Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 220134

Area Forecast Discussion
National Weather Service Raleigh NC
934 PM EDT Sun Oct 21 2018

Chilly high pressure will build across the middle Atlantic states
through early Monday, then offshore. A dry cold front will cross the
area Tuesday night, followed by another high pressure system that
will build into the region on Wednesday.


As of 930 AM Sunday...

Surface high pressure is currently located over central Kentucky
this evening with winds decoupling across the forecast area.
Over the western Piedmont multiple temperature readings near 40
degrees exist already with Person County even in the mid 30s.
Low level thicknesses are forecast to be around 1325 m and with
effective radiational cooling think temperatures will fall below
freezing across the west, in particular rural areas. Due to the
above have issued a Freeze Warning for the western Piedmont.
Have kept the frost warning as is for now with the Coastal Plain
being the last location to decouple.

Prev Discussion->
High pressure continues to pull east this afternoon, and is
currently located over the Missouri/ Kentucky border. This is
thanks to the upper level trough axis exiting the region to the
east. Winds have quickly fallen off this afternoon as the
pressure gradient has relaxed. Overnight tonight into Monday
morning surface high pressure will pull east and settle
overhead. Have decided to keep the frost advisory as is for this
issuance as high pressure will likely not move far enough east
fast enough allowing light winds to remain over the Coastal
Plain. The other concern was whether a freeze warning would be
needed across our western zones. Winds look to decouple here by
midnight and with clear skies efficient radiational cooling
looks likely. Guidance has kept lows above freezing with some
patchy 32 degrees in the rural western zones. The deciding
factor to hold against the freeze warning was a slow warming in
the 850 mb temperatures. This slow warming is supported with the
850 mb 12z hand analysis which shows the trough axis already
offshore. A slow warming in the low level thermal profiles were
then seen towards Missouri and Kansas. Either way, frost will be
possible across most of central North Carolina tonight.


As of 400 PM Sunday...

Monday morning, patches to areas of frost will slowly give way
to warming temperatures as sunrise occurs. Surface high pressure
will remain centered overhead, but will slowly loose cohesion as
the ageostrophic convergence pulls east. 850 mb temperatures
will also moderate allowing high temperatures to rise into the
60s for all of central North Carolina. Clear skies and no
precipitation is forecast Monday given the extremely dry air
mass (PWATs around 0.4").


As of 215 PM Sunday...

Through Thursday: Cool, dry weather will continue through mid-week.
The surface high will continue to ridge westward into the Carolinas.
An upper level shortwave trough is expected to pass over the region
on Tuesday/Tuesday night, but the only impact expected is some
increased cloud coverage. The dry surface cold front will push
through as well, bringing a reinforcing shot of cold air into the
region Wednesday night/Thursday. Temperatures will be near normal on
Tuesday, with highs in the mid 60s to low 70s and lows Tuesday night
in the low to mid 40s, but will depend on the progression of the
cold front into the NW portions of the area. (For reference, normal
highs are in the upper 60s to low 70s and normal lows are in the mid
to upper 40s). Temperatures will then decrease once again Wednesday
and Thursday in response to the Canadian high ridging southward into
the region. Highs in the low to mid 60s Wednesday and mid to upper
50s on Thursday. Lows will generally hold steady in the mid 30s
north to low 40s south.

Thursday night through Saturday night: Increasing likelihood of wet
and cool weather for this part of the forecast period. Forecast
confidence is still not very high. Generally, expect a shortwave
aloft to swing through the Southeast US Thursday into Friday night
while a trailing wave/low strengthens as it dives south through the
northern High Plains and Midwest, toward the Gulf Coast. The
deepening trough and closed low are expected to be to our west on
Saturday, while the axis of moisture/precipitation is expected to
shift eastward over the Atlantic. At the surface, the low over the
Gulf (associated with the initial s/w aloft) will strengthen as it
migrates eastward along the Gulf coast then northeast along the SE
US Coast. Although the timing is off between the models, consensus
is that it will stay along or just off the Mid-Atlantic coast. The
surface high will continue ridging south-southwestward into NC, thus
strengthening the pressure gradient and amplifying winds over the
area. Temperatures will depend greatly on the placement of the low
and the cloud cover and precipitation, but generally expect below
normal temperatures to continue, cooler NW and warmer SE and slightly
moderating through the period.


As of 755 PM Sunday...

Expansive, continental polar high pressure, analyzed from the mid MS
Valley to the middle Atlantic coast this evening, will build
directly over cntl NC through early Mon, then offshore by Mon night.
The presence of this cold and dry high pressure will result in (a
high confidence of) VFR conditions, with light and variable winds
as the center of the high passes overhead.

Outlook: A strong low pressure system is forecast to track across
the nrn Gulf of Mexico, then northeastward along the East Coast,
later this week and next weekend. Cool, wet, and breezy/windy
conditions will likely result in cntl NC by the end of the forecast
period (Friday), and particularly during the Fri night and Sat time


Freeze Warning until 9 AM EDT Monday for Ncz007-021>024-
Frost Advisory until 9 AM EDT Monday for Ncz028>011-025>028-


NEAR TERM...Haines
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