Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 110834

Area Forecast Discussion
National Weather Service Raleigh NC
333 AM EST Sun Dec 11 2016

High pressure overhead will drift offshore later this morning. A
warm front will push northward through the area tonight, followed by
the approach of a cold front Monday and Monday night. This front
will stall across the Carolinas Tuesday and Wednesday.


As of 333 AM Sunday...

Sfc high pressure overhead this morning will drift east and offshore
this afternoon. Sly low level return flow on the backside of this
retreating high will advect moisture into our region, resulting in
an increasing/thickening low level cloud deck that will spread
south-to-north during the course of the afternoon over central NC.

Models have trended slightly drier/less bullish with the probability
of patchy light rain breaking out over our region late today/early
this evening. At 06Z, WRF models are overdone with their depiction
of spotty light rain off the northeast Fl coast. Thus the trend may
be correct, suggesting that we will likely have a mostly dry
afternoon across much of the forecast area.

Afternoon temps still dependent on the arrival/thickness of the
cloud cover this afternoon. Made little adjustments to max temps
with mid 40s north and upper 40s/near 50 south/southeast.

Tonight, isentropic upglide increases, leading to a better potential
for spotty light rain over the area. Considering the depth of the
moisture layer (mainly in the lowest 10000ft), may see more drizzle
than actual light rain. Highest probability of measurable rain still
expected along and east of highway 1. With warmer air aloft
overspread the relatively cooler air at the sfc, will likely see
areas of fog develop overnight/toward daybreak with pockets of dense
fog possible. Arrival of a warmer air mass overnight suggest min
temps at most places will likely be observed this evening with temps
either holding steady or slowly rising overnight, especially in the
east. Min temps mid-upper 30s nw to the mid 40s se.


.SHORT TERM /Monday through Monday night/...
As of 333 AM Sunday...

Monday, precip chances increase in response to the approach/passage
of a lead s/w ahead of the main s/w crossing the Great Lakes. This
mid level feature interacting with the available moisture should
result in scattered showers across much of the region, particularly
the northern Piedmont. Low level sly flow will be enhanced over the
Sandhills and coastal plain, aiding to boost temperatures to near 60
or the lower 60s. A mini in-situ damming event may occur over the nw
Piedmont, holding their temps in the lower 50s. If this insitu
damming diminishes/dissipates before noon, then temps may
recover into the mid-upper 50s.

Threat for showers will begin to decrease Monday afternoon and more
so Monday night as we experience subsidence on the back side of the
exiting s/w. Residual low level moisture will maintain at a minimum
variably cloudy skies. Min temps near 40 far north-nw to near 50
far south-se.


As of 315 AM SUNDAY...

The general upper level pattern in the GFS and ECMWF continue to be
very similar, with a strengthening low over Central Canada slowly
progressing east and southeastward through the end of the week.
However, there are still somewhat significant differences between
the models with respect to precipitation chances and timing.

Tuesday and Wednesday: A cold front will slide southward into
Central NC on Tuesday, and models now have it progressing all the
way through the region by late Tuesday. Highs will be near normal to
slightly below normal in the upper 40s to mid 50s. Low confidence in
precip occurring Tuesday through early Wednesday, but will leave a
slight chance for showers in the forecast for now. Better chance for
showers will be Wednesday aft/eve as a low slides up the Carolina
coast. All precip should come to an end ahead of the arrival of cold
air advecting into the region Wednesday Night as the upper level low
moves into southeast Canada and the associated trough amplifies over
the eastern U.S. The current timing would result in lows about 8
degrees cooler Wednesday night (upper 20s to mid 30s) than Tuesday
Night (mid 30s to mid 40s).

Thursday through Sunday: Cold high pressure will move through the
High Plains/Midwest Thursday, then through the OH valley and into
New England through Friday. The ridge will build southward into NC
through Friday as well. Latest model runs indicate strong CAD
setting up for Friday Night into Saturday. Temperatures Thursday and
Friday will be well below normal (highs in the upper 30s to low 40s
and lows in the 20s). A low pressure system will make its way
through the heart of the country Friday Night and Saturday with the
associated cold front moving into Central NC Saturday Night or
Sunday. Ahead of the frontal passage, strong southwest flow will
result in a gradual increase in temperatures, particularly across
the southeast, as the front approaches. Although the GFS is a bit
slower in timing of the front, it and the ECMWF appear quite
similar. The big difference between the two is with respect to
precipitation. The GFS is dry through Friday Night, with rain moving
in as the temperature rises in response to strong southwest flow
into the area. The ECMWF is quite a bit wetter during that time and
would likely result in p-type issues Friday Night/early Saturday.
Will lean heavily toward the GFS for now and keep the forecast dry
until temps rise above freezing on Saturday, however some form of
wintry precipitation cannot be completely ruled out. Both models
generate a good bit of pre-frontal convection over the area on
Sunday, so will continue to monitor that, in addition to the precip
issues Friday Night.


As of 105 AM Sunday...

High confidence that VFR parameters will persist across central NC
through 18Z today as high pressure at the surface will be drifting
offshore. The return flow on the backside of the retreating high
will advect low level moisture into central NC this afternoon
through tonight, resulting in lowering ceilings into the MVFR/IFR
categories by this evening. In addition, expect patches of light
rain and/or drizzle to develop in vicinity of KFAY late this
afternoon, and elsewhere tonight. Also, an increasing low level jet
may produce marginal low level wind shear parameters overnight into
early Monday morning, mainly in the form of speed shear, as wind
speed 35-40kts probable between 1500-2000ft.

Mostly sub VFR conditions expected Monday through Monday night as a
cold front drifts slowly east across the region. A brief intrusion
of drier air may lead to a period of VFR conditions, mainly across
the northern terminals, on Tuesday. Another round of sub VFR
ceilings anticipated Tuesday night through Wednesday night with the
approach/passage of another low pressure system. VFR conditions
expected by Thursday as cold high pressure builds into central NC.





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