Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 300123

Area Forecast Discussion
National Weather Service Raleigh NC
920 PM EDT FRI JUL 29 2016

A weak upper-level trough will become centered over the eastern U.S.
through Saturday, bringing increased chances for showers and storms
late Saturday through Monday, along with a trend toward more normal


As of 920 PM Friday...

Widely scattered convection will continue to develop in the west
through midnight generated by advection of upstream perturbations in
the west to southwest flow regime. Modest shear is available, but
forcing is weak with waning instability...hence not expecting other
than isolated thunder chances.

Previous Discussion...Convection chances still appear small through
tonight. Surface troughing holds over the area, with a weak
vorticity axis spanning far western and northern NC within a weak
southwesterly mid level flow. Poor mid level lapse rate and slightly
lower temps and dewpoints have held down MLCAPE to less than 1500
J/kg so far, although effective deep layer shear is decent at 25-30
kts, enough to sustain organized convection. The latest HRRR takes
the existing showers and isolated storms over northern GA and
upstate SC eastward into the far SW CWA during the early evening
hours in a weakened state, reasonable considering the lack of upper
support and warm mid levels. Will maintain low chance pops, mainly
in the SW, through the evening, dwindling with just an isolated
shower or two overnight as the low levels stabilize. Heat indices in
the heat advisory area have been generally under 105 so far, a
result of the WNW low level flow across the area and resultant
greater mixing and lower dewpoints. See little value in dropping the
advisory now, so will leave it in place as is through early evening.
Lows 70-75. -GIH


.SHORT TERM /Saturday through Sunday night/...
As of 355 PM Friday...

Convection chances will rise over the weekend as the baggy upper
trough eases eastward through the Great Lakes and OH Valley, drawing
the surface trough back westward over the western Piedmont. As the
850 mb trough axis over central/eastern NC washes out, low-mid level
southwest flow will help pull greater PW over the area, with values
climbing to near 2.0" in the east, setting the stage for increased
shower/storm chances, greatest in the afternoon and evening. Will
top out pops at 50%, due in large part to disagreement among the
models on where the best location and timing of convection is apt to
be, but based on the pattern and concentration of greatest moisture,
we would expect areas along and east of Highway 1 to see the
greatest coverage of showers and storms, and this area may need to
be bumped up to likely pops or higher in future forecasts. The
expected increase in clouds, both from convective debris mid and
high clouds moving in from the MS and TN valley and from earlier
diurnal cumulus formation, should hold temps down a bit both days,
still above normal but yielding heat index values below advisory
criteria. Will hold off on another advisory for now for Sat, and
monitor trends tonight, but Sat could be the first day without a
heat advisory or warning in central NC since last Sat, the 23rd.
Highs both days 89-95, with morning lows in the lower-mid 70s.-GIH


.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 /00Z Saturday through Wednesday/...
As of 725 PM Friday...

24-Hour TAF period: High confidence that VFR conditions will prevail
through the TAF period, especially through tonight and Saturday
morning. The only exception will come Saturday aft/eve where/when
showers and storms develop. Based on latest high-resolution model
data, the best chances for storms will be at KRDU and KRWI from
approx 20Z Saturday to 03Z Sunday. There is still a chance, albeit a
bit lower, at KINT, KGSO (16Z-19Z), and KFAY (21Z-00Z). Storms will
bring the usual heavy rain with reduced visbys and gusty winds where
they develop. -KC

Looking ahead: 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 today until 8 PM EDT this evening for


SHORT TERM...Hartfield
LONG TERM...Hartfield
AVIATION...KC/Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.