Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 230252

Area Forecast Discussion
National Weather Service Raleigh NC
955 PM EST Sun Jan 22 2017

A potent low pressure system will track northeast from the Deep
South into the Carolinas tonight, linger over the area on Monday,
then track off the Mid-Atlantic coast on Tuesday.


As of 955 PM Sunday...

Little change from earlier thinking. Deep upper level low over
eastern Alabama this evening will lift slowly newd to a position
over upstate SC by early Monday morning. Strong upper divergence
ahead of this system interacting with a moist air mass and a stalled
sfc boundary draped west-to-east in vicinity of the SC border will
cause widespread showers through midnight or 1 AM. Afterwards a dry
slot rotating up ahead of the upper low will overspread central NC
from the south, leading to a diminishing trend in the shower
coverage and intensity.

Still cannot rule out the potential for a few rumbles of thunder
later tonight, mainly across the southern counties. However, the
threat for severe storms has greatly diminished.

Temperatures are expected to hold steady into the overnight, then
trend slowly downward toward daybreak. Min temps by early Monday
should vary from the upper 40s/around 50 northwest to the lower 50s


As of 400 PM Sunday...

A mean mid to upper level low --one consisting of at least three
distinct vortices over AL, LA, and AR, and associated pocket of
steep lapse rates/cold temperatures aloft characterized by 500 mb
temperatures of minus 22-24C-- is forecast to wobble across the Gulf
coast states this evening, then lift NEwd into SWrn NC by 12Z Mon,
and off the VA coast by 12Z Tue.

An associated 998-990 mb surface low will likewise migrate across
Srn and Ern NC during the day Mon, and up the Middle Atlantic coast
Mon night, while the preceding occluded front
--near the VA border at 12Z Mon-- will pivot Nwd into VA.

Sensible weather: Early day partial sunshine over the NE Piedmont
and Coastal Plain will yield to cloudy or mostly so skies that will
pivot ENEwd with the aforementioned deep layer/occluding cyclone.
While scattered "instability" convection will be possible throughout
central NC, as weak instability of up to several hundred J/KG
develops with diurnal heating (into the middle 50s W to lower 60s E)
amidst marginal surface moisture characterized by 45-50 F dewpoints,
and beneath the cold pool aloft, convective coverage and intensity
will be relatively maximized from the Sandhills to the Ern Piedmont
and Coastal Plain, where QG-forcing for ascent ahead of the cyclone
will best overlap with early afternoon heating. Both lightning and
small hail/graupel will probably accompany the convection here, with
lesser chances of each elsewhere. No severe weather is expected,
given very weak forecast wind fields as the center of the cyclone
passes overhead, and too-limited instability to support anything but
small hail.

While SW to NE clearing will take place overall Mon night, as the
low lifts away, a band of deformation-type low clouds may wrap SEwd
from near Roxboro to Goldsboro and points Ewd through early Tue
morning. Lows mostly in the lower to middle 40s.


As of 220 PM Sunday...

Tuesday and Wednesday: Any lingering cloudiness Tuesday morning
will be retreating rapidly to the northeast as the coastal low lifts
up the mid Atlantic coast. Unseasonably mild temperatures will stay
with us through mid week with copious sunshine and increasing heights
as mid level ridging migrates across the area. Highs on Tuesday
will range from the upper 50s north to lower 60s south, warming on
Wednesday to the mid and upper 60s.

A strong shortwave lifting out of a longer wave trof into the Great
Lakes region will push a cold front across the mountains Wednesday
night and rapidly east across central NC and out of the area by
mid afternoon Thursday. This front will be accompanied by scattered
showers and begin our transition to north west flow and attendant
cooler temperatures for late week and through the upcoming weekend.
Temperatures on Thursday will have time to warm to the mid 50s west
to lower 60s east before the cooler air arrives, and we will really
notice the end of our two week mild spell Thursday night as mins
fall to near freezing in the northwest to mid 30s elsewhere.

Northwest flow will produce dry, but much cooler conditions Friday
through Sunday, with highs in the 40s each day. Mins Friday and
Saturday night will range from 25 to 30.


As of 645 PM Sunday...

24-Hour TAF period: Another area of rain is lifting northward into
Central NC and will continue to move through the area through 12Z or
so Monday morning. Chances for thunder continue to diminish, though
there is still a chance, albeit fleeting, at KFAY and less so at
KRWI. Aviation conditions will largely remain IFR/LIFR through
tonight, with possible slight improvement while rain is occurring.
Also, winds may also get gusty in the stronger showers/storms, but
otherwise will be 10-12 kts, decreasing Monday morning. Conditions
should improve to MVFR/VFR after 12Z Monday, though another round of
rain is possible as the low swings through the area Monday afternoon
and could reduce cigs again as it does so. -KC

Looking ahead: Conditions are expected to improve /return to VFR/
sometime late Monday night or early Tuesday as the aforementioned
system tracks offshore the Carolina/Mid-Atlantic coast. A cold front
will cross the region by Thursday and may bring some adverse
aviation weather. -SMITH




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