Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
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FXUS62 KRAH 251352
Area Forecast Discussion
National Weather Service Raleigh NC
945 AM EDT Tue Apr 25 2017
An upper level low and attendant surface low pressure system will
track northeast along the North Carolina coast today, then progress
offshore the Mid-Atlantic coast tonight.
.NEAR TERM /Today and Tonight/...
-- Changed Discussion --As of 945 AM Tuesday...
Rainfall rates are improving, but flooding persists in many places
this morning. Flood warnings remain in effect for much of north
The mid level low analyzed over SE NC this morning will wobble to
the NNE over E NC through today. The band of heavier rain, supported
in part by strong upper divergence and steep (~6.5 C/km) 700-500 mb
lapse rates atop strong low level mass convergence, will continue to
pivot to the west across the NE Piedmont, although rates and
intensity have diminished in the last couple of hours with warming
cloud tops as the drier air pushing westward over eastern NC,
wrapping around the mid level low, steadily erodes the precip
shield. The latest HRRR runs and other CAMS support a trend toward
lighter rainfall as this band pivots W and WSW into the Sandhills
and W Piedmont over the next few hours and decreases in coverage.
Additional isolated to scattered convection is expected over NE NC
this afternoon beneath another batch of weaker upper divergence,
deep 6+ C/km lapse rates, and abundant low level moisture. Have
adjusted precip chances through today to account for this scenario.
Expect highs of 60-65 over much of the Piedmont and Sandhills, where
the stable pool should stay locked in with low level cold air
advection and considerable cloudiness, and 65-72 over the Coastal
Plain and far southern CWA, which are more likely to see a little
Earlier discussion from 745 am: Heavy rain will persist for several
more hours in the Triangle, northern Piedmont and NE Coastal Plain
before winding down ~15Z as the primary band of elevated convection
pivots SW-NE over the western Piedmont and weakens as the Atlantic
moisture feed is cutoff over central NC (on the western periphery of
the upper level low tracking NE along the Carolina coast). The watch
will be allowed to expire given that heavy rain will persist for
just a few additional hours and flooding is ongoing at this point
/numerous flash flood warnings are in effect/. -Vincent
400 AM Discussion: The NW-SE oriented band of elevated convection
streaming inland from the Atlantic early this morning has been
associated with strong low-level warm advection (~50 knot easterly
H85 flow) and DPVA assoc/w small amplitude waves rotating around an
upper level low centered in vicinity of the SC coast at 07Z. Now
that the upper level low is tracking east of -79 degrees longitude
(roughly), the aforementioned band of elevated convection has
pivoted toward a WNW-ESE orientation and will pivot W-E by ~12Z and
SW-NE over the N/W Piedmont by ~15Z. Expect the heaviest rainfall
/precip rates/ to shift along and north of Hwy 64 from Rocky Mount
to the Triangle over the next few hours before weakening after ~12Z.
The upper level low tracking eastward this morning will assume a NE
motion along the NC coast this afternoon/evening. As shortwave
energy /DPVA/ rotates cyclonically from the northern periphery to
the western periphery of the upper low centered along the NC coast
this afternoon, convection is expected to re-develop over portions
of the area. Confidence in coverage is lower than average, however,
the bulk of activity should be confined from the Triangle into the
northern Piedmont and NE Coastal Plain. Marginal destabilization,
low equilibrium levels, and close proximity to the upper low suggest
little potential for convective organization this afternoon. Given
weak steering flow near the upper low, an isolated flash flood
threat could accompany convection that develops in the NE Coastal
Plain this afternoon, assuming it persists for a few hours. -Vincent
-- End Changed Discussion --
.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 400 AM Tuesday...
In the wake of the low pressure lifting up the Mid-Atlantic coast,
low-level southerly winds and short wave ridging aloft will mark the
return of sunshine and warming temperatures. Highs ranging from
upper 70s NE to lower 80s south. Lows Wednesday night in the upper
50s to lower 60s.
.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 400 AM EDT Tuesday...
Lead short wave trough will lift from the Mid MS/TN Valley NE into
the Great Lakes on Thursday with trailing sfc cold front expected to
stall out west/northwest of the mtns.
Associated convection is expected to be ongoing Thursday morning
across Tn, Al, and Ga Thursday morning. However with the better
trough dynamics/forcing lifting off well to the north Thursday
afternoon and evening, the showers and storms should exhibit a
steady decline/weakening trend as they cross the mtns Thursday
afternoon/evening. Will leave isolated chances across the far
western zones Thursday afternoon, otherwise it should remain dry
with temperatures steadily rising in the SWLY WAA regime. Highs in
the lower to mid 80s west to upper 80s central and eastern areas.
The synoptic pattern will favor near record heat by Saturday, owing
to a 590+dm H5 ridge, Bermuda highs and H7 anticyclone over SC.
Thickness are progged at 1410m Saturday, 50m above normal and
indicative of upper 80s to lower 90s. The main question is how
quickly another shortwave ejecting out of the Central/Southern
Plains, this one potentially stronger, will cause the ridge to
retreat offshore a bit. Heights are forecast to lower slightly on
Sunday, more so across western NC. Highs in the mid 80s west to near
90 central and eastern area.
A cold front will bring the next chance for rain/storms to the area
on Monday with cooler temps following on Tuesday.
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
As of 745 AM Tuesday...
24 Hour TAF Period: Adverse aviation conditions are expected to
continue through the 24 hour TAF period (high confidence) as a deep
mid/upper level low moves across the region.
Expect IFR/LIFR conditions to prevail at most terminals through this
evening, though periods of MVFR/VFR conditions will be possible. The
primary band of elevated convection /heavy rain/ will affect the
RDU/RWI terminals through late morning. After a lull, scattered
convection may re-develop at the same terminals later this
afternoon. Ceilings are expected to improve by or shortly after
midnight at the GSO/INT terminals, though IFR/LIFR ceilings may
persist through the TAF period at eastern terminals.
Outlook: After the low shifts NE along the Mid-Atlantic late
tonight, VFR conditions are expected to prevail by mid-day
Wednesday. VFR conditions will prevail through Sat. -Vincent
As of 400 AM Tuesday...
The flood watch will be allowed to expire at 800 am EDT as
precipitation rates decrease and the primary band of elevated
convection weakens/pivots to a W-E orientation north of Hwy 64
followed by a SW-NE orientation over the W/NW Piedmont by 12-15Z. If
convection redevelops in the NE Coastal Plain this afternoon, an
isolated flash flood potential could briefly exist given weak
steering flow and slow/nearly stationary motion. -Vincent