FXUS62 KRAH 240801
Area Forecast Discussion
National Weather Service Raleigh NC
400 AM EDT Fri Mar 24 2017
A warm front will lift north across NC and VA today. Bermuda high
pressure will then extend across our region through early next week,
though interrupted briefly by the passage of a shortwave trough on
.NEAR TERM /THROUGH TONIGHT/...
As of 345 AM Friday...
1036 mb high pressure now centered a few hundred miles east of the
DelMarVA will drift to near and just north of Bermuda today.
Return Sly flow around the wrn periphery of the ridge will cause
warmer and more moist air to flood north through the Carolinas and
VA today, with afternoon temperatures in the upper 60s NW to lower
70s elsewhere in central NC, and surface dewpoints rising into the
40s to near 50 degrees. The increasing low level moisture values,
and broad WAA regime, will favor a scattering of flat/fair weather
cumulus trapped beneath a subsidence inversion that will have become
established courtesy of an amplified longwave ridge now building
east toward the Appalachians.
Not as cool tonight, and with a chance of patchy radiation fog owing
to the aforementioned increase in low level moisture values, with
low temperatures mostly in the upper 40s (45-50) expected.
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 355 AM Friday...
A mid-upper level trough axis extending south from a closed low now
over sern CO will migrate newd from the MS Valley early Sat to near
the srn Appalachians by Sun morning, as the parent upper low lifts
toward the Great Lakes. Associated mid level height falls on the
order of 20-30 meters will pivot NEwd across central and wrn NC Sat
and Sat night, but lingering influence of the preceding ridge axis
aloft/sub-tropical ridge will maintain a strong capping inversion
and dry air aloft. As such, precipitation chances will remain low
through Sat night, with perhaps just a slight chance of a shower
near the Yadkin River by 12Z Sun. Even then and there, however,
instability will be weak, shallow, and still capped by the
inversion, so the (relatively) better chances of any showers will
not occur until Sunday.
It will otherwise be warm Sat, with scattered to broken fair weather
cumulus, and mild Sat night with both thickening high level
cloudiness in Swly flow aloft, and a chance of stratus over the wrn
piedmont late. Highs in the lower to middle 70s, and lows in the
lower to middle 50s.
.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 /06Z FRIDAY THROUGH TUESDAY/...
As of 220 AM Friday...
A lingering continental (dry) air mass, deposited by strong high
pressure now drifting off the NC/VA coast, will result in continued
VFR conditions through the TAF period. Surface winds, in return flow
around the surface high, will become Sly to SSWly and increase into
the 8-13 kt range, strongest and with at least occasional gusts into
the upper teens kts at nrn TAF sites.
A warm front and influx of low level moisture will result in the
development of a scattering of flat cumulus, with bases around 4 k
Outlook: Patchy MVFR-IFR visibility restrictions in radiation fog
will be possible early Sat morning. Associated moisture may then
produce a few hour period of scattered to broken MVFR range cumulus
with diurnal heating mid-morning to midday Sat, especially at
Piedmont sites. Late night-early morning fog and/or stratus, then
MVFR range cloudiness as that moist layer is heated through midday
each day, will be possible through early next week. Otherwise, a
chance of showers and storms and sub-VFR conditions mainly at
Piedmont TAF sites will exist Sun, then again forecast area-wide on
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