Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 220619
Area Forecast Discussion
National Weather Service Raleigh NC
219 AM EDT Sat Apr 22 2017
-- Changed Discussion --A cold front will settle south through VA this morning and into
central NC this afternoon through tonight. The front will stall over
southeastern NC by Sunday, in advance of a slow-moving area of low
pressure that will track along the coast of the Carolinas through
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.NEAR TERM /THROUGH TONIGHT/...
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.
.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 /06Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 215 AM Saturday...
A series of disturbances in WSW flow aloft will interact with an
outflow boundary (from earlier and ongoing convection) that remains
draped from SW to NE across central NC from near CLT to JNX to EDE.
A continued threat of showers and associated sub-VFR visibility
restrictions will result along and north of the boundary,
particularly at Piedmont sites through daybreak. In addition, there
is a small chance of scattered to broken IFR-MVFR range stratus on
the north/cool side of that boundary, also at Piedmont sites, around
daybreak. VFR conditions and a warm and breezy SW wind will
otherwise result until another round of showers and storms fire
along both the aforementioned outflow boundary and a cold front that
will settle south from VA late this afternoon and evening. MVFR
ceilings, patchy light rain, and gusty post-frontal NEly winds will
develop behind, and with the passage of, the front this evening.
Outlook: A prolonged period of rain/showers and sub-VFR ceilings and
visibilities --in springtime cold air damming-- can be expected
later tonight through Tue night, as an area of low pressure tracks
east along the aforementioned front, then slowly up the coast of the
Carolinas. Conditions will be slow to improve as the coastal low
drifts only slowly away from our region, with a return to VFR on
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