Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 240555

Area Forecast Discussion
National Weather Service Raleigh NC
155 AM EDT Tue Oct 24 2017

A cold front will shift off the North Carolina coast early this
morning. A secondary cold front will move eastward through the
region this evening and tonight. A strong upper level disturbance
will cross the area Wednesday night, otherwise surface high pressure
will build in from the southwest from Wednesday through the end of
the week.


As of 1040 PM Monday...

A cold front across the NC Foothills late this evening will
push east overnight and approach the coastal region toward
daybreak. The air mass ahead of the front is weakly unstable
with ML CAPE values approaching 500 J/Kg across the Sandhills
and southern Coastal Plain with values around 250 J/Kg to the
north ahead of the front. The flow aloft remains vigorous with
0-6km shear values in excess of 60kts and near surface 0-1km
shear values of 35 to 45 kts. While weak low-level instability
combined with modest mid-level lapse rates has limited deep
convection across most of central NC, the potential continues
for isolated severe weather ahead of the front. The SHERB and
other its family of experimental parameters developed with NC
State researchers and other NWS offices still highlights the
potential for damaging wind gusts and still a chance of an
isolated tornado in a narrow instability axis ahead of the main
convective band. The severe weather threat will be short lived
as the band shifts east and exits the RAH CWA between 5 and 7

Recent GOES-16 satellite imagery shows fairly rapid clearing
behind the convection, closely in line with the 850 mb trough
axis. Gusty south to south-southeast winds ahead of the
convection relax quite a bit and become southwesterly at about
10 MPH. If winds relax enough, a short period of fog is possible
toward daybreak. Otherwise, cool advection will allow
temperatures to fall into the lower 50s in the Triad with warmer
lows, only in the lower 60s across the Coastal Plain. -Blaes

As of 325 PM Monday...

After low stratus early Tuesday, skies are expected to become partly
sunny. Highs will be cooler, 60s NW to 70s SE. A secondary cold
front will bring even drier and cooler air Tuesday night through
Thursday. Still, readings are expected to remain above the critical
threshold of a killing frost or freeze, even in the areas that fall
into the mid to upper 30s (rural Piedmont).


As of 210 PM Monday...

Cooler and dry weather continues into the latter half of the week
with highs in the upper 50s to mid 60s Thursday and near 70 degrees
for the end of the week. Lows will remain in the 40s for the
majority of the week and then climb back into the upper 40s to lower
50s for the weekend.

The next chance for rain comes from a frontal system that will move
through the area next weekend.  There is uncertainty with regards to
timing and also the evolution of a low pressure system riding up the
southeast coastline prior to the arrival of the cold front that
could cause a chance of precipitation earlier in the weekend.


As of 155 AM Tuesday...

The showers and storms associated with the cold front now sweeping
through eastern NC have mostly ended over central NC, although
lingering showers will affect RWI until around 07z. With the moist
ground and light winds, areas of IFR/LIFR fog and stratus have
already formed at INT/GSO, and this is likely to persist through
13z, and should spread eastward to RDU through daybreak, with IFR
conditions expected there 10z-13z. Confidence in sub-VFR conditions
is lower at RWI/FAY, but patchy fog and stratus can`t be ruled out
at these locations either. Conditions at all sites are expected to
trend to VFR by 13z at INT/GSO, but may linger until 14z at RDU. VFR
conditions are likely from late this morning through this afternoon,
with surface winds from the SW at 7-10 kts and infrequent gusts to
11-14 kts possible but not dominant. With passage of a secondary
cold front this evening, surface winds will veer to be from the W or
WNW starting 00z-02z this evening.

Looking beyond 06z Wed, VFR conditions will rule through Sat as
surface high pressure builds into and over the region. Passage of a
strong but somewhat moisture-starved upper level disturbance Wed
night may bring a period of MVFR cigs at INT/GSO/RDU. A strong upper
level trough and corresponding surface cold front will approach from
the west late Sat. -GIH




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