Area Forecast Discussion
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FXUS62 KRAH 291550
Area Forecast Discussion
National Weather Service Raleigh NC
1150 AM EDT FRI JUL 29 2016
A weak upper-level trough will become centered over the eastern
U.S. today through Saturday, bringing increased chances for showers
and storms late Saturday through Monday, along with a trend toward
more normal temperatures.
.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Friday...
Little change needed to ongoing forecast. The latest surface map
shows low pressure off the Northeast coast with troughing extending
down through central NC, aligned closely with the 850 mb trough. The
low level flow from the WNW is likely to hold down temps and
dewpoints enough to limit convection, although there may still be a
sufficient combination of low level mass convergence (along and east
of a weak lee low that is expected to form over the western
Sandhills) and higher temps/dewpoints along and east of the trough
for scattered storms this afternoon into early evening. The SSEO, 3
km NAMRR, and the NCAR ensemble output all suggest a weak
shower/storm cluster traversing the southern third of the forecast
area late today, fitting with this scenario, and will place chance
pops here with just isolated elsewhere. Despite the decent deep
layer bulk shear, CAPE values should be small today, at or under
1000 J/kg of MUCAPE, limiting storm intensity. Thicknesses this
morning are markedly lower than previous mornings, suggesting highs
around a category below yesterday`s highs, and in fact current temps
are already running 1-4 degrees below yesterday`s pace. Expect highs
in the lower-mid 90s, except upper 90s SE. Will keep the heat
advisory in place in the east, although a few spots may come up
short, especially if dewpoints mix out more than expected in the
eastern CWA. -GIH
Previous discussion as of 230 AM Friday: Mostly sunny skies today
with just slightly lowering heights/thicknesses will only yield
subtle changes to the heat. Highs will still reach 95-100 from
Fayetteville to Rocky Mount eastward to Goldsboro and Clinton. Heat
indices will still reach 105 or 106 in many areas this afternoon.
This will be another day to take precautions to prevent heat related
issues or illnesses.
Central NC will be on the back or subsidence side of the departing
mid/upper trough over VA this morning. Skies were clear this
morning over much of the region with partly cloudy skies near
the VA border. The mean flow is a bit more westerly into the
mountains and western Piedmont on the backside of the
departing trough. The SW-W low level flow has aided in some dry
advection from upstate SC into western NC, allowing dew points to
fall into the 60s. In the east, dew points remained very oppressive,
in the 70s. This lowering of dew points will eliminate the heat
advisory from the Piedmont today. Heat indices will be in the 95-100
range during the mid to late afternoon in the Piedmont. However,
highs will still reach the mid to upper 90s. Even though a heat
advisory will not be needed, this subtle lowering of the heat
indices from 105 to 95 to 100 will essentially not be that
noticeable; therefore, it will be good idea to treat today just as
the last few when advisories were in effect in the Piedmont.
Convection is expected to be at a minimum again today with the
subsidence this morning and more of a westerly flow. There will be
slight chance of thunderstorms this afternoon and early evening as
the surface trough develops and the low level flow begins to back to
the SW then S by evening. The best chances should be in the
Coastal Plain this afternoon. Dew points will again rise this
evening, back into the 70s in the Piedmont and remain high in the
east as the surface trough backs westward. An isolated storm is
possible, but the chances remain slim without a trigger aloft. Lows
generally in the 70s again.
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 225 AM Friday...
Yet another heat advisory appears likely in the south and east on
Saturday as strong heating and high humidity values will occur
again. There will be more clouds over the Piedmont and northern
areas, closer to the approaching mid/upper trough. This will bring
some cooling, even if the showers do not become widespread. Highs
should range from around 90 NW into the upper 90s in the Coastal
Plain. Heat indices should reach 105 again SE, but will be in the
As the trough aloft digs into Tennessee Valley and over the central
Appalachians, a surface trough will tighten over central NC.
However, the main focus for convection appears that it will be in
the northern and eastern section of NC, and especially over VA due
to the best lift... low level convergence... and moisture pooling to
our NE. We will continue to show 40-50 POP in the NE with only 20-30
POP to the SW. This chance of showers and thunderstorms will be
mainly during the afternoon and evening. Partly cloudy skies
otherwise, lows Saturday night in the 70s.
.LONG TERM /Monday through Friday/...
As of 1130 AM Friday...
Stormy weather early in the work week should give way to quieter
weather later in the week. The broad mid level trough axis will be
oriented along the East Coast Mon, with surface troughing extending
down through central NC. It still appears that the best convection
chances will be across the SE half of the CWA Mon/Mon night, with
lingering chances in the extreme SE Tue as the weak shear axis
slides ESE through the area, although even these shower/storm
chances should be largely to our east given the weak mid level flow
from the WNW and NW over W and central NC and post-trough subsidence
taking place. Heights aloft will continue to rise as the mid level
trough shifts further out over the Atlantic with strong ridging
building into and over the eastern CONUS during the mid-late week,
yielding low, below-climo precip chances Wed-Fri. The 00z/29 ECMWF
does favor some MCS activity riding from the OH Valley southeastward
through NC late Wed/Wed night and lingering through Thu with
widespread convection, however this is far from certain and lacking
support from other models, so prefer to stay with a tranquil forecast
for now. Models agree on low level thicknesses slipping to near to
just below normal Mon through Wed, then rebounding back to near or
just above normal for Thu/Fri as the surface high pressure ridge
extending overhead gradually modifies with steady warming aloft. -GIH
.AVIATION /18Z Friday through Wednesday/...
As of 1150 AM Friday...
VFR conditions will dominate through mid afternoon Sat, as a weak
low pressure trough holds in place across central NC. There is a
chance that isolated to scattered showers/storms may affect TAF
sites very late this afternoon through mid evening, bringing a brief
period of MVFR conditions and erratic gusty winds. Winds will be
generally light through tonight, before coming from the SW at 7-12
kts starting late Sat morning.
Looking beyond 18z Sat: Shower/storm chances will increase Sat
afternoon through the evening, as an upper level trough gradually
moves into the area from the west. There will be a better-than-usual
chance for sub-VFR conditions in showers/storms Sun into Mon as the
upper trough settles overhead with a series of disturbances crossing
the region. MVFR or IFR fog is possible each morning as well. Storm
chances will decrease Tue into Wed with VFR conditions becoming
dominant once again. -GIH
Heat Advisory from noon today to 8 PM EDT this evening for