Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 221303

Area Forecast Discussion
National Weather Service Raleigh NC
905 AM EDT Thu Mar 22 2018

Cool high pressure will build in from the northwest through Friday,
before moving east and offshore Friday night. An area of low
pressure will approach from the west Saturday and cross our region
Saturday night, bringing a period of unsettled weather.


As of 905 AM Thursday...

Little change to forecast. A potent but moisture-starved mid level
shortwave trough will move southeastward through the region today,
resulting in scattered to broken mid clouds across northern and NE
sections of the CWA. Otherwise, sunshine will be plentiful. Morning
thicknesses around 40 m below normal support highs of 51-57. -GIH

Previous discussion as of 330 am: Cloudiness will continue to
diminish slowly from the southwest with lingering wrap-around
cloudiness mainly across the north and east through the morning as
the stacked low off the mid Atlantic coast lifts northeast. Mins
this morning will benefit from the lingering cloudiness and modest
mixing overnight with northwest winds 4 to 8 mph, bottoming around
30 across the north to mid 30s south. The increasing sunshine will
be largely offset by cold air advection in breezy northwest flow
today, with highs only reaching low 50s across the north to mid 50s
across the south.


As of 330 AM Thursday...

Cold and dry surface high pressure will continue to spill southeast
into the area in deep northwest flow as the upper east coast trof
axis shifts east and offshore Thursday night. Loosening pressure
gradient will allow atmosphere to decouple and temps will again fall
to the 30 to 35 range, with some upper 20s across the northern tier.
The cool northwest flow will be maintained on Friday, with highs
edging up slightly into the mid and upper 50s.

We will see cloudiness increase rapidly in the west Friday night as
a developing low pressure system begins spreading moisture out of
the Gulf northeastward. This moisture will be lifted orographically
and isentropically late Friday night, with light rain expected to
hold off until early in the day Saturday. Lows will benefit from the
onset of cloud coverage in the west and south with mins mostly in
the 30s, while the clearer northeast will see lows below freezing
northeast of the Triangle.


As of 330 AM Thursday...

Complex weather pattern Saturday into Sunday across central NC with
another potential for accumulating light wintry precipitation across
the northern counties.

A s/w exiting the upper Midwest early Saturday will track sewd and
cross the central Appalachians Saturday night, and exit off the NC
coast Sunday. This s/w projected to weaken/dampen with time as it
encounters strong confluence associated with the deep low off of the
New England coast. The associated sfc and 850mb low expected to
remain west of our region through late Saturday night, with a
secondary low developing early Sunday along the NC coast (Miller "B"

Initial lift over our region will be induced by isentropic upglide
Saturday, and this is primarily focused across our NW Piedmont
counties. Currently appears that light precipitation may develop
around daybreak Saturday. The atmosphere, aided by evaporative
cooling, will be cool enough to support light snow early Saturday
across the far NW Piedmont before transitioning to rain later
Saturday morning. If the light snow does develop, no accumulation is
expected as the precip rates appear marginal/weak at this time.

As the s/w and associated low level wave gets closer and the
atmosphere moistens, expect widespread rain to develop over roughly
the northern two-thirds of central NC Saturday afternoon, continuing
into Saturday night. As the low level low develops near the NC coast
late Saturday night-early Sunday, circulation around this feature
will begin to advect a colder low level air mass into central NC,
especially the northern-ne counties. Also, the cool pool associated
with the passing of the s/w will further cool the column. These
combined actions should lead to the rain becoming a rain/snow mixed
late Saturday night-early Sunday, primarily across the far northern
counties. During times of heavier precip rates, snow will become the
dominate precipitation type, with a mixture of rain/sleet/snow
during lighter rates. Way too early to determine with a high degree
of confidence if any accumulation of significance will occur, though
a light dusting on grassy areas does appear possible by early Sunday
near the Virginia border. At this time will highlight the potential
for light wintry accumulation in the HWO.

As the sfc low exits off the coast Sunday afternoon, should see a
decrease in precipitation coverage and intensity.

Temperatures Saturday into Sunday have been adjusted downward based
on potential for overcast skies and widespread precipitation.

Central NC should see improving weather conditions Monday through
Wednesday as a deep low off of the eastern seaboard and a digging
l/w trough over the western U.S. will amplify an upper ridge from
the Deep South into the Great Lakes. Associated subsidence with this
feature should result in dry conditions across our region with a
warming trend. temperatures early next week will start out 6-9
degrees below normal. As the air mass modifies, temperatures should
return to near normal levels (highs in the mid 60s NW-near 70
south). Min temps in the low-mid 30s Monday and Tuesday mornings
with frost probable. Min temps Wednesday morning should moderate
into the upper 30s-lower 40s.


As of 700 AM Thursday...

VFR conditions are expected through the 24 hour TAF period as the
low pressure system off the mid Atlantic lifts northeast. Northwest
winds will pick up to 10 to 12 knots gusting to 20-22 knots by 15Z
this morning, mainly in the west, then diminish towards sunset.

High pressure will maintain VFR Friday through Friday night.
Aviation conditions will deteriorate rapidly early Saturday morning
as our next system approaches, with lowering ceilings and
precipitation overspreading the area from the south and west during
the day. Unsettled weather will linger through early next week, but
conditions are expected to improve to primarily VFR by late day





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