textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

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

KEY MESSAGES

1. Scattered showers and thunderstorms return to the area Sunday afternoon and evening, some of which could be severe. 2. A strong cold front will bring the potential for severe weather late Sunday night through Monday morning with the main hazards being damaging winds and isolated tornadoes. We are only one day out, so start preparing now. 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 light snow will develop in the mountains on Monday and Monday night, with light accumulations possible in the higher elevations. 4. Gusty winds are expected both 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 lows each night falling below freezing. Warmer temperatures return by late week with mostly dry conditions continuing.

DISCUSSION

Key message 1: Scattered showers and thunderstorms return to the area Sunday afternoon and evening, some of which could be severe.

The synoptic pattern becomes highly amplified tomorrow as an intense Pacific jet diving through the Rockies carves out a vigorous trough over the Great Plains. Lee cyclogenesis will be underway across the high plains of Colorado tonight with a rapidly deepening surface low lifting into the Midwest as pressures fall below 990mb. Resulting low-level mass response will foster the development of robust wind fields with a 50-60kt low-level jet transporting moisture north from the Gulf and Atlantic. Across the Carolinas, this will be further aided by southeast flow advecting additional moisture off the Atlantic. The 12z suite of CAMs is in generally good agreement that at least scattered showers will develop across the area and lift north tomorrow afternoon within this leading plume of moisture return as dewpoints surge back into the upper 50s to low 60s.

The uptick in moisture will also support an increasingly unstable airmass with surface-based CAPE in the 500-1000 J/kg range. As such, varying CAM members depict several embedded thunderstorms within the broader batch of showers. Any storms will reside in an environment characteristic of 40-50kts of deep-layer 0-6km vertical wind shear with 25-30kts of 0-1km shear and 200-250 m2/s2 of 0-1km SRH. Forecast soundings within the near-storm environment reveal strongly curved hodographs owing to impressively backed southeast winds at the surface. As such, transient supercell structures will be possible along with the potential for locally damaging winds and a couple brief tornadoes should any more robust supercells be able to take advantage of a favorable environment.

Key message 2: A strong cold front will bring the potential for severe weather late Sunday night through Monday morning with the main hazards being damaging winds and isolated tornadoes. We are only one day out, so start preparing now. 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 highly anomalous and amplified trough will take on a negative tilt as it lifts from the Lower Mississippi Valley and into the Appalachians late Sunday night through Monday morning. A very deep sub 980mb surface low will also shift northeast across the Great Lakes region with a strong cold front racing east. A well established line of deep convection will reside within a prefrontal surface trough with the line of storms rapidly approaching the mountains very early Monday morning. The line is expected to quickly push across the area through the morning hours before pushing east by early afternoon. The main focus will be the potential for a widespread damaging wind event. A 50kt low-level jet translating across the region in conjunction with extreme wind fields will support more than enough wind shear for organized convection. While thermodynamic parameters won't be as eye popping overnight, at least 300-500 J/kg of MLCAPE will likely be realized with values increasing closer to 1000 J/kg east of I-26 through mid to late morning. This will be more than sufficient for maintenance of a severe convective line, especially in light of intense forcing and dynamics. In these cases, strong synoptic forcing from such a powerful trough can offset poor thermodynamic fields. The main threat will be for damaging winds along with a few tornadoes, especially with any northeast bowing line segments or line breaks.

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 when it comes to tornadoes.

Key message 3: A brief period of light snow will develop in the mountains on Monday and Monday night, with light accumulations possible in the higher elevations.

A transition to snow is expected Monday in the higher elevations of the mountains as temperatures quickly drop below freezing behind the cold front. While initially impacting most mountain areas, the snow will focus mainly along the NC/TN border by Monday night. Accumulation amounts should be 1-2 inches in the higher elevations, so only minor impacts such as slippery road conditions are expected at this time.

Key message 4: Gusty winds are expected both 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 an approaching cold front Sunday evening. Wind speeds will remain elevated across the mountains Monday into early Monday night as wind direction turns NW behind the front. A Wind Advisory may be needed for portions of the forecast area Monday into Monday night, mainly across the higher elevations. Gusts east of the mountains still look to remain well below 45 mph so an advisory should not be needed in these locations. Gusty winds linger through Tuesday afternoon before gradually diminishing Tuesday evening into Tuesday night.

Key message 5: A much colder and drier air mass returns behind the front Monday night into Wednesday night with lows each night falling below freezing. Warmer temperatures return by late week with mostly dry conditions continuing.

Much colder temperatures are expected Monday night and Tuesday night across the area with generally lows in the teens in the mountains and 20s in the lower elevations both nights. Lows on Wednesday will be less cold, but still near to below freezing across the area.

Although the growing season has not officially started, the recent period of abnormally warm weather has allowed some vegetation to start blooming. Sensitive plants that have already started blooming will be particularly vulnerable to these cold temperatures each night.

Relative humidity will drop into the 20s percent across all but the highest mountain peaks each day Tuesday through Thursday. Winds will be light through this period. This could lead to some limited fire weather concerns.

Warmer temperatures return Thursday into Friday while mostly dry conditions linger over the region. Highs on Thursday will be noticeably warmer, but still a few degrees below normal before much warmer and above normal highs return Friday.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: VFR conditions expected to persist overnight and into Sunday morning as moisture steadily impoves and periods of cirrus occur through daybreak. Much stronger moisture advection will develop on Sunday, and MVFR ceilings are expected to develop at most terminals by late morning. A plume of showers and embedded thunder will develop across the Upstate and Piedmont by mid-afternoon, persisting into the late evening before lifting north. Periods of IFR could occur in association with this activity. For CLT, the first part of Sunday night will feature continued restrictions as even more moisture is pumped into the area, ahead of a cold front approaching from the west.

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.

GSP WATCHES/WARNINGS/ADVISORIES

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