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000
FXUS62 KRAH 212336
AFDRAH

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

.SYNOPSIS...
A couple of mid and upper-level disturbances will interact with a
frontal zone, which will settle off the coast of the Carolinas
through this evening. High pressure will otherwise build across the
Middle-Atlantic states through Tuesday.

&&

.NEAR TERM /TONIGHT/...
As of 205 PM Sunday...

Surface low pressure is currently just east of Cape Hatteras with a
cold front extending to the southwest along the Atlantic coastline.
An upper low over Hudson Bay has a trough extending south to the
eastern Great Lakes which then curves southwest back into Missouri.
As the surface low moves east, rain will steadily decrease from west
to east. Most rain should be east of I-95 by sunset, with all
locations expected to be dry by sunset. An additional quarter to a
third of an inch is possible, with high values south and east of
Raleigh. Skies should partially clear across the Triad during the
late afternoon, although mid/high level clouds will fill back in
after midnight, keeping skies mostly cloudy everywhere through the
rest of the night. Low temperatures should range from the upper 30s
to the mid 40s.

&&

.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/pwb
NEAR TERM...Green
SHORT TERM...CBL
LONG TERM...Hartfield
AVIATION...KC