Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
651 am EST Friday Mar 7 2014
a coastal low will strengthen and move from Florida up the Atlantic
coast today. Drier and warmer high pressure is then expected to
return to our region this weekend and persist through early next
week. Another low will approach the Carolinas from the west during
the middle of next week.
Near term /through Saturday/...
as of 650 PM...cooler temperatures have developed across portions of the
western County warning forecast area as expected. Rain still falling at kavl while khky is now
snow. Still getting reports of snow in across portions of the mountains
with only light accums south and higher accums north. A wide variety
of p-types and amounts continue across the I-40 corridor. Additional
heavy rain across the clt metropolitan area has caused additional flooding
to develop...and more could develop later this morning as the
heavy precipitation associated with the deformation zone rotates over the
area. Going forecast basically on track with only minor changes.
As of 355 am...tricky forecast continues with a variety of threats
across the County warning forecast area. Surface temperatures and wet bulbs show the largest threat of
wintry precipitation remains across the I-40 corridor and the northern mountains
have received reports of significant snow and sleet accums across
the northern mountains and Blue Ridge...while significant ice accretions have
been reported across the I-40 corridor. Of course...even in these
areas...heavy accums have been spotty. In fact...latest guidance
keeps the cold air in place across the mountains this morning that would
lead to additional snow across the high elevations. Therefore...
additional accums are likely...so will leave warning in place in
these areas. Accums have been much more spotty and limited to the
higher elevations over the central and southern mountains vertical profilers
from the National oceanic and atmospheric administration hmt-southeast program show snow levels remaining around 5000
feet. Last sounding at 06z from the sempe program and unc-Asheville
show the warm nose temperature remaining unchanged but the depth
decreasing... while the surface temperatures had risen. Therefore...expect
accumulating snow to be limited to the higher elevations...with only
a light accums of wintry precipitation in the valleys. Will downgrade
Buncombe...Henderson and the southern Blue Ridge to an advisory. In
addition to the precipitation... gusty north-northeast winds will help down trees with
the wet ground and possibly lead to power outages.
Conditions are even less uncertain across the southern foothills and southern
Piedmont. Temperatures and wet bulbs are above freezing across this area...
but are holding steady near freezing. Given the uncertainty...will
leave the advisory in place as some light ice accretions are
possible. Also...with the gusty north-northeast winds and wet ground...trees are
likely to fall and possibly lead to power outages.
Over the upstate and NE Georgia...temperatures are either holding steady or even
increasing keeping the chance of any wintry precipitation to a bare minimum at
best. Winds are not as strong here either...but cannot rule out an
isolated tree down or spotty power outage.
The final threat is the heavy rainfall rotating into the area in the
deformation zone around the approaching upper low. Models keep quite a
bit of upper divergence across the area through the morning as this
zone rotates over the area this morning. Have already had heavy
rainfall and a quick rise in creeks across portions of the clt metropolitan
area. With the heavy rainfall remaining over the area this
morning...additional areas of excessive rainfall and rising streams
are possible. Areal coverage of any flooding uncertain enough to
preclude the issuance of a watch...but will keep a close eye on
streams and rainfall and issue any flood warnings as needed.
The good news is that precipitation heavy precipitation should quickly taper off
and move east of the area during the afternoon as temperatures warm above
freezing. Any wintry precipitation threat should end by noon...so current
west-southwest expiration time still good. Winds should drop off significantly
by afternoon...but cannot rule out some lingering gusts. It is
possible that a wind advection may be needed across portions of the area
for the afternoon.
Conditions continue to improve tonight as short wave ridging moves
in behind the departing upper low. Skies clear and winds continue to
diminish. Temperatures will fall to near freezing across portions of NC...
so later shifts will have to entertain any special products for
potential black ice. Temperatures should remain above freezing...but still
below normal...for the upstate and NE Georgia.
Short term /Saturday night through Sunday night/...
at 310 am EST Friday...conditions should warm comfortably across the
region on Saturday. Short range models indicate that surface high
pressure will settle across the deep south as a weak front slides
over the Ohio River valley. Downslope flow...mostly sunny sky...and
mild thicknesses should result in high temperatures in the middle 60s
within the mountain valleys and around 70 east. Temperatures will remain
around 5 degrees above normal Saturday night. The mild temperatures
will be a result of return flow and increasing cloud cover
preceding the cold front.
The NAM and GFS indicate that a light round of primarily rain will
occur across the Tennessee border counties early Sunday morning. The precipitation
will likely not accompany the weak front across the eastern slopes
and foothills. However...I will increase clouds for Sunday.
Temperatures are forecast not to vary much from values observed on
Long term /Monday through Thursday/...
as of 240 am Friday...the medium range forecast picks up at 12z on
Monday with an upper shortwave moving off the Carolina coast and a
cutoff southern stream upper trough over northern Mexico and portions
of SW Texas. Over the next 24 to 36 hours...the pattern remains fairly
zonal over the southeast Continental U.S. While the southern stream trough drifts
eastward and begins to open back up. By late Wednesday...a broad upper
trough over the Great Lakes digs southward and towards our forecast area.
Both the GFS and European model (ecmwf) suggest that the trough axis will move over the
County warning forecast area by late Thursday...with the GFS being more progressive with the
At the surface..broad high pressure will be over the region at the start
of the medium range and is expected to remain over the region through
Tuesday. Another low will develop to our west late Tuesday/early Wednesday
and move into the County warning forecast area on Wednesday. The specific track and speed of the
low as it moves over the region remains somewhat unclear at this
point...however the appear more consistent than they did yesterday
morning. They do agree that by Thursday evening the low should be well
to our NE with dry high pressure pushing into the County warning forecast area. The only
significant/noteworthy changes I made to the sensible forecast included
ramping up probability of precipitation to solid chance by 00z Wednesday over essentially the
entire County warning forecast area and tapering them down sooner on Thursday. I now have
precipitation chances peaking by midday Wednesday as the low is expected to
approach the forecast area about 12 hours sooner. Temperatures will start out
well above normal on Monday and remain above normal through Wednesday
and then drop on Thursday as cold air advection works its way into the region.
Aviation /12z Friday through Tuesday/...
at kclt...temperature and wet bulb temperature have been above freezing all night
at the airfield. Cannot completely rule out a brief period of freezing rain
around daybreak. However...chance is very low and event would not last
very long if it did develop. Otherwise...expect IFR ceilings and MVFR to
low VFR visibility in rain this morning as rain continues to rotate across
the area. This rain pulls east of the area with the upper low by
early evening. IFR ceilings will become MVFR through the morning and linger
into afternoon. Low clouds should scatter out early evening with
mainly cirrus overnight. MVFR seems a good bet by daybreak Sat with
the wet ground and good radiational conditions. Gusty north-northeast wind
becomes northerly by afternoon with diminishing gusts. Light northerly wind this
evening becomes calm overnight.
At kavl...mainly rain expected through the period as surface temperatures and wet
bulb temperature remain above freezing and warm nose continues across the
area. Expect mainly MVFR ceilings with MVFR visibility during the heavier
rain. MVFR clouds scatter toward sunset with only high clouds
overnight. MVFR fog should develop by daybreak Sat. Light northerly winds
continue through the period.
Elsehwere...the upstate taf sites will see rain with conditions
varying from low VFR to IFR. Gusty north-northeast wind becomes northerly through the day
with diminishing gusts. Calm wind expected toward daybreak Sat.
Snow...possibly mixed with rain and sleet...will continue through the
morning at khky before changing all to rain. IFR conditions will
become MVFR for afternoon then low VFR near sunset.
12-18z 18-24z 00-06z 06-12z
kclt medium 77% medium 78% high 100% high 83%
kgsp high 84% medium 77% high 100% high 83%
kavl high 82% medium 76% high 100% high 88%
khky medium 78% high 83% high 100% high 88%
kgmu medium 75% medium 78% high 100% high 88%
kand high 96% medium 79% high 100% high 88%
The percentage reflects the number of guidance members agreeing
with the scheduled taf issuance flight rule category. Complete
hourly experimental aviation forecast consistency tables and ensemble
forecasts are available at the following link: (must be lower case)
NC...Winter Weather Advisory until noon EST today for ncz048-052-
Winter Storm Warning until noon EST today for ncz033-035>037-
SC...Winter Weather Advisory until noon EST today for scz003.