Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 260559

Area Forecast Discussion
National Weather Service Raleigh NC
159 AM EDT Sun Mar 26 2017

A backdoor front will settle into and stall over central VA today,
while a weakening upper level disturbance pivots northeast across
our region. Bermuda high pressure will otherwise extend west into
the southeastern U.S. through Mon.


As of 925 PM Saturday...

Weak southerly moist warm air advection between the Bermuda high
over the western Atlantic and a slow moving low pressure system
lifting NE through the Middle MS Valley will result in partly to
mostly cloudy skies overnight and continued mild temperatures.

With the strongest surge of warm air advection remaining along and
west of the mountains, it will remain dry overnight with  pockets of
low clouds possible,  primarily along the eastern slopes. Mild
overnight lows generally in the mid 50s.


As of 255 PM Saturday...

A lead s/w rotating around the mid MS Valley upper low will lift
newd from eastern TN into the central Appalachians Sunday, brushing
our nw sector. This system projected to weaken with time and while
atmosphere continues to moisten, model rh cross sections still
depict a decent layer of dry air in the mid levels of the
atmosphere. Accordingly, models have been trending drier, so will
follow a similar trend. Plan to confine chance PoPs to the NW
Piedmont, with slight chance PoPs elsewhere across the Piedmont.
Over the east and far south sections, will advertise PoPs less than
15 percent.

Expect quite a bit of cloudiness, limiting insolation. Still, warm
sly flow along with partial sun should be able to boost temperatures
back into the low-mid 70s.

Continued mild Sunday night under variably cloudy skies. Weak
confluence and a series of weak perturbations aloft will continue a
minor threat for a few showers over the NW Piedmont. Elsewhere,
probability of a shower appear too remote to mention at this time.
Overnight temperatures in the mid-upper 50s.


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 pressure 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.


As of 155 AM Sunday...

Mainly VFR. Morning to midday heating of a seasonably moist air mass
around Bermuda high pressure will favor the development of a field
of stratocumulus that will initially develop around 2500-3000 ft,
and may be briefly broken in that range this morning in the few
hours surrounding 15Z, before lifting into the 3500-5000 ft range
this afternoon. The passage of an upper level disturbance and
associated moistening aloft may allow a few showers to move into and
affect INT and GSO this afternoon and evening. Otherwise, SSWly
surface winds will increase into the 8-13 kt range after 14-15Z,
with occasional gusts up to 20 kts, then lessen after sunset.

Outlook: Late night-early morning fog and/or stratus, then MVFR
range cloudiness as that moist layer is heated through midday, will
be possible each day through the middle of next week. Otherwise, a
chance of showers and associated sub-VFR conditions will exist late
Mon through Tue. The probability of any such shower at any given TAF
site will be relatively low, however, given limited overall
coverage. Lastly, a backdoor cold front will settle into SC Wed
night; and "overrunning" flow atop the boundary will result in the
development of MVFR-IFR conditions and associated cold air damming
as early as late Thu, but more likely just beyond the outlook TAF
period - Thu night-Fri.





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