Area Forecast Discussion
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FXUS62 KRAH 010739
Area Forecast Discussion
National Weather Service Raleigh NC
240 AM EST Thu Dec 01 2016
A cold front will cross the area early this morning. High pressure
will then build over the Eastern U.S. from the west through the
upcoming weekend. An approaching upper level disturbance and
increasing moist flow from the Atlantic and Gulf will bring
increasing rain chances beginning Sunday night.
.NEAR TERM /today through tonight/...
As of 225 AM Thursday...
The cold front has just cleared the northwest CWA, where clouds have
cleared out, winds have taken on a primarily westerly component, and
dewpoints have fallen into the 40s. Such changes will progress
steadily eastward for the balance of the night, with the remaining
light showers over the eastern Carolinas including our far SE
sections (oriented along the departing 850 mb jet) ending in the
next few hours. The continental surface high that will build in
behind the front from the WSW today is sufficiently modified such
that this initial post-front drop in temps won`t be extreme, with
slightly above normal thicknesses supporting seasonably mild highs
of 59-68 under plentiful sunshine and lighter (yet still
periodically gusty) winds. The generally clear skies will continue
through tonight; however, a weak shortwave trough located over the
Front Range early this morning is projected to track quickly across
VA tonight, potentially bringing a few high thin clouds as mid level
winds remain rather brisk. Overall, though, expect fair skies at
most overnight, with a slackening MSLP gradient yielding light
winds. Expect lows of 32-39. -GIH
.SHORT TERM /Friday through Friday night/...
As of 240 AM Thursday...
Forecast soundings show deep dry and stable air across Central NC on
Friday, with a fairly flat and fast mid level flow and high pressure
still building in at the surface, leading to generally sunny skies.
As this southern stream surface high begins to merge with the larger
Canadian high to its NNW, low level thicknesses will drop further on
Friday, to around 10-15 m below normal, so temps should follow suit
with below normal highs of 53-60. High clouds are expected to being
increasing Friday night, spreading in ahead of convection over TX
and the lower Miss Valley (ahead of the digging low over NW Mexico).
These initial high clouds should be thin however as they encounter
the destructive effects of broad ridging over the Gulf States and
Southeast, and thus they should do little to impede radiational
cooling. Lows 30-35. -GIH
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 252 PM Wednesday...
In the Sunday time frame...moisture advection out of the Gulf will
stream east along a frontal zone setting up across the Gulf States.
With a cool dry airmass in place, we should see a thickening
cloudiness Saturday night with light rain breaking out due to
isentropic lift in the west by mid day Sunday, and will maintain
ongoing chance PoPs in the west during the morning spreading over
the east during the afternoon. Highs will be subsequently suppressed
by clouds and evaporative cooling, ranging from mid 40s in the
northwest to lower 50s in the southeast.
The forecast from Sunday night onward remains low confidence pending
consensus as to the progression of a cutoff low over northern Mexico
which will be lifting ENE across the plains early next week.
Initially, the high pressure over the area is reinforced by the
arrival of a second surge of cool dry air from a transitory surface
high oriented more classically from New England south down the east
coast, which would suppress moisture southward on Monday. This would
set the stage for another isentropically induced rain regime on
Tuesday/Wednesday as the moisture associated with the aforementioned
cutoff low and associated surface reflection ride up the cooler
denser air. Will keep PoPs on the low chance side for now, with
highs in the 50s Monday through Wednesday as we wait to see how
the scenario plays out.
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 105 AM Thursday...
Widespread MVFR cigs have given way to VFR at INT/GSO as the cold
front approached from the west. Similar improvement is expected at
RDU/RWI/FAY between 08z and 11z, with VFR conditions areawide by
12z, as the cold front sweeps through the area and high pressure
begins to build in from the west. Current surface winds from the SW
at 10-15 kts gusting occasionally to 20-25 kts will veer to westerly
then northwesterly later this morning with diminishing speeds to
around 10 kts and infrequent gusts to 15 kts, lasting into the
afternoon as VFR conditions persist. Winds will diminish further
after 22z late today, with VFR conditions holding through tonight.
Looking beyond 06z early Fri morning, VFR conditions will hold well
into the weekend as the ridge of high pressure builds into the area.
High clouds will spread in from the WSW on Sunday, and these clouds
will thicken with lowering bases to MVFR then IFR Sunday night as an
upper level disturbance approaches from the WSW, in conjunction with
increasing low level moisture from the Atlantic and Gulf. MVFR to
IFR cigs/vsbys will persist through Monday with light rain