Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 171047

Area Forecast Discussion
National Weather Service Raleigh NC
645 AM EDT Sat Mar 17 2018

A cold front will stall and remain stationary just south of central
NC through Saturday. An area of low pressure will cross the region
Saturday night, pushing the front farther away from our region. This
will allow an area of high pressure and associated cooler air mass
to build into the Carolinas on Sunday.


As of 500 AM Saturday...

08z Surface analysis shows a nearly stationary front draped west to
east near the SC/NC state line. North of that boundary, high
pressure continues to inch SE through the Ohio River Valley, likely
to cross the Appalachians by sunrise before pushing off the Mid
Atlantic Coast. This has allowed light and extremely dry northerly
flow to be the primary controller overnight, keeping surface
dewpoints in the teens (north) and twenties (south). This has
allowed temperatures to dip a bit lower than originally forecast,
with near to slightly below freezing temperatures witnessed across
much of central North Carolina. Light reflectivity returns continue
to push into the forecast area from the west, with little to no
precipitation expected to reach the ground prior to sunrise, thanks
largely to a rather impressive pocket of dry air in the low to mid
levels, depicted nicely via the RNK/GSO 00z upper-air soundings.

Winds will rebound after sunrise, as high pressure drifts offshore,
allowing southerly/southwesterly flow to re-establish by mid
morning. This will allow dewpoints to climb rather significantly
through the mid afternoon, likely to reach the upper-40s to lower-
-50s by supper. Temperatures should remain near normal, with a few
70 degree values in the south, with 60s prevalent north.

Mid to upper-level cloud cover along with a few scattered showers
will overspread the region from west to east thanks to an occluding
surface low over the Ohio River Valley. Most of the precipitation
with this surge will struggle to breach the dry air bubble at the
surface, however, a secondary push from the remnants of the surface
low will cross the area after dark, bringing about the possibility
of more widespread showers and possibly even an elevated rumble of
thunder. With impressive bulk shear and lapse rates in the late
evening to overnight hours, a strong storm capable of producing
isolated wind damage and small hail is not out of the question,
especially north and west where a small amount of cape may remain.


As of 500 AM Saturday...

A few showers or pockets of drizzle may linger pre-dawn Sunday, as
high pressure moves into the region albeit briefly. Clouds will
diminish throughout much of the day with northerly flow continuing
across much of the region, keeping temperatures slightly below
normal, rising into the mid 50s during the day and falling into the
40s overnight. The high will shift offshore in the evening, allowing
southwesterly winds to return ahead of the next developing storm
system, set to ride northeast into the Carolinas by Monday morning.


As of 430 AM Saturday...

The medium range portion of the forecast continues to look
unsettled, with a Miller B surface low configuration system expected
late Monday into early Tuesday morning, with rain/showers expected
to spread into the area on Monday, with precip chances expected to
be maximized on Monday night/Tuesday early morning. This should
result in a CAD air mass developing across the area, with
potentially a few thunderstorms across far southern/southeastern
portions of our area early Tuesday morning.

As the coastal low begins to intensify and lift off to the north and
east and becomes the dominate low on Tuesday morning chances for
showers will begin to decrease. However, given high variability in
recent model runs will keep chance pops in the forecast for Tuesday.

Additional mid/upper level energy is expected to dive southeastward
and into our area for Tuesday night into Wednesday. Model continue
to struggle with how this system will evolve, but there remains the
potential for a mix of rain/snow across northern/northeastern
portions of the area on Wednesday/Wednesday evening. Dry weather is
expected to generally return for late week with the mid upper level
trough axis expected to shift to the east.

Temps during the medium range are generally expected to remain below
normal, with temps well below normal in the heart of the CAD
(Piedmont) early this week and again on Wednesday with the threat of
wintry precip.


As of 645 AM Saturday...

24-Hour TAF Period: VFR conditions are expected to continue across
all TAF sites through roughly 03Z Sunday, with MVFR CIGS mixing in
between 04z - 06z and persisting into early Sunday morning. A cold
front has stalled near the NC/SC border late Friday night, with
little in the way of migration expected. Winds are expected to
remain calm overnight, with a gradual direction shift from out of
the southerly/southwesterly direction forecast to occur around
daybreak as a high drifts off the Carolina Coast. Upper-level clouds
will also be on the rise from west to east, and gradually lowering
from 25kft around daybreak to roughly 7 to 9kft by sunset Saturday
evening as the boundary layer begins to saturate. Model guidance
continue to indicate a brief reprieve from BKN/OVC CIGS around
sunset before MVFR/IFR CIGS/VSBYS enter the picture between 04z -
06z Sunday night. On/off precipitation will be possible during the
period, including a few areas of -RA/-DZ during the morning hours
Saturday (low confidence) and more widespread -RA/-SHRA after sunset
Saturday night. A rumble of thunder, especially at KINT/KGSO, isn`t
out of the question Saturday night, but confidence on the threat
remains low at this point.

Looking ahead: VFR conditions may return briefly Sun afternoon as
high pressure settles into the area, then another threat of sub-VFR
conditions arrives on Monday, likely to persist into the middle of
next week as a series of disturbances passes overhead. Confidence is
not high during the Sat-Mon time frame, with wide variation among
models regarding timing of these disturbances, so aviation interests
should check back for the latest.





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