Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 220011

Area Forecast Discussion
National Weather Service Raleigh NC
810 PM EDT Fri Sep 21 2018

High pressure will persist across the area through tonight.
A cold front will move south into northern NC Saturday night, then
stall over southern Sunday into Monday. High pressure is expected
to build into NC from the NE, Sunday into early next week bringing
a cool, moist, NE flow (or Cold Air Damming conditions).


As of 810 PM Friday...

Mostly clear skies were observed across NC at sunset. With strong
high pressure over the region, expect clear skies overnight with
lows in the lower to mid 60s NE, ranging to near 70 south.


As of 345 PM Friday...

Saturday morning mostly clear skies is expected as low level
flow veers from the northwest. High temperatures Saturday have
the potential to be pretty warm as 850 mb temperatures pool
ahead of the front. Latest runs of the GFS and ECMWF have 850 mb
temperatures approaching 18 degrees C across northern North
Carolina with 1000/850 mb thicknesses approaching 1415 m. 90
degrees will be possible across the Coastal Plain and Sandhills
Saturday afternoon. The mid- level ridge will slowly drift east
with an axis of PV shearing out over the Ohio Valley. In
association with this system will be a surface cold front the
looks to stall near the VA/ NC border Saturday afternoon/
evening. The best chance of convection with this will likely be
on our northern border or the VA/ NC border closer towards the
surface convergence. Lapse rates ahead of the front aren`t
impressive to say the least with modification of the mid- level
subsidence inversion slow to take effect. Did go ahead and raise
PoPs into the likely category Saturday night across the north
with the surface convergence from the front, but mid-level
support is severely lacking (500 mb height falls confined up
into Canada). Upper level lift will be a tad more favorable with
the tail of an upper level jet pushing east across the Ohio
Valley. Latest runs of the ARW and NMM show more of an upglide
scenario almost though with northeast surface winds and
west/southwest 925/ 850 MB flow.


As of 400 PM Friday...

During the day Sunday confidence continues to grow in a CAD
event setting up as a surface cold front is forecast to ooze
south down the eastern side of the Appalachians. By Sunday
evening the front is forecast to wash out across central North
Carolina with global models in fairly good agreement. The NAM is
the strongest and furthest south with the CAD while the ECMWF
and CMC are the weakest and furthest north with the event.
Overall thinking is that the front will stall likely near RDU.
Temperatures Sunday into Monday will be extremely tricky with a
15 to 20 degree temperature spread across the area. Due to the
strong CAD signal towards the Triad, have continued to tighten
and strengthen the forecast temperature gradient. High
temperatures in the Triad Sunday and Monday could possibly have
problems even making it to 70 while towards KFAY temperatures
will move into the mid 80s. Due to the above have continued to
trend high temperatures across the northwest down. The other
main question Sunday into Monday will be the chance of
precipitation.The isentropic setup mentioned in the short term
section of the discussion will likely transition towards our
area at this time. Latest guidance continues show a strong
signal here with continuity of partial upslope flow, along with
overrunning, and lowering condensation pressure deficits Sunday
evening into Monday morning. Due to the above have kept the
highest PoPs tucked against the mountains and northern zones.
This type of setup also highly favors a stratiform rain setup
north of the frontal zone.

By Tuesday the mid-level ridge will remain anchored across the
Atlantic with the CAD starting to break. The main question with
this is when will the CAD break. The remnants of Florence looked
initially to help this happen, but latest GFS guidance has
shown this not necessarily being the case. The ECMWF does show
the remnants of Florence breaking the CAD though. For now have
kept the forecast showing the CAD loosing cohesion Tuesday, but
this will need to be watched.

Towards the end of the extended a high amount of model
variability remains with the ECMWF showing a cold front nudging
into our northern zones, while the GFS is much slower with the
front. For now have kept the forecast trended towards the slower
GFS/ CMC solution.


As of 810 PM Friday...

Generally VFR conditions expected through 18z/Saturday. There is a
chance of thunderstorms after 18z Saturday at KGSO/KINT and KRDU.
During the day Saturday a surface cold front will approach from
the north with scattered thunderstorms, which may last into the
overnight Saturday.

Outlook: The surface cold front is expected to move south into NC
on Sunday. This will lead to MVFR to IFR CIGS and VSBYS at KGSO/KINT
and possibly KRDU Sunday into Monday - with periods of light
rain and drizzle. KFAY will have MVFR CIGS Sunday into Monday with
a chance of showers/thunderstorms Sunday and Sunday evening.

MVFR CIGS should return to VFR on Tuesday in all but the NW zones,
where KGSO/KINT may see persistent MVFR CIGS or lower into Wed. with
lingering CAD affects.




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