NWS Greenville-Spartanburg, SC wrote its last area forecast discussion before the first event at Feb 11, 3:41 AM EST, 1 hour 19 minutes earlier.
Area forecast discussion, Feb 11, 3:41 AM EST, 1 hour 19 minutes before
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
341 AM EST Sun Feb 11 2018
.SYNOPSIS...
Moist southwesterly flow will continue across the region today ahead
of a cold front slowly approaching from the northwest. The cold
front will lay over into the region on Monday and then gradually
settle southward through Monday night as high pressure builds to the
north. Cool and somewhat moist conditions will continue into Tuesday
before mid-week drying and warming occurs. Another cold front will
approach from the northwest late in the week.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM EST Sunday: With persistent, strong southerly flow
ahead of the next approaching system, a plume of moisture out of the
GOM continues to stream up across the Southeast this morning, as
latest radar imagery depicts widespread showers with a few embedded
thunderstorms moving northeastward across the western half of our
FA. A Flood Watch remains in effect for portions of the area (west
of the I-77 corridor) through the near term forecast period as
flooding has already become a concern this morning with flood
advisories & warnings already in effect along the escarpment.
With a stationary boundary to the west this morning, it's parent sfc
low currently resides over AR/LA/MS per latest analysis. As this
system propagates northeastward up through the TN Valley today, the
long anticipated approach of it's associated cold front will be well
on it's way towards our FA. With the system's forward track through
tonight, our forecast area will remain well within the warm
sector through this evening. Current temperatures in the low to
mid 60s, into the upper 50s back across the mountains this
morning will slightly warm today into the upper 60s across the
Upstate and Piedmont, with increasing southerly winds.
PWATs today and tonight will remain in the 1.25-1.50 inch range,
which for February is well above normal. This available moisture
along with upglide and increasing upper dynamic support will allow
for widespread showers to persist throughout the day, along with
patchy areas of fog and embedded convection as available
instability/increasing shear warrants. Expect higher QPF to
remain confined to areas along and west of the escarpment,
decreasing in amounts towards the I-77 corridor. Enhanced lift
later today with the approaching cold front will allow for
rainfall to expand eastward through into the evening hours, as
the front slowly pushes across the FA from west to east tonight.
Overall QPF totals for the near term forecast period will
remain the lowest across the eastern portions of the FA, with up
to three quarters of an inch possible along the I-77 corridor
before daybreak on Monday. However, localized higher amounts of
precip are possible as heavy downpours within any convection
today and tonight are likely. QPF amounts within the current
Flood Watch through early Monday morning will range between 1 to
2 inches, with higher amounts across the southern upslope
areas. Overnight low temperatures will remain well above normal.
&&
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 245 AM Sunday: The cold front arriving from the northwest will
start to lay over across western North Carolina early on Monday.
Meanwhile, a deep layer southwesterly fetch will continue aloft, so
it will take high pressure building to the north and weak returning
upglide to allow the boundary to ooze southward as a wedge front
late Monday through Monday night. Precipitation amounts should be
rather modest as some degree of mid-level drying will occur. Ahead
of the back-door wedge front, the southeast part of the region
should see some Monday afternoon instability - with scattered
thunderstorms developing. Fortunately, shear will be weak on the
warm sector side of the surface wedge boundary.
The flow pattern will gradually become more zonal aloft Tuesday
through Tuesday night, with the CAD-like shallow ridge persisting
over the western Carolinas and NE GA. Any precipitation amounts will
remain quite low, but some clouds remaining in place will keep the
diurnal temperature range quite small.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 300 AM Sunday: Swift zonal flow will continue from mid to late
week. Brief drying will likely occur by Wednesday, but with deeper
moisture returning in the westerly flow Wednesday night through
Thursday ahead of the next approaching cold front. Warm temperatures
reaching 70 degrees or better look likely for Thursday in the warm
sector ahead of the cold front.
Considerable model difference appear for Friday through Saturday.
The GFS features a fast-moving shortwave crossing the Appalachians
on Friday to give the front an eastward kick, but the ECMWF does not
advertise this feature, generally keeping height falls back over the
southwestern U.S. The Canadian solution and ensembles are in between
the GFS/ECMWF. The Fri/Sat forecast will thus remain a low
confidence one with shotgun chance PoPs for now using a blended
solution with a frontal zone somewhere in the vicinity.
&&
.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Expect a mixture of MVFR/IFR/LIFR due to low
cigs and reduced visibilities to prevail through the valid TAF
period, though cannot entirely out a brief improvement to VFR cigs
at any point.
A plume of moisture along with SW upglide flow will allow for low
cigs and widespread showers to persist through the forecast period.
These along with areas of fog will allow for deteriorated flight
restrictions to prevail today through early Monday morning. Per
latest radar imagery, the heaviest rainfall continues to move
northeastward through the area, though a brief lull in activity has
developed. Thus, an isolated shower is possible at
KCLT/KAND/KGSP/KGMU over the next few hours before the rain fills
back in. At all sites, breaks in the precipitation may allow for
cigs to briefly improve in some locations (VFR cigs) but do not
expect improvement to last.
Per latest obs, light SSE winds are slowly picking up already this
morning. Anticipate winds to increase to AOB 12 kts becoming SSW
throughout the day, which is expected to briefly alleviate vsbys at
times, but will not completely disperse fog. Gusts up to 20 kts are
possible this afternoon, which will subside tonight.
Outlook: Expect MVFR/IFR/LIFR to gradually improve on Monday,
possibly lingering into Tuesday. Otherwise, expect VFR.
Confidence Table...
08-14Z 14-20Z 20-02Z 02-06Z
KCLT High 91% Med 73% Low 58% High 96%
KGSP High 82% High 82% Med 75% High 95%
KAVL High 83% High 91% High 91% High 97%
KHKY High 90% Med 79% Med 70% High 87%
KGMU High 87% High 84% Med 75% High 91%
KAND Med 65% Med 76% Med 73% High 95%
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
&&
.HYDROLOGY...
Across the North Carolina mountains, soil moisture values
and streamflows remain near normal to above normal across most of
the area, with some exception across the extreme southwest
mountains. However, the somewhat drier antecedent conditions across
the southwest mountains are quickly becoming overcome by anticipated
rainfall. Reservoir pools are at or above target levels as well so
storage will be limited. Therefore, given the primed antecedent
conditions, runoff will be significant and the likelihood of
isolated to scattered small-stream flooding remains high, especially
across the southwest and southern mountains. Minor mainstem flooding
is most likely across the favored upper reaches of the French Broad
River, and remains possible along the Pigeon, Nantahala, and
Tuckasegee Rivers. While rainfall overnight into this morning were
very efficient given near-record moisture content, heavy rainfall
totals will occur over a time period generally not conducive to
flash flooding, which occurs within 6-hours from rainfall onset.
Nevertheless, small-streams will respond fairly quickly to any
locally intense rainfall that develops.
Across the Foothills and western Piedmont of the Carolinas and
northeast Georgia, soil moisture values and streamflows have made
significant recoveries with recent rainfall, eliminating lingering
dry conditions and increasing the likelihood of significant runoff.
Where bands of heavy rainfall can set up across these regions today
through early Monday, isolated to scattered minor small-stream
flooding is possible. Mainstem river flooding is less likely, but
cannot be ruled out, especially along the Saluda, Reedy, and upper
reaches of the Middle Tyger River.
For more information about the current state of hydrologic
conditions across the area, see http:/weather.gov/gsp/floodoutlook.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flood Watch through Monday morning for GAZ010-017-018-026-028.
NC...Flood Watch through Monday morning for NCZ033-035-048>053-058-
059-062>065-501>510.
SC...Flood Watch through Monday morning for SCZ001>007-010.
&&
SYNOPSIS...HG
NEAR TERM...SGL
SHORT TERM...HG
LONG TERM...HG
AVIATION...SGL
HYDROLOGY...JMPSpecial weather statement, Feb 11, 1:49 AM EST, 3 hours 11 minutes before
Special Weather Statement
National Weather Service Greenville-Spartanburg SC
149 AM EST SUN FEB 11 2018
SCZ001-002-004-005-110730-
Pickens Mountains SC-Greater Pickens SC-Greater Oconee SC-
Oconee Mountains SC-
149 AM EST SUN FEB 11 2018
...A THUNDERSTORM WITH TORRENTIAL RAINFALL AND GUSTY WINDS WILL
IMPACT PICKENS AND OCONEE COUNTIES UNTIL 230 AM EST...
At 147 AM EST, Doppler radar was tracking a thunderstorm with
torrential rainfall near Walhalla, moving northeast at 55 mph.
Locations to be impacted include...
Seneca, Walhalla, Pickens, Westminster, Six Mile, Salem, Lake Keowee,
Jocassee Gorges, Lake Jocassee and Devils Fork State Park.
Wind gusts up to 40 mph and very heavy rainfall rates in excess of
an inch per hour will be possible in these areas. Isolated flooding
of low-lying areas may result.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.
&&
LAT...LON 3476 8319 3502 8299 3505 8291 3509 8279
3507 8278 3507 8277 3505 8275 3506 8270
3507 8257 3506 8257 3506 8260 3504 8260
3503 8259 3501 8260 3501 8254 3498 8253
3498 8255 3497 8253 3490 8250 3461 8306
TIME...MOT...LOC 0647Z 233DEG 48KT 3474 8305
HG