Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 052049
Area Forecast Discussion
National Weather Service Raleigh NC
350 PM EST Mon Dec 5 2016
High pressure will build across the Middle Atlantic states through
tonight, ahead of a Miller B low pressure system and associated cold
air damming, which will result in the development and deepening of
an area of low pressure through the eastern Carolinas on Tue.
Another area of high pressure will build overhead for the middle of
.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Monday...
Today: The trend to a prominent downslope-directed component to the
low level flow will help scour out the lingering low clouds within
the trailing cool stable pool, to the northwest of the surface
frontal zone stretching across the southern Gulf states, GA, and the
coastal Carolinas. But the continued presence of the upper jet core
to our NW and N and steady elevated integrated WV transport to our
SW and S will keep a flow of mid and high clouds over the area
today, yielding milky sunshine at best over much of the area,
thicker across the south and a bit thinner in the north. Given the
lull in forcing for ascent today --including a brief uptick in mid
level heights in the wake of the shortwave trough shifting NE into
the Mid-Atlantic/Northeast as well as the weak surface high nosing
in from the NNW -- dry weather is expected, after a period of chance
pops in the southeast portion of the forecast area for a couple of
hours near and soon after daybreak. The period of fair skies today
balanced with above normal thicknesses should help push temps up to
near normal readings today, with highs mostly in the upper 50s.
Tonight: The respite in the rain will be short-lived, as lift and
deep moisture spread back in from the SW this evening. The mid level
shortwave trough tracking NE over TX today will de-amplify but remain
potent as it moves NE through the western Gulf States tonight. This
wave will coincide with a strengthening surface low that moves from
LA into the Mid South tonight, forcing strengthening and deepening
moist isentropic upglide from SW to NE during the evening hours.
Strong upper divergence in the right entrance region of an
accelerating jet to our north will also contribute to vigorous deep
lift. With a minor speed-up in timing, I have retained the ramp-up
in pops from SW to NE to categorical areawide by midnight. Expect
gradually increasing NE winds, especially across the south half, as
the MSLP gradient tightens between the exiting surface high and the
incoming low. Lows 41-47. -GIH
.SHORT TERM /Tuesday through Tuesday night/...
As of 255 AM Monday...
Widespread rain will persist through much of Tue with chilly temps.
The mid level wave will continue moving NE through the southern
Appalachians and VA, as a Miller "B" surface pattern develops,
featuring the primary low losing steam over TN into WV while
secondary low pressure forms along the front over SC early Tue and
tracks NE across SE and coastal NC through Tue evening, then
offshore Tue night. Lift will be its deepest and strongest Tue
morning with the vertical juxtaposition of the peak upper
divergence, strongest PW flux and IVT, and intense mass convergence
in the nose of the large 45-50 kt 850 mb jet. Total rainfall amounts
of 1-2" are likely, according to model consensus. Temps are likely
to budge little on Tue given thick clouds, steady rain, and a wedge
regime in place, so expect highs of just 43-49 over much of the
area, with highs of 50-53 in the far SE CWA, through which the
models show the warm sector edging northwestward during the day. An
end in precip from SW to NE is expected during the mid to late
afternoon as the mid level wave shifts to our north and NE, with an
eastward departure to the 850 mb jet, and as the secondary low
(which will have taken over as the primary low by that point) shifts
just off the northern Outer Banks by 00z Wed, rain chances should be
ending by mid evening or so, with dry weather overnight. We should
see a low level residual cool stable pool behind the low, however,
covering much of interior NC, suggesting a very slow dissolution of
the low level clouds Tue night as this air mass should be resistant
to dispersion either horizontally or vertically. Will taper down sky
cover gradually overnight. Expect lows from the upper 30s NW to
lower 40s SE. -GIH
.LONG TERM /Wednesday through Monday/...
-- Changed Discussion --As of 350 PM Monday...
In the wake of the departing low pressure on Tuesday, and preceding
a strong arctic front moving through the Midwest, the flow will be
weak over central NC on Wednesday. Forecast soundings show enough
drying to erode the lingering low clouds and/or fog early Wednesday,
with daytime heat into the mid 50s (per statistical guidance) likely
to result in a cu field, mainly east. Weak but moist southerly flow
should redevelop late Wednesday in response to weak height falls and
an intense upper jet associated with the aforementioned cold front
and result stratus Wednesday night. Lows 39-44.
The cold front, progged to be just west of the Yadkin early Thursday
morning, will will cross the area during the first half of the day,
with strong cold advection behind it Thursday evening and
overnight. The front itself is not expected to produce much precip,
if any, though the GFS cranks out some light qpf, owing likely to a
period of strong low-level FGEN and sufficiently deep moisture
across the northern half of the area. The current slight chance POP
will be maintained. Highs in the upper 40s to mid 50s.
Strong cold advection Thursday night should result in gusts to 15-
20kt and wind chills in the upper teens, as lows drop into the mid
to upper 20s. Arctic high pressure will then build in over the
weekend, with forecast thicknesses progged to approach 1270m Sat/Sun
morning. Lows should have little problem hitting the upper teens
and lower 20s. The high then quickly moves offshore and the
synoptic front return north with the next chance of rain early next
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.AVIATION /18Z Monday through Friday/...
As of 330 PM Monday...
Initially VFR conditions through this evening will yield to
progressively lowering ceilings tonight, into IFR-MVFR range late
tonight-early Tue, as lift and moisture increase downstream of a
complex low pressure system approaching from the SW. Patchy light
rain will also begin to fall from the VFR ceilings this evening,
then increase in coverage and intensity through early Tue. A few
rumbles of (elevated) thunder, whose cloud bases would be rooted
around 5000 ft owing to a cold and stable low level air mass, will
be possible roughly between 14-18Z Tue, as lapse rates aloft briefly
steepen with the passage of a mid-upper level trough. The passage of
the trough axis will also cause widespread rain to end, and
clearing to commence, from SW to NE throughout the afternoon and
early evening hours. The clearing, in conjunction with wet soil,
will result in the development of patchy fog Tue night.
Outlook: Chance of MVFR ceilings ahead of an arctic cold front Wed
night-Thu, and blustery NW winds behind the front late Thu-Thu