Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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498
FXUS62 KRAH 231914
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
315 PM EDT Thu Mar 23 2017

.SYNOPSIS...
Continental polar high pressure will continue to modify over the srn
Middle Atlantic states through tonight. A warm front will retreat
north across the region on Fri, as the high drifts east toward
Bermuda.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 315 PM Thursday...

Tonight...A parent high (1038mb) over the DELMARVA will drift
offshore tonight. Circulation around this sfc feature will result in
a veering low level flow from an easterly to a more sly direction.
This flow will eventually tap moisture residing to our south-
southwest and advect this moisture into our region. While the parent
high will be offshore, a ridge extending from the parent high will
extend west-to-east across our region by 12Z Friday. This will deter
to better moisture return until later Friday. Under a mostly clear
sky and a light/near calm wind regime, temperatures will tumble
after sunset through the 40s into the 30s by midnight. Overnight
temperatures in the upper 20s to around freezing.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 315 PM Thursday...

Friday...Upper level ridge axis currently extending along the spine
of the MS Valley will drift over the Southeast U.S. by Friday. Warm
air advection on the back side of the 850-500mb ridge currently
supporting a band of precip across the lower OH Valley into the TN
Valley early this afternoon. This precip area is farther south than
projected by most of the near term and CAM progs. Latest HRRR
depicts this band of mostly light precip dissipating as it lifts ewd
toward the Smoky Mtns.

Increasing low level sly flow will tap moister residing to our south-
sw which should led to scattered patches of cu, especially across
the southern coastal plain, and into the western Piedmont. The rest
of the column will remain dry, so precip chances will remain below
20 percent. The warming air mass and low level sw flow will push
temperatures back to normal levels, primarily in the 65-70 degree
range.

Milder temperatures anticipated Friday night as sly low level flow
continues and atmosphere continues to moisten. There will be a
greater probability for low stratus to develop after midnight.
Overnight temperatures in the mid-upper 40s.

&&

.LONG TERM /Saturday through Thursday/...
As of 240 PM Thursday...

High confidence in warm weather through the early part of next week,
with bouts of showery weather, primarily on Sunday and Tuesday.
Uncertainty grows midweek and beyond as differences emerge regarding
their handling of polar low deepening over SE Canada and the
adjacent NW Atlantic waters, however it appears certain that the
wavy active southern stream pattern will persist through next week.

Sat/Sat night: The potent mid level low will cross the central Miss
Valley as its southward-extending trough takes on a negative tilt
over the Mid South and Gulf States, leading to strengthening mid
level flow from the SW into the Carolinas. PW will remain elevated,
in the 75th percentile, with a light onshore-directed southeasterly
flow drawing in increasing low level moisture. We should see
considerable morning stratus and fog, particularly over the western
half of the CWA where low level moist upglide will be deepest, and
these clouds should lift to scattered to broken stratocumulus (more
clouds west than east) with heating, and these should persist
through the day, topped with high thin clouds. Very dry/stable mid
levels will keep the day mostly dry, apart from possible patchy
morning drizzle in the western Piedmont. Thicknesses will continue
to trend above normal, supporting highs of 70-76 NW to SE. The mid
level low tracks slowly from MO to IL Sat night, bringing the
negatively tilted trough axis and its DPVA into the western
Carolinas. This southerly steering flow will drive up PW to nearly
200% of normal just to our west and into the far NW Piedmont late
Sat night, in tandem with the arrival of 25-35 kt low level jetting
into the Srn Appalachians. Will bring in good chance pops very late
Sat night into the far W CWA. Lows Sat night mainly in the mid 50s.

Sun/Sun night: The mid level low will quickly weaken and fill as it
approaches Lower MI Sun, while the trailing trough axis pivots
northeastward through our area. The best precip chances (likely to
categorical) will track ENE through central NC (especially NW) Sun
morning into early afternoon beneath a band of enhanced upper
divergence, with PW rising further to 250% of normal as steering
flow becomes southwesterly. Despite the moist column, the dwindling
dynamic forcing for ascent as this system tracks NE through the Mid
Atlantic region will lead to a tapering down of precip chances
through Sun, especially over our SE sections, as the core of the
peak integrated water vapor transport shifts to our NNE. Only low
chances are expected Sun night as the dampening mid level trough
axis shifts to our NE with gently rising heights aloft, within a
continued very moist column. Expect highs of 70-78 followed by lows
in the upper 50s with overnight stratus developing.

Mon-Tue: Monday will feature just patchy light precip at most over
much of central NC as a mid level ridge axis shifts overhead with a
weak cap at 925 mb and dry mid-upper levels, although higher PW
settling over eastern NC and higher surface dewpoints may prompt
greater convection coverage over our SE. Our next mid level trough
in this active pattern will push through the eastern third of the
CONUS Mon night through Tue, accompanied by a surface cold front.
Important model differences start to emerge, with the GFS slower and
more amplified than the weaker/faster ECMWF. Will lean toward the
more progressive ECMWF given this active pattern, but confidence is
not high. Will maintain good chance of showers and storms Mon night
through Tue. Highs 75-80 Mon/Tue with thickness over 35 m above
normal. Lows in the upper 50s.

Wed-Thu: Model details differ, but in general, heights will rise
over the Southeast in the wake of the departing trough, as another
powerful and deep low tracks over the Southwest states. Expect dry
weather and cooler temps, still near or just above seasonal normals,
as surface high pressure builds in from the north. -GIH

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 125 PM Thursday...

High probability that VFR conditions will occur across central NC
through 00Z Saturday. The exception will be the potential for a few
patches of MVFR visibility due to fog in sections of the southern
Piedmont, the Sandhills, and the southern coastal plain, between 10Z-
12Z Friday.

The area of high pressure which has provided the VFR conditions will
drift offshore Friday. The return sly flow will begin to advect a
warm moist air mass into central NC. The arrival of this air mass
will lead to higher chances for early morning fog or low stratus
Saturday morning and Sunday morning.

An approaching low pressure system will increase the threat for
scattered showers Sunday through Tuesday. With the moist air mass in
place, there will be periods of IFR/MVFR ceilings during this same
period.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...MWS
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...Hartfield
AVIATION...WSS



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