Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 210541

Area Forecast Discussion
National Weather Service Raleigh NC
1240 AM EST Mon Jan 21 2019

Arctic high pressure will build into central NC today, and drift
overhead tonight through early Tuesday. This high will drift
offshore Tuesday night, permitting a slightly warmer air mass to
overspread the region. An approaching area of low pressure will
cause unsettled weather conditions Wednesday into Thursday.


As of 920 PM Sunday...

Blustery NW winds continue this evening and have even picked up in
the NW again, gusting to 30 mph in the Triad region. Actual
temperatures at mid-evening ranged from the mid 20s in the Triad
into the mid 30s from Fayetteville to Goldsboro. Wind chill readings
were already in the teens in the Triad.

There may be a few cirrus at times overnight, but the conditions for
Appalachian lee cirrus continue more favorable to our north
overnight. Regardless, strong CAA will lead the way in taking the
temperatures into the teens over the Piedmont, ranging into the lower
20s SE.


As of 220 PM Sunday...

We may see lingering breezes in the E on Mon as the mid level low
crosses New England, but the MSLP gradient will quickly slacken as
the surface high center drifts across the Great Lakes/Ohio Valley.
The low level thermal trough extending down into NC early Mon will
shift E, allowing for some modification through the day, but after
morning thicknesses 70-80 m below normal and continuous CAA, temps
should still struggle to the upper 20s to mid 30s. Mon night should
be generally clear, although passage of a warm front aloft (on the
NW side of the incoming longwave ridge) and associated shallow
upglide at 290-295K may bring a few mid clouds overnight. But this
would be insufficient to significantly impede radiational cooling as
surface winds diminish with the surface ridge settling overhead, and
lows should drop well down into the teens (and some single digits
near the VA border are certainly possible). The potential for patchy
mid clouds will continue until mid morning Tue, then we should see
clear to fair skies with an increase in high clouds late as the
ridge axis shifts overhead and mid level WAA moves in, with the
surface high sliding E off the Mid Atlantic coast. Expect highs in
the upper 30s to mid 40s. -GIH


As of 240 PM Sunday...

Tue night through Thu night: With the surface high pushing offshore,
ensuing onshore-directed southeasterly flow will introduce low level
moisture and spotty showers to SE sections starting Tue night.
Meanwhile, our next storm system, a deep trough extending from the
Upper Midwest through the central Plains to W TX/N Mexico, will ease
eastward with a positive tilt, yielding increasing and deepening SW
flow and WAA, primarily below 700 mb, on its approach. Rain chances
will start ramping up in the W late Tue night with strengthening low
level overrunning. Given predawn temps near or just under 0C, there
is a chance that this could begin as a little freezing drizzle in
parts of the NW Piedmont, but with low confidence in such details,
will leave precip as all liquid for now. Lows 28-34. As the trough
and its associated cold front draw closer, strengthening low level
WAA is projected to overtake the remaining cool air by the end of
Wed, placing all of central NC solidly in the warm sector. While
this is certain possible, given that the surface high will be along-
latitude and in an unfavorable position to keep the cool stable air
locked in E of the mountains, there may be enough of a residual cool
pool in the far W Piedmont to hold temps down there, especially with
early-day precip to encourage stability. Expect highs Wed in the low-
mid 50s NW and upper 50s to mid 60s elsewhere, with a chance of rain
spreading E over the CWA. Shower chances should increase by Wed
evening with the approaching deep/warm conveyor, and we still expect
peak pops between 9 pm Wed evening and noon Thu. Lows in the upper
40s NW to upper 50s SE Wed night, and this may even be too cool.
Model still have some timing differences (ECMWF slightly slower than
the GFS), but they generally show precip ending and cold front
passage Thu morning with some initial drying and CAA as the
dampening mid level trough axis shifts to our NW and N during Thu.
Highs just a category or two above lows, 53-67, likely steady or
falling in the afternoon. Colder air will keep filtering in Thu
night, although passage of a mid level polar wave within the trough
base may bring some mid clouds overnight into Fri morning, and
surface winds should stay up, tempering the fall in temps. Lows in
the upper 20s to mid 30s.

Fri through Sun: With chilly surface high pressure building in,
expect below normal temps Fri/Sat. Models show another mid level
speed max moving quickly through the area Fri, and this could bring
a round of enhanced clouds, but otherwise skies should be fair. As
the large mid level trough settles over much of central and eastern
NOAM, dry/cool conditions should continue into Sun, but forecast
confidence diminishes by that time as potentially prominent waves
rounding the trough base could prompt clouds and possibly some light
precip over NC by late in the weekend. Expect highs in the 40s Fri
and upper 30s to mid 40s Sat/Sun. -GIH


As of 1240 AM Monday...

There is a high probability that VFR parameters will occur across
central NC through 12Z Tuesday. Sfc winds will remain blustery
overnight through early this afternoon with gusts 20-25kts common.
Sfc winds will subside to less than 10kts prior to 00Z Tuesday.

A slightly warmer and more moist air mass will advect into central
NC from the south late Tuesday night. This will likely result in the
development of a low stratus deck, primarily over the western
Piedmont, after 06Z Wednesday through Wednesday morning. If lift is
strong enough and the moisture deep enough patchy light precip may
occur close to daybreak near or south of the Triad terminals. With
sfc temperatures hovering near or just below freezing, spotty light
freezing rain or freezing drizzle may pose a threat.

An approaching low pressure system will bring unsettled weather
conditions to central NC Wednesday through Thursday. This will
likely result in sub VFR ceilings and areas of rain across central
NC. Improving aviation parameters anticipated for the end of the
work week.




NEAR TERM...Badgett/Ellis
SHORT TERM...Hartfield
LONG TERM...Hartfield
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