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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 220159
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
959 PM EDT Sun Apr 21 2024

.SYNOPSIS...
-- Changed Discussion --
A vigorous, but moisture-starved mid and upper-level disturbance
will pivot across the southern Appalachians tonight and the
Carolinas early Monday. High pressure will otherwise build across
the Middle Atlantic states through Tuesday.
-- End Changed Discussion --

&&

.NEAR TERM /TONIGHT/...
-- Changed Discussion --
As of 955 PM Sunday...

Water vapor satellite and 00Z upr air data depict 1) a lead srn
stream shortwave trough, and wrn edge of deeper moisture
characterized by PWs greater than an inch, lifting newd across the
srn and middle Atlantic coasts and 2) a nrn stream, shortwave trough
pivoting across the mid-South. The former will continue sweep
ewd/coast-ward an area of light rain now moving across ern NC, with
some partial clearing likely in its wake over cntl/wrn NC early
tonight. The approach of the nrn stream shortwave trough, and
associated strong/80-100 m/12 hr 500 mb height falls across the
Piedmont of the Carolinas and GA by 12Z Mon, will cause particularly
mid/high-level ceilings to redevelop across cntl NC late tonight-Mon
morning.

At the surface, an offshore, wavy frontal zone will continue to move
ewd and away from the coast of the Carolinas tonight, while 1025 mb
high pressure centered over cntl/ern OK will build ewd. Between the
two, an inverted surface trough/convergence axis --and boundary
between residually moist surface dewpoints in the 40s to around 50F
to its east from markedly drier 20s-30s amid nwly flow to its west--
was evident in 0130Z surface observational data over the wrn
Carolinas and VA from near LYH to FQD to CEU. This boundary may
drift slightly ewd and into the nw NC Piedmont between 05-09Z, with
a more-marked push of drier air from cntl/nrn VA swd and throughout
cntl NC after sunrise Mon.

Despite the lack of signal in model guidance, the aforementioned
clearing in the wake of the srn stream shortwave trough will
probably contribute to the continued development of radiation fog
across the Foothills and srn and wrn NC Piedmont early tonight. Some
may become dense based on surface observational trends there since
00Z. Thereafter, a combination of low-level drying with the passage
of the inverted surface trough, and redevelopment of mid/high-level
ceilings, should cause the fog to disperse in most areas after 05-
06Z. Otherwise, virga will accompany those ceilings and associated
strong mid/upr-level forcing for ascent throughout cntl NC, while
patchy light rain may develop along the inverted surface trough and
drift across the nrn/nwrn Piedmont with a hundredth of an inch or
three early Mon morning.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 235 PM Sunday...

...Gradual moderation of Below-Normal Temperatures...

...Patchy Frost Possible Monday Night across the Piedmont...

Cool high pressure centered over the Lower MS Valley will build east
into the SE US through early Tuesday, and then off the SE coast late
Tuesday and Tuesday night. Aloft, a vigorous shortwave trough will
move through central NC during the day Monday, followed by strong
subsidence Monday night as Tuesday as shortwave ridging builds east
into the region.

Monday and Monday night: Considerable cloudiness and a passing
sprinkle Monday morning will give way to NW to SE clearing through
midday, leaving behind mostly sunny skies for the afternoon.
Otherwise dry with early day low-level CAA resulting in well-below
normal temperatures. Highs in the lower to mid 60s, which is 8-11
degrees below normal for late April. Clear skies and calm winds will
result in optimal radiational cooling Monday night. Expect lows in
the upper 30s to lower 40s, with some patchy frost possible over the
northern Piedmont, where temperatures could potentially cool to 34-
36 degrees. Will add a mention in the HWO.

Tuesday and Tuesday night: While still slightly below normal, the
onset of southerly return flow will yield moderating temperatures.
Under sunny skies, highs in the lower 70s. The approach of a clipper
style northern stream shortwave trough will lead to increase in
mid/high clouds over the northern/northwest Piedmont late Tuesday
nights. Lows 45-50.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 255 PM Sunday...

Minimal change from previous forecasts, as this still appears to be
a largely dry period, with a roller coaster of temps going from near
normal to below normal then above normal from mid week through the
weekend.

Wed/Wed night: A mid level shortwave trough zips by just to our N
Wed, along the base of a polar low over Quebec, and this will be
associated with a surface cold front approaching from the NNW. This
will result in a mid-upper level speed max sweeping over the Mid
Atlantic region including NC. But in the lower levels, high pressure
centered off the Southeast coast will ridge back westward across the
Southeast and Gulf States, such that we`ll be cut off from any
moisture tap from both the Gulf and Atlantic from the surface up
through 850 mb, and this will include a downslope wind component at
850 mb. Large scale forcing for ascent will be limited as well, with
the upper jet core shifting well to our N, keeping any upper
divergence N of our area, with minor to absent mass convergence in
the lower troposphere. But most models and ens systems suggest
potential for light precip falling out of high-based clouds ahead of
the surface front, so have maintained a period of sprinkles, NW
early then shifting to E and S in the afternoon, with the idea that
the chance of anything measurable will be very low due to the
downslope flow and lack of moisture influx. Low level thicknesses
will be near normal, so expect highs in the 70s. Cool high pressure
centered over the Great Lakes will build in from the N overnight,
resulting in cool lows in the 40s to around 50 with decreasing
clouds.

Thu-Sun: Confidence is high in dry weather Thu, with temps about 1
to 2 categories below normal, as cool high pressure shifts to New
England and continues to build in from the N, drawing in low level
thicknesses 25-30 m below normal. Uncertainty grows in the Fri-Sun
period. The surface high will shift E to off the Northeast coast Fri
while still nosing down into NC, setting the stage for a possible
damming event starting late Fri or Fri night/early Sat morning, with
the potential for increasing moist upglide up and over the cool
stable pool over the Piedmont. The ECMWF and its AIFS both suggest
patchy drizzle in the E slopes into the Foothills Fri night/Sat
morning, but the upglide further E is more in question, and will
keep it dry for now Fri night. While the overall pattern will
include mid level ridging building over the Southeast from the W Fri-
Sun, the op models do depict a subtle wave topping the ridge and
crossing the Mid Atlantic region sometime Sat, which could kick off
a little light rain or showers (depending on the degree of lingering
stability, if any) across the N Sat, followed by possible isolated
storms in the W Sun with increasing heating and afternoon
instability, but the rising mid level heights could suppress
convection, so will keep Sun dry and watch trends. Temps about a
category below normal Thu will warm well above normal Sun, with
highs well into the 80s expected Sun. -GIH

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
As of 735 PM Sunday...

24 hour TAF period: A bit tricky to time the final improvement back
to VFR given the potential for some fluctuation between scattered
and broken IFR/MVFR cigs on the back edge of the rain as it moves
eastward and out of central NC this evening. KINT should largely
remain VFR from her on out, and GSO should follow in the next hour
or so, with the back edge of the rain east of both terminals. Light
rain continues at the eastern 3 terminals as of 23Z. KRDU should be
next to dry out and improve to VFR, with KRWI an KFAY being last to
return to and stay VFR. Despite the return to VFR, and aside from a
potential brief period of sct mid/high clouds, skies should largely
be overcast in the 6-10 kft range through tonight and much of Mon
morning. Skies should finally clear from the north Mon aft. Winds
should generally be northerly tonight and nnely Mon, lightest
overnight and increasing through the morning/early aft. -KC

Outlook: Largely VFR conditions are expected through the week. There
are two possible exceptions. First would be a small chance for a
brief period of light rain and/or borderline VFR/MVFR cigs as a weak
cold front moves into/through the area on Wednesday. The other would
be possible sub-VFR low stratus Wed night/Thu morn as cool high
pressure builds in from the north. However, confidence in both
occurrences remains low at this time.

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...CBL
LONG TERM...Hartfield
AVIATION...KC