textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The forecast was updated to reflect the 00z TAF issuance.

Confidence continues to increase for a storm system to affect the area this weekend.

KEY MESSAGES

1. Low relative humidity (below 25%) develops again at many locations Wednesday afternoon. Dry conditions may be associated with an increased danger of wildfires where fuel moistures are sufficiently low. 2. A weak cold front will cross the area Wednesday evening into Friday bringing the chance for wintry precipitation across portions of the North Carolina mountains which may lead to minor travel impacts. Temperatures will be warm enough for all rain east of the North Carolina mountains. 3. A potential winter storm system may impact the area this weekend but details regarding precipitation amounts and type remain uncertain. Confidence continues to increase that moderate overall winter storm impacts could lead to hazardous travel and power outages. 4. Dangerously cold wind chills may develop Monday night into Tuesday morning which could result in hypothermia or frostbite if precautions are not taken. Snowpack may linger through early next week due to cold temperatures, which may keep travel issues and power outages around.

DISCUSSION

Key message 1: Low relative humidity (below 25%) develops again at many locations Wednesday afternoon. Dry conditions may be associated with an increased danger of wildfires where fuel moistures are sufficiently low.

Strong 1030+ mb sfc high associated with cold continental airmass remains centered over the southwestern NC mountains as of Tuesday evening, set to migrate to the East Coast by morning. Afternoon mixing has mostly subsided this evening, allowing winds to taper off and humidity to stabilize. The eastward migration of this high will allow SW winds to redevelop in the boundary layer by late Wednesday morning, however. Temperatures rebound slightly via airmass modification, and the SW winds do help to replenish moisture aloft, so diurnal mixing will be less effective at reducing RH than on Tuesday. Nonetheless, a slight downward adjustment is warranted from the NBM values, and at least isolated locations could see RH drop below 25 percent. No IFD Statement decision yet made for NC/SC pending further coordination about how fuel moistures change following another very dry day, and the low RH in GA may be too spotty to prompt issuance.

Key message 2: A weak cold front will cross the area Wednesday evening into Friday bringing the chance for wintry precipitation across portions of the North Carolina mountains which may lead to minor travel impacts. Temperatures will be warm enough for all rain east of the North Carolina mountains.

A cold front will approach out of the west Wednesday night, tracking across the forecast area on Thursday before stalling over the area on Friday. This will allow precipitation chances to return to the forecast area. Wintry p-types can be expected across portions of the North Carolina mountains with rain expected elsewhere. Mainly a mix of freezing rain and snow can be expected but some sleet may mix in at times as well Wednesday evening into daybreak Thursday. Temperatures should rise above freezing mid to late morning through the late evening hours Thursday across the North Carolina mountains allowing for a transition to rain. Temperatures will drop near or below freezing Thursday night into Friday across the mountains behind the front allowing for a transition to mainly snow. Snow totals should remain light and below advisory criteria, with accumulations expected above 4,000 feet. However, forecast soundings depict the potential for some freezing rain to develop at times, mainly above 4,000 feet, so some light ice accumulations cannot be ruled out. Light snow and ice accumulations may lead to minor travel impacts across the higher elevations. Temperatures will remain above normal through Thursday night before below normal temperatures return Friday.

Key message 3: A potential winter storm system may impact the area this weekend but details regarding precipitation amounts and type remain uncertain. Confidence continues to increase that moderate overall winter storm impacts could lead to hazardous travel and power outages.

Focus turns to the potential winter storm this weekend and per usual this is shaping up to be a messy forecast in regards to p-types (this is the South after all). Timing appears to be late Friday night into late Sunday night for now, although this is subject to change. Majority of model guidance is on board with a wintry mix of snow, sleet, and/or freezing rain. However, p-types will be highly dependent on the timing of precip. If precip arrives later when the cold air is in place, we could end up with mainly snow and sleet. If the precip arrives prior to the cold air, then we will get a mix of freezing rain, snow, and sleet. The 06Z GFS depicts less ice and more sleet while the 06Z ECMWF depicts more ice and less sleet. The 12Z GFS is showing precip coming in slower compared to the 06Z (after the cold air is already in place) and now shows mainly snow and sleet. For now it appears that we have a high chance for warning criteria snow, sleet and/or ice over the weekend. NBM shows the probability of greater than 4" of snow/sleet ranging from ~20% to 50% across the South Carolina Upstate and northeast Georgia to ~50% to 80% across most of western North Carolina. NBM also shows the probability of greater than 0.25" of ice accumulation ranging from ~20% to 40% along and north of I-40 to ~40% to 60% south of I-40. All this to say, confidence on p-types remains low but confidence of getting warning criteria snow/sleet and/or ice accumulations is increasing. Regardless of exact p-types and amounts, confidence continues to increase that this system could lead to hazardous travel and power outages. Make sure to stay up to date with latest forecast information in the coming days as this is an evolving system. Temperatures are expected to remain well below normal through much of the weekend.

Key message 4: Dangerously cold wind chills may develop Monday night into Tuesday morning which could result in hypothermia or frostbite if precautions are not taken. Snowpack may linger through early next week due to cold temperatures, which may keep travel issues and power outages around.

Dry conditions return early next week but cold and well below normal temperatures will stick around leading to the possibility of dangerously cold wind chills as well as lingering snowpack Monday night into Tuesday. If the current NBM trends hold, a Cold Weather Advisory may be needed for the entire forecast area. Travel issues and power outages may linger through early next week depending on how much snow/sleet/ice melts. There is plenty of time for this to change with this being towards the end of the forecast period so make sure to stay up to date with the latest forecast information in the coming days.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR on tap for the 00z TAF period, with clear skies and light/variable winds overnight. Could see the occasional passing cirrus, especially over the Upstate terminals, overnight, but generally expect predominantly SKC through Wednesday morning. Gradually increasing cirrus is expected through the day Wednesday, while a steady 5-10kt SW wind develops everywhere. Toward the end of the period Wednesday night, could see some increasing mid-level moisture resulting in a mid-level altocu deck...but confidence is low. Also expect light precipitation west of I-26 after 00z Thu...but this is after the KAVL TAF period, and shouldn't affect KCLT within the 30-hour window.

Outlook: Restrictions across the NC mountains could develop Wednesday night and linger through Thursday morning. A winter storm with accumuluating snow and/or ice looks increasingly likely Saturday and Sunday, but confidence on precip type and total accumulation remains very low.

GSP WATCHES/WARNINGS/ADVISORIES

GA...INCREASED FIRE DANGER until 7 PM EST this evening for GAZ010- 017-018-026-028-029. NC...None. SC...None.