Area Forecast Discussion
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FXUS62 KRAH 270137
Area Forecast Discussion
National Weather Service Raleigh NC
935 PM EDT TUE JUL 26 2016
Strong high pressure aloft will extend over the Southeast U.S.
through the work week, as weak disturbances pass by just north of
the region. A cold front will approach from the northwest on Friday,
then stall out just to our north and west next weekend.
.NEAR TERM /THROUGH TONIGHT/...
As of 330 PM Tuesday...
Scattered showers and storms have already begun to fire over the
mountains, foothills, and into the northern and western Piedmont,
where CINH has vanished and MLCAPE has already risen well over 2000
J/kg. Deep layer bulk shear still isn`t great but is better than in
the last several days, as shortwave energy tracks eastward across
the OH valley and mid-Atlantic, nudging the westerlies slightly to
the south and inducing sufficient acceleration aloft to boost values
to around 20 kts across northern NC this evening. Have retained
isolated to scattered showers and storms through the evening,
starting first over the Piedmont (better coverage north and fewer
storms south), then shifting eastward into the NE Piedmont and
northern/central Coastal Plain through the evening before weakening
and dissipating with loss of heating overnight. This scenario is
supported by the latest CAM runs. A few storms could become strong,
given the degree of instability, improving wind field aloft, and
high downdraft CAPE over 1000 J/kg, but the mid level lapse rates
remain meager with no good low level mass convergence, so widespread
strong storms aren`t expected. Persistence will be followed for lows
tonight, in the lower to mid 70s. Temps over much of the CWA won`t
drop below 80 until well after midnight, exacerbating the adverse
health effects of this ongoing hot spell. -GIH
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 345 PM TUESDAY...
The two main concerns for Wed are the storm threat and the heat. The
mid-upper level ridge will remain centered just to our SE while
extending across the Southeast states, while the weak mid level wave
continues to pass by to our north, crossing the mid-Atlantic coast.
Deep layer bulk shear will remain marginal, and the warm mid levels
will continue to curb instability over the southern sections of NC.
But both factors will be sufficient for convection initiation and
maintenance Wed afternoon across the northern CWA. With a
thermodynamic environment tomorrow similar to that of today, we
should again see scattered storms mainly across the north Wed
afternoon, lasting into the evening before weakening and exiting.
Once again, a few strong storms are possible, but weak lapse rates
and marginal winds aloft will limit this potential. A few debris mid
clouds from this evening`s convection may linger early in the day to
temper heating slightly, however thicknesses and forecast soundings
still support persistence, with highs again in the mid to upper 90s,
and dewpoints starting out in the mid-upper 70s before dropping to
70-75 in the afternoon with mixing. Heat index values are expected
to top out near or above 105 over all but the NW Piedmont tomorrow,
so will go forward with another heat advisory, along and east of a
line from Albemarle to Burlington to Kerr Lake. Lows Wed night in
the mid 70s. -GIH
.LONG TERM /Thursday through Tuesday/...
As of 230 PM Tuesday...
Beginning Thursday, the high pressure system gets suppressed ever so
slightly to the southeast and allows the remnants of the frontal
boundary over VA to creep southward, increasing pops a bit for the
northern tier of the CWA but otherwise points south should remain
fairly dry but afternoon showers and thunderstorms will be favorable
east of the Piedmont trough. Thursday night a wave is expected to
develop just north of the area and move northeastward leaving Friday
fairly dry. Afternoon convection will be possible again Friday and
Saturday afternoons as the upper level flow turns more
southwesterly. By Sunday, central NC becomes increasingly squeezed
between a surface high to our southeast and another to our
northwest. This will set up a more active pattern over the area
which will funnel moisture into the area. This should help keep
skies cloudier and bring temps down a few degrees for the beginning
of next week. Early next week an upper trough develops to help push
the frontal boundary through the area and hopefully provide some
relief to temperatures. Until then expect continued highs in the mid
90s with heat index values approaching 105 degrees.
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --As of 935 PM Tuesday...
Humid airmass in place still supporting widely scattered
thunderstorms this evening. Eastern TAF sites will need to be
monitored through 04Z for isolated lingering showers and storms,
otherwise VFR conditions will prevail through the 24 hour valid
period. Expect another round of convection tomorrow under similar
heat and moisture conditions, mainly across the northern tier during
the late afternoon...with activity migrating slowly south in the
evening and early night. Winds through the period will be
light...less than 8 mph...and generally westerly...
Looking beyond 18z Wed: Mostly VFR conditions are anticipated,
although late night and early morning MVFR fog is possible each day
through Fri, with a better chance of sub-VFR fog/stratus Sat/Sun.
Scattered showers/storms are again expected Wed afternoon, mainly at
the northern TAF sites. Storm chances will drop once again for Thu
and Fri, before rising again over the weekend.
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-- Changed Discussion --Heat Advisory from noon to 8 PM EDT Wednesday for NCZ008>011-023>028-
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