Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
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FXUS62 KRAH 240038
Area Forecast Discussion
National Weather Service Raleigh NC
838 PM EDT FRI SEP 23 2016
An upper level low and the remnant low from Julia will linger and
weaken near the southern Carolina coast through Saturday. A cold
front will drop south into the area late Saturday and stall south
of the region on Sunday. A stronger cold front will push through the
region late Tuesday or early Wednesday.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 325 PM Friday...
18 UTC surface analysis shows the persistent remnant low from
Julia becoming elongated and located off the northeast SC coast.
A weakening mid level vortex that was located across the eastern
Carolinas was beginning to shear out and open up as a well defined
shear axis drops into NC. The air mass across the eastern
Carolinas remains very moist with precipitable water values in
excess of 1.9 inches in the southern coastal region and Coastal
Plain with much drier air, noted by PW values of 1.5 inches or
less moving into northern and northwestern NC. The latest visible
satellite imagery shows clearing skies moving into northern and
northwestern NC with the widespread stratus across southeaster NC
giving way to an increasing amount of breaks in the overcast.
Widely scattered showers have developed to the south and southeast
of Rocky Mount, Raleigh and Troy with more numerous showers and
thunderstorms along the immediate NC coast.
Convection allowing models fit current trends well and gradually
push the scattered showers in central south this afternoon before
dissipating early this evening. While the latest analysis shows
the air mass weakly unstable with MLCAPE values between 500 and
1000 J/Kg, we have omitted the inclusion of thunder in the
forecast. Skies should continue to clear this evening with the
loss of heating and the arrival of drier air and subsidence behind
the shear axis. Some clouds may persist across the southeast
before areas of fog and perhaps some low stratus develop
overnight. The stratus will be most widespread from the northern
Coastal Plain southwest across the remainder of the Coastal Plain
into the Sandhills and eastern Piedmont. Lows tonight will range
in the mid 60s northwest to near 70 southeast. -Blaes
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
As of 320 PM Friday...
Fair weather and warmer temperatures are expected on Saturday as
weak high pressure is present across the region at the surface and
ridging to the west extends into the area. The air mass dries out
considerably from previous days with precipitable water values
during the day ranging less than 1.25 inches across most of
central NC. With a good deal of sunshine and an increase in low
level thickness values, have adjusted maxes for Saturday upward a
couple of degrees. Both the NAM and GFS MOS gives a high of 88 for
RDU but the most recent EC MOS provides a high of 91. If we get a
good amount of sunshine as expected, highs should easily range in
the upper 80s to around 90, perhaps a couple of degrees warmer.
A cold front will drop south across the Mid Atlantic Saturday
morning and move into NC during the late afternoon or evening and
then push toward the SC border on Saturday night. NWP guidance has
trended wetter with this system. There may be some light
precipitation generated behind the front overnight that pushes
south across the northeast Piedmont and northern Coastal Plain.
The boundary layer is initially rather dry but it moistens
overnight with some low stratus and drizzle possible by morning.
Overnight lows should range in the mid to upper 60s. -Blaes
.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 245 PM Friday...
The timing of the back-door cold front through the area on Sunday is
still in question. The GFS and NAM are much quicker to blow the
front south through the area late Saturday night/ear Sunday, while
the ECMWF suggest the frontal boundary will tend to "hang up" or
slow down across the forecast area on Sunday, which is very
plausible given weak sfc pressure rises from the transitory parent
high center retreating off the Northeast-Southern New England Coast.
These models discrepancies are leading to lower than average
forecaster confidence, making for a challenging temperature forecast
on Sunday and likely setup a sharp temperature gradient across the
area. For now will continue a "middle of the road approach" with
highs ranging from mid 70s northeast to mid 80s southwest.
Additionally, given the potential for the front invof the area, will
continue isolated to slight chance chance pops.
Mid/upper level ridge will build east over the area on Monday in
advance of a closed low and upper trough progressing eastward into
the Upper Great Lakes/Southern Canada. With the transitory parent
high quickly moving off the Southern New England Coast, south-
southeasterly return flow will quickly return to the area late
Monday with rain chances generally restricted to
upslope/differential heating over the higher terrain, while ridging
aloft should keep the remainder of NC dry. SELY moisture advection
and resultant weak isentropic upglide in advance of a cold front
approaching from the west could produce showers across the area as
early as Monday night/Tuesday morning with another round of showers
and storms expected to accompany the frontal passage Tuesday
afternoon/evening. Highs Monday and Tuesday slightly above normal
with mild overnight lows in the 60s.
In the wake of the cold front, high pressure will bring dry
seasonable weather for the later half of the work week. Highs 75-80.
Lows the 50s.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 835 PM Friday...
24 Hour TAF Period: VFR conditions are expected to continue this
evening, with any isolated showers from early today having
dissipated with the loss of daytime heating. While the weak area of
low pressure has moved further to the south and east of the area
this evening and skies have generally cleared, we still expected
some sub-VFR conditions to develop overnight. Given mostly clear
skies and calm to light and variable winds overnight, coupled with
recent rainfall, expect we will see some sub-VFR visbys develop
after midnight through around sunrise. Conditions are expected to
range from VFR/possibly MVFR at KGSO/KINT to IFR/LIFR at
KRDU/KFAY/KRWI. Any reduced visbys that develop should lift and
scatter within a couple hours of sunrise.
VFR conditions are expected to continue after the morning fog
lifts/dissipates, with generally light wind with a northerly
Outlook: VFR conditions are expected on Saturday evening before a
cold front moves into the region from the north Saturday night. A
period of adverse aviation conditions including reduced ceilings and
visibilities in showers are possible beginning late Saturday
night/Sunday morning and continuing through early Monday. Another
period of adverse aviation conditions is possible late Monday into
Tuesday as another cold front approaches the region.
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