textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for 00Z TAFs.

KEY MESSAGES

1. Scattered showers and gusty winds return late tonight into Friday in association with a cold front. 2. A complex pattern will bring continued rain chances over the weekend, with generally light rainfall amounts expected. 3. Winter returns early next week, with very gusty NW winds, accumulating northwest flow snow showers, and below normal temperatures expected Sunday through Tuesday night.

DISCUSSION

Key message 1: Scattered showers and gusty winds return late tonight into Friday in association with a cold front.

Dry conditions return briefly this evening into late tonight before rain chances return Friday morning as a cold front tracks across the area. Moisture return and forcing will be enough for numerous showers in the North Carolina mountains and at least scattered showers elsewhere. Weak instability may be enough for a rumble of thunder or two, but any thunderstorms will be isolated at best. QPF will remain light, although a few heavier downpours are possible with stronger showers. Showers will taper off from west to east behind the front, with dry conditions returning area-wide by early Friday afternoon. Gusty winds will linger in association with the front, but should remain shy of Wind Advisory criteria. Lows tonight will be warmer than the normal highs for this time of year. Despite the frontal passage, any colder air will be delayed with more of a westerly flow in place behind the front. Thus, highs will make run at records east of the mountains thanks to the return of mostly sunny skies during peak heating. Highs across the mountains will remain well above normal but should fall short of records.

Key message 2: A complex pattern will bring continued rain chances over the weekend, with generally light rainfall amounts expected.

An initially broad upper trough will deepen as it progresses across the eastern half of the country over the weekend, as a series of speed maxima eject from the Great Plains through Sunday. The leading edge of a frontal zone is forecast to loiter near the southern boundary of the CWA through Sat. In response to one round of height falls moving out of the Plains, lift near the leading edge of the boundary is expected to increase Friday night into early Sat, warranting an increase of PoPs to 60-80% across roughly the SE half of the CWA...with solid chances to the NW. Weak elevated instability is likely to develop across southern areas on Sat...and can't rule out some surface-based instability being realized depending upon where the frontal boundary sets up. With deep layer shear of 70+ kts expected, the potential will exist for a few thunderstorms producing locally heavy rainfall and perhaps an isolated severe weather...although this threat appears to be marginal at most.

A lull in the precip appears likely later Sat...but forecast confidence decreases Sat night into early Sun, owing to uncertainty regarding the evolution of cyclogenesis near the Southeast Coast. The GFS...an to a lesser extent the Canadian suggest some frontogenetical response, with another round of precip over the forecast area, while other global deterministic guidance paints a drier scenario, with weaker cyclogenesis occurring a little too far south and east. Signals in ensemble guidance suggest token chance PoPs to be the path of least regret Sat night. Overall temporal trends in guidance have been toward lower QPF...and our latest forecast features weekend total QPF mostly in the 0.25-0.33" range.

Key message 3: Winter returns early next week, with very gusty NW winds, accumulating northwest flow snow showers, and below normal temperatures expected Sunday through Tuesday night.

Upper trough and attendant strong cold advection regimes slams into the southern Appalachians and vicinity Sunday. Very gusty NW winds will set up within this regime, with at least Wind Advisory-level winds looking like a good bet in the usual downslope areas along the eastern escarpment of the Blue Ridge through early Monday. Additionally, the strong NW flow interacting with lingering moisture from the TN Valley into the western slopes of the mountains will result in upslope showers beginning Sunday, when temps will mostly be supportive of snow. Ingredients for accumulating snow showers are expected to be best aligned late Sunday into early Monday, as moisture deepens in response to one last speed max that is forecast to dig west of the Appalachians Sun night. Temperatures in the moist layer are expected to cool to as low as -20 during this time, which would result in efficient production of dendritic snow crystal growth...and at least minor accums of snow appear to be a good bet in the favored upslope areas along the TN/NC border.

Cold advection will yield max temps of 5-10 degrees below normal Sunday into Sunday night, and more like 10-15 degrees below climo Monday and Monday night. Heights will steadily rise through mid- week, with the air mass steadily modifying as a warm sector becomes established in advance of the next frontal system. As a result, temps are forecast to warm above normal again by Wednesday night/ Thursday. PoPs associated with the approach of this frontal system increase to solid chance by early Thursday.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Dry and VFR through late tonight before a cold front brings -SHRA chances and associated restrictions back by the early morning hours Friday. Cigs should drop to MVFR to IFR levels ~08-10Z, lingering through the morning hours east of the mountains, before VFR returns early Friday afternoon. However, KAVL will likely see restrictions lift by mid-morning. PROB30s for -SHRA and associated restrictions were maintained across the terminals during the morning hours Friday. Dry conditions will gradually return from west to east behind the front during the mid to late morning hours Friday. Wind direction east of the mountains will remain SW through Friday morning before toggling more W/WSW Friday afternoon. Wind direction across the mountains will remain S/SW through daybreak Friday before turning NW behind the front ~14-16Z. Gusty winds return late tonight and will linger through early Friday evening, ranging from 18-25+ kts.

Outlook: Rain chances and associated restrictions return this weekend. Gusty winds return Sunday into Monday night. Restrictions should end Monday for all but KAVL where low clouds may linger.

CLIMATE

RECORDS FOR 02-20

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 75 1939 26 1908 54 2018 4 2015 KCLT 77 2014 31 2015 59 1939 7 2015 1890 KGSP 75 2014 33 2015 57 1939 9 2015 1986

GSP WATCHES/WARNINGS/ADVISORIES

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