Area Forecast Discussion
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FXUS62 KRAH 222100
Area Forecast Discussion
National Weather Service Raleigh NC
400 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.
.NEAR TERM /THROUGH TONIGHT/...
As of 330 PM Sunday...
Less severe threat than previously expected tonight...
The upper low is currently over the Lower Miss Valley region,
while the associated surface low pressure appears to
transitioning from the earlier ArkLaTex to a dominate low over
AL. Still expect intense deep layer lift as upper diffluence
and DCVA increase rapidly after 00Z and a 50kt LLJ translates
east across SC/GA. The QLCS will getting going over southwest
GA and the FL Panhandle this afternoon will expand north toward
the Carolinas this evening. The biggest question in central NC
continues to be the northward extent of the warm sector and
efficiency of CAD erosion before QLCS arrives, which is not
looking favorable for the severe weather.
The wedge front has retreated into the southern CWA, though
destablization has been hindered by convection blow off from the
overnight convection in southern GA and weak moisture transport
so far. The true warm sector is still suppressed way south over
southern GA by the aforementioned high clouds and diabatic
effects of morning convection. By all accounts, the warm sector
will never reach the Piedmont and may even struggle to extend
into the southern Coastal Plain before being swept out by the
cold/occluded front. Most guidance suggests a narrow corridor of
~500 J/KG of MUCAPE that may stay slightly elevated east of US
1, and even HRRR simulated reflectivity is rather unimpressive.
As such, current thinking is the best threat of strong storms is
southeast of a line from Laurinburg to Fayetteville to
Goldsboro between 01Z and 05Z.
The main segment of convection will be departing after midnight, but
the threat of showers and isolated storms may continue from the
southwest overnight as the upper low wobbles toward the area.
Deep layer shear 60-80kt and 200-400 J/KG of MUCAPE, owing to 7
C/KM mid-level lapse rates rounding the upper low, may still
support some elevated cells in the Piedmont and a small hail
threat between 06-10z as the occluded front pushes north through
the area, but even that looks questionable.
Temps should hold mostly steady across the north and rise a
little into the mid 60s in south this evening, and then rise
later tonight with mixing associated with the occluded front.
.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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
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.
.LONG TERM /TUESDAY THROUGH SUNDAY/...
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.
.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
As of 100 PM Sunday...
LIFR is holding strong across the Piedmont, while there have just
recently been some signs of the wedge airmass beginning to erode
around the FAY area, allowing ceilings to lift to IFR and MVFR. This
will stay fairly steady for a few more hours - northwest wind and
IFR at RDU/GSO/KINT/RWI - with some minor improvements through 00Z.
After 00Z, there is a lot more uncertainty, as the northern end of a
severe QLCS will cross NC from southwest to northeast. Right now it
appears conditions will remain fairly stable over central NC, and
the threat of storms and severe winds will be confined to FAY (maybe
RWI) and southeast between 01-05Z. Any storms around around
RDU/GSO/INT should remain elevated and not pose a significant wind
threat. A warm front will eventually move through the area tonight
and cause ceilings to lift to IFR/MVFR by Monday morning, but the
primary ow pressure system responsible for tonight`s storms will
cross the area cause ceilings to lower again Monday, along with
scattered showers and possibly a few storms. -Smith
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.