Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
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FXUS62 KRAH 251710
Area Forecast Discussion
National Weather Service Raleigh NC
110 PM EDT Wed May 25 2016
.SYNOPSIS...Surface high pressure will extend into the region through
Friday. Meanwhile, a storm system will develop over the sub-tropical
Atlantic and drift toward the Southeast coast through the weekend.
.NEAR TERM /through tonight/...
As of 1045 AM Wednesday...
Little change/adjusted required to the near term forecast.
Anti-cyclonic flow, a result of a mid/upper level ridge over the
Deep South and TN Valley, will maintain warm and dry conditions
today across central NC. While the lower layers of the atmosphere
will become slightly unstable this afternoon, a subsidence inversion
between 750-650mb will act as a cap, inhibiting convective
Low level thicknesses this afternoon projected to reach the 1410-
1415m range, a solid 15m warmer than normal. This suggest max temps
in the mid-upper 80s, in line with current forecast. -WSS
Conditions will again be good for radiational cooling tonight, the
exception being the western Piedmont where patchy mid/high clouds
associated with upstream convection may become mostly cloudy for a
period late in the night. Lows in the upper 50s and lower 60s. -BLS
.SHORT TERM /Thursday through Thursday Night/...
As of 350 AM Wednesday...
While high pressure, both at the surface and aloft, will remain over
the region on Thursday, increasing PW to near 1.5" and a little
better instability (500-1000 J/KG) will support a better chance of
convection, mainly in the western Piedmont from storms moving off
the higher terrain. The environment won`t be supportive of organized
convection, so the threat of any strong storms is low and will be
limited to enhancement from steepening low-level lapse rates. highs
again in the upper 80s.
The GFS appears much too aggressive with convection continuing into
Thursday night given that the ridge will begin to restrengthen in
response to the subtropical system developing over the northern
Caribbean. Instead, skies should end up mostly clear and lows will
dip back into the low/mid 60s.
.LONG TERM /Friday through Tuesday/...
As of 405 AM Wednesday...
Little change in the overall forecast rationale...driven by a
pattern aloft characterized by a western CONUS trough and a ridge
from near Bermuda to central Canada. A southern stream mid to upper-
level low will meanwhile develop/evolve in the vicinity of the
Bahamas, at the base of/beneath the eastern ridge.
Model guidance now unanimously support some degree of low pressure
development over the western Atlantic Ocean/east of the Bahamas,
along an old, weakening frontal zone. This low may acquire sub-
tropical or tropical characteristics as it is steered WNW toward the
southeast U.S. coast, between the aforementioned low/ridge couplet,
though model spread with the eventual track of the low is large.
Regardless, it still appears Fri into the first part of Saturday
should remain under the influence of ridging at the surface and
aloft, with mid-upper 80s warmth on Fri remaining comfortable owing
to surface dewpoints in the upper 50s to lower 60s. This relatively
dry BL, in conjunction with a capping inversion aloft, should
maintain generally dry conditions throughout central NC.
Later Sat-Tue: A deep feed of SE flow between the low/ridge couplet
will promote increasing clouds/deep moisture, with precipitable
water values forecast to climb to between 1-2 standard deviations
above normal. While this increase in moisture will prime the
environment for above average chances of showers and storms, the
ultimate track of the aforementioned low will play a role in
rainfall coverage and amounts (I.E. an enhancement if the low were
to move into the Carolinas, or conversely a reduction if the low
were to remain offshore and promote peripheral subsidence of the
otherwise moist air mass). Given the large model spread, will
largely defer to the WPC fronts/pressure and forecast elements,
which takes the low into the Savannah Basin early next week, with
PoP maximized diurnally in the 40-50 % range Sun-Tue.
Temperatures, tempered by clouds and convection, should be near
normal, albeit with high humidity owing to the mT air mass that will
have infiltrated at least the central and eastern Carolinas.
.AVIATION /18Z Wednesday through Memorial Day/...
-- Changed Discussion --As of 110 PM Wednesday...
An area of high pressure at the surface and aloft will maintain VFR
conditions across central NC through Thursday night. The exception
will be a slight threat for isolated afternoon-early evening
convection on Thursday, mainly over the western Piedmont. Where the
isolated convection occurs, expect MVFR ceilings and visibility as
well as gusty sfc winds.
Aviation conditions varying between VFR and MVFR will occur Friday
and Saturday, mainly due to early morning fog and/or low stratus,
and isolated-scattered afternoon through early evening convection.
The probability for adverse aviation conditions will increase Sunday
and Memorial Day as an area of low pressure off the southeast U.S.
coast spreads deep moisture into our region resulting in sub_VFR
ceilings and an increasing threat for scattered convection.
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