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FXUS62 KRAH 270121
AFDRAH

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
825 PM EST Tue Jan 26 2021

.SYNOPSIS...
A weak cold front will stall over the region overnight. Another wave
of low pressure will track along the front later tonight and early
Wednesday. Yet, another storm system will affect the region
Wednesday night into early Thursday. This will be followed by a dry
and cold air mass for late week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 825 PM Tuesday...

Dense fog potential and aviation forecast concerns continue to be
the highlights tonight.

This has been and continues to be a stubborn CAD event. Some dense
fog and very low stratus likely to continue through part of the
overnight, with rain arriving again across the south late.

The latest satellite and data analysis indicate the CAD related low
status and fog lingering over much of the Piedmont Damming Region.
The clearing has still not passed the Blue Ridge, but has arrived at
mountain top level (Boone, Sparta, etc...). Yet, nearby Winston-
Salem and Greensboro in the Piedmont remained in the soup, with 1/2
to 1/8 mile visibilities in fog and low stratus. This fog and low
stratus extended across 95 percent of central NC as of mid-evening,
with locally dense fog at some locations.

A weak meso-high was still located over our CAD region, with the
weak cold front over the Appalachians. Essentially, there continued
to be weak pressure fields over the region, with little advection to
push out the CAD conditions. The winds were finally increasing to 10-
15 mph over the higher terrain, but it will still be hours before
the front can move out into the Piedmont. Temperatures having
held in the 40s for the most part today, some lower to mid 50s SE,
were holding steady.

The latest models suggest the front will slowly move into the
Piedmont tonight, with yet another wave of lower pressure forecast
to track NE along the front later tonight. This will increase the
shower/rain chances once again - mainly in the southern and eastern
part of our region. Otherwise, dense fog may become a problem in the
Piedmont in the next few hours, before some improvements may develop
as the front slips in from the NW later and the mid/high clouds
again surge up from the SW.

Temperatures tonight should only vary or fall by 5 degrees or so.
That would place lows in the upper 30s to mid 40s.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 258 PM Tuesday...

An upper low will move out of the Desert Southwest tonight and into
the southern Plains early Wednesday morning. Surface cyclogenesis is
expected during the daytime hours and the low will move eastward
roughly along I-40 during the day, arriving in NC by late
afternoon/early evening. The stalled boundary to our south will
retreat northward during the day tomorrow, with modest forcing for
ascent and moisture advection to produce widespread rainfall from
mid/late morning onward. Rainfall amounts will be relatively light,
generally less than half an inch as the frontal boundary moves
through the area. It's hard to say just how much of the area will
truly reside in the warm sector tomorrow afternoon but it looks
promising that all sites will make it into the 50s by tomorrow
afternoon. As such, no mixed precip type concerns during the daytime
hours. There should be a few hours tomorrow afternoon where precip
tapers off although attempting to pin down that exact timing is
challenging at best.

Meanwhile, the surface low will move through the area tomorrow
evening and off the coast early Thursday morning, deepening rapidly
as it does so. As would be expected, strong cold advection will
commence tomorrow evening with a rain to snow changeover looking all
but certain for areas along and north of US 64. Partial thicknesses
would indicate the best potential for a changeover would be in the
06Z - 12Z time frame, but that could occur a few hours earlier if we
get any sort of CSI banding or intense snowfall rates to develop.
While some accumulations appear likely (an inch or less) north of US
64, little if any accumulation is expected to the south where cold
air will arrive too late and moisture will have run out by the time
it gets there.

Today's probabilistic guidance from the GEFS has increased storm
total snowfall accumulations quite a bit but EC ENS is a bit more
reserved and more realistic looking. There's a handful of factors
that would lend themselves toward lower snow totals. The lack of a
strong surface ridge over eastern Canada is concerning and while
there is cold air upstream, we'd be much more confident in
significant snow totals if the ridge was parked over Ontario vs
Manitoba. Secondly, the surface wave rapidly moves out of the area
and offshore, really only giving us a good 6 hours of snow potential
vs a slower moving system. Surface soil temperatures aren't overly
cold either (40s) but that could be overcome with intense snow
rates. Overall given the variety of solutions out there, erring on
the lower end of the distribution seems to be prudent at this time.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 217 PM Tuesday...

The long term will start off with a storm system exiting the NC
coast. In the wake of that system, look for clearing skies and
turning cooler as high pressure builds in from the northwest. A dry
and cool period will then be the case through at least the daytime
Saturday as the high moves across the region. Given the origin of
the high and its airmass, temps will average 5+ deg below normal.

The next storm system will approach the Carolinas during the latter
half of the weekend, with sfc low pressure lifting north across the
Ohio Valley. WAA-driven precip will break out over our area as
early as Saturday evening, and given the cool and dry antecedent low
levels, the precip could begin as a period of light snow or mixed
precip. Then as the cold airmass gets scoured out Saturday night by
vigorous pre-frontal WAA, the bulk of the precip event should move
through as rain Sunday morning through mid-afternoon Sunday. It's
worth noting that the latest ECMWF features more of a Miller-B type
low pressure system with Coastal low redevelopment (rather than one
low moving up across the Ohio Valley). If this turns out to be the
case, then the risk for a more prolonged winter precip event could
exist for the western Piedmont. With either solution, as we head
through Monday, there are suggestions that some light moisture assoc
with the upper trough axis, coupled with CAA behind the front (or
exiting low) could manifest in some very light snow or mixed precip
as the large scale system exits the area. Given all these
uncertainties, you'll want to stay tuned to future updates and more
details on this complex system.

Behind that system, another period of dry weather is in store for
central NC for the mid-week period next week.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 825 PM Tuesday...

Widespread LIFR ceilings remain in place this evening with
lingering CAD. The lingering LIFR conditions are forecast to last
through 09z to possibly 12z, before improving somewhat later
tonight.

Widespread stratiform rain is again expected to overspread the
area (southern Piedmont and Sandhills first) between 12 and
18z.

Looking at later in the day Wednesday, widespread IFR/LIFR
conditions will prevail through the day into the overnight hours as
a storm system moves through the area. Conditions should improve
Thursday through Saturday, with non-VFR conditions possible once
again on Sunday.

&&

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

&&

$$
SYNOPSIS...Badgett/Leins
NEAR TERM...Badgett/Leins
SHORT TERM...Leins
LONG TERM...np
AVIATION...Badgett/Leins
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