Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
FXUS62 KRAH 300136
Area Forecast Discussion
National Weather Service Raleigh NC
936 PM EDT THU SEP 29 2016
A large upper level low will hold over the Ohio Valley through
Friday, as a surface front holds along the North Carolina Foothills.
The upper low will weaken and drift north over lower Michigan
through the weekend, as the surface front slowly dissipates
over central North Carolina.
.NEAR TERM /through tonight/...
As of 925 PM Thursday...
The Flash Flood Watch will be canceled.
The significant rain chances have essentially lowered enough for our
region that we can allow the watch to be canceled. Additional
scattered storms are expected Friday, but only isolated to widely
scattered showers are now anticipated overnight.
Low level stability over eastern NC essentially led to a mostly dry
afternoon and evening. Water vapor satellite data indicted deep
moisture was confined to eastern NC, with a dry slot noted sweeping
from GA into SC and southwest NC. A surface trough was located over
the foothills where scattered thunderstorms were still ongoing just
to our west from Hickory to Mount Airy at mid-evening. There have
been isolated thunderstorms over our SW Piedmont but these have
weakened in the past hour around Albemarle and High Rock.
The mid/upper level low was still located over the Ohio Valley with
a general SE flow from the Atlantic across NC. It appears that
stratus and fog will be likely overnight with the moist advection
from off the Atlantic. This stability will also aid in keeping
thunderstorm chances limited to areas closer to the upper low to our
NW. The deep moisture plume flowing over areas along and east of I-
95 may lead to some light showers but additional heavy rain
overnight is not expected. Lows generally in the mid to upper 60s.
.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 325 PM Thursday...
The large upper low will wobble and drift slowly northward over IN
during this period, while weak surface low pressure holds over the
far western Piedmont along the increasingly diffuse north-south
oriented surface front. This front will weaken further as it eases
just a bit eastward into central NC through the day, with the
greatest PW over the eastern fringe of the CWA and over coastal
sections. The bulk of the DPVA pivoting around the mid level low
appears to hold just to our west, while the better upper divergence
shifts just to our north and NW, so we should see a lessening of
both deep moisture and of large scale forcing for ascent. Will
maintain high chance pops across the far N and NE trending to slight
chance pops over the SW, decreasing after nightfall. Expect highs
from the upper 70s to lower 80s, followed by lows in the mid 50s
west to mid 60s east. -GIH
.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 350 PM Thursday...
The persistent upper low over the Tenn Valley will finally lift
north into the Great Lakes and weaken, as a trough deepens over the
Pacific Northwest. This will lead to a general trend toward higher
heights over the eastern U.S, a surface high pressure ridge down the
East Coast and temps near at or just slightly above. Before the low
fully departs the region, some diurnal convection is possible across
the far south/east Saturday and Sunday given the continued presence
of the front that sinks over the area this weekend, but with
diminishing in coverage with each day.
Most of the long term focus is with the uncertainty in the track of
what is currently Hurricane Matthew over in the Central Carribean.
The official NHC track brings Matthew north across the Bahamas early
next week in response to an upper trough cross the Gulf Coast
region. This is still rather uncertain at day 7, however, and quite
likely to change in the coming backs.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 840 PM Thursday...
24 Hour TAF Period: A Warm moist air mass is expected to remain
across the area tonight as a slow moving cold front approaches the
area from the west, moving into the area on Friday. Thus, IFR to
LIFR cigs and/or visbys are expected to develop again tonight across
the entire area. Cigs and visbys will slowly lift Friday morning,
with VFR conditions generally expected by 15-18Z or so (though it is
possible for some sites across the east to linger in the MVFR
category into the mid/late afternoon hours). Expect generally dry
conditions overnight, however, an isolated shower/storm or two can`t
be ruled out. Isolated to scattered showers and storms will be
possible again on Friday, with the best coverage expected across the
eastern TAF sites. However, confidence is low enough to not include
any mention of convection in the TAFS at this time.
Outlook: Isolated showers and storms are expected mainly across
eastern portions of the area into the early Friday evening as a
surface front shifts slowly eastward across central NC. This front
will weaken and dissipate heading into the weekend, allowing the
better rain chances to shift to our east. Except for a potential for
MVFR or IFR fog/stratus at RWI early Sat morning, otherwise VFR
conditions will dominate through Tue with low rain chances.