Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 220132
Area Forecast Discussion
National Weather Service Raleigh NC
935 PM EDT Fri Apr 21 2017
A pre-frontal surface trough will linger over western NC tonight.
Meanwhile, a cold front will approach from the north tonight, then
sag into NC Saturday. The front will stall over far southern NC late
Saturday into Sunday, as a slow-moving area of low pressure tracks
along the front through the weekend.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 935 PM Friday...
Highest threat for scattered showers and isolated thunderstorms into
the overnight expected to occur across the Piedmont into the far
northern coastal plain. Air mass across the region fairly moist with
precip water values hovering around 1.25 inches. At the sfc a weak
sfc trough extended from the foothills of western NC newd into VA.
The main sfc cold front stretched from western PA southwest into
middle TN. Aloft a weak perturbation was traversing eastward,
entering the western sections of central NC. This feature aloft
interacting with available moisture and weak convergence along the
sfc trough will maintain a threat for scattered showers, primarily
prior to midnight across the western Piedmont, and into the
overnight across the northeast Piedmont and the far northern coastal
plain. Severe storm parameters barely register across our region
while the better shear and instability reside well to our west and
Plan to maintain broken-overcast skies across the north half, and
variably cloudy skies across the south. Temperatures should be
fairly uniform in the 60-65 degree range.
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.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 355 PM Friday...
The focus for showers and thunderstorms is expected to remain over
the western and northern zones of the Piedmont, as far south as
Albemarle to Raleigh to Rocky Mount - mainly Saturday afternoon into
the evening. This is where the low level boundaries should aid in
focusing the convective development. A blend of the Hi-res models
along with the GFS/EC were used in trying to place the main synoptic
cold front that is forecast to dive into the northern Piedmont
Saturday afternoon. Convection and associated outflows tonight will
greatly aid in convective initiation Saturday. The latest Hi-Res HRRR
suggests this may occur by early afternoon in a SW-NE corridor from
west-central NC to just north of the Triangle area. The main push of
much cooler and damp NE flow should hold off until late afternoon
and evening, which will eventually stabilize the boundary layer and
spread a low deck of clouds with it. Therefore, the temperatures
should show a very large range from upper 50s NE into the mid 80s
south during the late afternoon. A few marginally severe storms may
occur especially along the leading temperature/cloud gradients.
Showers and a few thunderstorms (elevated north of the cold front)
are expected for much of the Piedmont, Sandhills, and Coastal Plain
Saturday night. Widespread activity is expected in the west into the
central portions of NC, with more scattered activity down east. The
cold front should backdoor much of central NC, except the far SE
zones by 12z/Sunday. This will eliminate much of the severe threat,
but elevated storms will likely produce locally 1 to 2 inches of
rain in the western and central Piedmont by 12z/Sunday.
Since it has been dry recently, flash flooding is not likely through
12z/Sunday unless 1.5+ inch/hour rates and/or 3+ inches
in 3 hours materialize.
Lows will cool into the 50s, except 60s south Saturday night with
POP nearly 100 all zones.
.LONG TERM /SUNDAY THROUGH SATURDAY/...
As of 255 PM EDT Friday...
An amplifying upper level low digging SE from the Rockies into the
Lower Midwest this afternoon will track eastward through the TN
valley on Saturday, progress ESE/SE toward the Southeast coast on
Sun/Mon, then shift offshore the GA/SC coast on Tue. Shortwave
ridging /WSW flow aloft/ is expected in the wake of the upper wave
on Wed/Thu. Even though the upper wave has moved ashore and been
sampled by the RAOB network, confidence in forecast specifics
(precip amounts, severe weather potential, temperatures) remains
below average due to the potential interaction between the
aforementioned upper low and northern stream shortwave energy
progressing east across the Great Lakes into New England, with
additional uncertainty assoc/w the effects of upstream convection
(heavy precipitation /latent heat release/) progged over portions of
the Carolinas/Southeast late this weekend. Broadly speaking, expect
mostly cloudy skies, cooler temperatures, and increasing chances for
convection over the weekend, particularly Sunday/Sunday night. The
best potential for surface based convection will be on Sat, though
coverage is difficult to ascertain at this time. Elevated
convection is more likely on Sunday, though some potential for
surface based convection may exist in the far S/SE. Chances for
precipitation will diminish from west-east and skies will clear by
Tue/Tue evening as the upper level wave progresses offshore. Expect
dry conditions and a warming trend Wed-Sat as an upper level ridge
builds over the Southeast CONUS. The next best chance for
precipitation may not materialize until early next week. -Vincent
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 840 PM Friday...
24 Hour TAF Period: Several rounds of isolated to scattered showers
and thunderstorms are expected over the next 24 hours across central
NC in advance of a cold front.
Convection this afternoon/evening has generally remain isolated to
widely scattered and is expected to generally remain so into the
overnight hours. However, KGSO/KINT stand to see the best chance of
seeing some showers and storms for the remainder of the evening into
early Saturday morning as another round of showers and storms is
expected to clip the NW Piedmont of central NC. Brief IFR/MVFR
conditions will be possible with any convection this evening along
with perhaps a wind gust or two to around 25 to 30 kts. Otherwise,
VFR conditions are generally expected tonight. However, there is a
small chance we could see some sub-VFR cigs at KGSO/KINT/KRDU around
A cold front will approach the region from the north-northeast on
Saturday, possibly move south-southwestward across KRWI and KRDU
near the end of the TAF period. Near and behind the front, expect we
will see some showers and storms, along with accompanying sub-VFR
conditions and possible strong wind gusts. Thus, have included a
prob30 group for all the northern TAF sites for the last 4 hours or
so of the TAF period. Behind the front, expect cigs will quickly
fall to low end MVFR or IFR, with winds out of the north to
Outlook: The cold front should stall over the region through Sunday
night, though likely just to the south of the central NC TAF sites.
This will allow for several waves of low pressure to track along the
front and bring numerous showers and possibly some thunderstorms.
Periods of showers and storms with MVFR to IFR CIGS and IFR VSBYS
will occur Sat PM through Monday night, possibly lingering into