Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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478
FXUS62 KRAH 121811
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
111 PM EST Tue Dec 12 2017

.SYNOPSIS...
A pair of dry cold fronts will cross central North Carolina today.
Cold high pressure will build in tonight through Wednesday. A fast
moving upper level disturbance will move through the region
Wednesday night.

&&

.NEAR TERM /today through tonight/...
As of 1022 AM Tuesday...

As of 10 AM...the initial cold front was analyzed in sfc obs moving
across the Triad. It will continue moving east and will cross the
rest of our CWA by early afternoon.  As the upper BL and mid levels
cool, we`re likely to see some shallow cu develop, but given the
overall dry airmass preceding it, we are expecting the weather to
stay dry today.  The midlevel trough axis, and secondary sfc front
assoc with the more potent surge of colder air, is now crossing the
Ohio River Valley. The secondary front, ushering in the surge of
colder air, is expected to arrive this evening.  In terms of temps
the rest of today... behind the first front temps may rise only a
few more degrees (highs in the upper 40s), while east of the front
we should see temps climb into the lower-mid 50s for highs today. No
signif changes with the morning update.

Prev disc as of 255 AM Tuesday...High and mid clouds have begun
streaming SW to NE across the CWA on schedule, along a mid level
speed max ahead of the approaching trough and initial surface front.
This mid level jet and leading cold front will shift east off the
coast by mid afternoon, leading to a decrease in mid/high clouds but
an increase in flat cu with the onset of deep mixing. Overall, skies
should average out partly to mostly cloudy. Post-front surface winds
will veer to WNW and NW and surge to 12-16 kts with gusts to 22-28
kts, and perhaps periodically higher. A secondary uptick in winds
will arrive with the next reinforcing cold front late in the day,
which will bring the substantially colder air. With the mountains
serving to delay the onset of strong cold air advection, high temps
should still be within a couple degrees of normal, from the upper
40s to near 50 NW to the mid-upper 50s SE. Much colder and drier air
will start to pour in by mid to late afternoon, with clearing skies
toward nightfall. Dewpoints will fall through the 20s and teens
overnight, as temps bottom out in the 20-26 range, with perhaps some
upper teens in outlying areas. We will stay mixed through the night,
so expect sustained winds to stay up around 7-14 kts overnight, with
sporadic gusts to 15-22 kts possible, mainly across the N and E.
Morning wind chills should drop to 10-20 degrees. -GIH

&&

.SHORT TERM /Wednesday through Wednesday night/...
As of 320 AM Tuesday...

A chilly day with thicknesses starting out 45-55 m below normal,
suggesting highs from the upper 40s to mid 40s N to S despite mostly
sunny skies. A fast moving clipper that will be dropping over the
Midwest early Wed will dive through the Mid Atlantic region Wed
evening, followed immediately by a second potent wave passing by
further north late Wed night. The initial and more southern-track
wave will bring a batch of scattered to broken mid clouds across the
area Wed evening, with the greatest cloud cover across the northern
sections of NC. This moisture aloft may be deep enough and the
attending DPVA strong enough to generate some precip, although the
subcloud layer should be too dry for much (if any) of this to reach
the ground, given the expected large surface dewpoint depression.
Have opted to mention a brief period of possible flurries across the
far N, between Roxboro and Roanoke Rapids, Wed evening. Skies should
trend back to fair after midnight as the wave departs. Lows from the
mid 20s to around 30. -GIH

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 300 AM Tuesday...

Predominantly zonal flow aloft mid week will slowly transition to
weak troughing in the east by mid day Friday. Several waves of
energy will rotate along the trough axis out of the upper mid west
during the long term period. The first system should pass just to
our north Thursday morning, introducing only a short period of
enhanced cloud cover to the northern piedmont counties. A second,
much stronger wave, will rotate around a digging trough axis Friday
night into Saturday, bringing a surge of much cooler temperatures
and enhanced POPs to the area. This wave looks to initiate the
frontogenesis process just off the VA/NC coast, keeping most of the
precipitation offshore. This trend will be worth keeping an eye on
though, as faster development could see POPs sneak a bit further
west into our coastal plain counties. A brief period of high
pressure builds in from the south Saturday into early Sunday,
allowing southerly to southwesterly flow, along with near normal
temperatures to reestablish ahead of an approaching cold front set
to move through early Monday.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
As of 111 PM Tuesday...

The main concern for the 24 hour TAF period will be gusty winds
behind a cold front that is moving across central NC attm.  In the
wake of the fropa, winds will become NW and increase to 15-20kt with
gusts up to 30kt at times.  Winds will finally begin to diminish
after 13/06z, but remaining from the W around 10kt.  Otherwise, VFR
conditions are expected with dry wx assoc with the fropa and mainly
high clouds passing across the area.  Skies will clear out as well
after 13/00z.

After 13/18z:  Westerly flow and lack of any signif moisture
advection into our area should result in VFR conditions through the
rest of the period.

&&

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

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...np/Hartfield
SHORT TERM...Hartfield
LONG TERM...JJM
AVIATION...np



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