227
FXUS62 KRAH 231423
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
920 AM EST Mon Dec 23 2024

.SYNOPSIS...
Arctic high pressure over the northeastern United States will move
offshore today and tonight. Weak low pressure will move along the
coast late tonight and Tuesday.

&&

.NEAR TERM /TODAY THROUGH TONIGHT/...
As of 920 AM Monday...

Surface high pressure is currently centered over Long Island, with a
pressure ridge extending southwest through the Carolinas and into
Georgia and Alabama. Local research has shown that the 10th and 25th
percentiles usually do better for temperatures under a classical CAD
scenario, so with the morning update, blended these percentiles into
the forecast and this brought the high temperature down 2-3 degrees
in most locations. This was the primary change made to the forecast
at this time. Have not made any changes to this evening`s part of
the forecast, and will wait until all 12Z guidance comes in before
making any changes to tonight`s freezing rain potential. Previous
discussion follows.


As of 245 AM Monday...

Only a very low end and limited chance of some light freezing rain
over the eastern Piedmont, NW Sandhills, northern Coastal Plain late
tonight and very early Tuesday.

Models are drier with the QPF, weaker with the wave of low pressure
along the coast.

Today is expected to be mainly sunny and chilly with cold high
pressure overhead. Highs generally in the low to mid 40s. Expect
some increase in cloudiness late today especially in the SE.

Strong and cold high pressure (1038+ mb) extends from New England
down the eastern seaboard into FL. early this morning. The skies
were mainly clear with the exception of a few cirrus from time to
time. The atmosphere is very dry under the high pressure which will
slowly move off the New England coast today. The high pressure will
extend into the southern Appalachians from off the New England coast
tonight as weak low pressure is expected to develop along the
inverted surface trough off the SC/GA coast. There continued to be
plenty of differences in the model solutions with the EC holding off
any light rain until it warms after 12z/Tuesday. The NAM is
essentially dry for our region. The suite of models overall is drier
as well. However, some of the 00z CAMS were a bit wetter overall,
only to revert back to drier again with the 06z run.  Since we have
very dry air deposited over our region with the current high
pressure - and it is expected to linger over the Piedmont tonight -
the drier or slowly solutions are certainly possible. The guidance
is likely a bit too cold tonight especially if the cloudiness really
thickens up and lowers later tonight per the needed precipitation
generation. It appears that the areas east and south of Raleigh will
have the higher chances of rain and mostly very late tonight into
Tuesday morning. There is still a slight chance of light
rain/freezing rain in a very narrow zone of the NW Sandhills and E
Piedmont between 09z and 13z; however using the non-diurnal curve
for temperatures, the lows will occur early in the night in the mid
20s to lower 30s. The temperatures are expected to rise later
tonight as the clouds thicken and lower from the southeast. QPF has
been reduced to a few hundredths for most areas, and mainly from
Raleigh east and south - well east of the Triad region. Also, there
is only a slight chance (20 percent or less) of Trace to 0.01 of
icing in the narrow corridor of the eastern Piedmont around 12z.
This is where most guidance depicts the 31-32 degrees wet bulb
around 12z, quickly rising above 32 between 13-14z. Obviously, this
forecast can and will change to some extend as the weak system
evolves. It only takes a trace of freezing rain to cause issues;
therefore this certainly bears watching for later tonight.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 245 AM Monday...

...Light rain across eastern NC early Christmas Eve...

...Drying out by the afternoon...

An upper-level disturbance over the SE US will move across eastern
portions of the Carolinas through the afternoon. Meanwhile,
associated weak area of low pressure off the SE coast will lift
north towards Cape Lookout, before curving east, out to sea.

Model spread remains high WRT how far inland the western/northern
periphery of the overrunning precip shield will set up Tuesday, with
an eastward shift in QPF noted in the latest 00z guidance. With that
said, measurable precip should largely be confined along and east of
US 1, and quite possibly restricted to areas along and east of I-95.

Given the in-situ CAD setup, any light freezing rain/drizzle Tuesday
morning over the central Piedmont/north coastal plain will be self-
limited and very short-lived, changing over to rain as the warmer
air overspreads the area. The rain is expected to exit east of the
afternoon during the afternoon, if not earlier. Given the very dry
air entrenched over the Piedmont, expect a very tight precip
gradient with 0.1-0.2" across the far SE counties to a trace across
the Triangle.

Highs will depend on the inland extent of the rain shield. Coolest
across the coastal plain and warmest across the western Piedmont,
where a decent amount of sunshine is expected. Highs ranging from
mid/upper 40s to mid 50s.

Clouds should clear out Tuesday night. Lows in the upper 20s north
to lower/mid 30s south.


.LONG TERM /WEDNESDAY THROUGH SUNDAY...
As of 300 AM Monday...

An active and progressive split flow regime will dominate the
extended period with a series of southern stream shortwave troughs
expected to impact the area through the weekend.

Models are in fairly good agreement wrt a lead shortwave trough that
is forecast to undergo significant shearing as it advances east into
the area late Wednesday/early Thursday. Rain chances are looking
negligible east of the mtns, so will keep Christmas Day/Night dry.

Shortwave ridging building over the area should secure dry
conditions through Friday. Then towards next weekend, model spread
increases with the eastward evolution of multiple shortwave systems
and when/where interactions between the northern and southern stream
energies take place. For now will keep rain chances in the slight
chance category Saturday, with the higher rain chances holding off
until Sunday.

Seasonable temperatures Christmas Day will gradually moderate to
above normal by the weekend.


&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
As of 648 AM Monday...

24 hour TAF period: High confidence VFR conditions will prevail
through around 09z/Tue. There is a chance of light rain between 09z
and 15z and KFAY and possibly KRWI.

Outlook: A period of light rain is possible around KFAY and possibly
KRWI between 12z and 15z Tuesday. Also, a brief period of sub-VFR
cigs possible Wed night/Thu as a mid/upper level disturbance moves
through the area. Otherwise, VFR conditions are expected through
Fri.

&&

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

&&

$$

SYNOPSIS...Badgett
NEAR TERM...Green/Badgett
SHORT TERM...CBL
LONG TERM...CBL
AVIATION...Badgett