Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 251828
Area Forecast Discussion
National Weather Service Raleigh NC
230 PM EDT Sat Mar 25 2017
Bermuda high pressure will extend west into the Carolinas and VA
through the weekend. A weakening upper level disturbance will cross
our region on Sunday.
.NEAR TERM /THROUGH TONIGHT/...
As of 1050 AM Saturday...
Little change to near term forecast as 12Z upper air analysis
supports current forecast.
An area of high pressure stretching west-to-east from the eastern
Gulf and across the FL peninsula coupled with an area of low
pressure lifting ne from the southern Plains into the mid MS Valley
will result in a warm sw flow across central NC today and tonight.
While the atmosphere overhead will gradually become more moist, most
of the moisture advection is occurring in the lowest 5k ft of the
atmosphere, and above 20k ft, with a bone dry mid layer. While skies
will not be totally sunny due to the presence of patchy cirrus and
scattered cu, the dry layer in the mid levels will permit partly
Considering that most places are starting out 10-15 degrees warmer
than Friday, and warm air advection will continue, should see
afternoon temperatures solidly in the mid 70s with upper 70s
probable east of highway 1. ~WSS
Tonight: SSWly stirring around the wrn periphery of the sub-tropical
ridge/Bermuda high, and considerable high clouds topping probable
late-night stratus, should result in milder-than-guidance low
temperatures, in the middle to upper 50s. While glancing forcing for
ascent downstream of the lifting upper low will continue to pivot
NEwd across central and wrn NC late tonight, associated forecast
omega is centered in the mid levels where dry air from the subsident
sub-tropical ridge will be maximized. As such, it seems unlikely
that any band of upstream showers will survive and/or arrive even in
the wrn Piedmont prior to 12Z, so the forecast will be a dry one
through early Sun. ~MWS
.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 400 AM Saturday...
The upper low over the southern Plains states will lift to
toward the Great lakes and weaken today through Sunday, while a
Bermuda High continues to provide a warm southerly wind over the
Carolinas. Ongoing convection in the Southern Appalachians
Sunday morning should weaken as it moves out ahead of the
primary cold front and the upper low, while becoming negatively
tilted, weakens and passes well to our northwest. Aside form the
western Piedmont, where 40-60m height falls appears to erode a
fairly stout capping inversion, the rest of central and eastern
NC remains capped by the sub-tropical ridge. Models continue to
trend drier for most of central NC, and POPs have been adjusted
down to just a chance west of US 1 on Sunday. Widespread cloud
cover and possible showers will likely hold temps back a little
in the west, but southerly flow should still allow highs to
reach the mid 70s in the east.
Models cranks out some light qpf Sunday night, but this looks
over done, and stratus looks to be the only really issue, with
mild lows in the mid and upper 50s.
.LONG TERM /MONDAY THROUGH SATURDAY/...
-- Changed Discussion --As of 230 PM Saturday...
A warm, moist airmass will be in place to kick off the work week.
Precipitable water in excess of 1.2 inches and highs Monday through
Wednesday reaching the mid 70s to lower 80s will provide modest
instability and widely scattered showers Monday, with coverage
ramping up somewhat on Tuesday as a progressive but relatively weak
short wave moves east across the area. Timing of the short wave will
be favorable to tap afternoon instability and a few thunderstorms
will be possible in the afternoon...especially east where
instability and upper diffluence are favorably aligned ~18-21Z.
Dry and continue warm temperatures are initially on tap Wednesday as
ridging aloft builds over the area ahead of another upper low moving
into the central Plains. High presssure over the Great Lakes will
surge south ahead of the Plains system, pushing a dry backdoor cold
front south into the state later Wednesday, but highs will have time
to reach the mid and upper 70s ahead of the cooler air.
The "seasonally-adjusted" cold air damming setup will promote
overrunning rain in the west as early as Thursday afternoon. PoPs
will be ramping up Thursday night and lingering all the way through
Friday night as low level southerly flow increases ahead of the
Plains system. Low level instability will be meager at best, with no
indication as yet that we might see a thermal moisture boundary
encroach inland, As such, will have only a slight chance for
elevated thunderstorms on Friday. Highs both Thursday and Friday
will be mainly in the 60 to 65 range, with some lower 60s across the
piedmont and northern coastal plain where cool air will be deeper.
Lot of uncertainty as to how the Plains system evolves, i.e. the
latest GFS re-establishes cool air advection with development of a
coastal low, while the 00Z ECMWF was scouring out the cool airmass
and allowing highs to rocket quickly back to the upper 70s...will go
middle of the road 70 to 75 for now to await some consensus.
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.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 1240 PM Saturday...
While VFR conditions will exist across central NC through Monday
night, there will be occasional periods of MVFR/IFR ceilings late at
night/early morning beginning tonight and again Sunday night. The
adverse ceilings will be most likely in the 10Z-15Z time frame, with
the chances higher across the western Piedmont (including the Triad
terminals), and less so over the east.
The highest threat for showers will occur mainly west and northwest
of our region, though a stray shower or two may skirt in vicinity of
the Triad terminals Sunday, and again Monday.
The weather pattern will be unsettled through mid-week, suggesting
that periods of sub VFR conditions are probable, primarily in the
form of low ceilings during the overnight into the early morning
hours. An approaching low pressure system will trigger scattered
showers across central NC late Monday night through Tuesday. A
backdoor cold front may drop into the region Wednesday, setting up a
possible CAD event for the later half of the work week, and
attendant sub VFR conditions.