Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 162024 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 324 PM EST Tue Jan 16 2018 .SYNOPSIS... A cold front will approach from the west today and cross the area tonight. This front will usher in a quick shot of cold air, with light snow possible across the forecast area tonight into early Wednesday. High pressure will slide off the East Coast by Friday, allowing a warming trend for the end of the week. && .NEAR TERM /THROUGH WEDNESDAY/... As of 1245 PM EST: Frontal band of light snow across the TN Valley continues to edge its way into the southern Appalachians this afternoon, and will continue to push across the area into the evening. Clear skies in advance of the band has allowed temps to warm well above freezing across the mtn valleys, thus precip will begin as liquid there, with wet bulb effects allowing for a gradual transition to snow by early evening. Meanwhile, all-snow is expected above 3500 ft or so. At this point, the shortened duration of any snowfall, and a possible general decreasing trend to precip rates will limit accums in the valleys and across much of the foothills through this evening. This is essentially what we`ve been forecasting, with only about .5-1" of accums (with locally higher amounts) likely in these areas. However, with temps expected to plummet as arctic cold front blasts through the area late this evening into the overnight, wet surfaces will refreeze, likely making the roads a mess for the morning rush. The advisory will therefore be maintained for these areas, but the black ice will be highlighted as much as the snow. Additionally, while only a dusting appears likely across far northwest SC, and the northeast GA foothills, the same black ice concerns will exist there, and these areas will be added to the advisory for that reason. Tonight, the main point of contention is the uptick in precipitation amounts forecast across the far southern and eastern zones, as the strong short wave trough transitions from positive to more of a neutral tilt, resulting in an increase in deep layer forcing. This has always been the primary concern with this event (and always is in these situations): whether the increase in precip rates will occur across our area, or more across the central/eastern Carolinas. Based upon the current trends in guidance (along with a dash of climatology) a warning will be issued for Union-NC. Locations roughly along/east of a line from Chester->Rock Hill->Concord-> Salisbury could flirt with warning criteria, but confidence in that is moderate at best. Interests in those areas locations should be cognizant of the potential for a warning upgrade with relatively short lead time. Despite decreasing cloud cover on Wed, with && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 315 PM EST Tuesday: The forecast period begins Wednesday night with dry conditions in place across the entire forecast area, persisting through the end of the week. Latest GFS/ECMWF remains in agreement placing an eastward propagating upper trough over the Carolinas Wednesday night, which will extend from the northeast, down southward into FL. This feature will exit the eastern seaboard late overnight into early Thursday morning, leaving dry conditions and NW flow in it`s wake as sfc high pressure builds in. Though wintry precipitation will come to an end Wednesday afternoon, temperatures Wednesday night through Thursday morning will dip into the teens across the forecast area, with single digits across the higher elevations. While increased NW winds during the day on Wednesday will help to dry ground sfcs somewhat, any residual water from snow melt on roadways/elevated surfaces will refreeze overnight Wednesday into Thursday morning (while noting high temperatures on Wednesday will have struggled to reach freezing to begin with). As confidence increases with expected overnight low temperatures, do expect areas of black ice on roadways/elevated surfaces, likely causing slippery roads and hazardous travel conditions for Thursday morning`s commute. Temperatures will fall below freezing again overnight into Friday morning, thus again, any residual water will likely refreeze. For the rest of the day on Thursday, sfc high pressure will continue expand into the Southeast, gradually moving overhead on Friday as flow aloft becomes zonal and the pressure gradient relaxes. With plenty of sunshine both days, temperatures will warm into the low to mid 40s across the Upstate and Piedmont and upper 30s/lower 40s across the mountains, warming even more and rising to near or just above normal for Friday. With increased winds and temperatures, wind chill values Thursday morning will again near dangerous values of around - 5F to -10F across the higher elevations, single digits across the mountains, into the teens across the Upstate and Piedmont. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 210 PM EST Tuesday: The ext range continues with good confidence thru the weekend. The op models are showing a strong srn stream sfc high dominating the pattern while overcoming a dry trof axis east of the mtns Fri/Sat then centering offshore on Sun. Soundings indicate a very dry atmos which will aide in allowing max temps abv normal thru the period and increasing thicknesses helping to hold min temps abv normal as well. The pattern becomes more dynamic Sun as a 130 kt ulvl jet coincides with 300 K isent lift and continued moist adv associated with an incoming cold front. With a wide open GOM...a deep moist layer will encompasses the area Sun night thru Mon. Heavy rain will be possible in this environ...esp across the favored srn BR upslope regions. Expect diurnally driven higher elev -snsh in NW flow as the frontsl system begins moving east Mon night...however snowfall amounts shud remain low-end as available moisture quickly wanes. && .AVIATION /21Z TUESDAY THROUGH SUNDAY/... At KCLT and elsewhere: VFR through the afternoon, with increasing chances for precipitation, with onset times ranging from early evening at around midnight at KCLT. While precip is expected to begin as -RA at most locations, a transition to -SN is expected, with a deterioration to IFR once the snow settles in. Periods of LIFR or even VLIFR cannot be ruled out within heavy bursts of snow. Conditions begin improving around daybreak, with VFR expected at all terminals by around late morning, with SKC by early afternoon. S/SW winds at 5-10 kts transition to light NW winds behind the front this evening into the early part of the overnight. Outlook: Dry/VFR condition are expected to continue through the weekend. Confidence Table... 20-02Z 02-08Z 08-14Z 14-18Z KCLT High 100% High 100% Med 61% Med 66% KGSP High 100% Med 71% High 96% High 89% KAVL High 94% Med 68% High 92% High 100% KHKY High 100% High 85% High 81% High 93% KGMU High 100% Med 69% Med 62% High 92% KAND High 100% Med 69% Low 56% High 97% 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: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...Winter Weather Advisory from 10 PM this evening to noon EST Wednesday for GAZ018-026-028-029. Winter Weather Advisory until 7 AM EST Wednesday for GAZ010- 017. NC...Winter Weather Advisory from 10 PM this evening to noon EST Wednesday for NCZ035>037-056-057-068>072-501>510. Winter Weather Advisory until 7 AM EST Wednesday for NCZ051- 052-058. Winter Weather Advisory until 7 AM EST Wednesday for NCZ033- 048>050-053-059-062>065. Winter Storm Warning from 10 PM this evening to noon EST Wednesday for NCZ082. SC...Winter Weather Advisory from 10 PM this evening to noon EST Wednesday for SCZ001>014-019. && $$ SYNOPSIS...Carroll NEAR TERM...JDL SHORT TERM...SGL LONG TERM...SBK AVIATION...JDL is the U.S. government's official web portal to all federal, state and local government web resources and services.