textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The wind forecast was tweaked based on the latest CAM guidance, which appears to have a decent handle on overnight winds despite failing to capture extremely gusty winds earlier this afternoon.

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

KEY MESSAGES

1. Snow showers are underway across the Appalachians. Accumulating snow is most likely above 3500 ft along the TN border, where 2 to 4 inches are expected with locally higher totals at the highest elevations. 2. Strong winds will continue behind the cold front into the first half of the night. Though the strongest gusts are likely over, gusts of 25 to 30mph may continue for several more hours. 3. A return to freezing temperatures is expected the next few nights, with the highest confidence Tuesday night. Early blooming vegetation may be vulnerable. Much warmer temperatures return late week, with highs approaching 80 by the weekend.

DISCUSSION

Key message 1: Snow showers are underway across the Appalachians. Accumulating snow is most likely above 3500 ft along the TN border, where 2 to 4 inches are expected with locally higher totals at the highest elevations.

As of around sunset, precipitation had mostly cleared the area, with the exception of a few bands of what would appear from radar presentation to be a rain-sleet mix crossing the NC Foothills...and of course scattered NW flow showers...now entirely snow...along the NC-TN border and portions of the Balsams. The bands of rain/sleet outside the mountains should be the last gasp for the non-mountain zones...while across the mountains snow could linger for much of the night. Lower elevations still look to have received just about as much snow as they're going to. Higher elevations should see sustained snowfall the first half of the night...becoming increasingly confined to high-elevation zones directly along the Tennessee border through the night.

The greatest snowfall totals are expected across the Smokies and higher elevations along the Tennessee border. Current forecasts support totals of around 2 to 3 inches above 3500 ft, with locally higher amounts possible above 5000 ft where upslope enhancement will be strongest. Ensemble guidance from the HREF and REFS continues to indicate a high probability of heavier snowfall at the highest elevations.

Snowfall rates combined with strong winds may result in brief periods of reduced visibility, especially across the higher terrain. Travelers in the mountains should be prepared for rapidly changing conditions through this evening.

Key message 2: Strong winds will continue behind the cold front into the first half of the night. Though the strongest gusts are likely over, gusts of 25 to 30mph may continue for several more hours.

Widespread gusts of 30-40mph have been reported across much of the area, especially in the vicinity of I-77, where strong leading-edge CAA and prefrontal pressure falls resulted in a strong isallobaric wind that wildly exceeded what most of the hi-res guidance was forecasting even 12 hours ago. With this configuration now shunted to our east, we're likely past the strongest winds, but gusts of 25mph or greater may continue through the first half of the night.

A Wind Advisory remains in effect for the higher elevations of the western North Carolina mountains. Although strong winds will occur across the broader area, probabilistic guidance from the NBM and REFS indicates the highest likelihood of advisory level gusts remains confined to the same high elevation locations already included in the advisory.

Winds will gradually weaken the second half of tonight. On Tuesday, northwest winds will persist with daytime mixing supporting gusts of 15 to 25 mph during the afternoon. Gusts Tuesday should be much more sporadic than they have been today.

Key message 3: A return to freezing temperatures is expected the next few nights, with the highest confidence Tuesday night. Early blooming vegetation may be vulnerable. Much warmer temperatures return late week, with highs approaching 80 by the weekend.

A much colder air mass settles over the region behind the departing cold front, with temperatures dropping well below recent values through midweek. The coldest conditions are expected Tuesday night when clear skies, diminishing winds, and strong radiational cooling allow temperatures to fall below freezing across nearly the entire forecast area.

Current NBM guidance shows probabilities of temperatures falling below freezing Tuesday night approaching 100 percent across almost the entire region. Freezing temperatures are also likely tonight across most locations, with probabilities generally ranging from 70 to 90 percent across the southern and eastern Piedmont and near 100 percent elsewhere.

Confidence decreases somewhat for Wednesday night as the air mass begins to slowly modify. NBM probabilities for sub-freezing temperatures range from around 30 to 40 percent in the urban corridor, 50 to 60 percent across much of the Piedmont and foothills, and 70 to 90 percent across the mountains, with even higher probabilities above roughly 4000 ft.

While the climatological growing season has not officially begun for most locations, the recent stretch of unusually warm weather has prompted early budding and blooming in some areas. These sensitive plants could be vulnerable to freezing temperatures during the next few nights.

Temperatures will begin a steady rebound late in the week as upper level ridging develops across the eastern U.S. Highs on Thursday will trend closer to seasonal normals before rising well above normal by Friday and into the weekend. By Saturday and Sunday, many locations may see highs climb into the upper 70s to near 80 degrees, which is 10-15 degrees above climo. .

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Precipitation has mostly exited the area this evening, with the exception of a few bands of light rain/sleet mix over the NC Foothills. PL has been reported in the vicinity of KHKY (though not at the actual ASOS site), and light SN has been reported at KAVL. Over the next 1-3 hours, could see brief frozen precip at either site; have handled these with TEMPOs for MVFR. Otherwise...expect VFR to prevail the remainder of the 00z TAF period; the big challenge will be postfrontal CAA winds, which this afternoon have pushed gusts of 30+ knots across much of the area...wildly exceeding expectations. Gusts should persist for much of the overnight period, not truly subsiding until a few hours before dawn...and even then, a consistent 5-10kt NW breeze will prevail. By day, gusts will ramp back up to a blustery but intermittent 20kts or so, becoming lighter by the end of the TAF period Tuesday evening.

Outlook: Light and variable winds persist on Tuesday night, and widespread VFR conditions are expected through the period.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Winter Weather Advisory until 3 AM EDT Tuesday for NCZ033- 048>052-058. Wind Advisory until 5 AM EDT Tuesday for NCZ033-048>053-058- 059-063-064. SC...None.