Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
FXUS62 KRAH 271441
Area Forecast Discussion
National Weather Service Raleigh NC
1042 AM EDT SAT AUG 27 2016
An upper level ridge will persist over the region through the
weekend. An upper level disturbance over the Atlantic will then
drift west and linger over the Southeast states early next week.
.NEAR TERM /THROUGH TONIGHT/...
As of 1042 AM Saturday...
12Z upper air analysis along with the 14Z meso analysis suggest that
best chance for scattered convection this afternoon across roughly
the south half of our forecast area. A mid/upper level anti-cyclone
positioned to our north will maintain a deep ely flow over our
region with the best moisture confluence across the sandhills and
the southern piedmont. While the atmosphere will be slight-
moderately unstable across the northeast piedmont/northern coastal
plain, difficult to discern any mechanism to initiate lift, aside
from strong heating. Even across the southern counties, little if
any support discernible aloft to initiate/sustain convection. Thus,
appears we will need to rely on orographic lift and residual outflow
boundaries from previous days convection along with strong heating
to initiate lift. With the meso analysis depicting the best moisture
axis residing across our southern and western counties, should see
the greatest concentration of convection in this part of the
forecast area (though no worse than scattered (30-40 percent)).
A few strong storms possible with the main hazard being strong gusty
winds ~40-45kts and frequent lightning. This has been addresses in
the latest HWO product.
Afternoon temps in track to reach the low-mid 90s. Counting on some
cloud build up/scattered convection to moderate temps a little this
afternoon. If this does not occur, places such as Fayetteville and
Laurinburg may reach the upper 90s. Afternoon heat index values
expected to vary from 98-102 degrees across the north and 102-105
degrees across the south. Do not plan an advisory at this time but
will continue to monitor.
What convection is occurring at 6 PM will quickly diminish/dissipate
around sunset. Under clear-partly cloudy skies, overnight temps will
lower into the low-mid 70s.
.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 350 AM Saturday...
The upper level ridge will continue a northward drift on Sunday,
while an upper disturbance over the Atlantic slowly drifts west
and undercuts the ridge, essentially settling over the Southeast
US through early next week. This disturbance along with increasing
moisture flux off of the Atlantic - PW increasing to around 2
inches - and weak to moderate instability will likely result in
enhanced convective coverage along the coast, drifting inland
through the day. Coverage will be best over the coastal plain,
diminishing with westward extent into the Piedmont where deeper
mixing and drier air will limit coverage. Some of the showers may
continue into the evening and overnight hours, mainly across the
southern coastal plain. Highs 89-92, warmest west. Lows 69-74.
.LONG TERM /MONDAY THROUGH FRIDAY/...
AS OF 350 AM Saturday...
WV imagery this morning depicts an increasingly well-defined mid to
upper level low a few hundred miles SW of Bermuda. The forecast
models continue to indicate this feature will drift W --around the
SRN periphery of an initially strong sub-tropical ridge over the
Central Appalachians and Middle Atlantic states-- and stall along
the SE U.S. coast early next week. Divergence and upper level
venting in the deformation zone to the N of the low /over NC/ in
conjunction with convergence along the sea breeze, will support a
chance of diurnal convection over the ERN half of our forecast area,
also where boundary layer moisture is forecast to be most plentiful,
The presence of the mid-upper low and associated height falls will
also cause the preceding sub-tropical ridge to split, with an
associated positively-tilted trough/shear axis expected to evolve
invof the SERN and SRN Middle Atlantic coasts through mid week.
While this weakness in the ridge will provide a corridor through
which low pressure associated with the tropical wave now over the
central Bahamas could pass --up the coast and mostly E of central
NC-- this system remains disorganized and the probability of any
appreciable development at all decreases with each passing day - now
40 percent or less per the NHC. It will nonetheless bear watching
and remain a forecast concern for FL and the adjacent Gulf and SERN
U.S. coastal areas during the next few days.
Thereafter, the aforementioned split in the sub-tropical ridge will
cause the main ridge center to retrograde and strengthen over the
central U.S., with accompanying downstream trough development in the
ERN U.S. through the end of the week. The models indicate an
associated NRN stream cold front will settle through the SRN Middle
Atlantic states and Carolinas Thu-Fri, with an accompanying chance
of convection maximized in central NC on Thu, followed by cooler and
drier conditions in post-frontal high pressure ridging across the
Middle Atlantic region, on Fri.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
As of 640 AM Saturday...
Currently VFR at TAF sites, with MVFR vsbys around the northern
Piedmont. Vsbys may still briefly fall to 4-6sm at the TAF sites
prior to 13z. There are also a few isolated showers moving
southwest through the northern coastal plain, but the chance of one
moving over RWI is very low. Models continue to suggests widely
scattered showers and storms are possible this afternoon with an
easterly flow setting up. These should mostly be confined to an area
from KFAY to just south of KGSO/KINT, though confidence is low given
very little forcing to initiate storms. Will indicate the best
chance at KFAY after 19z.
Afternoon storms will diminish after sunset, and most of the night
will be VFR. East-northeasterly flow will support stratus across
the coastal plain late tonight, so have included some IFR ceilings
at KRWI and KFAY after 09z.
Long Term: VFR conditions are expected to prevail over the next few
days, with after noon showers and storms mostly confined to the
eastern areas of NC. Some early morning fog/stratus will also be