Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
FXUS62 KRAH 290546
Area Forecast Discussion
National Weather Service Raleigh NC
145 AM EDT THU SEP 29 2016
A strong upper level low over the Great Lakes will drift southward
through the Ohio valley tonight, stall over eastern Tennessee and
Kentucky Thursday and Friday, then move back north through the Ohio
valley and lower Great Lakes this weekend.
.NEAR TERM /THROUGH TONIGHT/...
As of 935 PM Wednesday...
Severe thunderstorm watch will expire at 1000 PM...
Localized flash flooding continues a threat.
We will allow the Severe Thunderstorm Watch to expire at 1000 PM.
Parameters indicate stabilizing of the boundary layer while large
scale lift arrives from the west. Additional severe threat should be
localized and not widespread. However, the threat of additional
flash flooding is increasing as training of storms continues in
Two areas of strong to severe thunderstorms continue through our
region. One line was located SW to NE through the southern Piedmont
into the Sandhills. The other was located from near Charlotte NE
through the Triad region.
Both of these lines have been problematic with flash flooding around
or north of Fayetteville into Harnett County, and over Greensboro.
Large hail has been the main severe weather hazard with both lines.
It appears that the low level jet will increase with strong surface
moisture convergence into central NC overnight. The two distinct
lines of storms may merge into one line toward late evening or just
after midnight. This would place the main severe and flash flood
threats from the Triad to the Triangle overnight.
Some areas have already had 1 to 3 inches of rain with locally 4
inches in Harnett and NW Cumberland Counties. The Triad is currently
in line for additional very heavy rain with additional flash
flooding appearing likely, especially east of Winston-Salem, with
Greensboro to Burlington targeted at the moment.
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 120 PM Wednesday...
Additional showers and storms with training moderate to heavy
rain remains likely over Central NC Thu, with a gradual shift to
the ENE on Fri.
The powerful mid level low will continue to sit and spin over KY on
Thu before drifting/wobbling slightly northward to IN on Fri, with
lobes of DPVA sweeping through western and central NC, along/atop
the very slow-moving north-south oriented cold/occluded surface
frontal zone. PW values remain elevated (over 1.5") over all but the
far west Thu, shifting to east of I-95 Fri, beneath nearly
continuous bands of pronounced upper divergence. The WRF-ARW/NMM
both start the day Thu with a band of convection bisecting the
forecast area, drifting slowly eastward through the far eastern
Piedmont and Coastal Plain through Fri, filling in with better
coverage with time, with a cell motion that presents a threat for
training and resultant localized flooding. Will retain, with minor
tweaks, the overall pattern of the earlier forecast, with lower
chance pops west and high pops in the central/eastern CWA Thu,
trending lower WSW to ENE through Fri but remaining high in the far
eastern/NE forecast area Fri, tapering off further Fri night.
Temps both days will be held down by clouds/precip in the east and
by lowering post-front thicknesses in the western CWA. Highs in the
upper 70s to lower 80s Thu and in the mid 70s to lower 80s Fri,
still slightly above seasonal normals. Lows 60-68 Thu night and 54-
65 Fri night. -GIH
.LONG TERM /Saturday through Wednesday/...
As of 320 PM Wednesday...
A few showers are likely to linger Sat into Sun in the eastern CWA,
along and east of the frontal zone, but otherwise this period
appears mostly dry. The large mid-upper low centered over IN early
Sat will drift across lower MI and slowly fill through Sun before
being drawn across the St. Lawrence Valley and Northeast states by a
shortwave trough rotating around a northern Atlantic polar vortex.
This, in conjunction with a large longwave trough shifting onto the
West Coast and over the western CONUS, will gradually build ridging
over the eastern CONUS heading into early next week. The surface
front over the East will continue to ease eastward and wash out with
a weakening low level wind field fostering frontolysis. A few mainly
afternoon showers are possible along this diffuse frontal zone over
the far eastern counties of NC early next week, but the PW will be
quite low elsewhere with a lack of instability, and will keep the
forecast mostly dry. Temps should hold a bit above normal through
the period, following thickness trends, with highs mostly in the
upper 70s and lower 80s, and lows in the upper 50s to mid 60s.
Uncertainty grows during the middle of next week, with a lot of
questions regarding the fate of what is now Tropical Storm Matthew,
located north of Venezuela this afternoon. However, at this time, it
appears that it will still be far from NC through Wed. Check with
the National Hurricane Center for the latest on Matthew. -GIH
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 145 AM Thursday...
The two distinct bands of showers and thunderstorms across Central NC are
currently in the process of merging into one broader band across the central
Piedmont and Sandhills. KRDU and KFAY will be the most impacted terminals, with
KRWI to a lesser extent with Sub-VFR conditions in heavy rain along with the
potential for gusty winds of 25 to 30 kts. Convective coverage and intensity
should gradually decrease towards daybreak.
In addition, a blanket of low (LIFR) stratus is expected to redevelop mainly
over the Piedmont (INT/GSO) late tonight, before lifting and scattering to VFR
with diurnal heating between 13-16Z Thu. That heating, in
conjunction with lift supplied by a slow-moving wave of low pressure
and associated frontal zone, will also cause showers and storms to
re-develop by mid afternoon and linger into the evening.
Outlook: Moist low-level air will continue to support early morning stratus/fog
Friday morning and possibly again Saturday morning. Otherwise,
Drier air is finally expected to filter into the region on
Friday, leading to improved aviation conditions through the weekend.