Area Forecast Discussion
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FXUS62 KRAH 230147
Area Forecast Discussion
National Weather Service Raleigh NC
945 PM EDT Wed Mar 22 2017
Cold high pressure will build into the region from the north
tonight through Thursday. Warmer conditions will arrive
this weekend as the high shifts offshore into the the Atlantic.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 945 PM Wednesday...
Forecast is on track. The opaque high clouds which covered the
southern half of the forecast area for much of the afternoon have
been shunted southward with the push of deep dry air into the area.
Skies should remain clear for the next several hours, although high
level moisture to our NW (evident on upstream soundings) should lead
to increasing high clouds late, and these may be orographically
enhanced yielding thicker cloud cover over the western CWA. Temps
are running a degree or two warmer than the forecast pace, although
as northeasterly surface winds die off later tonight, readings
should plunge given the low dewpoints and expectation of good
radiational cooling. Lows in the upper 20s to lower 30s. -GIH
Earlier discussion from 250 pm: An upper level ridge over the
central U.S. and a l/w trough along the eastern seaboard will funnel
cold dry air into central NC tonight. This drier air already made
evident by sfc dewpoints in the teens across the western Piedmont at
18Z. This drier air will continue to spread south and east through
Orographic induced high clouds will slowly fade/dissipate through
early evening as the atmosphere aloft dries out and the winds field
weakens. Sfc winds will remain 4-8kts after sunset, though should
decouple after midnight. With the cold dry air mass in place and
near calm sfc winds, should see temperatures drop into the upper 20s-
lower 30s overnight. Patchy frost possible in the well sheltered
areas though most places will see little if any frost due to the dry
low level air mass.
-- End Changed Discussion --
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 250 PM WEDNESDAY...
Thursday, 850mb thermal trough overhead signals a day of well below
normal temperatures. While skies will be sunny, the cold dry air
mass deposited by the high pressure system will yield max temps in
the low-mid 50s, a solid 10-12 degrees below normal.
Thursday night, l/w trough will lift to the ne while the upper ridge
will extend across our region. This set-up will maintain mostly
clear skies and chilly overnight temperatures. Under clear skies and
a light wind regime, temperatures will quickly fall after sunset
with overnight temperatures generally near 30 to the lower 30s with
the coldest temperatures across the far northeast Piedmont and the
northern coastal plain.
.LONG TERM /Friday through Wednesday/...
As of 305 PM Wednesday...
Expect above normal temps and below normal precip chances at least
into Tuesday, with high confidence. Divergence in model
solutions beyond this time leads to increased uncertainty Tue
Fri/Sat: Deep troughing featuring a closed low over SE CO early Fri
will continue to build downstream ridging over the Gulf into the Mid
South and Southeast heading into the weekend as it tracks slowly
eastward into the S Plains, while surface high pressure along the
East Coast shifts east out over the ocean. A batch of elevated
moisture now over the N/C Plains is poised to ride atop the ridge
Fri, bringing some mid and high cloudiness, but otherwise the column
will be sufficiently dry and stable for a precip-free forecast and
partly to mostly sunny skies, dominated by scattered to broken flat
cumulus, within light but long-fetch onshore-directed low level
Atlantic flow. Thicknesses start out a bit below normal Fri then
rise through Fri/Sat, indicating highs of 64-71 Fri and 71-76 Sat,
with lows of 46-50.
Sat night-Sun night: The aforementioned deep low will move from the
mid Miss Valley Sat evening northeastward with a negative tilt as is
opens up over the Great Lakes region Sun night. This system will be
reflected at the surface as an occluding front passing to our NW,
dragging only a weak trough into N/W NC, so we`ll stay in the warm
sector of this system as weak ridging begins to build in anew from
the SW by Sun night. Low level moisture transport will steadily
increase through this period, as PW surges from the SW to over 1
inch, focusing on the W CWA Sun morning before shifting east to
central and E NC late Sun through Sun night, corresponding with
passage of the broadening mid level trough axis and weak DPVA, as
well as a zone of enhanced upper divergence and erosion of the 850-
700 mb cap. With minor changes to delay onset, will keep the trend
to good chance pops Sun morning, spreading east through Sun night,
with partly to mostly cloudy skies. Lows in the low-mid 50s, highs
70-78 Sun, followed by lows in the mid-upper 50s Sun night.
Mon-Wed: The overall pattern becomes increasingly active, wavy, and
progressive next week. The open wave will move ENE through the
Northeast states then offshore to the ESE, as a mostly phased trough
shifts eastward through the E CONUS. The GFS greatly amplifies the
northern portion of this trough over the NE on Wed, while the ECMWF
is weaker with a later amplification over the NW Atlantic late in
the week and, as a result, it builds ridging back into the Gulf
States and Southeast from the west on Wed. The result is a cold
frontal passage and cooler temps Wed with the GFS, and much warmer
temps Wed with the ECMWF. Given the dominance of the southern
stream, with less polar air injection through mid week, will lean
toward the ECMWF and keep temps above normal. Will have low chance
pops over the SE on Mon near the sea breeze, then better chances
areawide Tue as the trough axis moves through. Dry/warm Wed. -GIH
.AVIATION /00Z Thursday through Monday/...
As of 755 PM Wednesday...
24 Hour TAF Period: Very high confidence of VFR conditions through
the TAF period with winds out of the northeast for much of the
period, potentially shifting to east southeasterly very late in the
forecast period. Skies will remain mostly clear through the period
and fog or low stratus will not be a problem overnight.
Long term: Mainly VFR conditions until late in the weekend when the
next storm system approaches from the west bringing a chance for
rain and adverse aviation conditions.