NWS Greenville-Spartanburg, SC wrote its last area forecast discussion before the first event at Dec 20, 9:58 PM EST, 17 minutes earlier.
Area forecast discussion, Dec 20, 9:58 PM EST, 17 minutes before
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
958 PM EST Thu Dec 20 2018
.SYNOPSIS...
A slow moving low pressure system will continue widespread
precipitation across the region through Friday. As the low moves
north of the area Saturday, dry high pressure will build in and
remain in control through early next week.
&&
.NEAR TERM /THROUGH FRIDAY/...
As of 955 PM EST: Wedge erosion appears to have stalled along the I-
77 corridor. However, visibilities have begun to crash over the
Upstate, which is usually a precursor to wedge erosion, although it
could take a while over those locations. Still watching for thunder
potential over the I-77 corridor where surface based instability may
develop with the wedge erosion. Creeks and streams seem to have
crested at most locations, but may take a while before falling below
advisory levels. The exception is the Upper French Broad, the South
Fork Catawba, and Broad Rivers. Blantyre will likely crest just
above flood stage, while Fletcher, Lowell, and Blacksburg likely
crest at action stage. Initial gusty winds seem to have subsided,
but expect gusts to return after daybreak. Temps are running well
above expectation over the I-77 corridor and slightly warmer
elsewhere. Have adjusted temp trends to match.
Otherwise, there are a few details worthy of discussion. The models
depict the next sfc low moving northward over the foothills, which
might allow parts of the western Piedmont and metro Charlotte to be
uncovered by the wedge by around daybreak on Friday. If that
happens, we could see a window of time on Friday morning when sfc-
based CAPE creeps up into the neighborhood of 300 J/kg while shear
of about 30kt remains overhead. Not really high shear/low
CAPE...more like medium shear/really low CAPE...but as some of us
are fond of saying...we've done more with less. The convection-
allowing models are not showing anything particularly frightening at
this time, but suffice to say there is a non-zero chance of a severe
storm mainly in the Charlotte metro area in the morning. Will
monitor.
After the sfc low passes in the morning, the upper low moves
overhead in the afternoon while the deeper forcing also pulls
out to the northeast. Precip will become more scattered and more
showery through the day away from the TN border. Could be some
graupel (really small hail) falling out of showers east of the
mtns in the afternoon because of the cold air aloft. Temps will
remain close to normal west of I-77 where the wedge is likely to
persist until the NW flow begins in the wake of the sfc low.
Meanwhile, near the TN border, the passage of the low and arrival of
the upper low will bring in the cold air aloft and allow remaining
precip to begin changing over to snow in the late morning to early
afternoon from SW to NE with snow level falling from 6k feet down
to about 3k feet by sunset. Strong W to NW flow behind the low and
deep moisture remaining in place should allow for decent snow rates
on the ridgetops and mountain peaks, especially over the Smokies,
where a significant accum of a few inches could happen before
sunset. Being that it is a high travel weekend, think it best to
issue a Winter Weather Advisory for the high elevations of the NC
mountains Avery County southward with this package so people can
alter travel plans if necessary. Have chosen an Advisory based on
the average accum across the area above 3500 feet, but note that
some of the peaks above 6k feet have the potential to get closer
to warning criteria by sunset Friday before the deeper moisture
starts to pull out. Winds will also be increasing in the afternoon,
and that will be factored into the Advisory.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
As of 215 PM Thursday: The axis of a full-latitude, sharp trough
will cross the Southern Appalachians Friday night, with flat flow
quickly setting up as the trough lifts out. The sfc low pressure
center will migrate north to Upstate NY and then into Quebec, while
high pressure builds in across the Gulf states. By 00z Saturday, the
850 mb flow should be out of the NW with temps dropping into the 0
to -5 C range overnight. So ongoing NW flow showers should
transition to all snow by late evening, while becoming confined to
the TN border areas. Additional snow accums overnigth look to be 1-
2", with isolated higher amounts possible. Guidance is in good
agreement that moisture pulls out quickly from SW to NE Saturday
morning, resulting in a fairly sharp cut off in shower activity.
Along with the snow showers, it will be windy. The 850 mb winds of
40-50 kts in strong CAA should result in advisory-level gusts,
especially in the northern mountains. This is in line with our
Winter Weather Advisory above 3500 ft for Friday aftn into Saturday
morning. Temps will fall into the 20s in the mountains and mid to
upper 30s in the piedmont.
By Saturday aftn, winds should be decreasing and skies clearing.
Despite sunny to mostly sunny skies, temps will top out a category
or two below normal.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
As of 230 PM EST Thursday: With quasi-zonal flow setting up aloft
for the latter half of the weekend, another cold front will quickly
cross the forecast area on Sunday. It still looks fairly moisture-
starved; however, guidance has trended a little wetter on the 12z
cycle. Thicknesses/temps are marginal for some high-elevation snow
showers, while the valleys looks to be all rain. With that said,
PoPs are still only in the low- to mid-chc range. The eastern 2/3rds
of the CWFA look to just see a brief period of cloudy to mostly
cloudy skies. Temps will be near normal.
The air mass behind the front will be seasonably cool and dry, with
temps expected to remain near normal Monday and Tuesday under partly
cloudy skies. So unfortunately, no white Christmas expected this year
(except if any snow remains from the NW flow event).
The dry weather will be short-lived, as another southern stream low
pressure system takes shape to our west heading into midweek. Precip
may start moving back in from SW to NE, as early as Wednesday
evening, with PoPs ramping up to likely by Thursday. A
transitory high pressure tracking from the Great Lakes to the
Canadian maritimes will support a hybrid or in-situ cold air
damming wedge. It looks like thicknesses will be too warm for
any wintry precip type concerns. This system does look like another
soaker.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Tricky forecast as wedge is beginning to
erode as the first of a series of surface low pressure centers
passes north across the area. Widespread rainfall and vsby
restrictions area ending, but IFR to LIFR cigs will continue. Winds
have also become S to SE and gusty where wedge has eroded. These cig
trends will continue overnight with vsby deteriorating. Winds will
become southerly but not as gusty. TSRA still possible at KCLT near
daybreak as weak instability develops. Kept PROB30 in place. Expect
vsby improvement after daybreak but only a slow cig improvement
during the day. Winds will become SW then westerly with gusts
returning. Precip chances diminish as well.
Outlook: Expect improving conditions for the weekend everywhere
but KAVL, where moist NW flow will continue.
Confidence Table...
03-09Z 09-15Z 15-21Z 21-00Z
KCLT Low 47% Med 71% High 83% High 98%
KGSP Med 77% High 81% Med 79% High 89%
KAVL Med 77% Med 77% Med 76% Med 62%
KHKY Med 73% Med 72% Med 73% Med 68%
KGMU Med 78% Med 77% Med 75% High 98%
KAND Med 79% High 89% High 87% High 100%
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:
www.weather.gov/gsp/aviation
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Winter Weather Advisory from noon Friday to noon EST Saturday
for NCZ033-048>052-058-059.
SC...None.
&&
SYNOPSIS...SBK
NEAR TERM...PM/RWH
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...RWHSpecial weather statement, Dec 20, 10:13 PM EST, 2 minutes before
Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1013 PM EST Thu Dec 20 2018
GAZ010-017-018-026-028-029-NCZ035>037-056-057-068-069-501>510-
SCZ001>008-010>013-019-210700-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Alexander-Iredell-
Davie-Catawba-Rowan-Cleveland-Lincoln-Caldwell Mountains-
Greater Caldwell-Burke Mountains-Greater Burke-McDowell Mountains-
Eastern McDowell-Rutherford Mountains-Greater Rutherford-
Polk Mountains-Eastern Polk-Oconee Mountains-Pickens Mountains-
Greenville Mountains-Greater Oconee-Greater Pickens-
Greater Greenville-Spartanburg-Cherokee-Anderson-Abbeville-
Laurens-Union-Greenwood-
Including the cities of Clayton, Pine Mountain, Mountain City,
Cornelia, Baldwin, Demorest, Clarkesville, Hollywood, Boydville,
Toccoa, Royston, Whitworth, Lavonia, Franklin Springs, Canon,
Hartwell, Nuberg, Reed Creek, Elberton, Fortsonia, Middleton,
Ruckersville, Bethlehem, Ellendale, Millersville, Taylorsville,
Hiddenite, Stony Point, Statesville, Mooresville, Farmington,
Fork Church, Mocksville, Advance, Hickory, Newton, St. Stephens,
Salisbury, Shelby, Kings Mountain, Lincolnton, Crouse, Patterson,
Kings Creek, Lenoir, Sawmills, Granite Falls, Jonas Ridge,
Morganton, Pleasant Grove, Valdese, Ashford, Sugar Hill,
Woodlawn, Old Fort, Marion, Nebo, Dysartsville, Fero, Glenwood,
Lake Lure, Forest City, Rutherfordton, Spindale, Saluda, Tryon,
Columbus, Lake Adger, Mill Spring, Mountain Rest, Walhalla,
Westminster, Pumpkintown, Tigerville, Gowensville, Caesars Head,
Cleveland, Marietta, Seneca, Oakway, Easley, Dacusville, Clemson,
Greenville, Taylors, Greer, Mauldin, Fork Shoals, Simpsonville,
Berea, Spartanburg, Gaffney, Anderson, Abbeville, Calhoun Falls,
Laurens, Clinton, Union, Monarch Mills, Ware Shoals,
and Ninety Six
1013 PM EST Thu Dec 20 2018
...PATCHY DENSE FOG OVERNIGHT...
Patchy dense fog has developed and will continue overnight across
portions of the foothills and piedmont of North Carolina, Upstate
South Carolina, and Northeast Georgia. Expect widely varying
visibilities, with less than one-quarter of a mile in some
locations. A dense fog advisory may be needed by morning as the
dense fog could become widespread.
Be alert for reductions in visibilities. Remember to slow down and
use low beam headlights if traveling.