Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 270557
Area Forecast Discussion
National Weather Service Raleigh NC
156 AM EDT MON SEP 26 2016
-- Changed Discussion --A cold front will stall across the Carolinas today through late in
the work week, bringing unsettled weather through the period.
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.NEAR TERM /OVERNIGHT/...
As of 910 PM Monday
Have adjusted PoPs upward over the western-nw Piedmont as a band of
convection has arrived and has begun to slow its eastward
progression. This is raising concerns for a localized excessive
rainfall, mainly just south of Winston-Salem and Greensboro,
encompassing Lexington and Asheboro, and west of RDU, affecting the
Chapel Hill/Carrboro area. Some locations in the area described
above may receive 2-3 inches of rain in less than 3 hours before 2
Am Tuesday. This may cause a few creeks and streams to leave their
banks and may lead to an isolated road closure or two. Believe the
threat is too isolated for a flash flood watch but will continue to
The scenario is a classic set-up with a slowing band of convection
becoming perpendicular to a sly feed of moist air. Tonight, this
west-sw/e-ne band is encountering a sly south of 15-20kts in the 925-
850mb layer, advecting moist air with precip water values 1.6-1.8
inches, close to 150 percent of normal. Additional lift being
supplied aloft by 100kt jet crossing the eastern Great Lakes,
placing the nw Piedmont in the favored right entrance region.
Farther east, mainly for areas east of highway 1, overcast skies and
and a few spotty showers are expected though overall coverage and
intensity are expected to be spotty and light.
Overnight temps will be fairly uniform due to the overcast skies and
light sly flow. Min temps mid-upper 60s.
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 250 PM Monday...
The cold front will inch eastward into the Piedmont on Tuesday,
slowed further by system parallel flow induced by the upper low
that will close off and dig toward the Tenn Valley. PW will remain
relatively high at 1.75", though the source of higher PW off the
coast looks to be cut off by a surface wave that lights northeast
along the NC coast. Forcing is pretty much limited to moisture
convergence along the front, with better height falls later
Tuesday night ahead of the aforementioned upper low. Despite weak
lapse rates aloft, highs in the upper 70s/lower 80s should result
in weak instability and trigger scattered to numerous showers and
a few isolated, mainly in the Piedmont. Increasing mid-level wind
fields will increase the shear over the region Tuesday afternoon,
but weak instability (better Wednesday) will ultimately limit the
threat of severe storms. Based largely on WPC guidance, 0.5-1.0"
of rain is generally expected.
As mentioned above, forcing aloft is a little better late Tuesday,
albeit with less instability (though forecast soundings do show
some thin MUCAPE that may enhance parcel lift). The front isn`t
expected to make much progress eastward, so there may be a
limited flooding threat worth watching Tuesday evening, largely
dependent on how active the front is tonight and Tuesday. Lows
again in the upper 60s.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
As of 345 AM Monday...
PoPs will be higher...chance category...in the east on Wednesday
due to proximity of the lingering frontal zone where moisture
advection will maintain precipitable waters in excess of 1.5
inches. Dry air wrapping into the area around the upper low will
be sufficient to produce a chance of thunder...especially I95
eastward. Highs will be similar to Tuesday...mid-upper 70s with
some lower 80s in the southeast.
Upper cutoff low over the Great Lakes throws a lot of uncertainty
into the forecast heading into the late week...but at this point
both GFS and ECWMF stall the southerly and easterly progress of the
system in the Tennessee Valley and lift it back north into the Great
Lakes over the weekend. Dry trajectory and maintenance of neutral
temperature advection around the low supports our ongoing dry and
seasonable forecast with highs mostly in the mid to upper 80s.
Morning lows will feel nippy...with mins falling into the mid to
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --As of 156 AM Tuesday...
A pre-frontal band of showers and thunderstorms over the NC Piedmont
will move slowly eastward this morning and into the midday hours,
diminishing/weakening along the way. IFR to MVFR ceilings through
12z should remain confined to KINT, KGSO, and KRDU, along the axis
of stronger low-level moisture transport. These sub-VFR ceilings
should gradually lift to VFR between 15 to 18z, with additional
showers and storms re-developing across western NC and moving
eastward this afternoon and evening as the sfc cold front stalls
across western NC. Otherwise, at KFAY and KRWI, expect predominately
VFR ceilings with some isolated shower or two possible.
Looking beyond the 24 TAF Period: The combination of a quasi-
stationary front across the Carolinas and a cut-off upper level low
settling over the Tennessee Valley will keep unsettled weather in the
form of scattered to numerous showers and storms through Thursday.
Drier air from the west should gradually advect east into the area
late Thursday and into Friday, leading to improving conditions
with dry VFR conditions expected Friday and Saturday.
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