Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 181556
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1055 AM EST Sat Nov 18 2017

.SYNOPSIS...
A cold front will sweep east across the area tonight. Chilly high
pressure will return for Sunday through Tuesday.

&&

.NEAR TERM /THIS AFTERNOON AND TONIGHT/...
As of 1055 AM Saturday...

A breezy and warm afternoon...

High pressure continued to move east and offshore late morning. A
return flow from the southwest was overspreading NC. SW winds had
already increased to 15 mph in the western Piedmont. As the cold
front, seen on visible satellite and radar moving rapidly east
toward the Mississippi River late morning, continues to approach
this afternoon, winds will increase to 15-20 mph with gusts to 30
mph. These breezy conditions will continue well into the evening
hours as the line of showers (prefrontal) will hold off until well
after dark in the west, and late night in the east. Highs this
afternoon are expected to reach the mid to upper 60s. Readings near
70 will occur in the Sandhills and SE Coastal Plain regions. -PWB

...Showers hold off until tonight...

The aforementioned and quickly-moving band of showers is expected
ahead of the cold front, which is
scheduled to arrive across central NC 07z-12z.

Forcing for ascent will be on the upswing this evening/tonight with
a 130+ kt upper jet inducing improving upper divergence and weak
DPVA aloft accompanying broad mid level trough passage (although the
best DPVA heads to our north), but the overall lift will be modest,
and CAPE will be absent. High PW advects in ahead of the front, with
values well over 200% of normal in a narrow band which crosses the
area tonight, and this combined with the quick shot of lift should
bring about fairly high rain chances (mainly over the NW and N CWA)
but with low QPF (a tenth of an inch or less) given the fast
movement. SW flow will ramp back up after nightfall and remain
strong and gusty overnight, as 925 mb winds strengthen to 40-50 kts,
although not all of this will be realized at the surface, given the
low level buoyancy ahead of the front. It is worth noting, though,
that just behind the front, where we`ll still be well-mixed but with
low level subsidence taking place, and with 925 mb winds still
rather stout post-front at around 30 kts, we could see a period of
higher gusts from the NW just behind the front. The coolest air will
be delayed until after daybreak, and will stick with milder lows,
ranging from the mid 40s NW to the mid 50s SE. -GIH

&&

.SHORT TERM /Sunday through Sunday night/...
As of 245 AM Saturday...

Skies will be clearing early Sun morning, with the entire area
expected to be clear by 15z as surface high pressure builds in from
the west in conjunction with a trend to rising heights aloft behind
the exiting mid level trough axis. The tight MSLP gradient between
the departing cold front and incoming high will result in blustery
surface winds from the NW, although not as strong as today`s and
tonight`s SW winds. Expect sustained winds of 9-14 kts with gusts to
15-20 kts. Thicknesses should drop to around 20 m below normal, so
despite the plentiful sunshine, highs will be cool, 53-62. We may
see a brief resurgence in wind gusts Sun evening as one last mid
level vorticity lobe drops through the region (strongest across our
north and NE into VA), causing 925 mb winds to rebound to 25-35 kts
especially over the NE CWA. Otherwise, though, winds will be
diminishing Sun evening and night. Lows 27-32 with decent
radiational cooling under clear skies. -GIH

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 325 AM Saturday...

The first portion of the long term forecast remains fairly unchanged
as there will be a warming trend and dry weather through Tuesday.
Expect highs in the low to mid 50s Monday rising into the upper 50s
to low 60s on Tuesday as high pressure moves off the east coast and
southerly return flow overspreads central NC. Tuesday night expect a
slight chance of showers as an upper trough crosses the area. At
this time the ECMWF representation of this feature is deeper and
more robust and slightly negatively tilted brining the chance for
some more dynamics to at least the eastern part of the forecast area
as a low pressure system moves northeastward offshore of the
Carolinas. A weaker version of both these features in the GFS keeps
the forecast dry during this period. Both models keep Wednesday dry
regardless of Tuesday night scenarios. Warm again on Wednesday with
highs in the upper 50s to mid 60s.

The forecast really diverges and confidence is very low from
Thanksgiving Day onward. Major differences in the handling of a late
week low pressure system moving out of the Gulf of Mexico and across
the Florida Peninsula have the forecast in flux for Thursday. The
GFS is showing a cutoff upper low driving the development of the
surface low which is much stronger and thus drives much more
moisture into the area for Thursday. This upper feature has not yet
shown up in the ECMWF version of the forecast and thus the surface
low never develops and stays well offshore for Thursday. This is
more consistent with previous forecasts and at this point I am
highly suspect of the GFS forecast. As a compromise, have introduced
some slight chance pops in the forecast for Thursday and Friday but
did not feel comfortable going any higher than that until more
consistency in the solutions is achieved. Temperatures will be
cooler Thursday and Friday regardless. Expect low to mid 50s in most
locations.

&&

.AVIATION /12Z Saturday through Wednesday/...
As of 645 AM Saturday...

VFR conditions will dominate at all central NC sites today, with the
exception of the potential for a few hours of MVFR cigs 14z-17z this
morning at INT/GSO. The bigger story will be the increasing winds
from the SW this morning, peaking this afternoon with periodic gusts
to 20-25 kts. There is a slight chance of low level wind shear this
morning near INT as a 35-40 kt jet from the SW near 2000 ft AGL.
LLWS chances increase after 00z tonight as winds restrengthen from
the SW around 2000 ft AGL to 40-50 kts. A few hours of MVFR to IFR
conditions in showers are expected late tonight (after 05z) as the
cold front crosses the forecast area. VFR conditions will return
after 08z at INT/GSO, after 10z at RDU, and after 11z at RWI/FAY,
all with a drastic shift in winds from SW to NW as the front moves
through.

Looking beyond 12z Sun:  VFR conditions are likely Sunday through
Tuesday as high pressure moves over the area. A storm system will
develop over the Gulf Coast and approach our area Tue night/Wed,
bringing possible sub-VFR conditions. -GIH

&&

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

&&

$$
SYNOPSIS...Hartfield/Badgett
NEAR TERM...Hartfield/Badgett
SHORT TERM...Hartfield
LONG TERM...Ellis
AVIATION...Hartfield



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