 15z Fri morning.

Outlook: Winds aloft will increase Fri night into Sat morning to 35
to 45 kts and result LLWS for most of the night at all TAF sites,
strongest and most prolonged at RDU, FAY and RWI. VFR conditions are
expected through the beginning of next week. Afternoon gusty winds
of 15 to 25 kts are expected Sat before relaxing through early next
week. A dry cold frontal and northerly wind shift is expected on
Tuesday.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Freeze Warning from 3 AM to 9 AM EST Friday for NCZ007>011-021>028-
038>043-073>078-083>086-088-089.

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield/Green
SHORT TERM...Green
LONG TERM...Swiggett
AVIATION...Swiggett/Helock