textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Confidence continues to increase regarding severe weather late tonight into Monday afternoon.

Snowfall accumulations on Monday increased slightly but still appear to remain below Winter Weather Advisory criteria outside of the highest elevations. Additionally, northwest flow snow now looks to linger through at least daybreak Tuesday.

KEY MESSAGES

1. Scattered showers and thunderstorms return to the area this afternoon. 2. A strong cold front will bring the potential for severe weather late Sunday into Monday afternoon with the main hazards being damaging winds and isolated tornadoes. Make sure you have multiple ways to receive warnings and think about where you would seek safe shelter if a warning was issued for your location. 3. A brief period of northwest flow snow will develop in the North Carolina mountains Monday into Monday night, with light accumulations possible. 4. Gusty winds will develop ahead of and behind the cold front Sunday night through Tuesday before finally tapering off Tuesday evening. A Wind Advisory may be needed for portions of the North Carolina mountains Monday into Monday night. 5. A much colder and drier air mass returns behind the front Monday night into Wednesday night with most areas seeing lows each night falling near or below freezing. Warmer temperatures return Thursday into the weekend with mostly dry conditions continuing.

DISCUSSION

Key message 1: Scattered showers and thunderstorms return to the area this afternoon.

Low level moisture and isentropic lift increase through the day in increasing low level southeasterly flow. Increasing cloudiness expected through the day. The latest guidance shows some weak CAD- like development during the afternoon, limiting any sbCAPE potential. Even muCAPE is limited across much of the area. The CAMs show scattered showers and isolated storms given the forcing. That said, they have backed off on the severe potential for the afternoon despite the increasing shear and helicity. Still, should any sbCAPE develop, any resulting storms could take advantage of the better environment, possibly becoming severe. Overall, the better severe storm chances begin tonight.

Key message 2: A strong cold front will bring the potential for severe weather late Sunday into Monday afternoon with the main hazards being damaging winds and isolated tornadoes. Make sure you have multiple ways to receive warnings and think about where you would seek safe shelter if a warning was issued for your location.

A strong cold front will approach out of the west Sunday evening before tracking over the forecast area Sunday night into Monday afternoon, bringing the potential for severe weather. The severe threat will be highest from the early morning hours Monday through mid-afternoon Monday. Confidence continues to increase regarding the damaging wind and tornado potential as instability will gradually increase across the area Sunday night into Monday afternoon and as plentiful moisture and forcing will be available ahead of and along the frontal boundary. Some storms may develop ahead of the main line, but the severe threat with this activity should remain low.

00Z CAMs depict the QLCS (line of storms) pushing across the western half of the forecast area from roughly 5 AM to 10 AM Monday before pushing across the eastern zones from roughly 11 AM to 3 PM Monday. Although the western two-thirds of the GSP CWA will see the front track overhear prior to peak heating, there will be enough forcing and instability in place to allow for severe storm development. MUCAPE across these zones will range from a few hundred to several hundred J/kg, but will generally remain below 1,000 J/kg per the 00Z HRRR and NAMNest. Some SBCAPE may develop across these zones after sunrise, but will also generally remain less than 1,000 J/kg. The eastern third of the GSP CWA (areas south of I-85 and near the I-77 corridor..which includes the Charlotte Metro) will have the best potential to see the line swing through during peak heating. Thus, these areas will be of most concern regarding severe weather as SBCAPE from 1,000 to 1,500 J/kg should available per the 00Z NAMNest and HRRR. Thus, the SPC Day 2 Severe Weather Outlook showing an enhanced risk over the eastern third of the GSP CWA with a marginal to slight risk elsewhere, appears warranted. The entire GSP CWA will have the potential to see damaging winds and isolated tornadoes with this line of storms, despite the lack of impressive instability, thanks to 50 to 60 kts of deep layer shear, a 40 to 50 kt LLJ tracking overhead, and 200 to 300 J/kg of 0-1km of SRH developing ahead of the front. Additionally, the 00Z HRRR and NAMNest depict updraft helicity swaths ahead of and along the front, showing the potential for rotating updrafts which further increases confidence regarding the potential for embedded tornadoes and damaging wind gusts near the leading edge of the line.

Now is the time to make your severe weather preparations. Make sure you have multiple ways to receive warnings such as NOAA Weather Radio, Wireless Emergency Alerts (WEA), social media, or local TV and radio. If you live in a mobile or manufactured home make plans ahead of time to stay with friends or family who live in a sturdy building as mobile/manufactured homes are not safe shelters from tornadoes.

Drier conditions will gradually return from west to east behind this system from the mid-afternoon hours to the early evening hours Monday.

Key message 3: A brief period of northwest flow snow will develop in the North Carolina mountains Monday into Monday night, with light accumulations possible.

Temperatures will drop steadily behind the cold front throughout Monday, falling below freezing across the North Carolina mountains Monday afternoon into Monday evening. This will allow northwest flow snow showers to develop, especially along the NC/TN border. Although snowfall accumulations have increased slightly this forecast cycle, they are still expected to remain light and below advisory criteria for most locations. However, the Smokies, as well as areas above 5,000 ft in the northern North Carolina mountains, should see totals near or just above advisory criteria (around or greater than 2"). With advisory level accums remaining confined to the higher elevations, and the NBM only showing a 20% to 30% chance of greater than 2" of snowfall in 24 hours along the NC/TN border, a Winter Weather Advisory remains unlikely. Lower elevations across the North Carolina mountains could see anywhere from a dusting to up to an inch of snowfall.

Key message 4: Gusty winds will develop ahead of and behind the cold front Sunday night through Tuesday before finally tapering off Tuesday evening. A Wind Advisory may be needed for portions of the North Carolina mountains Monday into Monday night.

Winds will steadily increase ahead of the cold front Sunday evening into Monday afternoon, with speeds continuing to increase across the North Carolina mountains behind the front Monday afternoon into Monday evening as winds shift NW. A Wind Advisory may be needed for portions of the North Carolina mountains Monday into Monday night, mainly for the higher elevations. Gusts east of the mountains still look to remain below 45 mph so an advisory looks less likely for these zones. Gusty winds will linger through Tuesday afternoon before gradually diminishing Tuesday evening into Tuesday night. However, wind speeds will be much lower on Tuesday compared to Monday.

Key message 5: A much colder and drier air mass returns behind the front Monday night into Wednesday night with most areas seeing lows each night falling near or below freezing. Warmer temperatures return Thursday into the weekend with mostly dry conditions continuing.

Surface high pressure builds in from the west behind the departing front Monday night into Wednesday, allowing drier and much colder conditions to return. Temperatures will run well below normal through mid-week. Temperatures Monday night and Tuesday night will fall below freezing. Although slightly warmer low temperatures are expected to return Wednesday night as the center of the surface high pushes offshore, most of the area will see lows fall near freezing to below freezing as the NBM has trended slightly colder. Sensitive plants that have already bloomed from the recent abnormally warm weather will be particularly vulnerable to these cold temperatures each night.

Warmer temperatures return Thursday into the weekend with mostly dry conditions continuing as the southwestern periphery of the surface ridge remains extended over the Carolinas. Highs on Thursday will be noticeably warmer, but will still end up a few degrees below normal (outside the mountain valleys) before much warmer and above normal highs return Friday into Saturday.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Tricky forecast this period with low level moisture and isentropic lift increasing this morning. Some guidance has backed off on the development of restrictions, keeping them more spotty or low VFR, while others show MVFR cigs developing. Given the pattern, have MVFR cigs developing by mid morning, closer to noon for KCLT and KHKY. Cigs fall through MVFR with IFR by evening. Scattered showers and possibly a thunderstorm move north across the area during the afternoon, have PROB30s in place for these, but kept at SHRA for now. IFR cigs continue overnight, although some improvement to MVFR is possible. Shower and thunderstorm chances increase overnight as a cold front moves into the area from the west. SE wind early this morning turns more ENE after daybreak. Winds turn back to the SE for the afternoon into the evening. Occasional gusts are possible.

Outlook: A strong cold front will swing across the region early Monday morning before pushing east by the afternoon. This will bring a fast moving line of thunderstorms, some of which are expected to be severe. Associated restrictions will be possible along with low stratus ahead of the line. VFR conditions return thereafter, albeit with continued wind gusts. Gusts end by Wednesday with VFR through Thursday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.