Area Forecast Discussion
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FXUS62 KRAH 181803
Area Forecast Discussion
National Weather Service Raleigh NC
105 PM EST Sat Feb 18 2017
An upper level trough will approach from the west today and cross
the southeastern U.S. tonight through early Sunday. High pressure
will build into our region behind the exiting low pressure system
Sunday night and Monday.
.NEAR TERM /today through tonight/...
As of 1010 AM Saturday...
Just minor adjustments this morning, mainly to reduce RH and speed
up onset of light precip from the SW. The mid level shortwave ridge
axis located overhead will shift steadily off the coast today as an
upper low crosses the Mid Miss Valley and moves into the Mid South.
Observed and high-res forecast soundings depict relatively little
moisture with this feature below 700 mb, with weak to absent low
level moisture transport and a light non-confluent SW flow. DPVA
weakens as the low/trough approaches and dampens later today,
contributing to reduced forcing for ascent. Large scale models
continue to show no measurable precip in central NC, although the
RAP, which has caught up with reality and is now doing a pretty good
job, does rotate a band of decent showers from GA and upstate SC
into our SW sections late this afternoon. Based on the limited low
level moisture and lift but with a nod to high-res model trends,
will have a slight chance of measurable showers over the far SW,
with just sprinkles elsewhere, taking these sprinkles NE through the
CWA as we head into the evening. Expect increasing clouds from the
west today, with a trend to mostly cloudy areawide by nightfall.
Rising thicknesses balanced with this increase in clouds favors
highs in the upper 60s to lower 70s. Still-low dewpoints will
translate to a min RH in the 20-30% range for much of the area. -GIH
Earlier discussion from 255 AM: S/W ridge over the Carolinas early
this morning will scoot quickly east and offshore in advance of an
upper low pressure system that will cross the lower MS Valley today.
Diffluent upper flow ahead of this system will result in increasing
and thickening mid/upper level clouds later today, spreading sw-ne
across the area. The arrival of this thicker cloud cover will play a
role in how warm it will be this afternoon. Based on satellite
trends, the broken/overcast skies will spread into our southern
counties during the late morning/mid day hours, and over the
northern counties during the afternoon. Thus, appears to be some
potential for warming, especially across the northeast half of the
forecast area. Will lean high temps toward the full sun values from
the low level thickness scheme which favors highs in the upper 60sw-
lower 70s, warmest along our eastern periphery.
The low pressure system will be weakening as it approaches from the
west. Thus, little if any moisture advection expected in the low
levels which remain quite dry this afternoon. While some forcing
noted aloft, any precipitation that develop will likely evaporate
before reaching the surface. Thus have opted to mention a chance of
sprinkles rather than slight/chance measurable rain.
Variably cloudy skies and a threat for a few sprinkles will linger
into tonight as the weakening upper level low passes overhead. The
variably cloudy skies and light sfc wind regime will maintain
relatively mild nighttime temps for mid-February. Overnight
temperatures in the mid-upper 40s.
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 255 AM Saturday...
Our stretch of mild/warm temperatures will persist Sunday and
Monday. The upper level low, which will reside overhead early
Sunday, will depart by afternoon. Subsidence behind this system and
developing nw flow in its wake will aid to diminish the cloud cover
leading to mostly sunny skies during the afternoon. Considering the
mild start to the day and the potential for increasing sun in the
afternoon, temperatures should recover back into the upper 60s-lower
70s Sunday afternoon.
An amplified upper ridge will extend from the eastern Gulf into the
Great Lakes Monday. The resultant nw flow aloft will drive a dry sfc
cold front across our region Monday afternoon. Warmer air ahead of
this system will yield highs temps in the 70-75 degree range across
much of central NC. The exception will be the far northeast where
the earlier arrival of the sfc front may result in cooler
temperatures in the upper 60s.
Low level easterly flow Monday night may cause in patchy low-mid
level clouds to form in the upslope region of the Foothills,
possibly spilling into our far western Piedmont. Otherwise expect
mostly clear skies Monday night. It should be slightly cooler with
min temps in the 40-45 degree range.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 205 AM Saturday...
The surface high that had been ridging into the region will lift off
to the northeast on Tuesday, with a more southeasterly then
southerly return flow setting up over Central NC by Wednesday
morning as a subsequent warm front slides north through the area.
Aloft, the ridge over the eastern U.S. will shift off the coast and
weaken as the next weather system approaches. A closed low will
break away from the northern stream trough late Tuesday, then slide
slowly east-southeast over the Gulf of Mexico on Wednesday (well
south of the North Carolina). Meanwhile, the northern stream energy
will largely pass to the north of Central NC. Some light rain is
possible over the area Wednesday/Wednesday Night, but accumulations
should be minimal as the best moisture will be well south of the
area. A better chance for descent rainfall will come Friday or
Saturday a low pressure system develops over the northern high
plains and progresses east. The parent low will track northeast
through the Great Lakes as the attendant cold front extends south
into the Gulf. The strongest warm advection into the Carolinas will
be just ahead of the front Friday/Friday night, with the frontal
passage on Saturday. Expect moderating temperatures through Friday
Night (highs maxing out in the mid 70s Friday and lows in the low to
mid 50s Friday Night), decreasing thereafter.
.AVIATION /18Z Saturday through Thursday/...
-- Changed Discussion --As of 105 PM Saturday...
High confidence in VFR conditions through Sunday. As an upper low
crosses the region late today through tonight, clouds will increase
across central NC from SW to NE during this afternoon, with a period
of broken to overcast skies very late afternoon through the evening.
However, cigs are likely to stay above 5000 ft AGL. A few sprinkles
or light showers are possible at central NC terminals 21z-03z, but
vsbys will stay VFR. Light winds mainly from the SW are expected
this afternoon, veering to W then NW tonight, lasting through
Looking beyond 18z Sun, VFR conditions will dominate through at
least Mon evening. Model differences then crop up regarding a
passing mid level trough through the region, reducing confidence,
but there is at least a chance of sub-VFR conditions late Mon
night/Tue morning, and again late Tue night/Wed morning and Wed
night/Thu morning as we get into moist SW flow. -GIH
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