Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 230126

Area Forecast Discussion
National Weather Service Raleigh NC
925 PM EDT Thu Mar 22 2018

Cold high pressure will build in from the northwest through
Friday, before moving offshore Friday night. An area of low
pressure will approach from the west Saturday and cross our region
Saturday night and Sunday.


As of 925 PM Thursday...

Through tonight: Surface high pressure was located over the
Mississippi Valley. The pressure gradient still remains tight
and the boundary layer well mixed. With nocturnal cooling,
expect some areas to decouple later tonight allowing good
radiational cooling in this cold/dry air mass. Clear skies are
expected with lows 27-34 (a larger range due to the expected
occasional stirring of the surface winds at 5-8 mph.

Fri/Fri night: The mid level trough takes on a negative tilt out
over the Atlantic Fri, keeping NC beneath northwesterly mid level
flow as the surface ridge extends through the area. With a continued
lack of moisture and descent through the column, expect fair to
sunny skies Fri. Temps should top out a few degrees warmer than
today, 53-60. A mid level shortwave trough over the Rockies Fri
morning will top the ridge through Fri night, moving through the
Midwest. An associated surface low will move E over the central
Plains, while the preceding southerly flow out of the Gulf will
prompt deepening moist upglide to our west and NW. As this moist
ascent spreads eastward late Fri night, low chance pops will spread
into W NC, and based on the average timing from the models, will
bring in isolated precip chances late. The vertical thermal and
moisture profiles (including the near-surface wet bulb trace)
suggest that this may fall as a little light snow or sleet in the
Triad late Fri night at onset, but impacts will be minimal to
nothing. Given that clouds will be increasing from the west
overnight, temps in the Triad may level off at milder readings, such
that even low level wet bulbs may be at or above freezing. Expect
lows of 28-37 with increasing clouds. -GIH


As of 330 PM Thursday...

A low pressure system forming over Missouri will drop southward
through the Carolinas over the weekend bringing a fair amount of
rain and possibly some winter P-Types to the northern portions of
our forecast area. Synoptically this system is neither a true Miller
A or B scenario as the low drops in from the northwest instead of
from the southwest and true secondary low never forms west of the
mountains. Most of the jet dynamics with this system remain well to
the north of the area, but as the low comes through Early Sunday
morning an upper level jet streak passes to the southwest which will
help bring some lift to the area. There is high confidence that this
event will bring a good amount of rain to the area through the
weekend, which won`t be favorable for any outdoor plans. At this
time, models are predicting up to an inch of rain for this event
with higher amounts across the northern half of the forecast area.

Winter P-Types: There are many factors that make this a low
confidence event for winter p-types at this time. An analysis of
surface wet bulb temperatures show period Saturday morning of below
zero wet bulbs across the Triad and VA border counties. The best
chance for some snow mixing in would be right around 12z but the
precipitation may not actually be in the Triad yet at that time or
just arriving. When it does, it will have a lot of dry air to
overcome in the low levels making sublimation a possibility for any
snow. By the time those surface layers moisten up, temperatures may
be too high to support snow. At that point, expect much if not all
of the precipitation on Saturday to fall as rain. Expect high
temperatures in the low to mid 40s across the north with mid 40s to
low 50s in the south.

Sunday morning will be the best chances for some accumulating snow
as thermal profiles are more supportive of it and moisture and cold
air are in place simultaneously. The problem is that forecast
soundings lose a lot of the lift at this time and moisture in the
dendritic growth zone is drying out. That would favor more sleet
than snow. Therefore have added very small accumulations north of I-
85 and east to Halifax of less than a half of an inch on Sunday
morning. Otherwise this should be a rain or rain/sleet event for
points south. Sunday, temps will be in the low 40s across the Triad
for highs with closer to 50 degrees in the south.


As of 130 PM Thursday...

Mostly dry weather is expected during the beginning and mid part of
the work week, although the clouds should hang on through at least
Mon evening (and perhaps into Tue in the western CWA) as a semi-
anchored surface high, centered over SW Quebec into the Maritimes,
ridges SSW through NC, locking the wedge air mass over central NC.
Mid level ridging will steadily build over the eastern CONUS through
mid week, between deep closed lows over the Desert Southwest and
over the NW Atlantic, ensuring a lack of forcing for ascent and
continued tranquil weather (albeit with periodic cloudiness). Model
solutions start to diverge Wed/Thu with the GFS trending more
progressive, weakening and lifting out the NW Atlantic low, which
allows the E Coast ridge to weaken and move east. The ECMWF and
Canadian keep the Atlantic low in play with a southward drift, which
keeps the mid level ridge over the Southeast. The slower blocking
pattern is preferred, which will mean a trend to increasing sunshine
and warming temps starting Tue and especially Wed/Thu, when low
level thicknesses will reach or exceed seasonal normals with a
modifying surface air mass. -GIH


As of 840 PM Thursday...

24 Hour TAF Period: VFR conditions are expected to continue through
the 24 hour TAF period as surface high pressure moves across the
Southeast U.S. This will lead to continued VFR conditions with
generally mostly clear/mostly sunny skies through early afternoon
Friday. However, a few mid/high clouds will affect KRWI and KRDU
this evening as the departed mid/upper level trough continues to
shift further to the east of the area overnight and some flat
cumulus at around 5 to 7 kft areawide Friday afternoon. Otherwise,
VFR conditions will continue, with possibly some wind gusts of up to
20 kts out of the WNW on Friday afternoon. -BSD

Outlook: VFR conditions will hold through Fri night, although an
approaching storm system from the NW will result in a trend to MVFR
Sat morning at INT/GSO/RDU, and Sat afternoon at RWI/FAY, with
precip moving in from the NW. INT/GSO will likely trend to IFR Sat
afternoon. Precip is expected to start off wintry at all sites
except FAY Sat morning before trending to mostly rain. Low level
wind shear may also be a concern Sat afternoon/Sat night at FAY. IFR
conditions should dominate at all terminals Sat night, followed by a
slow trend to MVFR Sun, although IFR cigs may redevelop late Sun
night at INT/GSO and persist through Mon, while other sites trend to
VFR Mon. A trend to VFR is expected at all sites Tue. -GIH





NEAR TERM...Badgett
LONG TERM...Hartfield
AVIATION...BSD/Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.