Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 301138
Area Forecast Discussion
National Weather Service Raleigh NC
738 AM EDT Thu Mar 30 2017
Weak high pressure will extend across eastern NC through Thursday.
An area of low pressure will bring unsettled weather to the area
Thursday night and Friday.
.NEAR TERM /THROUGH TODAY/...
As of 425 AM Thursday...
The southern edge of a surface high extending down into the area
from the north is bringing easterly flow to the area but
southeasterly flow along the Appalachians and as a result a growing
area of MVFR stratus is starting to build in across the northwest
Piedmont. This feature will be influential on today`s weather when
it comes to sky cover, precipitation and ultimately temperatures.
Later this morning drizzle or even light rain will be possible
across the northwest Piedmont as more moisture flows into the area.
Depending upon how thick the stratus becomes, and model soundings
show a significant cloud deck about 8 kft thick, high temperatures
under the stratus could be overdone. As a result have slashed
temperatures across the north to below guidance with upper 50s in
the Triad but a fairly tight gradient with lower 70s across the
southern counties. The triangle will be a major gamble today with
anything from lower to upper 60s possible. For now have chosen to go
on the lower end but a safe bet will be the middle 60s.
.SHORT TERM /THURSDAY NIGHT AND FRIDAY/...
As of 420 AM Thursday...
Attention will turn to the southwest on Thursday night as a warm
front surges in and temperatures should actually begin to rise
overnight at most locations. Good isentropic lift in the west will
begin to encourage precipitation over the western portion of the CWA
between 0-6Z Friday. Model forecast soundings are virtually
saturated throughout the column with PW values near 1.3 inches. The
low level jet structure is fairly unorganized early Friday morning
and there are several small disturbances in the flow so expect
several smaller waves of precipitation which could be scattered in
nature at times. As the precipitation pushes eastward it could
become a bit more organized into more multicellular or broken lines
but shear will be decreasing at this time particularly in the lower
levels as winds become southwesterly and more unidirectional with
height. Instability will increase slightly with peak heating and a
dynamic push from the left exit region of a 500 mb jet could cause a
storm or two to become severe. SPC has the eastern half of the area
in a marginal risk for severe wx with damaging winds the most likely
threat. With decent moisture in this system expect rainfall totals
anywhere from a half of an inch on the low end to about an inch on
the high end.
Temperatures will be tricky on Friday given the convection but with
central NC in the warm sector for much of the day expect highs in
the low to mid 70s in most locations.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
As of 405 AM Thursday...
An energetic Pacific jet will send a series of significant
shortwave perturbations into the west-central U.S., where the
models indicate they will amplify toward the Four Corners/Srn
Plains region and interact with an equally energetic southern
stream. That interaction will ultimately shear the
perturbations ENEwd into the Middle Atlantic states, with
associated episodes of precipitation/convection, about every 72
hours in central NC. This a relatively persistent pattern from
recent days, which included the round of convection from this
past Mon night, and which will likely result in another one
later tonight (highlighted in the short term discussion above).
Fri night: The models are now in good agreement with the
progression of the upper low initially over the Central Plains,
to the nrn Middle Atlantic coast by late Fri night. An
accompanying surface trough axis/secondary front will cross the
ne Piedmont/nrn Coastal Plain with a lingering chance of
showers and a storm or two Fri evening. Otherwise, clearing and
cooling will occur, with lows in the lower to middle 50s.
Sat-Sun: Beneath longwave ridging bulging Nwd from the Caribbean
to central Canada, the weekend is expected to be dry, and mild,
with a reinforcing dry frontal passage (the leading edge of a
Pacific high) Sat night. Periods of stratocumulus may bubble
beneath a strong, 5 k ft subsidence inversion, but not with
enough coverage to significantly impact temperatures through the
period. Highs in the upper 60s to 70s, warmest ahead of the
reinforcing front on Sat. Lows, coolest Sun morning in the 40s,
and about a category higher in return SEly flow and increasing
deep moisture by Mon morning.
The next couple of strong shortwave perturbations will follow
on schedule and cross central NC late Mon-Mon night and again
just beyond this forecast period (Thu). The result will be
another likely probability of showers and storms late Mon-Mon
night, preceded by possible weak in-situ CAD during the day
Mon. It will otherwise be mild through the period, with
temperatures mostly in the 70s and 50s for highs and lows,
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --As of 740 AM Thursday...
24 Hour TAF Period: MVFR ceilings now covering much of the forecast
area this morning. Over the NW Piedmont these ceilings should stay
locked in all day whereas locations in the south and east may
scatter out with daytime heating. Some drizzle may occur over the
next few hours at KINT or KGSO. Expect southeasterly winds today
with gusts up to 15 kts or so. By Friday morning, more significant
precipitation is expected to move in with a warm front that will
cross the area from southwest to northeast. This will bring a line
of rain into the western Piedmont by 9z or so and into the Triangle
area and KFAY by 12z and exiting to the east thereafter.
Long term: After the warm front rolls through the area at the end of
the TAF period, a cold front will follow on its heels on Friday
sparking another round of convection. This will clear out on Friday
night and give way to quiet conditions until Monday when another
strong low pressure system is progged to cross central NC causing
potentially adverse aviation conditions.
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