FXUS62 KRAH 300721

Area Forecast Discussion
National Weather Service Raleigh NC
320 AM EDT Fri Jun 30 2017

Warm and moist southerly flow will persist over the Carolinas
through the weekend, bringing unsettled weather as a surface trough
holds over the region.


.NEAR TERM /Today through tonight/...
As of 305 AM Friday...

Typical warm and humid summertime weather will dominate today and
heading into the weekend, albeit with higher-than-climo chances
today into tonight. The sheared mid level vorticity now extending
from LA across AL/GA into the W Carolinas will continue tracking
slowly NE through the Carolinas through this afternoon, within the
weak southwesterly steering flow, accompanied by deepening moisture
(noted on WV imagery) with PW over 2", and a subtle surface warm
frontal zone. Overall, the available mechanisms to generate lift
today are rather weak, apart from the mid level DPVA. And CAPE will
be marginal at best, with only the extreme S and SE CWA expected to
see enough heating to push MUCAPE up above 1000 J/kg, all with poor
deep-layer shear, under 25 kts. But the abundant moisture will be
sufficient for scattered to numerous showers and storms today. Will
bring likely pops into the SW portions of central NC this morning,
then this activity should spread eastward through the afternoon
hours. Loss of heating and continued shearing of the mid level
vorticity in this weak flow should result in decreasing coverage and
intensity from mid evening onward through tonight, although the
persistence in the anomalously high PW overnight mainly east of the
Triad necessitates retaining 20-40% shower chances through tonight.
Expect highs from the lower 80s west to upper 80s east, where
filtered sunshine will be plentiful through the first part of the
day. Lows tonight 69-73. -GIH


.SHORT TERM /Saturday through Saturday night/...
As of 320 AM Friday...

The surface pattern Sat will feature a very weak trough holding over
the Piedmont while a better-defined frontal zone shifts into the S
Appalachians in the afternoon and into the Foothills and W Piedmont
by evening. Today`s weak mid level perturbation will be heading ENE
and away from central NC Sat morning. We will become increasingly
influenced by the broad northern stream trough over the north
central US, with today`s weak SW steering flow trending to a
slightly stronger, gently cyclonic WSW flow featuring low-
confidence, difficult-to-track minor waves. This slight veering of
the mid level flow will help nudge the very high PW values east and
offshore during the latter half of the day. So while scattered
showers and storms are still anticipated starting as early as mid-
late morning Sat, these should be focused on areas just E of the
Triad, pushing to the ENE through the afternoon, leaving dwindling
precip chances in the east Sat evening and only patchy showers in
the SE CWA overnight as we lose our best moisture and lift. Temps
are tough as we`re unlikely to see a lot of insolation, but what
little we do see will cause temps to shoot up, as thicknesses rise
steadily through the day ahead of the frontal zone. Will have highs
in the upper 80s to near 90. Lows 70-75 Sat night with skies
trending to partly cloudy over all but the E. -GIH


.LONG TERM /Sunday through Wednesday/...
As of 200 AM EDT Friday...

For Sunday, expect the upper level trough axis to remain over the
Ohio Valley extending down through the Tennessee Valley. The trough
is not very deep and most of the dynamics remain well to the north
of the area. Winds may briefly shift around to northwesterly in the
morning but by afternoon the lee trough sets up and southerly flow
will help bring temperatures up into the lower 90s. By late
afternoon there will be much more instability in the south and east
and this is where convection may be concentrated. SPC maintains only
an area of general thunder over all of NC at this time.

As we move into early next week the upper trough axis pushes
eastward but begins to flatten out into more zonal flow aloft.
Instability will be concentrated in the south and east and that is
where much of the diurnal convection is expected to occur. Still no
dynamics to sustain afternoon showers and thunderstorms and
therefore minimal severe threat is expected through Tuesday.
Temperatures will remain in the low 90s during this period with
dewpoints in the lower 70s across the southeastern counties. This
will result in heat indices approaching or slightly over 100 degrees
both Monday and Tuesday in these areas. Overnight lows in the upper
60s to lower 70s.

By Wednesday, instability becomes more evenly distributed across the
CWA and so we may see an uptick in diurnal convection in the west as
well. The Gulf of Mexico will supply a steady stream of moisture to
the area with southwesterly flow over the deep south. The real
uncertainty with the forecast is with a low pressure system that the
GFS has very well developed coming out of the central plains and
moving east through the Ohio Valley by Thursday. The ECMWF solution
is much less certain on this low as it is not maintained like in the
GFS. The upshot is the same with fairly good instability and little
shear across the area resulting in diurnal convection with a minimal
severe threat as the forecast soundings show less than 10 kts of
wind up through 25 kft. Highs still in the low to mid 90s with heat
indices in the southeastern counties topping out between 100-105


.AVIATION /06Z Friday through Tuesday/...
As of 215 AM Friday...

VFR conditions will hold through daybreak, but central NC will see a
gradual west-to-east deterioration to primarily MVFR conditions from
mid morning through this afternoon. An upper level disturbance now
tracking NE through AL/GA along with deepening moisture is prompting
numerous showers extending across the SW half of SC into W NC, and
this activity and its accompanying sub-VFR conditions will slowly
spread into the area this morning. Best chance for MVFR to briefly
IFR conditions will be at INT/GSO this morning through mid afternoon
(13z-20z), with lesser chances confined to this afternoon at
RDU/RWI/FAY as showers and a few storms move into these TAF areas.
MVFR conditions are expected this evening after 00z at INT/GSO and
after 02z or 03z at RDU/RWI/FAY with weakening and diminishing
showers. Surface winds will be mostly from the SSW at 8-12 kts,
decreasing to 5-9 kts starting this evening.

Looking beyond 06z Sat, cigs are expected to drop to IFR at INT/GSO
with MVFR cigs dominating at RDU/RWI/FAY overnight. Scattered
showers and a few storms will continue through Sat with a slow
improvement to VFR by 16z-18z and winds from the SW 8-12 kts. Shower
chances diminish Sat night from NW to SE with mostly dry weather
overnight and largely VFR conditions, although shallow fog will be
possible only at RWI/FAY late. Then, VFR conditions are expected to
dominate across central NC Sun through Wed, although scattered
showers and storms are expected each afternoon and evening mainly
over the SE CWA, affecting RWI/FAY. Sub-VFR conditions are possible
with any such showers/storms. -GIH





NEAR TERM...Hartfield
SHORT TERM...Hartfield

NWS RAH Office Area Forecast Discussion