Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 240614
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
214 AM EDT Tue Apr 24 2018

.SYNOPSIS...
An area of low pressure will track northeastward across the
Carolinas and VA through tonight. A weak cold front will then cross
our region late Wed and Wed night.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1020 PM Monday...

Light to moderate rain continues this hour across the western
Piedmont. For the most part breaks in the rainfall have led to about
a half of an inch across the west with far less rainfall in the
east. Expect western counties to be the focus for rainfall for the
next several hours as a heavier band of showers continues to move
through. Winds are still gusting to 15-20 kts in several locations.
Looking at forecast soundings, there isn`t a strong decoupling in
the boundary layer and therefore, expect sporadic gusts to continue
into the overnight hours. Previous discussion follows. -Ellis

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.


&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
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.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
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
states.

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.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 210 AM Tuesday...

Widespread rain, and deteriorating aviation conditions to IFR-MVFR
range, will increase in coverage and intensity this morning, ahead
of an upper level trough that will pivot northeastward across cntl
NC early today. A warm front will then retreat nwd into srn and cntl
NC this afternoon; and this will result in a lifting and scattering
of the low ceilings to VFR at FAY around 18Z, with subsequent
destabilization and threat of a strong thunderstorm with gusty winds
this afternoon. The warm front and brief scattering to VFR may edge
as far nwd as RWI and RDU between 19-22Z, while INT and GSO are
likely to remain in a cooler and saturated, cold air damming and IFR
regime, throughout the TAF period. While the highest probability of
a storm will be at FAY, a few elevated rumbles of thunder will be
possible throughout cntl NC today, and again late tonight-early Wed,
as an upr lvl low and associated pocket of cold temperatures aloft
drift overhead. Otherwise, strong easterly winds will maintain
breezy conditions through this afternoon, before subsiding by this
evening.

Outlook: A low lvl deformation band of MVFR ceilings will pivot ewd
across cntl NC early Wed. VFR conditions are otherwise expected
until another upper level trough and period of unsettled weather
(threat of rain and sub-VFR conditions) spread east across cntl NC
Thu night into Fri.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NC...None.

&&

$$

SYNOPSIS...MWS
NEAR TERM...WSS/Ellis
SHORT TERM...WSS
LONG TERM...MLM
AVIATION...MWS



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