Area Forecast Discussion
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FXUS62 KRAH 201805
Area Forecast Discussion
National Weather Service Raleigh NC
1250 PM EST Fri Jan 20 2017
A strong storm system is expected to affect the region over the
weekend into Monday.
.NEAR TERM /THROUGH TONIGHT/...
As of 1250 PM Friday...
Showers continue to exit to the NE with residual cool stable air
left behind over central NC. Low overcast stretched back to the base
of the Blue Ridge (Buncombe to Alleghany Counties), west of Winston-
Salem. There were some breaks in the overcast in the SE part of the
region from the Sandhills into the Coastal Plain. With the departing
system this afternoon, the pressure gradient was weak and the
subsidence behind the weak upper system was also weak. Therefore, it
will be hard to scour out the residual low overcast over the
Piedmont. This will affect highs today. Expect readings in the 50s
NW ranging into the lower 70s in the Fayetteville to Goldsboro
Multiple guidance sources show high probabilities of fog tonight into
Saturday morning with saturation near the surface all night. Lows
generally in the 50s expected, with some upper 40s NW.
.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 400 AM Friday...
After a brief break in precipitation, weak isentropic lift will
continue on Saturday keeping a chance for rain in the forecast, with
the better chances later in the day when a 500 mb vort max moves
through the area. High resolution models are depicting a line of
heavier showers and perhaps a an isolated thunderstorm moving
through Saturday afternoon. Model forecast soundings are more wet
than unstable and so moderate to heavy showers should be more of the
characterization of the precipitation as opposed to more widespread
thunderstorms. The line will move through and out of the CWA by
Saturday evening. A quarter to a half an inch of rain will be
possible but due to the linear and progressive nature of the system,
the entire day should not be a washout. Despite the clouds and rain,
an increase in warm air advection will help temperatures rise into
the mid to upper 60s with a few 70s across the south.
Precipitation chances will continue to increase on Saturday night
ahead of a developing set of low pressure centers that will affect
the area Sunday and Monday. Southwestern areas will be most
vulnerable to precipitation. Lows in the 50s.
.LONG TERM /Sunday through Thursday/...
As of 220 AM Friday...
Earlier thinking remains valid. Warm and stormy weather will rule
Sun through Mon, followed by dry and mild weather Tue through Wed. A
pattern shift toward lower (higher) heights over the eastern
(western) CONUS will commence Wed night, with cooler temps arriving
Sun through Mon night: Widespread showers and perhaps a storm or two
should be ongoing across central NC early Sun, within vigorous
forcing for ascent generated by DPVA with a wave tracking NNE
through the area, having emanated from the deep low over the lower
Miss Valley, along with a 50 kt low level jet punching into the area
from the south, and intense upper divergence. PW of 200-300% of
normal in conjunction with this strong lift will support a period of
heavy rain Sun morning into early afternoon, as an occluded surface
low tracks NE over the NC Piedmont. A slug of relatively drier mid
level air will move in from the south Sun afternoon, leading to a
short relative lull in coverage and intensity, and will have
categorical morning pops dipping to good chance/likely for a period
in the afternoon within brief shortwave ridging between the exiting
wave and the upper low crossing the Gulf States. This lull will be
short-lived as the upper low shifts east over AL/GA then NE over the
Carolinas, bringing another round of strong deep lift. The ECMWF/GFS
have come into better agreement on timing, although the ECMWF is
still a bit faster than the GFS. The slightly slower GFS speed is
preferred based on the strength of this system. Will ramp pops back
up to categorical Sun evening into the early overnight hours,
followed by another downturn in coverage and intensity late as a mid-
upper dry punch arrives along with cooling low levels. Scattered to
numerous showers will persist through Mon as the upper low crosses
the region with ~7 C/km mid level lapse rates and lower but still
above-normal PW. Precip chances will wind down Mon night as the low
shifts to our north. A few strong storms remain possible, mainly
from midday Sun into Sun evening, with a 70+ kt mid level jet streak
accompanying powerful upper divergence and steep 700-500 mb lapse
rates over 7 C/km according to the GFS. CIPS analog guidance
continues to suggest more of a severe threat for FL compared to our
area, historically speaking, although GFS forecast soundings for
central NC still show long wavy hodographs and marginal to moderate
instability, suggestive of at least a modest risk of a few strong
wind-producing storms, and perhaps a tornado as well along and north
of the occluding frontal system. Highs in the mid 60s to around 70
Sun, lows from the upper 40s to mid 50s Sun night, and mid 50s to
lower 60s for highs Mon. Lows in the low-mid 40s Mon night.
Tue through Thu: Mid level heights rise over the Southeast as a mid
level ridge axis shifts over the region, while surface high pressure
crosses the northern Gulf and FL. Expect fair skies Tue/Wed with
slightly cooler but still above normal temps. The aforementioned
pattern change will begin late Wed night or Thu morning (ECMWF
brings a cold front through earlier than the GFS) as a strong EPac
trough this weekend shifts eastward and begins to tap into cooler
polar air that has been bottled up well to our north. Expect highs
back down into the 50s Thu. A few showers are possible with the cold
front, although will keep pops on the low side given the significant
model timing differences. -GIH
.AVIATION /18Z FRIDAY THROUGH TUESDAY/...
As of 1258 PM Friday...
24 Hour TAF period: VFR ceilings will exist in the KFAY region this
afternoon, with all other sites expected to remain IFR to MVFR CIGS.
Areas of fog and drizzle will continue over the KINT and KGSO areas.
With light wind overnight, areas of fog and low overcast will
develop, mainly after 03Z/21. Most TAF sites should fall into the
LIFR VSBY and CIG range between 09z and 13z/21. Some minor
improvement will occur after 13z - with some MVFR CIGS from KFAY to
KRWI, but lower IFR conditions from KRDU to KINT through into the
Long term: Sub-VFR conditions are expected with showers and even
some thunderstorms at times Saturday nigh through Monday morning.
A return to VFR conditions expected Monday afternoon and Tuesday.