Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 072019
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
319 PM EST Wed Dec 7 2016

.SYNOPSIS...
Weak high pressure over the Carolinas will weaken and shift east
tonight today. An arctic cold front will move through the area
Thursday, followed by an expansive arctic high for the weekend.

&&

.NEAR TERM /THROUGH THURSDAY MORNING/...
As of 320 PM Wednesday...

Clear skies across most of central NC this afternoon, with a patch
of cu in the northern coastal plain and some stratocu, remnants
of stratus/fog this morning, drifting east across the southern
Piedmont. There is significantly more moisture to our south
pooling along a stalled boundary near the Savannah River Basin,
which is connected to a weak surface trough over the western
Piedmont.

Weak southerly warm advection is forecast develop tonight ahead
of the cold front, or leading edge of the arctic high over the
Midwest, though surface winds remain very light. Moisture below a
subsidence inversion near 850mb is expected to return north and
lead to stratus overnight, though guidance is in very poor
agreement on how low the stratus will be and whether or not there
will be any light rain or drizzle. The NAM and GFS are dry and
keep the moisture mostly confined to the base of the inversion.
The HRRR, while dry, slams stratus and/or fog across the area (fog
being more likely north and east). The WRF NMM and ARW actually
show some light simulated radar returns spread in from the
southwest as early as 06z, though this may be more indicative of
stratus than actually precip. The HRRR appears to be too moist in
the lowest levels, based on observed ceilings surrounding central
NC this afternoon, so it may be overdone in the amount of low
clouds tonight, and the answer may actually be in between the
larger scale models and the hires guidance. Thus, the potential
for some patchy light rain or drizzle late isn`t ruled out. Skies
should be overcast by Thursday morning either way, and lows will
be in the upper 30s to mid 40s.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 320 PM Wednesday...

Any light warm advection driven precip Thursday morning will
shift east and may consolidate or become a little more showery as
fgen strengthens and the cold front sweeps across the area.
Northwest flow and increasing cold advection will clear skies by
midday to early afternoon, though the brunt of the cold advection
will likely be delayed until later Thursday night. Highs should
reach the low to mid 50s.

Strong CAA will continue Thursday as expansive Arctic high begins
east into the region. Overnight will fall into the mid 20s to
upper 20s with a steady wind near 10mph and wind chills in the
teens.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 245 PM Wednesday...

Cold air tap will be turned on Thu night as an Arctic ridge builds
south and east out of the central plains. The leading cold front
will be offshore with clear skies and dew points falling into the
teens on Friday. It will be brisk, with northwest winds gusting up
to 20 mph coincident with highs struggling to reach the lower 40s,
with upper 30s more likely across the northwest. Associated wind
chills will top out in the upper 30s in the afternoon. Near ideal
radiational conditions are expected Friday night, and we will see
our coldest temperatures thus far this season, with most areas
falling to the low 20s by sunrise Saturday, and some outlying areas
will see mins bottom out in the upper teens. The high pressure will
be overhead and the cold airmass in place will be hard to warm up
due to the low sun angle, and highs Saturday will again be mostly in
the lower 40s.

The surface high will be edging off the mid Atlantic on Sunday, and
ensuing return flow will begin to moderate temperatures as well as
spread moisture progressively north and west into the area during
the late day. Should see increasing clouds throughout the day and
maybe some patchy light showers in the west by evening, with chance
PoPs across the entire area after midnight. Highs will edge into the
mid to upper 40s.

There are significant timing and feature detail inconsistencies
concerning our next system approaching from the west early in the
work week, with a weaker but faster frontal passage Sunday night per
GFS vs. a stronger, sharper frontal passage later Monday per the
ECMWF. As such, will maintain chance PoPs from Sunday night through
Monday afternoon, with dry weather and near-seasonable temperatures
Tuesday into Wednesday in faster zonal flow. Highs Monday through
Wednesday will be mostly in the 50s with morning lows in the 30s.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
As of 115 PM WEDNESDAY...

Clear skies and VFR through early evening.  The main forecast issue
overnight will how quickly sub-VFR conditions return, and given wide
ranging solution from our models, this is a rather low confidence
forecast.  Brief clearing this morning has resulted in clear skies
and VFR this afternoon, but there is ample low-level moisture south
and east of the area to support the return of low clouds tonight as
weak warm advection develops ahead of a cold front in the Midwest.
There are starkS differences between the NAM/GFS and RAP/HRRR, with
the RAP and HRRR indicating IFR and LIFR stratus as early as 03Z.
However, with light wind, its possible some fog may develop, and
this would make more sense around KRWI.  In general, expect A mix of
LIFR, IFR, and MVFR conditions areawide by 06-08Z, with some patchy
light rain also possible.

The aforementioned cold front will cross the area between 12Z and
18Z Thursday, clearing out the low clouds and possibly consolidated
the precip into a few showers that will exit to the east by midday.
West-northwest winds will increase to 8-12kt, with gusts into the
upper teens during the afternoon.

Outlook: VFR conditions are expected through the weekend.  The next
chance of sub-VFR conditions will be early next week.

&&

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

&&

$$
SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...SMITH
LONG TERM...MLM
AVIATION...SMITH


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