Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 260755

Area Forecast Discussion
National Weather Service Raleigh NC
355 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 345 AM Sunday...

On the sern periphery of an upper low that will become an open wave
as it lifts from the Middle MS Valley NEwd across the Great Lakes
through tonight, a lead mid level trough axis now extending across
the TN Valley will edge Ewd into the wrn NC Piedmont this afternoon.
An associated axis of moisture aloft, and weak forcing for ascent,
will likely result in the slow NEwd maintenance of a band of showers
now moving through W-central GA. While these showers will likely
weaken with Ewd extent into the W-central Carolinas, as they near
the wrn periphery of a sub-tropical ridge and associated dry and
capping influence centered near Bermuda, a few may drift into the
wrn Piedmont by mid-late afternoon. While CAM`s also indicate the
potential for much shallower showers to the east, ones capped above
by the aforementioned subsidence inversion sampled by proximity
RAOBS around 5-6 k ft last evening, it`s unlikely that barely
positive CAPE would support deep enough cumulus to indeed support
any showers elsewhere.

Otherwise, like Sat, diurnal heating of a seasonably moist BL
characterized by surface dewpoints generally in the lower 50s should
again support a scattered to broken cumulus field by midday-early
afternoon, but with enough breaks of sun to allow temperatures to
again reach the middle to upper 70s.

While shortwave ridging aloft behind the departing mid level trough
will likely yield dry conditions tonight, the mid level moist axis
accompanying the trough will be left behind; and this may support a
lingering shower or two over the wrn Piedmont tonight. Low
temperatures centered in the middle 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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