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fxus62 krah 112019 

Area forecast discussion
National Weather Service Raleigh NC
320 PM EST Wed Dec 11 2019

a mid-level trough will cross the southeast states through this
evening. Arctic high pressure will gradually filter into the region
through tonight before settling over New England and extending
southward through central NC through Thursday. This high will then
slide offshore but continue to extend down through our area, as low
pressure forms over the Gulf and tracks northeast over the southeast
states late Thursday through Friday.


Near term /through Thursday/...
as of 225 PM Wednesday...

Quiet/dry weather is expected the next 24-30 hrs. The southern
portion of the large scale eastern noam trough will continue to
dampen and shift slowly east-northeast over the southeast states through
tonight, with a flattening, decelerating, and slightly backing mid
level flow and modest height rises. We remain in the right entrance
region of a 170+ kt upper jet over the St Lawrence Valley,
responsible in part for the steady stream of high clouds over the
region, and this too will weaken and shift away from the area,
leaving US within a dry and neutral-to-sinking column. After seeing
lingering high clouds into this evening, expect clear skies
overnight. Based on the very low dewpoints in the upper teens to mid
20s pouring into the area as the surface high begins to build in
from the northwest and N, lows tonight in the mid 20s to around 30 seem

Largely cloud-free skies will extend through Thu. The center of the
parent high is expected to be over PA in the morning before drifting
NE near the New England coast and over the coast of the Canadian
Maritimes, propelled by a mid level shortwave trough moving through
the Southern Plains toward the mid/lower miss valley. The surface
ridge will continue to extend down through central NC during this
time, ensuring dry and stable low levels. It looks like the increase
in low level moisture transport with the greater low level Atlantic
inflow will hold off until evening, when we will start to see
stratocu advecting into our southern sections. Low level thicknesses
are expected to be around 20 M below normal with weak cold air advection through
the day, favoring highs 2-3 categories below normal, mainly in the
mid 40s to near 50. -Gih


Short term /Thursday night through Friday night/...
as of 235 PM Wednesday...

..brief period of freezing rain across the northwest Piedmont early Friday
morning before changing over to rain; minimal impacts expected...

Little change to the overall pattern. Still expect the strong 1040
mb high over the mid-Atlantic Thursday morning to lift northeast
toward/through New England by 00z Friday. The high will continue
ridging southwestward into central NC, setting up a cad wedge over
the area. Although skies will be clear and dewpoints in the upper
teens/low 20s are expected to start the period, The Wedge will
become pinched/elongated NE-SW as the parent high lifts away. As a
result, return flow off the Atlantic will advect increasingly moist
and warm air into the area Thursday night into Friday increasing
cloud cover, temperatures and chances for precipitation. The main
forcing for precipitation Thursday night and Friday will be
isentropic lift with warm air advecting into the region over The
Wedge of cold air at the surface. Meanwhile, an inverted trough off
the southeast and mid-Atlantic coast, extending northeastward from a
developing surface low over the Gulf.

The threat for a brief period of freezing rain will be limited to
along and west of the I-85 corridor. Do not expect saturation in the
dendritic growth zone, thus no sleet or snow it expected. However,
within the lingering cad wedge where temps and dewpoints will be
lowest, wet bulb temperatures will be below freezing for a few
hours. There is expected to be a 4-6 degree warm nose above the
surface (h8-h9) where the best saturation will be, while a shallow
dry layer is expected at the surface. Precipitation into the dry
surface layer will help temperatures cool to the wet bulb
temperatures, resulting in a brief window where freezing rain is
possible. The most likely time frame for freezing rain will be between 6a and
8a and be limited to primarily The Triad and points north and west.
Temperatures should rise above freezing Friday morning, with
increasing rain chances and melting of any freezing rain that may
have managed to accumulate. No significant accumulation is expected,
however some elevated surfaces could see a light accumulation of ice
before it melts. Road temperatures will likely remain too warm to
accumulate ice, though bridges, especially in areas that remain
shaded most of the day and are not highly traveled, may cool to
around freezing.

Elsewhere, precipitation should be all rain, moving in from the
southwest as isentropic lift increases Thursday night/Friday
morning. Outside of The Wedge airmass to the northwest, temperatures
will be allowed to rise as warm, moist air is advected into the
area. The coastal trough and Gulf low will strengthen on Friday,
with the low sliding northeast along the southeast and mid-Atlantic
coast late Friday into Friday night. As the low approaches the
Carolinas, The Wedge should largely erode and more convectively
driven rainfall moves into the area. Friday eve/night will have the
more significant rainfall amounts across central NC. Highs Friday
will vary greatly from northwest to se, from upper 30s to mid 50s. Lows
will be similar to highs, albeit a few degrees lower, mid 30s northwest to
low 50s southeast. When all is said and done, total liquid precipitation
for the period Thursday night through Friday night could range from
an inch to an inch and a half in most places.


Long term /Saturday through Wednesday/...
as of 320 PM Wednesday...

Rain chances will continue through the first part of Sat as the
negatively tilted mid level trough shifts NE through the region. The
surface low should have moved NE into the Delmarva area by Sat
morning, leaving the lingering frontal zone extending down through
central/eastern NC. The surface low will continue its swift
northward movement toward the St Lawrence Valley Sat, pushing the
frontal zone eastward, but we'll maintain a moist column through the
early part of the day with above normal pw, necessitating good
chance pops early, trending down from S to north by Sat afternoon and
evening as the trough axis pivots overhead and to our NE. We should
see minimal Post frontal cooling as the parent high will be centered
well over the upper Midwest, so expect above normal highs in the mid
50s to around 60, and lows Sat night in the upper 30s to lower 40s.

A brief quiet period is expected sun into early Mon, with an initial
flat flow backing over NC in response to a trough digging over The
Rockies and plains. The front will start to retreat back north into NC
as a warm front, and while a weak stable pool will remain to its north
over the northwest Piedmont into Mon, the departure and weakening of the
parent surface high and the lack of preceding clouds or precip to
lock in the stable pool should make it vulnerable to the warming
advancing from the S. Thicknesses will continue above normal as
ridging builds over and off the southeast coast, so expect mild
highs sun/Mon, in the mid 50s to lower 60s, and perhaps some mid 60s
in our southeast Mon.

The approaching trough will merge with northern stream energy into a
large positively tilted trough late Mon through Wed. The warm front
should continue moving north Mon night, with a surface low moving NE
over the S Appalachians and across VA, dragging the cold front
through our area early Tue morning. Rain chances will start late Mon
in our NW, peaking Mon night into early Tue before tapering back
down west to east during the day Tue. As the mid level trough axis will
still be to our northwest through Tue night, we should see drier air moving
in late Tue but considerable mid and high clouds should hold in the
east into Tue night, followed by dry weather and fair skies Wed. -Gih


Aviation /18z Wednesday through Monday/...
as of 1205 PM Wednesday...

VFR conditions dominate much of central NC early this afternoon
under just some high clouds, however the far NE sections including
ixa/rwi/gsb are seeing MVFR to IFR stratus lingering within moist
and confluent low level flow from the north-northwest and north. These clouds should
slowly break up and diminish by 20z. Otherwise, even the high clouds
will be moving NE and slowly exiting the area through this evening,
yielding fair to clear skies and unrestricted vsbys tonight through
Thu as high pressure builds into central NC from the northwest. Surface
winds mostly from the north will become more north-northwest and northwest tonight, and
sporadic gusts through this afternoon will diminish by nightfall,
with winds staying light through Thu.

Looking beyond 18z Thu, VFR conditions will hold through the
evening, but ahead of the next storm system, MVFR cigs will start to
spread into SW portions of central NC (areas east of clt) very late Thu
evening. The entire forecast area should see sub-VFR conditions and
patches of light drizzle or freezing drizzle (the latter mostly
confined to The Triad area terminals) late Thu night through
lunchtime Fri. This precip will be light. But a more solid area of
rain is expected to spread in from the SW Fri afternoon, with
unsettled weather and predominantly sub-VFR conditions holding
through Sat night. Quiet VFR weather is expected sun/Mon beneath a
ridge of surface high pressure. -Gih


Rah watches/warnings/advisories...



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