Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 061941

Area Forecast Discussion
National Weather Service Raleigh NC
235 PM EST Tue Dec 6 2016

Cool and wet conditions are expected today, ahead of a Miller B low
pressure system and associated cold air damming. An arctic cold
front will approach the area Wednesday night and cross the Carolinas
on Thursday.


As of 935 am Tuesday...

Spotty light rain continues this morning ahead of a slowly shearing
upper wave lifting out of the Lower Mississippi Valley and a Miller
B low transitioning across the locked in CAD airmass.  Radar returns
are still pretty unimpressive and have really fallen off over
Upstate SC as the dry slot is surging north.  Expect this trend of
spotty rain diminishing from southwest to northeast to generally
continue this morning. There is an area of convective elements to
watch upstream over northern GA, where dry air aloft looks to create
a little potential instability (100-200 J/KG MUCAPE) between 800mb
and 600mb, per RAP soundings, which may be enough to enhance or
fill in precipitation as the upper lifts across the area through
early afternoon.  Any instability will remain elevated above the
strong cold dome, with guidance keeping the warm sector well
southeast near the NC/SC coastal areas.

Changes to the forecast have been relatively minor; mainly tweaks to
POPs in the next few hours and reductions in QPF, with a focus of
best rain rates in the 15Z to 21Z period.  Temps will hold
relatively steady in the 40s areawide, possibly rising a few degrees
in the southeast as the surface low passes by this afternoon. -BS

Low-level moisture could be slow to mix out tonight. However, in
areas that do clear out, wet soils could result in some areas of
fog, potentially dense in spots. Lows in the upper 30s to lower 40s.


.SHORT TERM /Thursday and Thursday Night/
...As of 230 PM Tuesday...

The leading edge of an arctic cold front diving southeast through
the TN/OH valley begins to ooze across the Appalachians by 12Z
Thursday morning. The front will be progressing slowly as it aligns
with predominantly westerly flow, which will also serve to limit
moisture advection available for precip. Forcing aloft will be
limited as well in relatively broad cyclonic flow and channeled
vorticity, with models squeezing out less than a tenth of an inch of
rain with the system. As such will maintain only a small chance for
PoPs as the front moves through during the day. Skies should be
clearing from the northwest by mid to late afternoon. Cold air
advection will be underway for much of the day across the northern
tier with northwest winds 10 to 15 mph gusting 20 mph. This produces
a low level thickness fall of ~20 meters across the north...
indicative of 5-6 degrees cooler temps...resulting in highs from the
low 50s across the north to upper 50s in the south. Pressure
gradient relaxes overnight, but not enough to decouple and fully
realize the airmass` potential for cooling. Mins should bottom out
in the mid to upper 20s.


.LONG TERM /Friday through Tuesday/...
As of 230 PM Tuesday...

Expect clear, cold, and brisk conditions on Friday with highs in
the upper 30s to lower 40s with a northwest breeze gusting to 20 mph.
Radiational conditions are more ideal Friday night as an arctic high
settles over the region. Mins will fall into the upper teens across
the north to lower 20s in the south Saturday morning. Chilly airmass
will benefit only marginally from strong but low-angle insolation on
Saturday...with highs ranging from 40 to 45. Return flow will ensue
on Sunday, with modest warmup and initiation of some moisture
advection and cloudiness. Highs will edge to the mid and upper 40s
on Sunday after morning mins mostly in the mid 20s.

Our next frontal passage on Monday will be better defined/cleaner.
With the mid level short wave and parent surface low well north of
the area we maintain near zonal flow behind the front to inhibit
cold air advection. Does look like a respectable low level jet and
convergence zone will accompany the front resulting in chance PoPs
Sunday night through Monday afternoon with clearing by Tuesday.
Highs in the 50s both Monday and Tuesday.


As of 1245 PM TUESDAY...

24-Hour TAF period: Widespread light rain will give way to drizzle
and fog this afternoon as low pressure along the coast lifts north
and drier air filters in from the west and southwest. The drying
will be initially at the mid levels, and IFR/LIFR ceilings and
visibility in fog will linger through most of the overnight. Should
see conditions gradually improve in the west after 06Z as a second
low over the Tennessee Valley weakens and lifts into the Ohio Valley
after midnight, with ensuing westerly flow drying out the low
levels. The drying trend will reach the eastern TAF sites towards
sunrise, with VFR conditions prevailing area-wide after around 12Z
tomorrow morning.

Looking ahead: VFR conditions will return on Wednesday. However, sub-
VFR ceilings could return Wednesday night and linger into the day on
Thursday ahead of an arctic cold front moving through the area.
High pressure building in behind the front by Thursday night will
produce VFR conditions through Sunday.





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