462
FXUS62 KRAH 092302
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
603 PM EST Sat Nov 9 2024

.SYNOPSIS...
High pressure will continue to build into the area from the north.
Moisture will begin to overspread the area from the west Sunday,
ahead of a cold front that will move through the area Monday night.

&&

.NEAR TERM /TODAY AND TONIGHT/...
As of 225 PM Saturday...

Upper level ridge over the MS valley will shift eastward today an
and tonight with the ridge axis expected to be over the eastern Mid-
Atlantic region by Sunday morning. At the surface, high pressure
centered over the Lower Great Lakes region  will push eastward and
continue to influence much of the Mid-Atlantic region will cool dry
weather. Satellite observations are showing an increase in cloud
coverage especially in the Western Piedmont. While high clouds are
expected to continue to move into/across the region today, lower and
thicker clouds will move in overnight ahead of an approaching cold
front. While gusts are expected to subside later this afternoon
winds will generally be light from the NE through early Sunday. High
temperatures today will top out in the low to mid 60s in the north
and mid to upper 60s (maybe a few spots will hit 70) in the south.
Above average lows tonight will be in the low 40s north, to
mid/upper 40s south.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 400 PM Saturday...

* Sharp temperature gradient in developing cold air damming over the
  Piedmont Sun
* Becoming wet Sun afternoon-night
* Areas of dense fog possible over the srn/wrn Piedmont Sun night-
  Mon morning
* Well above average temperatures on Mon

Sun and Sun night: In progressive mid/upper-level flow, a sub-
tropical high will progress across the swrn Atlantic and a cyclone
will accelerate across the Great Lakes. Between the two, a
convectively-amplified mid-level trough and tropical moisture plume,
including remnant vorticity from Rafael, will move across the ern
US. 40-60 meter mid-level height falls and PWs of 200-300% of normal
will maximize over cntl NC late Sun and Sun night.

At the surface, the center of ~1030 mb high pressure now over the
nrn Middle Atlantic and lwr Great Lakes will progress quickly
offshore on Sun, but a lingering dry air ridge axis and calm/light
flow regime will extend across the wrn Carolinas, while a return,
onshore flow regime will otherwise expand across ern-cntl NC.

Considerable mid/high-level cloudiness and patchy virga will
overspread cntl NC early Sun, while the aforementioned onshore flow
regime will promote warm/moist advection and low-level isentropic
upglide and saturation later Sun-Sun night. The latter regime will
also favor the development of weak, elevated instability amid the
deep, tropical moist axis progressing across NC. An associated area
of showers will develop across the Piedmont of the Carolinas during
the afternoon-evening, with subsequent waves of showers, and slight
chance of storms roughly along and east of I-95, overnight. While
12Z HREF mean QPF depicts generally a couple of tenths to near one
half inch over cntl NC during that time, LPMM values indicate
localized amounts of 1-1.5" will be possible where MUCAPE becomes
maximized along the I-95 corridor. Periods of light rain and
drizzle, and areas of fog -locally dense- will otherwise result in
in-situ cold air damming over the srn/wrn Piedmont Sun night-Mon
morning. Wide-ranging high temperatures are expected Sun, ranging
sharply from the mid-upr 50s over wrn Forsyth Co. to lwr 70s in the
Coastal Plain. Well above average lows in the 50s to lwr 60s will
follow for Sun night.

Mon-Mon night: Broadly cyclonic mid/upr-level flow will result
across cntl NC this period. Within that regime, the convectively-
amplified mid-level trough and tropical moist axis will be swept off
the coast of the Carolinas early Mon.

At the surface, in-situ damming centered over the Piedmont should
weaken and erode from the edges through the day, with partial
sunshine and temperatures in the lwr-mid 70s expected area-wide by
afternoon. Meanwhile, a cold front will approach from the northwest
and move into the nw Piedmont around sunset, then progress sewd
across the rest of cntl NC through midnight. Cooler, but still above
average temperatures in the upr 40s to mid 50s will result Mon
night. Regarding precipitation chances, the last round of elevated
convection should be in the process of moving across and out of the
Sandhills and Coastal Plain during the morning. While the airmass
will then diurnally destabilize with respect to surface-based
parcels through the afternoon, a lack of forcing for ascent at the
surface or aloft suggest limited precipitation chances will exist
after the elevated morning convection exits.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 247 PM Saturday...

In wake of the exiting upper trough, flow aloft will turn nwly over
central NC Tuesday through much of Wednesday.  PWAT will crash to
~25 to 35 % of normal, as dry sfc high pressure extends cool nnely
flow into our area.  Expect dry conditions with highs in the upper
60s Tuesday afternoon. The colder air will arrive Tuesday night into
Wednesday, as lows dip into the upper 30s in some locations Tuesday
night. Dry conditions and daytime highs in the lower 60s are then
expected Wednesday afternoon.

Upper ridging will shift offshore as a low-amplitude short-wave
moves across the eastern seaboard Thursday into Friday. Ensembles
continue to suggest this system will be moisture starved, and
forcing for ascent will be weak over our area. As such, expect a low
QPF cold front to pass through sometime Thursday into Friday. Upper
ridging returns quickly returning dry conditions and slightly above
normal temperatures next weekend.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 603 PM Saturday...

VFR conditions are forecast to start the TAF period. The main
forecast challenge with this forecast package will be the onset of
RA and associated sub-VFR conditions across GSO/INT Sun afternoon
and evening. There is reasonably high confidence that VFR will
dominate through much of the period at RDU/FAY/RWI. However, with
increasing onshore flow set to take hold Sun morning, some guidance
from the RAP/HRRR/ARW suggest some brief MVFR CIGs could move
northward and impact the terminals between 12 and 18z. The HREF
probabilities for this range from 20-50 percent, highest at GSO/INT.
With moisture and lift increasing Sun afternoon and especially
evening with an approaching system, CIGs are forecast to lower to
low-end MVFR at GSO/INT between 18 and 21z, but remain VFR at the
other terminals. Our current forecast may be too pessimistic with
the onset of MVFR at GSO/INT, but given the development of in-situ
CAD, we decided to go with the earlier onset guidance.

Outlook: Restrictions in light rain/showers are expected to lower to
LIFR/IFR Sun night into midday Mon. Some patchy fog and LLWS is also
possible. A brief period of thunder is possible at FAY/RDU/RWI early
Mon morning. Aviation conditions are expected to trend to VFR Tue-
Thu with high pressure building back into the region.

&&

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

&&

$$
SYNOPSIS...CBL
NEAR TERM...CA
SHORT TERM...MWS
LONG TERM...Luchetti
AVIATION...Kren