textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

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

Minor tweaks were made to the rainfall forecast overnight and early Thursday. Still expect all-liquid precipitation, with the exception of extremely high elevations (above 5000 feet) in the Appalachians, which may receive a dusting of snow or freezing rain.

A Winter Storm Watch remains in effect from Saturday morning through early Monday afternoon for the entire forecast area.

KEY MESSAGES

1. A weak cold front will cross the mountains tonight and lay out across the area east of the mountains Thursday through Friday, bringing the chance for wintry precipitation across portions of the North Carolina mountains tonight and Friday, which may lead to minor travel impacts. Temperatures will be warm enough for all rain east of the North Carolina mountains. 2. Winter Storm Watch is in effect Saturday morning through early Monday afternoon as a storm system will bring heavy mixed precipitation to the entire forecast area leading to hazardous travel and power outages that may last for days. 3. Dangerously cold wind chills may develop Monday night into Tuesday morning which could result in hypothermia or frostbite if precautions are not taken.

DISCUSSION

Key message 1: A weak cold front will cross the mountains tonight and lay out across the area east of the mountains Thursday through Friday, bringing the chance for wintry precipitation across portions of the North Carolina mountains tonight and Friday, which may lead to minor travel impacts. Temperatures will be warm enough for all rain east of the North Carolina mountains.

Thick prefrontal cloudiness continues to impinge on the western extent of the CWA this evening in a band stretching from northwest Georgia all the way to West Virginia. Radar returns still lag significantly behind the leading edge of this cloudiness, and METARs from eastern Tennessee indicate a 20+ degree dewpoint depression that advancing precipitation will still need to overcome to make it to the ground. Model fcst soundings still suggest the precip type could be just about anything in the high elevations, but fortunately the expected amounts are light and sub-advisory...with little if any change made to accums in the most recent forecast update. So, an inch or so of wet snow would be possible above roughly 5K feet in the Smokies and Nantahala mtns, or possibly a few pockets of freezing rain at the very high ridges, but there'll be neither enough nor large enough an extent to contemplate an Advisory.

The front will eventually arrive over the mtns later tonight and then will move out across the area east of the mtns on Thursday before laying down Friday night. Forcing along the front will be minimal, but the model blend keeps precip chances mainly over northeast GA and Upstate SC. Fortunately, temps/thickness will be too warm/high for anything other than rain (or some stray brief sleet reports). Temps are expected to remain about a category above normal through Thursday night. Eventually, another short wave moving along in what should be a nearly-zonal flow will move over top of the stalled boundary, bringing another round of light precip. Some of the ridges and peaks above 5K feet could get additional light snow accums...less than an inch...mainly Friday morning...but only rain should fall otherwise with temps falling down just below normal. In the wake of this wave, it stands to reason that we should develop a lull before the arrival of the main event, though for now the timing differences in model blend do not allow the reflection of the precip lull in the fcst.

Key message 2: Winter Storm Watch is in effect Saturday morning through early Monday afternoon as a storm system will bring heavy mixed precipitation to the entire forecast area leading to hazardous travel and power outages that may last for days.

Attention now turns to the winter storm this weekend into early next week. A Winter Storm Watch was issued and is in effect Saturday morning through Monday morning. Although wintry precipitation is expected to come to a gradual end early Monday morning, impacts such as hazardous road conditions and power outages will likely linger through at least early next week. The main changes this forecast cycle are that the NBM is now trending a few degrees warmer for highs this weekend and the 06Z guidance has trended much farther north with the system. These two changes have led our forecast to trend more towards ice and sleet and less snow. P-types as well as exact snow, sleet and ice accumulations remain the main forecast challenge as wintry p-types and accumulations will be highly dependent on the exact track the system takes. A lot can still change between now and Friday but we should start to get a better handle on the system once the high-res guidance becomes available for this system. Make sure to check the latest forecast information from trusted sources frequently in the coming days as this is an evolving system. For now, it appears that heavy mixed precipitation is possible area-wide, with the highest snowfall accumulations possible north of I-40 and the highest ice accumulations possible across the southern mountains of North Carolina, the mountains of northeast Georgia, and the mountains of South Carolina. NBM 48 hour probabilities of 0.25" or greater ice accumulation ranges from 50% to 80%, with 48 hour probabilities of 0.50" or greater ice accumulation ranging from 25% to 45% for the NC/TN border counties and 45% to 65% for the rest of the forecast area. NBM 48 hour probabilities of 1" or greater snow accumulation ranges from 35% to 45% across the South Carolina Upstate and northeast Georgia, with 45% to 75% across western North Carolina. NBM 48 hour probabilities of 4" or greater snow accumulation ranges from 35% to 50% along and north of I-40.

Now is the time to prepare. Regardless of exact p-types and accumulations this will be an impactful storm leading to hazardous road conditions and power outages that could last for days. Be prepared to adjust travel plans if a warning is issued. Prepare an emergency kit for your car and home and replenish fuel for your car and other heating sources such as generators. Don't forget about your pets!

Key message 3: Dangerously cold wind chills may develop Monday night into Tuesday morning which could result in hypothermia or frostbite if precautions are not taken.

Dry conditions return early next week as surface high pressure builds into the region behind the departing winter storm but cold and well below normal temperatures will stick around which should allow dangerously cold wind chills to develop area-wide. The latest NBM is trending a few degrees colder regarding Tuesday morning lows compared to the previous cycle, and if current NBM trends hold, at least a Cold Weather Advisory would be needed for the entire forecast area. Elevations above 3,500 ft in the North Carolina mountains are now flirting with Extreme Cold Warning Criteria (which starts at -15 degrees F). Travel issues and power outages are likely to linger through early next week depending on how fast wintry precipitation melts.

The time to prepare is now. Keep enough non-perishable food, water, and medications for at least 3 days. Ensure you have warm clothing and blankets as well as an updated first aid/emergency kit. Charge your phone in advance so that you are able to receive alerts and check-in with loved ones. Practice portable generator safety by putting your generator outdoors and at least 20 ft away from doors/windows/garages to avoid carbon monoxide poisoning.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR conditions are expected to linger the rest of the evening, and into the overnight for most of the area. Still expect some valley stratus to begin developing after midnight, possibly resulting in MVFR ceilings at KAVL and other mountain terminals before and shortly after dawn. Overnight and early morning precipitation in the NC mountains is still expected to be minimal, but from mid-morning through early afternoon Thursday, high rain chances develop along I-85...with potential to affect KCLT and all the Upstate terminals. For now, have kept, and extended past 18z, PROB30s from the previous TAF issuance, for -RA and brief MVFR ceilings. Light and variable winds overnight will pick up out of the WSW during the day Thursday, but should remain <5kts all day. Restrictions may redevelop - mainly across the Upstate - Thursday night. At KCLT, this fell out in the 00z TAF; at the other terminals, all of which have 24-hour TAFs, restrictions are still expected to begin developing after the end of the TAF window.

Outlook: Confidence continues to increase regaring a winter storm that would affect the entire forecast area beginning Saturday morning and continuing through the weekend. Accumulating snow/sleet/ice is likely with significant impacts to travel expected, though confidence on precip type transitions and total accumulation remains low. Long term prevailing flight restrictions should be expected into Monday when the system finally moves east.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Winter Storm Watch from Saturday morning through Monday afternoon for GAZ010-017-018-026-028-029. NC...Winter Storm Watch from Saturday morning through Monday afternoon for NCZ033-035>037-048>053-056>059-062>065- 068>072-082-501>510. SC...Winter Storm Watch from Saturday morning through Monday afternoon for SCZ008>014-019-101>109.