Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 250814
Area Forecast Discussion
National Weather Service Raleigh NC
414 AM 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 350 AM Wednesday...
height rises (90m at KGSO last evening) continue across much of the
eastern US, while a surface high has become established off the
Southeast coast. Moisture recovery is underway but will be slow
with dewpoints only in the upper 50s today. A modest subsidence
inversion noted on the 00Z/25th KGSO RAOB and weak instability will
inhibit any convection today. There is a weak disturbance upstream
that will drift over western NC and may weaken the cap a bit, but hi-
res WRF/HRRR guidance keeps all convection over or west of the
mountains today. H10-H85 thicknesses starting out about 15m higher
than Tuesday morning suggest highs about 5 degrees warmer, 84-89.
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.
.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/...
-- Changed Discussion --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.
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.AVIATION /06Z Wednesday through Sunday/...
As of 155 AM Wednesday...
As high pressure expands over the Southeast US, VFR conditions will
prevail through the current TAF period with a light southwesterly
wind. Showers and storms remaining over or west of the mountains
today, with just some increase in mid-clouds from the west late
Outlook: VFR conditions will prevail across central NC through
Friday. Meanwhile, the chance afternoon showers and storms will
increase, mainly across western NC, with adverse aviation much more
likely by Sunday as a low pressure system develops off the Southeast