-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 200740
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
340 AM EDT Fri Oct 20 2017

.SYNOPSIS...
A ridge of high pressure will extend across the eastern United
States through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 940 PM Thursday...

Another night of calm winds and clear skies over central North
Carolina. A slightly modified airmass that added a few degrees to
our high temperatures today will do the same for the lows overnight.
Expect most locations to bottom out in the 40s with some scattered
upper 30s sprinkled in.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 245 PM Thursday...

The strengthening high aloft and associated subsidence coupled with
the sfc ridge will maintain a dry atmosphere across central NC
Friday and Friday night. This dry air will support diurnal
temperature swings of 30-35 degrees. The warming aloft in
conjunction with the ridge at the surface will translate to mild
afternoon temperatures in the mid-upper 70s, with a few locations
across the far south possibly reaching 80 degrees.

While temperatures will be in the 70s late Friday afternoon, the dry
air in place will permit temperatures to cool into the 60s early
Friday evening, and solidly in the 50s by midnight. Minimum
temperatures in the upper 40s to around 50 should be common.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
As of 340 AM Friday...

The ridge over the southeast will move east Sunday as a trough over
the Midwest and Mississippi Valley deepens. We`ll have another nice
day Sunday to round out the weekend`s weather, featuring partly
cloudy skies (mainly high clouds) and return flow resulting in warm
temps with highs in the upper 70s to around 80.

Monday will feature increasing and lowering clouds as a closed
trough ahead of the upstream longwave trough moves across the TN
Valley and moist S/SW flow aloft increases over our area ahead of
this trough.

GFS and ECMWF solutions diverge Monday night and Tuesday. The ECMWF
shows the lead short wave getting absorbed into the larger longwave
trough and ejected to the northeast 12+ hours faster than the GFS.
The ECMWF solution would result in a band of showers quickly moving
across our CWA early Tuesday morning before exiting to our east by
noon Tuesday.  The slower GFS brings multiple bands of showers
across our area Monday night through about mid-day Tuesday, with
perhaps a brief opportunity for a few gusty tstms during the late
morning Tuesday before the showers exit to our east.  This thanks to
the proximity of the passing mid-level trough and subsequent
stronger wind fields and resultant shear; however GFS forecast
sounding show limited instability, thus perhaps a high-shear/low-
CAPE setup with isolated strong wind gusts the main concern if any
severe weather threat materializes. Finally, there will be another
brief opportunity for a few showers late-day Tuesday with the
passage of the sfc cold front.  Coverage and intensity should be
limited though, thanks to the earlier passage of the lead short wave
and subsidence and mid-level drying in its wake.

Tuesday night we`ll drying and strong CAA commence in the wake of
the cold front, with additional CAA behind the passage of the
longwave trough axis which is progged to move across our CWA late
Wednesday.  The main weather story for Wednesday and Thursday will
be the chilly temps, with highs only in the low 60s both days, and
potential for lows dipping down into the upper 30s in some spots
Thursday morning.
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&&

.AVIATION /06Z Friday through Tuesday/...
As of 155 AM Friday...

High pressure building east across the middle Atlantic states, and
associated strong radiational cooling and risk of "persistence"
(relative to similar conditions 24 hrs ago) radiation fog at RWI
this morning, will otherwise result in mainly clear, VFR conditions
with light and variable to light n/nely surface winds, through the
TAF period.

Outlook: Continued persistence radiation fog will be possible mainly
at RWI each morning through the weekend, followed by a higher
probability of more-widespread sub-VFR conditions in stratus and
fog, in increasingly moist east to southeasterly low level flow, Sun
night-Mon morning. An approaching frontal system will then result in
a good chance of sub-VFR conditions, showers and storms, and
strong/shifting winds with height late Mon-Tue.

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...Ellis
SHORT TERM...WSS
LONG TERM...np
AVIATION...MWS