Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 231930

Area Forecast Discussion
National Weather Service Raleigh NC
330 PM EDT Mon Apr 23 2018

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


As of 330 PM Monday...

Latest near term model guidance in good agreement depicting a stout
sfc ely wind across central NC tonight, thanks to the difference in
pressure between a sfc low over northern GA, and a sfc high
positioned offshore of New England. This tight gradient will produce
sustained sfc winds 15-20 mph with gusts around 30 mph. This east-se
fetch off of the Atlantic will tap a very moist air residing
offshore where satellite imagery/blended precip water product depict
precip water values hovering around 2 inches. The upslope component
of the low level flow coupled with lift associated an mid-upper
level s/w crossing the SE U.S. will interact with the available deep
moisture to produce widespread showers. Rainfall intensity expected
to increase late this evening into the overnight as the upper level
s/w approaches our vicinity. While current rainfall rates are
averaging less than a tenth of an inch per hour, rainfall rates
associated with the better dynamics may be closer to two-tenths or a
quarter of an inch per hour. This will lead to rainfall amounts on
the order of one-two inches by early Tuesday morning. Where the
heavier rainfall rates occur in urbanized areas, minor/nuisance
flooding of streets and poor drainage areas may occur.

Temperatures tonight will not cool as normal due to the widespread
cloudiness and breezy ely sfc winds. Min temps should vary from the
lower 50s NW to the mid-upper 50s elsewhere.


As of 330 PM Monday...

A deep upper level low over the TN Valley will drift ever so slowly
east. The primary sfc low associated with this upper system will
edge east-northeast across northern GA tonight, and South Carolina
Tuesday morning. A warm front stretching east from this low will
also drift slowly northward with time, with an expected Tuesday
morning position near or south of the NC/SC border. The approach of
the sfc low will likely enhance low level convergence enough to lead
to the possibility of elevated isolated convection by daybreak in
proximity of our southwest counties. As the morning wears on, the
bulk of the shower activity will lift into southern VA.

As the sfc low migrates into upstate SC/southern NC, the sfc warm
lift will lift into central NC, likely bisecting the region west-to-
east in vicinity of highway 64. By mid-late afternoon, the
atmosphere along the south of the boundary has the potential to
destabilize to permit isolated strong/severe thunderstorms to
develop. The main severe weather hazard will be locally damaging
wind gusts. An isolated, weak tornado cannot be ruled out es. as the
sfc wave immediately to our west-sw will lead to low level backing
of the sfc winds, increasing the 0-3km helicity, especially in
vicinity of the sfc warm front.

The threat for scattered convection and isolated strong/severe
storms will diminish early Tuesday evening as the low-mid level
winds just above the surface become wly with the passage of a mid
level trough.

High temperatures Tuesday dependent on extent of cloudiness/showers
or peeks of sun. In anticipation of the sfc warm front remaining
south of the VA border, will have the coolest max temps along this
region, extending west into the Triad (low-mid 60s). Probabilities
for temps in the low-mid 70s look good over the southeast counties.
Potential for max temperature bust will lie in vicinity of the
western Piedmont into the Triangle region and east towards Wilson.
If showers and the warm front remain closer to the South Carolina
border, max temps in vicinity of Asheboro, Raleigh and Wilson could
be no higher than the low-mid 60s.


As of 150 PM Monday...

An active, energetic upper pattern featuring a long wave trof over
the eastern CONUS will persist from mid week into the weekend. There
is a lot of uncertainty regarding the timing and potential for
phasing of a couple of short waves which will be digging into the
longer wave pattern, which will ultimately determine the potential
for their producing rain over central NC.

A reinforcing, but dry, cold front will be pushed southeast through
the area on Wednesday into Wednesday night as our initial upper low
lifts northeast to be absorbed by a stronger cutoff low moving
across the Great Lakes. There will be a small chance of showers
across the northern tier of the area, with highs Wednesday in the
low to mid 70s. Lows Wednesday night will be in the low and mid 50s.
Skies will be at least partly sunny on Thursday with cooler highs in
the upper 60s to lower 70s as the cold front stalls across the Gulf

A southern stream short wave moving across the Gulf states Thursday
night will spur development of a surface wave along the front, which
could slide east along the front and offshore or possibly lift more
northeasterly into the area and produce showers on Friday. Highs
will be below normal regardless, ranging from 70 to 75, possibly
cooler if we get significant shower coverage. All this while, the
primary long wave upper trof has been edging east, and the trof axis
will pass over the area on Saturday, possibly squeezing out a final
few showers. Highs Saturday will be in the upper 60s to lower 70s.

Heights finally begin to build late in the weekend as upper ridging
moves into the Midwest, with strong sunshine as the associated
surface high builds over the area. Highs Sunday will be in the low
to mid 70s, with mid and upper 70s expected on Monday.


As of 155 PM Monday...

There is high confidence that aviation conditions will deteriorate
to IFR/LIFR ceilings this evening, persisting through Tuesday
morning. Additionally, widespread showers will cover the region
ahead of a sfc warm front that will gradually lift nwd across SC
this evening, and into central NC overnight through Tuesday morning.
The presence of this warm front will create low level wind shear
conditions, primarily at KRDU, KFAY, and KRWI. While sfc winds will
be east-northeast 15-20 mph with gusts around 30 mph, winds at 2000
ft are forecast to be sely around 45 mph. These low level wind shear
conditions are expected to diminish after 15Z Tuesday.

Aviation ceilings will slowly improve to MVFR ceilings through
Tuesday afternoon. A few thunderstorms may develop during the the
late morning into the afternoon.

MVFR/low end VFR ceilings appear likely across central NC Tuesday
night into Wednesday. VFR parameters will most likely occur through
Friday with brief instances of MVFR conditions probable. The next
threat for widespread MVFR ceilings appears to be late Friday into
Saturday as an area of low pressure affects the region.





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