Area Forecast Discussion
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FXUS62 KRAH 260106
Area Forecast Discussion
National Weather Service Raleigh NC
905 PM EDT SUN SEP 25 2016
A cold front will move into northern South Carolina and stall
this evening and overnight. High pressure will build south into our
region from New England tonight. The front will return north as a
warm front late Monday as a cold front approaches from the west.
.NEAR TERM /OVERNIGHT/...
As of 905 PM Sunday...
A band of moisture in the lowest 8k ft of the atmosphere underneath
a mid/upper level ridge will result in a deck of low clouds over
most of central NC overnight. The exception will be the far southern-
southwest sections where skies may remain partly cloudy.
Most of the convective allowing models as well as successive runs of
the HRRR suggest scattered showers in vicinity of the Triad late
this evening into the overnight hours. Based on current moisture
profile and upper air analysis, moisture appears too shallow and
synoptic lift virtually non-existent to suggest anything more than a
slight chance PoP for the western counties through the night. May
see pockets of fog over the western and southern counties though
dense fog not anticipated at this time.
Overnight temps will vary from the upper 60s over the southwest to
near 60/lower 60s over the northeast.
.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As of 245 PM Sunday...
Monday will be a murky day as hybrid CAD is expected to develop over
the western Piedmont as a warm/moist advection pattern sets up
between the surface and 850 mb. This occurs as the low level ridge
axis begins to shift east and the next cold front approaches the
Appalachians from the west. Expect the moisture profile further
increase though the day, except for the far eastern zones were some
drying will linger with the ridging. As a mid level trough and the
cold front approach the mountains late, the associated lift and
upslope easterly flow generate areas of rain. This will aid in
locking in the hybrid CAD over the damming region. This pattern will
persist overnight with rain likely in the west, spreading east into
the rest of central NC overnight. We will cap of POP in the high
chance category in the SE Coastal Plain through 12Z/Tue as they will
be farther away from the approaching trough and cold front through
then. Highs Monday from the lower 70s NW to mid 80s south. Lows
Monday night 65-70. QFP of 0.25 to 0.50 forecast for the NW with
less than 0.10 in the SE through 12Z/Tue.
.LONG TERM /Tuesday through Sunday/...
As of 330 PM Sunday...
Tuesday through Wednesday night: A mid/upper low will settle
southward across the Great Lakes on Tuesday, with an associated cold
front moving into central NC Tuesday... before stalling across
eastern portions of central NC Tuesday night. Given sufficient
moisture advection in advance of the cold front, PW`s increasing to
around 1.75", we should see scattered to numerous showers and some
storms on Tuesday into Tuesday evening with potentially even some
localized minor flooding in urban areas/poor drainage areas. With
regard to a severe threat, instability still looks to be weak to
(maybe) modest (with the NAM more robust with its instability).
Deep shear of around 20 to 30 kts is expected. The best height falls
and stronger winds are expected to remain to our north though,
yielding poor mid level lapse rates. Thus, any severe threat will
remain low. However, as noted in the day 3 convective outlook from
SPC, we still could see a few strong to potentially severe storms
with the main threat from damaging winds. High temps on Tuesday are
expected to be generally be in the upper 70s to lower 80s. Lows
temps, with the front stalling across eastern/southeastern half of
the area are expected to range from the mid to upper 50s nw to the
mid 60s se.
The deep mid/upper low will continue to slowly sink
south/southeastward into the Ohio Valley region on Wednesday, with
the mid level flow across our area becoming parallel to the
lingering front. As the mid/upper low approaches, an area of low
pressure is expected to form along the stalled front and track
north/northeastward across central NC, allowing for a continued
chance for showers and some storms on Wednesday into Wednesday
night, with the best chance across the eastern half of the area.
Highs Wednesday are expected to range from the the mid to upper 70s
north to around 80 south/southeast. Lows Wednesday morning are
expected to range from the mid to upper 50s north/northwest to the
lower 60s southeast.
Thursday through Sunday: Forecast confidence is low for this period
of the medium range, with uncertainty about what will happen with
the deep mid/upper low expected to be near the Southern Appalachians
to start the period. The GFS lingers the mid to upper low just to
the north of the area late week, before it lifts off to the
northeast over the weekend. Meanwhile, the latest ECMWF retrogrades
it westward and northward to around IN/IL by 12Z Sunday, allowing
the front to dissipate across our area. The GFS on the other hand
allows the front to shift to the east of the area allowing for below
to near normal temps for the remainder of the period, and dry
conditions generally by Friday. The GFS has been more consistent
with the medium range ensemble guidance. Thus, plan to stay closer
to the GFS (which is wetter than in previous days through Thursday
thank to the GFS now not being as progressive as it past runs).
.AVIATION /00Z MONDAY THROUGH THURSDAY/...
As of 809 PM Sunday...
MVFR/IFR conditions at KRDU, KINT, and KGSO will likely lower to
IFR/LIFR overnight. VFR conditions currently at KFAY, in the
vicinity of the boundary, and KRWI, where some drier air has been
filtering down the east coast and into northeastern areas of the
state. Some uncertainty exists as to whether IFR CIGS expand back
into these areas, though this seems most likely at KRWI. IFR
conditions will hold through Monday at the Triad sites, where
wedging will be slowest to erode, with some improvement to MVFR at
KRDU/KRWI, and VFR at KFAY.
Looking beyond 00Z/TUE, CIGS again will lower with areas of rain and
fog in the west, with an increasing chance of rain and fog in the
east. IFR to MVFR CIGS and VSBYS are expected Monday night into
Conditions are expected to improve Wednesday and Thursday.