textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

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

KEY MESSAGES

1. Scattered showers and an isolated thunderstorm continue this afternoon through tonight. A line of severe thunderstorms will then cross the area early Monday morning through the early afternoon hours with a threat for damaging wind and 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. 2. Precipitation will change to snow across the higher mountain elevations tomorrow afternoon with a brief period of northwest flow snow through Monday night. Gusty winds will develop behind the cold front tomorrow night through early Tuesday morning. 3. Cold and dry air returns Monday night into Wednesday night with overnight lows falling to near or below freezing. Warmer temperatures return Thursday into the weekend and remains dry.

DISCUSSION

Key message 1: Scattered showers and an isolated thunderstorm continue this afternoon through tonight. A line of severe thunderstorms will then cross the area early Monday morning through the early afternoon hours with a threat for damaging wind and 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 potent storm system continues to evolve today as an intense Pacific jet dives through the Rockies and digs a highly anomalous trough across the Great Plains. The trough will strengthen through tonight as it takes on a negative tilt and lifts through the Mississippi Valley and into the Appalachians. Farther north, a deepening surface low is lifting through the Midwest and into the Great Lakes with the low situated beneath a coupled upper jet. This will allow for further deepening with pressures forecast to fall to near 985mb. Resulting low-level mass response will foster robust wind fields through the column with a very impressive 50kt low-level jet translating across the region.

Through this afternoon, well in advance of the approaching cold front, a plume of deep moisture residing within an inverted surface trough extending from the Coastal Plain will promote the development of a batch of showers. This activity will lift north through the afternoon and into this evening along with the potential for a few embedded thunderstorms. An isolated severe storm cannot be completely ruled out with sufficient deep-layer wind shear for transient supercell structures along with cyclonically curved hodographs owing to backed southeast surface flow. Locally damaging winds and a brief tornado will be possible with any deeper storms, but the coverage of any severe threat should remain isolated.

By early tomorrow morning, strong height falls will overspread the Southern Appalachians with a surface cold front racing towards the area. The 12z suite of CAM guidance is in good agreement that a line of severe thunderstorms will reside within a prefrontal surface trough and will be knocking on our door by ~4am. The line will push across the area through the morning hours before shifting off to the east by early afternoon. Strong moisture advection will draw a plume of upper 50s to low 60s dewpoints into the western Carolinas and northeast Georgia. Given cool profiles aloft, this will be sufficient to support moderate buoyancy with 300-500 J/kg of MLCAPE during the pre-dawn hours. Values increase to around 1000 J/kg by mid to late morning, mainly east of I-26. Wind shear will be plentiful with around 60kts of 0-6km deep-layer shear and 30-35kts of 0-1km shear along with 200-300 m2/s2 of 0-1km SRH. The thermodynamic and kinematic environment in concert with intense synoptic forcing should support maintenance of the line of severe thunderstorms through the area. The main threats will be for damaging straight line winds along with the potential for line embedded tornadoes, especially with any northeast surging line segments or line breaks.

Key message 2: Precipitation will change to snow across the higher mountain elevations tomorrow afternoon with a brief period of northwest flow snow through Monday night. Gusty winds will develop behind the cold front tomorrow night through early Tuesday morning.

Strong cold advection behind the front will likely change trailing showers over to snow across the higher mountain elevations tomorrow afternoon. A brief period of northwest flow snow showers will also continue through Monday night before tapering off early Tuesday morning. Generally light accumulations of snow will be possible above 3500 ft with the highest totals of 4-6" expected across the highest elevations of the Smokies. Winds across the high terrain will also be quite gusty in the post frontal cold advection regime. Gusts will peak tomorrow afternoon into early Tuesday morning with frequent gusts of 50-60mph expected above 3500 ft. A wind advisory has been hoisted for most of the mountains along the Tennessee border through 5am Tuesday. Overnight lows Tuesday morning will be quite cold compared to the warm start to March. Lows are forecast to fall into the teens across the mountains with mid to upper 20s outside the mountains. These temperatures combined with gusty winds will result in rather unpleasant wind chills following well above normal warmth to start the month.

Key message 3: Cold and dry air returns Monday night into Wednesday night with overnight lows falling to near or below freezing. Warmer temperatures return Thursday into the weekend and remains dry.

Behind the strong cold front, surface high pressure builds into the southeast. Along with the drier conditions, much colder air returns Monday night through at least Wednesday night. Overnight lows are expected to reach freezing and below, with Tuesday night looking to be the coldest. The latest NBM probabilities for below-freezing low temperatures are 70-80 percent in the southern and eastern Piedmont and 100 percent elsewhere across the area for Monday night, and nearly 100 percent across the entire area Tuesday night. The deterministic forecast advertises widespread teens and low 20s for the mountains and 20s elsewhere. By Wednesday, the air mass starts to modify as moisture starts to return with winds veering more southerly. Temps Wednesday night should warm a tick and be closer to freezing with a few locations at the higher elevations confidently remaining well below freezing. This is relfected in the NBM probabilities for sub-freezing temperatures Wednesday night which were 30-50 percent in the cities, 50-60 percent in the Piedmont and Foothills, and 60-80 percent in the mountains (except higher at elevations above 4 kft). Sensitive plants that have already bloomed from the recent abnormally warm weather will be particularly vulnerable to these cold temperatures each night. Temperatures increase steadily Thursday and through the weekend. Dry conditions dominate after Tuesday onward.

AVIATION /00Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: An axis of scattered showers and very isolated embedded thunder is marching north across the terminal forecast area circa 23 UTC, and progged to exit the area within the next 2 hours. In conjunction, sites have toggled between MVFR and even IFR ceilings, and isolated IFR vis where rain rates are highest. Short-range guidance points to a lull after midnight, when showers are long gone and the boundary layer manages to briefly recouple with the surface...resulting in some potential for actual improvement between, say, 05Z and 09Z. Spotty showers will ramp back up after that, resulting in widespread MVFR to patchy IFR ceilings redeveloping.

Thereafter, a line of strong to severe thunderstorms is expected to cross the area from west to east in tandem with a cold front, arriving in the NC mountains as early as 11z, and making it east of I-77 by 18z or so. With these storms will come the potential for IFR flight restrictions as well as gusty and erratic winds - to the tune of 40kt or greater gusts. In the wake of the storms, some patchy MVFR fog should linger, before rapid improvement to VFR Monday evening as winds turn NW behind the cold front. Gusts of 20-30kts are expected within this NW flow...higher in the NC mountains...and light NW flow snow is expected along the NC-TN border. It's unlikely to impact any of the TAF sites, but smaller terminals in some mountain locations might at least see flurries.

Outlook: Gusts subside on Tuesday and come to an end by Wednesday morning, with VFR through at least Thursday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Wind Advisory from 4 PM Monday to 5 AM EDT Tuesday for NCZ033- 048>053-059-063-064. SC...None.