Area Forecast Discussion
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FXUS62 KRAH 230558
Area Forecast Discussion
National Weather Service Raleigh NC
155 AM EDT Sun Apr 23 2017
A cold front will push southward through North Carolina overnight,
reaching the South Carolina border by daybreak. A strong low
pressure system will slowly cross the region through Tuesday.
.NEAR TERM /THROUGH TONIGHT/...
As of 950 PM Saturday...
Colder air has begun to overspread central NC from the north.
Temperatures at mid-evening ranged from the lower 50s far north to
the mid-upper 70s far south. The cold front, which marked the
leading edge of the change in air mass, stretched west-to-east from
Albemarle to Ft Bragg to south of GSB at 01Z. This boundary should
exit our southern counties prior to midnight.
Area of showers will overspread most of central NC behind this
boundary overnight as an upper level disturbance exits the TN Valley
and crosses our region. Could see a few isolated elevated storms
though severe parameters are much weaker than compared to earlier in
the day. Still expect the bulk of the showers overnight to occur
across the Piedmont counties and the northern coastal plain where
better forcing will exists. Rainfall amounts expected tonight will
total a half inch or less, so not expect anything to set off any
flooding. The rain tonight into early Sunday will prime the soils
for the heavier, more prolonged rain expected later Sunday into
Main adjustment to the near term forecast was to bring the colder
air in faster than previous forecast as temperatures at mid evening
were running some 2-4 degrees colder across the north than expected.
This required a downward tweak in the minimum temperatures,
primarily across the south.
.SHORT TERM /SUNDAY THROUGH TUESDAY/...
As of 355 PM Saturday...
...Flood Watch from midnight tonight through 800 AM Tuesday...
The beginning of a long duration rain event will be underway over
the western and central Piedmont by 12z/Sunday. The mid/upper trough
is forecast to become negatively tilted during this period as it
drifts ESE from the Tennesse Valley region across the southern Mid-
Atlantic states. At the surface, a backdoor cold front will also
begin Sunday either over far southern NC or near the NC/SC border
region. This will place nearly all, if not all of central NC in the
cooler stable air. Models suggest that a surface low pressure will
be located over NW Georgia around 12z/Sunday, then move east across
eastern GA and SC Sunday PM. As the low pressure slowly strengthens
as it moves east across SC Sunday night and Monday, the low level
boundary should back NW and just inland of the coast Monday. This
still leaves central NC on the cool, wet side of the boundary with
copious amounts of very moist warm air advection from off the Gulf
Stream and western Atlantic expected to ride up and over the frontal
zone. This occurs as the mid/upper system becomes more negatively
tilted as it essentially crawls eastward, just to our south Sunday
night and Monday. The heaviest rain is expected to fall along and
north of the frontal zone through the period as the strong dynamic
forcing slowly advances east across the area. This will place the
Piedmont and Sandhills in the heaviest rain Sunday. The heaviest
rain is forecast to spread east with time, covering much of our
region Sunday night into Monday. Models are not as robust with the
elevated instability Sunday night and Monday as they are on Sunday.
However, the influx of very high precipitable waters off the Gulf
Stream and western Atlantic should will aid in heavy rainfall at
The threat of flooding will be the main hazard with this system
since our region will be in the more stable area north of the main
frontal zone. QPF storm total for the entire event is on the order
of 3-5 inches, with potentially 6 inches locally. The main time
frame for the heaviest rain should be from midnight tonight through
midnight Monday night.
Flash Flood Guidance numbers will lower with time, which are
currently running high. 6 hour FFG is on the order of 2.5 to 3
inches, and this will lower to around 1.5 inches by Sunday
afternoon. Urban areas have much lower thresholds, and they will
become an issue well before the rural locations. The soils, which
have recently been dry will become wet and saturated with the
showers/storms this evening into Sunday. This will lead to runoff
issues with the widespread heavy rain Sunday afternoon through
Monday evening. Gusty NE winds will be felt in all zones with
sustained winds of 15-25 mph, gusts to 30-35 Sunday into Monday.
Less important forecast parameters include the temperature forecast
which will be much cooler with the heavy rain and breezy NE winds.
Highs Sunday should only be in the 50s/60s NW/SE both Sunday and
Monday. Lows will be only about 5-7 degrees lower than daily maxes,
The heaviest rain should move offshore on Tuesday or Tuesday
evening, with the threat of moderate river flooding on the main stem
rivers expected into late week.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 345 PM EDT Saturday...
Much warmer air associated with a building subtropical mid level
ridge can be expected late week into the weekend when highs should
solidly get into the 80s.
.AVIATION /06Z Sunday through Friday/...
As of 155 AM Sunday...
High confidence in poor aviation conditions over the next 24 hours,
With IFR conditions common in all locations except mostly MVFR at
FAY. A cold front dropped southward into and through NC this past
evening, and is now settling near the NC/SC state line. This front
will remain stretched across northern SC and southeast NC through
the next 24 hours, while surface low pressure drifts slowly from
northern AL toward southwest NC, and strong mid level low pressure
passes over the Mid South. This will all keep unsettled weather over
central NC, with deep moisture leading to low cigs, lowest at
INT/GSO, through Sunday night, with periods of MVFR to IFR rain,
most widespread at INT/GSO but likely everywhere. Surface winds will
be mainly from the NE at 10-15 kts gusting to 15-20 kts infrequently
through Sunday night. While winds aloft (4000-5000 ft AGL) will be
strengthening from the SE late Sunday through Sunday night to 25-35
kts, however the shift of winds in the vertical from NE to SE
through the low levels will not meet low level wind shear criteria,
although it may make handling of small aircraft difficult.
Looking beyond 06z Mon: Poor aviation conditions will continue to
dominate through Monday night as the deep low pressure system slowly
crosses the region, with periods of rain through Mon, tapering down
from south to north Mon night, and persistent low MVFR/IFR cigs and
vsbys. Cigs should rise gradually to MVFR areawide Tue as the mid
level low slowly departs the area, then trend to VFR Tue night
lasting through Fri with a drier air mass and deep SW flow,
although a few afternoon showers are possible Thu/Fri. -GIH
Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043-