Area Forecast Discussion
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FXUS62 KRAH 050758
Area Forecast Discussion
National Weather Service Raleigh NC
258 AM EST Mon Dec 5 2016
Low pressure will move off the Southeast coast this morning. High
pressure will build in briefly from the northwest this afternoon,
then a second stronger low pressure system will cross the Gulf
States and Carolinas Monday night through Tuesday. This system will
shift off the coast Tuesday night, followed by high pressure
building in for Wednesday into Thursday. An arctic cold front will
cross the area Thursday night.
.NEAR TERM /today through tonight/...
As of 240 AM Monday...
Through today: Widespread light rain and drizzle over the area will
taper off by mid morning, followed by a fairly quiet and dry day.
Deep moist isentropic upglide from 285K through 305K will drop off
rather swiftly from west to east this morning as the 850 mb trough
sweeps through the Mid-Atlantic and Northeast, pushing a 40-50 kt
southwesterly low level jet to our east. 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 deamplify 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 resistent
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 SUNDAY/...
As of 335 PM Sunday...
Look for dry weather to return for Wednesday in the wake of
Tuesday`s system and as high pressure builds to our north. The
airmass will moderate as well as SW flow aloft resumes. Meanwhile,
a deep longwave trough will take shape of the middle of the country,
and will move east through the latter half of the week, pushing a
potent cold front across our area on Thursday. GFS and ECWMF agree
that any rain assoc with the front will be fairly light, generally
less than 1/2 inch, and gone before the colder air arrives. Highs on
Wednesday and Thursday expected to reach the mid-upr 50s in the
prefrontal airmass. Lows Wednesday night in the mid 40s.
The big weather story for the long term will be the cool-down that
comes in the wake of the aforementioned front. Cold high pressure
will build in for Friday through Saturday, resulting in dry weather,
however the accompanying airmass will support highs only in the
upper 30s across the Triad and lower 40s elsewhere, both Friday and
Saturday. Lows Thursday night from the mid 20s nw to lower 30s se.
The coldest night of the weekend now appears to be Friday
night/Saturday morning, with lows expected to bottom out from around
20 NW to mid 20s across the coastal plain.
Otherwise, will be closely watching the pattern evolution late next
weekend into the early part of the following week, as a couple weak
short waves embedded in broad cyclonic flow are progged in the
models to move across the eastern US during that time.
.AVIATION /06Z Monday through Friday/...
As of 1245 AM Monday...
Poor aviation conditions will persist areawide until at least
daybreak. An upper level disturbance passing through the region
combined with low pressure tracking SW to NE over the Southeast
states has brought widespread IFR/LIFR conditions in steady light
rain and drizzle. This will persist until around daybreak, with a
period of LIFR vsbys/cigs in fog not out of the question. Soon after
daybreak, improvement to VFR from NW to SE is likely as the low
moves off the coast and the disturbance exits with rain/drizzle
ending. INT/GSO will see the improvement to VFR occur approximately
11z-13z, RDU at 12z-14z, and RWI/FAY at 13z-16z. VFR conditions and
dry weather will hold through much of today into early evening. The
approach of another stronger disturbance and a stronger surface low
tracking ENE toward the Mid South and Southeast states will bring an
increase in VFR clouds toward the end of the TAF valid period,
although the trend down to MVFR then IFR conditions will likely not
occur until after 06z Tue. Surface winds will be light mainly from
the north this morning, becoming NE this afternoon into tonight.
Looking beyond 06z Tue, a trend to MVFR then IFR conditions is
expected 06z-09z at INT/GSO, 07z-10z at RDU/FAY, and 08z-11z at RWI,
with steady rain spreading in from the SW. IFR/LIFR conditions in on-
and-off rain will persist through all of Tue and Tue evening.
Improvement to VFR is anticipated very late Tue night into Wed
morning as this storm system moves east off our coast, although
areas of fog may linger into early Wed morning in the east. VFR
should dominate much of Wed, then sub-VFR conditions may return Wed
night through much of Thu as a cold front approaches from the NW.
Much colder air and VFR conditions are expected Thu night through