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Area forecast discussion
National Weather Service Raleigh NC
922 PM EST Sat Dec 14 2019

a strong shortwave trough and accompanying surface cold front will
sweep east across ern NC early tonight. High pressure will otherwise
build across the southeastern US and offshore through Monday, while
another front approaches from the northwest and stalls over central
Virginia. Low pressure will then deepen while tracking across the central
Appalachians and middle Atlantic on Tuesday, with a related,
preceding warm frontal passage in central NC Monday night and early
Tuesday and following cold frontal passage Tuesday afternoon.


Near term /tonight/...
as of 915 PM Saturday...

WV satellite imagery and 00z upr data depict a strongly-negatively-
tilted mid-upr lvl trough extending from swrn on sewd across and
offshore the Carolinas, with a related preceding corridor of ~250
meter height falls maximized at 300 mb across the Middle Atlantic
States, including 200 meters and with a remarkably low tropopause
around 430 mb at gso - the latter courtesy of a potent pv anomaly
now pivoting across sern NC. Increasingly-zonal and fast wly flow
aloft-- and rising heights, subsidence, and clearing-- will follow
and expand across the Carolinas through Sun morning.

At the surface, a cold front was analyzed at 02z from just se of
kwal (with a passage there in the past hr) swwd to near korf,
through the coastal plain of cntl NC, and then increasingly
stationary wswwd across wrn SC and the cntl Gulf Coast states. The
front was accompanied by scattered showers, amidst up to a couple of
hundred j/kg of SBCAPE fueled by very cold temperatures (minus 26c
at 500 mb at gso) and steep lapse rates aloft related to the
aforementioned mid-upr lvl trough, and following wind gusts
highlighted most recently by 20 kts at rdu and 27 kts a few hrs ago
at gso. Surface winds will lessen in cntl NC overnight, as a weak
(1015 mb) surface high over srn Georgia/Alabama expands across the sern US and
the mean sea level pressure gradient relaxes. Light wly stirring between
periods of calm in sheltered areas, including some of the latter
already at scr, vuj, and rcz in the past hr, will result; and as
such low temperatures have been adjusted downward slightly to depict
some lwr 30s in those cooler spots to mid-upr 30s elsewhere.


Short term /Sunday through Sunday night/...
as of 130 PM Saturday...

In the wake of today's departing trough, high pressure will build
over the southeast portion of the country and will slide to the east
through the day ushered by westerly flow aloft. Meanwhile, moisture
emerging across the Central Plains and setting up across the Ohio
Valley by late day will mostly stay to our north late Sunday and
Sunday night, thanks to flow around the aforementioned high pressure
to our south. As such, look for dry weather on Sunday with a fair
amount of sunshine during the day and partly cloudy conditions
Sunday night. It's Worth noting that both NAM and GFS forecast
soundings suggest some low clouds Monday morning, mainly across the
western Piedmont and triad, as moist south low level flow gradually
encounters modest terrain induced lift. Highs Sunday once again in
the 50s and lows Sunday night in the mid to upper 30s.


Long term /Monday through Saturday/...
as of 245 PM Saturday...

Mon/Mon night should be dry and warm, as mild surface high pressure
shifts further east off the southeast coast, with an increasing low
level flow from the S and SW ahead of an approaching cold front
being propelled by a large mid level trough digging over the central
Continental U.S.. the approach of this trough will result in growing ridging
aloft over the southeast and rising heights over NC. The cold front
and associated precip still look to hold well to our west and northwest
through Mon, and will keep the forecast dry with fair to partly
cloudy skies. With a trend toward overcast skies, will bring small
pops into the northwest Mon evening, following model consensus, with higher
pops to follow, ranging from likely northwest to lower chance se, overnight
Mon night within the strengthening low level warm and moist air
advection and rising pws. Thicknesses are expected to start the day
over 25 M above normal with a steady rise through the day and night.
While we may see some lingering stable air in the far northwest Mon, the
mild character of the surface air mass and the lack of a tap of both
very dry air and precip into it to reinforce it will make the stable
layer vulnerable to mixing. Have raised highs across the board to
range from around 60 northwest to lower 70s se, and even this may not be
warm enough if we get some decent sunshine. Temps will not drop much
Mon night with a steady warm breeze and thickening clouds, so have
bumped up lows to around 50 to the upper 50s, close to the normal
highs for this time of year.

Will continue likely to categorical pops across central NC as the
front progresses eastward Tue. Minor timing differences persist,
with the GFS a bit faster than the European model (ecmwf) and the NAM the slowest,
but overall it looks like the front will be pushing offshore late
Tue with precip chances winding down Tue evening. Clearing should be
gradual as the positively tilted mid level trough axis will lag the
front, sweeping through central several hours after surface frontal
passage and precip departure. Expect warm highs Tue, mostly in the
60s, with plunging temps Tue night behind the front. Surface high
pressure will build in from the west Wed through Fri with below normal
thicknesses, yielding quiet weather with plenty of sunshine but
chilly highs in the mid 40s to lower 50s. Broad mid level ridging
builds in from the west starting mid week then stalls and amplifies
over the southeast Fri as the surface high also stalls over our
area, all due to a deep shortwave trough and low amplifying over the
central Continental U.S.. models differ in their position and handling of this
low, and this ultimately leads to vast differences in sensible
weather as we get into next weekend, with the GFS blowing up a
strong frontal system and coastal low right over the southeast coast
and Carolinas, while the European model (ecmwf) is delayed, further offshore, and not
as intense. For now, given this uncertainty, have kept pops low
(just below climatology) with a trend toward near normal temps for
Sat. -Gih


Aviation /00z Sunday through Thursday/...
as of 630 PM Saturday...

24 hour taf period: VFR conditions are expected to prevail through
the taf period. Some lingering mid to high clouds and isolated
showers are moving east across central NC this evening in response
to a surface boundary. In the wake of this boundary, skies will
begin clearing out. Strong, gusty winds may persist for the next few
hours, but gusts should abate by midnight. Winds will likely remain
a little breezy tonight, generally 5-10 kts at all terminals through
the rest of the taf period. -Kc

Looking ahead: some MVFR cigs assoc with cloud may develop across
the western Piedmont Monday morning. Flight conditions will then
enter of period of reduction late Monday through Tuesday assoc with
low clouds and rain chances with the next front. Look for improving
flight conditions by Tuesday night in the wake of that front. -Np


Rah watches/warnings/advisories...



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