Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 190129

Area Forecast Discussion
National Weather Service Raleigh NC
929 PM EDT THU AUG 18 2016

A series of mid-level disturbances in generally westerly flow
aloft will track across the Southern Middle Atlantic states, atop
a lee surface trough over the same areas, through Saturday.


As of 925 PM Thursday...

A couple of MCV`s are evident in regional radar and model
analyzed vorticity data this evening between KINT and KIGX. These
disturbances appear to be situated on the south side of a SRN
stream mid-upper jet axis stretching from the Mid MS Valley to
the Middle Atlantic coast.

At the surface, a generally E to W-oriented surface trough /former
weak frontal zone/ was analyzed from the NC Outer Banks WWD across
the NE NC Piedmont, where it intersected a NE to SW-oriented
lee/Piedmont trough extending across the WRN Carolinas. A
relatively well-defined, and slightly NWD-retreating outflow
boundary also remains evident in KRAX data this evening, from SRN
Wilson Co. WWD to NRN Lee and SRN Chatham Co.

Recent HRRR solutions that have depicted the development of a
large convective cluster over central NC this evening seem
overdone, given radar trends of the past several hours.
Nonetheless, the current minimal coverage of showers and storms in
central NC may indeed experience a slight uptick during the next
few hours from the Central and SRN Coastal Plain WWD into the ERN
Piedmont, as the aforementioned MCV`s track EWD and interact with
the E to W-oriented surface trough and outflow boundary. It will
otherwise remain very mild, and humid/muggy, with lows in the
lower to middle 70s.


As of 350 PM Thursday...

Shortwave impulses interacting with moderate instability within the
moist 2-2.25 PWAT airmass pooling invof the stalled surface trough
will support scattered to numerous showers and storms Friday
afternoon and evening. While deep layer shear of 20 to 25kts is
progged to be a bit stronger, instability is forecast to be less
than recent days with MLCAPE in the 1000-1500 J/Kg range. So still
expect a low end/isolated severe threat. High PWATS around ~2" will
also support the threat of heavy rain and localized flooding of
urban and poor drainage areas. Storm coverage and intensity should
decrease with loss of heating, but presence of stalled surface
trough and intermittent of DPVA from shortwave disturbances tracking
through the area justifies continuation of small chance pops

High temps are expected to be in the upper 80s to lower 90s. Low
temps in the lower to mid 70s.


As of 315 PM Thursday...

Saturday and Sunday: With mostly zonal flow aloft and a lingering
frontal zone to our south, Saturday will feature plenty of moisture
available for convection but only marginal shear and instability.
One thing that could help is a small shortwave disturbance that
moves across the area and could provide some additional lift for
convection, particularly in the east. Temperatures mainly in the
upper 80s.

Sunday the attention will turn to the approaching cold frontal
system to the west. Models have been speeding up the passage of the
front the last couple of runs and that trend continues with both the
ECMWF and the GFS brining in pre-frontal convection Sunday afternoon
and evening with the actual front moving through very early Monday
morning. As far as convection on Sunday is concerned the best
chances should be across the south where the front will set up a
little better with diurnal heating. The good 30 kt shear looks to be
hanging back behind the front and will not line up with the best
instability. Therefore not expecting much as far as severe weather
goes and the front should move through fast enough that flooding
should not be as big of a concern as it has been early this week.
Temps in the upper 80s to low 90s.

Monday through Thursday: After the cold front pushes through early
Monday a much drier and more comfortable airmass moves in for much
of the work week as high pressure moves overhead. High temperatures
are expected to be in the mid 80s with lows in the mid 60s and
dewpoints in the upper 50s to low 60s.


As of 800 PM Thursday...

Outflow moving west through the coastal plain and an upper
disturbance crossing the Blue Ridge have been largely inactive today
but may still pop a few showers or an isolated storm this evening,
mainly from RDU south to FAY through midnight.  Otherwise, VFR
conditions are expected, with a period of sub-VFR possible at INT by
12z given the brief shower that passed over that terminal this
evening. Another upper disturbance tracking near the NC-VA border on
Friday and a continued hot and unstable airmass will support the
potential for scattered storms after 18z.

Looking ahead: Scattered afternoon/evening showers and storm
will be possible through the weekend in advance of a cold front
passage early Monday. In addition, patchy morning stratus/fog
will be possible, especially for locations that receive
afternoon/evening showers/storms.




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