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872
FXUS62 KRAH 231755
AFDRAH

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1050 AM Monday...

Little adjustment required to the near term forecast.

12Z upper air analysis depicts a stout se flow in the lowest 10k ft
of the atmosphere. This flow expected to strengthen later today into
tonight as the pressure gradient tightens between a sfc low
immediately to our west-southwest to a strong high offshore of New
England. Sustained sfc winds 15-20 mph probable with gusts around 30
mph common.

This fetch off of the southern Atlantic will pull abundant moisture
into the region. This available moisture in conjunction with lift
provided by an approaching s/w and  central NC in the favored left
exit region of a 80-90kts crossing the Deep South will result in
bands of moderate to locally heavy rainfall across the region this
afternoon, through tonight. Rainfall amounts on the order of one-two
inches look reachable.

The rain encroaching upon central NC from the southwest will cause
temperatures to hold steady this afternoon roughly south and west of
Raleigh, while temperatures should continue through mid afternoon
for locations north and east of Raleigh. Temperatures will change
little this evening into the overnight, ranging from the low-mid 50s
NW to the upper 50s SE.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 350 AM Monday...

An elongated srn stream mid-upr low over the mid-South this morning
is forecast to wobble to near Nashville, TN 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.

&&

.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 /18Z MONDAY THROUGH SATURDAY/...
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.

&&

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

&&

$$

SYNOPSIS...Badgett/Hartfield
NEAR TERM...WSS
SHORT TERM...MWS
LONG TERM...MWS
AVIATION...WSS