Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 231053

Area Forecast Discussion
National Weather Service Raleigh NC
659 AM EDT Mon Apr 23 2018

Strong high pressure will remain nearly stationary or slowly drift
off the New England coast through tonight. Low pressure approach
from the Tennessee Valley today and tonight, then track slowly east
over SC on Tuesday, then NE across eastern NC late Tuesday and
Tuesday night.


As of 659 AM Monday...

Increasing easterly winds and timing/amount of rain are the main
issues today and tonight...

Current projections suggest that East winds will increase to 20 to
30 mph late this afternoon and tonight, with gusts to 35 mph.

QPF on the order of 1 to 1.5 inches expected through 12z/Tuesday.

Severe thunderstorms not expected through 12z/Tuesday.

The mid/upper low near Memphis is forecast to slowly drift NE
toward southern KY by 12z/Tuesday. The associated surface low is
expected to slowly weaken and move east through the Tennessee
Valley and weaken with time, with secondary development over
SC by 12z/Tue. An impressive 40-45kt SE low level jet will bring
the plume of deep subtropical moisture from the Caribbean and SW
Atlantic NW into our region.

Rain is expected to continue to expand northward with time today,
reaching the southern and western Piedmont between 12z and 15z, then
the western Sandhills and rest of the Piedmont between 15z and 21z.
The rain will be light to start, then gradually pick up in intensity
through the day from SW to NE. The steady rain should reach into the
far NE counties before sunset today. Rain, some heavy is expected
for all areas tonight.

As far as the impacts, the wind will be an issue beginning by early
afternoon as the easterly winds increase to 15-20 mph. The winds
will increase through the afternoon and evening as the H85 SE low
level jet increases to 40-45kt. This jet will help drive and
increase surface winds to 20-25 mph with gusts to 30-35 mph as
mixing occurs with the steady rainfall. The main timing of these
stronger winds appears to be 21z/today through much of the night.
With the newly leafed out trees, the heavy rain and wind gusts may
down some limbs and we will mention this in the Hazardous Weather

The other impact from this system will be the rain, potentially
heavy at times. There continues to be signal within many of the
ensemble solutions that there may be a minimum of QPF over a portion
of inland NC (possibly the southern Piedmont of NC / Sandhills).
This is due to the favored maximums of QPF to be in the upslope
areas of western NC and along the coast. The maximum (if if it
develops along or near the coast) may be convectively driven from a
secondary low pressure circulation along the coastal front. If this
develops, it may focus the convection and heaviest rain there and
there may be a shadow or minimum of QPF to the NW of this area. Even
if this shadow or minimum occurs, there should still be "healthy"
totals in the 1 inch range, with 1.5 to 2.5 inches in the upslope
or higher Piedmont areas to the NW, but focused even more so along
the east slopes of the Blue Ridge. Locally 3+ inches may occur

The higher QPF (locally 1.5 to 3 inches in 12-24 hours) would
still fall short of the Flash Flood Guidance criteria. Therefore,
with the uncertainty in the heavier QPF to fall over all the region
and with the FFG being rather high after the drying out period this
past week, we will simply mention the chance of some minor flooding
in urban and poor drainage areas in the Hazardous Weather Outlook.

Severe thunderstorms are not expected through at least 12z/Tuesday
as the entire area will have widespread stratiform rain that will
keep the instability at near zero. The warm/coastal front will still
be south and southeast of our region by 12z/Tuesday, with the only
chance of convection expected to be elevated on the cool side of the

Sensible weather includes: Rain developing/overspreading central NC
(west this morning, east this afternoon). Highs upper 50s west, to
near 70 east. Winds increase to 20-30 mph late today and tonight
with rain. Lows in the 50s to near 60 (SE).


As of 350 AM Monday...

An elongated srn stream mid-upr low over the mid-South this morning
is forecast to wobble to near BNA by 12Z Tue and to swrn VA by 12Z
Wed. Preceding the upr low, the right entrance region of a
strengthening sly to ssely, 80-100 kt upr level jet will stream
across e-cntl NC and sern VA through 18Z Tue. Associated divergence
aloft, atop a strong low level WAA/isentropic upglide regime
courtesy of a 40-45 kt low lvl jet, will support ongoing widespread
rain and embedded elevated convection (showers), early Tue. This
regime will lift newd into and offshore VA through early afternoon,
followed by a mid level dry slot that will nose across the Carolinas
Tue afternoon and evening.

At the surface, the models indicate a triple point low over nern
GA/wrn SC at 12Z Tue will track newd into the srn NC Piedmont/wrn
Sandhills by 00Z Wed, then track nnewd roughly along US Highway 1
Tue night. A preceding warm front will arc enewd across srn and sern
NC early Tue, with the trailing cold front extending swd along the
srn SC and GA coast. The cold front is forecast to progress ewd more
quickly than the warm front retreats nwd, with an associated
increasingly narrow wedge of warm sector characterized by low-mid
60s surface dewpoints and mainly weak sfc-based instability, which
is forecast to pivot newd across nern SC and ern and e-cntl NC Tue
afternoon, beneath the aforementioned mid lvl dry slot. Low lvl and
deep layer flow will have weakened considerably and veered in the
wake of the early day WAA/isentropically-driven rain, though
lingering effective SRH on the order of 100-150 m2/s2 immediately
preceding the surface wave may support episodic low level rotation
in showers/storms late Tue aft-evening. However, a lack of more
appreciable instability and shear suggests any severe weather threat
over cntl NC should be limited. Showers will linger Tue night,
particularly over the Piedmont, as the mid-upr low and associated
cold pool aloft pivot overhead.

Temperatures Tue are expected to range from low-mid 60s in a
lingering damming regime over the NW Piedmont (nw of the track of
the surface low), to low-mid 70s across the Sandhills and srn-cntl
Coastal Plain, with lows in the 50s.


As of 400 AM Monday...

An energetic, unsettled pattern will persist through most of the
medium range, though uncertainty regarding amplitude and phasing of
associated shortwave troughs migrating through the energetic flow
lend low forecast confidence for prospects for rainfall in cntl NC.

A trough now over the PAC NW will have amplified into the cntl
Plains by 12Z Wed, and into the TN Valley/srn Appalachians by 00Z
Fri, before then deamplifying across the Carolinas/srn middle
Atlantic states through early Fri. A full latitude trough will
follow quickly on the heels of the lead trough and pivot ewd across
the Appalachians and NC Fri night-Sat. Following NW flow downstream
of progressive ridging aloft will overspread the srn middle Atlantic
region for end of weekend and early next week. This pattern will
favor variably to mostly cloudy conditions and above climo chances
of rain by late Thu-Fri, followed by lingering slight chances Fri
night-Sat given the aforementioned uncertainty regarding shortwave
details, and dry conditions as the NW flow takes hold by Sun.High
temperatures will be seasonable/slightly below average - mostly in
the lwr-mid 70s, with near to slightly above average low
temperatures, in the upr 40s to lwr-mid 50s.


As of 659 AM Monday...

MVFR to VFR CIGS will lower to IFR TO LIFR CIGS and IFR VSBYS with
rain and fog later today and tonight. Winds will increase from the
east at 15-20kt with gusts to 30kt this afternoon and tonight.

Looking beyond 12z Tue: Poor aviation conditions will dominate all
sites through Tuesday. Mostly IFR CIGS and IFR to MVFR VSBYS with
areas of rain and showers are likely on Tuesday, before tapering off
Tuesday night. Sub-VFR stratus/fog may linger into Wed morning. VFR
conditions should return Wed, although a few showers are possible
Wed afternoon, and again Thu into Fri, as a series of upper level
troughs cross the region, bringing unsettled weather and perhaps
brief periods of sub-VFR conditions.





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