Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 120822 AAA

Area Forecast Discussion
National Weather Service Raleigh NC
407 AM EDT Sat Aug 12 2017

A cold front will approach from the northwest today and settle into
central NC tonight through early Sunday. The front will then become
quasi-stationary over NC through the middle of next week.


As of 345 AM Saturday...

A humid boundary layer, and deep moisture characterized by
precipitable water values near or in excess of 2 inches from west to
east across central NC, will maintain a conditionally unstable and
weakly capped environment that will be supportive of multiple rounds
of showers and storms through tonight, and beyond for the next
several days. Flooding may result; and a Flash Flood Watch may
ultimately be needed. This risk has been introduced to the HWO.

NC will remain on the srn fringe of the main belt of westerlies in
broad cyclonic flow aloft over the ern U.S. Embedded within this
flow are a couple of notable perturbations, including one now
crossing the Carolinas and supporting the ongoing area of showers
and storms that is forecast to be exiting our forecast area around
or shortly after 12Z. Another perturbation now crossing the lower OH
Valley will move east of the Appalachians and across NC this
afternoon; and the timing of this feature coincident with peak
diurnal heating is likely to support renewed shower and storm
development and west to east propagation across central NC this
afternoon and evening. Additional showers and storms may develop
along and east of I-95 in the time between the two convective
regimes outlines above, courtesy of the nnewd lifting/shearing of an
elongated low to mid level trough off now off the SC/GA coast, which
the models suggest will cross the ern Carolinas during the late
morning to early afternoon hours. Near persistence high temperatures
in the middle to upper 80s.

Later tonight, a cold front and associated deep low level
convergence axis through the 925-850 mb layer will settle
southeastward and into central NC through early Sunday; and the
arrival of this convergence axis amidst a continued very moist air
mass will favor continued, at least scattered showers and storms,
overnight. Very muggy lows in the lower to middle 70s, with the
high humidity again favoring low cloud development late.


As of 400 AM Saturday...

The models continue to indicate the front will become quasi-
stationary from the srn NC Piedmont enewd to the central Coastal
Plain on Sunday. Continued high precipitable water values in excess
of 2 inches, and convergence along the boundary, and isentropic
upglide courtesy of moist sswly 850 mb flow across it, will favor a
continued high chance to likely probability of showers and storms.
Generally persistence temperatures in the middle to upper 80s, with
perhaps some lower ones over the nrn Piedmont/on the "cool" side of
the front. Muggy lows again in the lower to middle 70s.


As of 310 AM Saturday...

Monday and Tuesday: Shortwave disturbances moving over the region in
southwest flow aloft will result in overcast skies, above normal
chances for convection and below normal temperatures. Highs Monday
around 80s degrees northwest to mid 80s South. Lows in the upper 60s
to mid 70s. A tropical system could be off the Carolina coast Monday
Night, however the impacts for Central NC appear minimal at this
time. The upper level trough will move through the region Tuesday
night, however the surface cold front will likely stay north and
northeast of the area. Chances for convection will decrease Tuesday
Night. Highs in the low to mid 80s Tuesday and lows Tuesday night in
the mid 60s North to low 70s South.

Wednesday through Saturday: There should be a relatively dry period
mid to late week as high pressure builds over the deep south and
zonal to weak cyclonic flow prevails over Central NC, although it`s
more likely the typical summertime pattern of diurnal showers and
storms will prevail. There is still a good deal of uncertainty with
regard to precipitation in this period and thus confidence is below
average. Highs will gradually rebound from the low to mid 80s on
Wednesday back into the upper 80s to low 90s by Saturday. Overnight
lows will also begin increasing once again, back into the upper 60s
to low 70s by the end of the week.


As of 150 AM Friday...

High humidity at the surface and aloft will favor both IFR-MVFR
stratus this morning, and scattered to numerous showers and
thunderstorms throughout the forecast period. Like Fri, associated
ceilings will lift through MVFR range, to VFR, by midday to early
this afternoon.

Outlook: Continued humid conditions will favor the redevelopment of
low stratus later tonight. A frontal system will settle into, and
stall over central NC late tonight through early Sun, where it will
then stall and become quasi-stationary over our area through the
middle of next week. This pattern will favor an associated above avg
probability of showers and storms, and late night-early morning





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