Area Forecast Discussion
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FXUS62 KRAH 290018
Area Forecast Discussion
National Weather Service Raleigh NC
818 PM EDT Tue Mar 28 2017
An upper-level disturbance and cold front will push across the
region today, and offshore this evening. Weak high pressure will
follow the front for tonight and Wednesday. Another storm system
approach our area Thursday night and Friday, bringing another round
of stormy weather.
.NEAR TERM /THROUGH TONIGHT/...
As of 225 PM Tuesday...
Little has changed in the forecast philosophy for this afternoon and
evening. There continues to be a marginal risk for isolated severe
thunderstorms this afternoon. Clearing has allowed for an increase
in instability from the Foothills into much of the Piedmont. MLCapes
have increased in some areas to near 1000 J/KG over southern VA and
portions of the NC Piedmont. Temperatures were rising through the
70s with near 80 at Fayetteville. Dew points were in the lower 50s
NW ranging to 60 SE. The wind shift line was located from near
Hickory NE to Lynchburg at 200 PM. The main area of instability out
ahead of the wind shift line will continue to progress with the wind
shift SE into our Piedmont in the next few hours. Cumulus were
developing with some organization noted along the wind shift line to
our NW. In addition, there was another area to watch from near CLT
NE to RDU where another low level boundary was draped. A couple of
showers and thunderstorms were already ongoing along these
Hi-Res models and current data suggest widely scattered
thunderstorms will continue to develop along both these features
this afternoon as they progress rapidly eastward, exiting the
Coastal Plain region by early evening.
The favorable instability and timing of the wind shift line is
expected to be mainly east of the Triad region; therefore, the
isolated severe potential should be confined to the far eastern
Piedmont to the coast 20z-23z or so. Even over these areas, MLCapes
and many other severe weather parameters especially wind shear are
only marginal. Pea to nickel hail may end up being common in most of
the stronger cells, with isolated 1 inch hail possible.
The action will shift offshore by sunset and dry/quiet conditions
will return for tonight. Lows in the 50s.
.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
As of 335 PM Tuesday...
Wed-Wed Night: With shortwave ridging aloft, expect mostly sunny to
partly cloudy skies and above normal temps in the mid/upper 70s Wed
afternoon. Subsidence in the wake of an upper level low moving
offshore New England Wed evening will result in pressure rises along
the eastern seaboard as an inverted sfc ridge extends southward
through the Mid-Atlantic into the Carolinas, the leading edge of
which will be marked by a backdoor cold frontal passage /wind shift
to the NE at ~15 mph/. Lows Wed night will be determined by the
precise timing of fropa. Based on the latest guidance, expect temps
ranging from the mid 40s NE Coastal Plain to lower 50s in the SW
Thu: In the wake of the backdoor cold front, NE low-level flow will
veer to the E/ESE during the day, allowing temperatures to recover
into the mid/upper 60s to lower 70s across the Sandhills and SE
Coastal Plain Thu afternoon. A cold air damming wedge is expected to
develop across portions of the Foothills and N/NW Piedmont as warm
advection (via SW H85 flow) strengthens atop the shallow cooler
airmass in place near the surface. As a result, broken/overcast
cloud cover should largely offset diurnal heating across portions of
the N/NW Piedmont where highs may struggle to exceed the mid 50s,
esp in Forsyth county. -Vincent
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 335 PM Tuesday...
Thu night: Expect an increasing potential for elevated showers
across the western half of the state (west of Highway 1, primarily
the NW Piedmont) between midnight and sunrise Fri as an upper level
low progresses across the central MS river valley into the western
TN valley and low-level warm advection strengthens downstream over
the Carolinas. Expect lows Fri morning ranging from the mid/upper
40s (N/NE) to lower 50s, warmest Sandhills and SW Piedmont.
Fri-Fri Night: Uncertainty in the evolution of the approaching upper
level low and attendant sfc cyclone has decreased over the past 24
hours now that the ECMWF is in much closer agreement to the GFS,
however, confidence in temperatures, precip amounts and convective
intensity remains relatively low due to the expected presence of a
CAD wedge and potential for upstream convection /latent heat
release/ to alter low-level height/wind fields over the
Southeast/Carolinas. Although precip amounts remain uncertain,
precipitation chances Friday/Friday night remain solid. As such,
have increased pops to categorical (~80%). A potential for organized
severe thunderstorms will exist Friday afternoon and evening given
the synoptic pattern progged by the GFS/ECMWF, however, the overall
extent/character of the threat remains difficult to ascertain at
this range, as do forecast temperatures for Fri/Fri night. With the
most recent guidance in mind, will indicate highs ranging from the
lower 60s in the Triad to the lower/mid 70s in the Sandhills/SE
Coastal Plain. A clearing trend from SW-NE is expected in the wake
of a cold frontal passage after midnight. Lows Sat morning will
depend primarily upon fropa timing, ranging from the lower 50s N/NW
to mid 50s S/SE.
Sat-Sun night: A potential for isold showers may surface Saturday
afternoon east of Hwy 1 if DPVA attendant shortwave energy digging
SE along the western periphery of the departing upper level low
occurs in vicinity of peak heating. Otherwise, expect dry conditions
and a warming trend over the weekend as a shortwave ridge builds
east across the Mid-Atlantic and Carolinas. Expect highs in the
lower/mid 70s Sat and mid 70s Sunday as a shortwave ridge aloft
tracks across the region from the west.
Mon-Tue Night: Expect increasing cloud cover during the day Monday
and a chance for convection by Tue as the next upper level low
/attendant sfc cyclone/ approach from the west. -Vincent
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --As of 815 PM Tuesday...
24 Hour TAF Period: The initial surface cold front has pushed to the
south of central NC this evening, along with any convection and sub-
VFR conditions. VFR conditions are expected to continue this evening
into early Wednesday morning as surface high pressure builds/extends
into the area. However, a reinforcing back-door cold front is
expected sink southward into central NC close to daybreak Wednesday.
This will usher in the potential for some IFR/MVFR cigs from around
daybreak through around noon (before lifting and/or scattering).
KRWI stands the best chance of seeing any sub-VFR cigs as moisture
in northeasterly low level flow is expected to surge into the
northeast/eastern portions of central NC early Wednesday morning.
Otherwise, generally light northwesterly winds tonight will become
north to northeasterly on Wednesday generally in the 7 to 12 mph
range, with possibly a few gusts into the mid teens.
Outlook: With surface high pressure building/extending into the area
Wednesday night into Thursday in advance of yet another approaching
area of low pressure, we may see the development of some sub-VFR cigs
early Thursday morning, possibly continuing into Thursday as a CAD
wedge develops. A low pressure system will cross the area on Friday
through Friday night with the potential for showers and
thunderstorms. High pressure with VFR conditions should
generally return for the weekend.
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