Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 181700
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1200 PM EST Wed Jan 18 2017

.SYNOPSIS...An upper level ridge will build into the region from the
west tonight as as a shortwave trough tracks offshore. Ridging aloft
will prevail over the Carolinas and Mid-Atlantic on Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1200 PM Wednesday...

A clearing/drying trend will prevail this afternoon into tonight in
association with subsidence in the wake of a compact upper low
progressing offshore the DELMARVA coast. Given that skies cleared
early in the day and that cold advection in the wake of the recent
cold frontal passage will be delayed until later this afternoon,
expect warmer highs than previously anticipated, in the upper 60s to
lower 70s. Lows tonight will be driven by a combination of cold
advection and radiational cooling, in the lower 40s. -Vincent

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 1200 PM Wednesday...

An upper level ridge and associated surface high building into the
region from the west tonight will be situated directly over the
Carolinas/Mid-Atlantic on Thursday. As such, expect a pleasant/
sunny day with above normal highs in the upper 50s to lower 60s.
Widespread precipitation is expected to develop upstream over the
Deep South/TN Valley during the day Thursday as a potent upper level
low lifts NE through the Central Plains toward the Upper Great
Lakes. As a result, clear skies will quickly give way to increasing
cloud cover by sunset as mid/upper level ceilings advect downstream
of the mountains. Southerly return flow will quickly strengthen over
western portions of the Carolinas as shortwave energy rounding the
base of the upper low in the Central Plains Thu afternoon ejects
E/NE through the Deep South into the Carolinas Thursday night.
Expect a further increase in cloud cover overnight as mid/upper
level ceilings are complimented by low ceilings assoc/w
strengthening warm advection. In fact, light rain will be possible
by sunrise (09-12Z) Friday morning in the Western Piedmont as
moisture deepens via warm advection in the presence of DPVA (assoc/w
the aforementioned shortwave energy). Low temps Thu night may be met
by Thu evening, particularly in the west, as a result of warm
advection and thickening cloud cover. Expect temps ranging from the
low/mid 40s E/NE to upper 40s W/SW. -Vincent

&&

.LONG TERM /Friday through Tuesday/...
As of 420 AM Wednesday...

Model agreement with the general pattern continues to be better than
usual through the weekend, although some important differences in
the low level pattern are evident, and notable timing differences
crop up by Mon/Tue. Models are overall trending wetter in this time
frame. Temps will remain quite mild, with all cold air staying
bottled up over northern Canada and the Arctic region.

Fri/Fri night: The mid level trough extending from the Midwest
through the Ohio Valley to SC early Fri will continue to pivot to
the NE through NC and into the Mid-Atlantic and Northeast Fri, and
will be followed by prominent shortwave ridging over the Southeast
Fri night. Focused mid level DPVA and upper divergence associated
with passage of the trough, along with high PW, will support a band
of rain shifting through central NC Fri morning, with a west-to-east
tapering down Fri afternoon, and dry but mostly cloudy conditions
Fri night as low level moisture pools over the area with a light
surface flow. Will go with likely pops Fri morning, trending
downward Fri afternoon. The ECMWF/NAM bring today`s surface front
back northward into NC, albeit in a very diffuse form, while the GFS
is more defined in keeping the frontal zone near the NC/SC border,
favoring thick low clouds and cooler temps, especially over northern
NC. With well-above-normal thicknesses tempered a bit by the morning
rain and lingering clouds late Fri into Fri night, expect above
normal temps with highs from the mid 50s N to lower 60s S. Lows 45-
50.

Sat/Sat night: What once appeared to be a fairly dry day now looks
be trending wetter. Thanks to a powerful mid and upper jet from CA
across the Desert Southwest and adjacent Mexico to TX, a strong low
will be closing off over OK/TX before shifting to AR/LA through Sat
night. Subtle perturbations ejecting from this low/trough will swing
NE into the Carolinas Sat afternoon/night, while bands of enhanced
upper divergence spread in from the SW, a product of ideally
juxtaposed upper jetlets over the Ohio Valley and over the NE Gulf.
Low level flow will be ramping up with an 850 mb jet nosing into the
Carolinas, fostering moist isentropic upglide along/above the
diffuse surface frontal zone. And models agree on PW staying well
above normal as they generate precip over the area, mainly across
the southern and western CWA Sat and areawide Sat night as heights
aloft continue to fall with the approaching trough. Will bring in
low chance pops mainly S on Sat, trending up to good chance Sat
night. The rain and clouds will lead to a tighter diurnal temp
range. Highs in the low-mid 60s Sat followed by lows in the mid 40s
to lower 50s.

Sun into Mon: The mid level low is expected to cross the lower Miss
Valley, Gulf States, and Carolinas before moving into the interior
Mid-Atlantic region through late Mon. This system will be
accompanied at the surface by a complex but likely occluded frontal
system, with vigorous deep forcing for ascent promoted by a 40-50 kt
low level jet punching into the area, intense upper divergence
within a zone of ascent between two ideally juxtaposed upper jets,
and large mid level height falls. Confidence is high in a period of
potentially heavy rain and embedded storms with strong kinematics
and marginal instability and lapse rates, but the timing is less
certain, as the GFS becomes much slower (farther SW) than the ECMWF
with the upper low and trough as it swings ENE through our area with
a negative tilt. Will lean toward the faster ECMWF, which has good
agreement with its ensemble mean. Will have likely pops Sun/Sun
night, with the best chance of heavy rain and storms Sun evening,
followed by a SW-to-NE tapering down of pops on Mon as some drier
mid level air works in from the SW. A strong storm or two remains
possible given the energetic wind field, despite the weak
instability noted by the models. Lingering instability showers and
isolated storms will persist Mon with indications of high lapse
rates and abundant moisture. Temps should remain above normal
despite the clouds/precip.

Tue: We should be on the west side of the departing low/trough
shifting to our east and north, with yet another mid level ridge
building in. Expect dry weather and a trend to fair skies. With no
cold air available, temps will remain above normal. -GIH

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 1200 PM Wednesday...

24-Hour TAF period: VFR conditions /clear skies/ will prevail
through the TAF period, with winds becoming light/variable overnight
as high pressure builds over the region from the W/NW.

Long term: Sub-VFR conditions will be possible late Thu night or
Friday morning as southerly return flow strengthens over the
Carolinas. Adverse aviation conditions may prevail Fri through much
of the upcoming weekend as a series of upper level disturbances
track across the region. -Vincent

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Vincent
NEAR TERM...Vincent
SHORT TERM...Vincent
LONG TERM...Hartfield
AVIATION...Vincent


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