Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 170111

Area Forecast Discussion
National Weather Service Raleigh NC
811 PM EST Mon Jan 16 2017

High pressure along the Mid-Atlantic coast will gradually shift
offshore tonight and Tuesday, in advance of a cold front approaching
the mountains from the west. The cold front will progress east of
the mountains Tuesday night, track southeast through North Carolina
Wednesday morning, then southward offshore the Carolina coast
Wednesday afternoon as an associated upper level disturbance tracks
offshore the Mid-Atlantic coast.


As of 1245 PM Monday...

Expect little change in sensible wx conditions this afternoon into
tonight. High pressure centered along the Mid-Atlantic coast will
gradually shift offshore (though continue extending SW into central
NC) late tonight as a shortwave ridge progresses through the Mid-
Atlantic. Weak southwesterly warm advection atop the cool/shallow
airmass extending into the region from the NE will help maintain the
CAD wedge in place for the remainder of this afternoon. Weak
nocturnal cooling of the shallow moist layer in place over central
NC should result in lowering ceilings and perhaps fog /lowering
visbys/ tonight. Expect only several degrees of diurnal variation
between highs this afternoon and lows tonight. -Vincent


As of 105 PM Monday...

The lingering CAD wedge is expected to undergo top-down erosion
during the day Tuesday as southwesterly low-level flow strengthens
in advance of a shortwave approaching the Mid-Atlantic from the
W/NW. Initially overcast skies should become broken by early
afternoon, perhaps scattering out entirely from the Triangle
southward and eastward. Broken to overcast cloud cover is most
likely to persist the longest across the N/NW Piedmont where
occasional sprinkles cannot be ruled out. Challenging temperature
forecast. Expect highs in the upper 50s (N/NW) to mid 60s (S/SE)
Tuesday afternoon. Expect rather mild lows Tuesday night as the MSLP
gradient tightens in advance of the approaching cold front and a
southwest breeze persists much of the night. Expect lows in the mid
to upper 50s, possibly a few degrees cooler in the Northern
Piedmont/NE Coastal Plain where precipitation assoc/w the front is
most likely to occur prior to sunrise Wed. It should be noted that a
large amount of uncertainty persists with regard to the precise
coverage/timing of precip assoc/w the upcoming cold frontal passage
early Wed. -Vincent


.LONG TERM /Wednesday through Monday/...
As of 230 PM Monday...

Fast progressive flow through the extended period will produce
several frontal passages Wednesday through early next week. The
sensible airmass change behind each system will be minor as arctic
air will remain blocked across the northern tier of the CONUS and we
will remain unseasonably mild through the period.

A rather vigorous short wave skating across the Ohio valley will
nudge a backdoor front south into the area by sunrise on Wednesday,
with fairly widespread rain in the morning tapering off during the
early afternoon. Despite the modest cold air advection, we will
benefit from a warm overnight min in the mid 50s bolstered by
increasing sun as the day progresses to allow highs to reach the mid
60s over most of the area, with some readings near 70 along the
southern tier. Lows Wednesday night will be cooler under mostly
clear skies...40 north to 45 south.

Dry weather will linger through Thursday night as upper ridging and
surface high pressure migrate overhead. The modestly cooler airmass
will be in place and highs on Thursday will stall within a degree or
two either side of 60. Will see some light rain begin to spread into
the west by late Thursday night as overrunning ensues in south to
southwest flow as the stacked ridging moves offshore. Mins will
remain mild in the southerly flow under increasing cloudiness...
again mostly in the 40 to 45 range.

A quick and perhaps vigorous round of showers is on tap on Friday as
a low over the plains rotates northward and deep southwest flow
lifts the stalled surface front north concurrent with reasonably
supportive mid and upper dynamics. Will increase PoPs to likely
across the entire area as uncertainty is on the rise with time in
this fast flow regime. Highs Friday should uptick a degree or two in
the warm air regime with mainly upper 50s north to lower 60s south.
We then see a repeat of a short-lived dry spell with low amplitude
mid level ridging Friday night and Saturday. Lows Friday night will
be in the mid 40s with highs Saturday mostly in the lower 60s.

Somewhat similarly, a stronger short wave moving across the mid west
will reassert southerly flow Sunday, pushing another mild but
potentially much wetter front across the area through Monday night.
This upper low will be deepening as it moves into the Tennessee
Valley, and as such, will produce more favorable conditions for
convection as H85 winds are progged to 50kt and supported aloft by a
favorably aligned upper jet. Will have 50-60 PoPs both Sunday into
early Monday as we let the details resolve themselves. Mild temps
linger both days...mid 50s northwest to lower 60s southeast.


AS OF 740 PM Monday...

24 Hour TAF period: MVFR cigs are expected to spread areawide this
evening, before falling into the IFR/LIFR range during the overnight
hours in assoc/w a lingering CAD wedge. Cigs will gradually lift on
Tuesday in advance of a cold front approaching from the west. Winds
will increase in advance of the front Tuesday morning into the
afternoon as cigs slowly lift. We could see some gusts of up to 20-
23 mph or so.

Looking Ahead: Any improvement in conditions Tue aft/eve will be
short-lived, as conditions are likely to deteriorate from N/NW to
S/SE (earliest at Triad and latest at FAY) Tue night/Wed morning as
an upper level disturbance tracks through the central Appalachians
into the Mid-Atlantic and an attendant cold front /SFC-925 trough/
progresses east of the mountains into VA/NC. Expect the best
potential for rain and low ceilings to occur between midnight and
noon Wed as the slow moving front progresses SE through central NC.
Expect a clearing trend in the wake of the front with a brief return
to VFR conditions Wed night/Thu. A pattern similar to the one
affecting the region today is progged to develop over the region
again late this week. With this in mind, expect ceilings to begin
deteriorating Thu night/Friday.





NEAR TERM...Vincent
SHORT TERM...Vincent
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