textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for 12Z TAFs.

Confidence continues to improve on the potential for record warm highs on Friday and widespread rain on Saturday.

KEY MESSAGES

1. Spotty showers possible through today and tonight along with more gusty winds this afternoon and warm temperatures. 2. Record warm temperatures possible Friday alongside increasing rain chances. 3. A complex weekend setup brings more widespread rain to the area on Saturday, and ushers in much colder air for the start of the new workweek.

DISCUSSION

Key message 1: Spotty showers possible through today and tonight along with more gusty winds this afternoon and warm temperatures.

The synoptic pattern remains largely unchanged with a belt of west/southwest flow extending from the Desert Southwest to the Appalachians on the poleward side of a flat ridge over the Gulf. A lead shortwave perturbation embedded within the background flow regime will slide across the Central Plains and lift into the Midwest today and tonight. An attendant surface low will also lift into the Great Lakes region by Friday morning. This will keep much of the region entrenched in an open warm sector. Precipitation will blossom along and south of a warm front draped just north of the Ohio Valley where height falls in advance of the approaching trough will be maximized. Farther south, height falls will be much more nebulous with only subtle forcing to instigate showers. Nonetheless, at least a few isolated to widely scattered showers are expected through this morning, mainly along and south of the I-85 corridor and across the mountains. Temperatures will also continue to warm with highs today surging into the low to mid 70s. Solid wind profiles within a fairly deeply mixed boundary layer will also support frequent wind gusts again this afternoon. By tonight, a trailing surface cold front will push across the lower Mississippi Valley and will make a run at the mountains by daybreak Friday morning. A band of broken showers are expected to accompany the frontal boundary with precipitation chances ramping up along the immediate Tennessee border.

Key message 2: Record warm temperatures possible Friday alongside increasing rain chances.

Operational models variously depict ripples of z500 vort energy making tracks across the Carolinas and Mid-Atlantic on Friday embedded within a broader quasi-zonal upper pattern. That'll manifest in the low levels as continuing WAA through at least mid-morning. Although the hi-res guidance now stretches out far enough to depict a loosely-organized band of showers crossing the area from west to east through early afternoon, which should somewhat hinder diurnal heating, the result of sustained WAA and deep low-level thicknesses will support high temperatures on Friday some 15-20 degrees above normal across the area. We can expect to flirt with daily records at all three climate sites, unless rainfall becomes significantly more widespread and prolonged than is currently depicted in the CAMs.

A somewhat stronger short wave is depicted in the bulk of guidance arriving late Friday evening, resulting in the cessation of low-level WAA and the arrival of a weak surface cold front by mid-afternoon. Notably lower-theta-e air will filter in through Friday night, and the boundary will settle in or just south of the Upstate by Friday night, as it becomes increasingly parallel to the upper flow. This will curb temperatures somewhat, as well as bring a short-lived end to rainfall.

Key message 3: A complex weekend setup brings more widespread rain to the area on Saturday, and ushers in much colder air for the start of the new workweek.

As more pronounced DPVA forcing arrives early Saturday morning and interacts with the pre-existing baroclinic zone laid out across the forecast area, a surface wave will develop within an area of strong moist upglide, resulting in a resurgence in rainfall and thick cloud cover early Saturday morning and persisting for most of the day. Ensembles are now in much better agreement on an early-morning onset, which certainly points to less chance of any surface-based instability developing - confidence is increasing that the setup will be more of a hybrid CAD-like configuration, with a quasi-stationary boundary to our south, and rainfall only stabilizing/reinforcing the surface wedge located over us. Indeed, none of the operational guidance depicts any sbCAPE over our southern zones, and the latest long-range ensembles depict a <10% chance of significant instability over even our southernmost counties.

Surface cyclogenesis appears likely somewhere over the eastern Carolinas as the upper pattern rapidly evolves into a pronounced longwave trough spanning the eastern 2/3 of the CONUS...with the resultant surface low lifting up the Mid-Atlantic coast and into New England on Sunday and Sunday night. In response, strong low-level CAA will develop across the Carolinas Sunday, ushering in a much colder, much drier cP air mass that will linger across the region for much of next week. Temperatures Sunday, Monday, and Tuesday nights could fall well into the 20s amid excellent radiative cooling. Thereafter, the air mass will steadily modify, and temperatures will climb to within a couple degrees of normal on Wednesday and Thursday.

AVIATION /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: A mix of restrictions are common this morning as a low stratus deck has enveloped the area. Most ceilings are MVFR, but a few instances of IFR cannot be ruled out through the morning hours. Isolated to widely scattered showers also continue to push across the area and will continue through early afternoon. Very brief visibility reductions may occur with the heaviest rainfall rates, but fast movement should keep any impacts brief. Gusty southwest winds will once again be common this afternoon before subsiding tonight. Another low stratus deck may develop tonight ahead of an advancing cold front. Winds should keep the boundary layer sufficiently mixed to limit fog, however. A broken band of showers is expected to accompany the front as it pushes into the area from the west during the early morning hours Friday.

Outlook: Better rain chances return over the weekend along with associated restrictions. Restrictions should end Monday but gusty winds will continue.

CLIMATE

STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 72 2014 16 2015 54 1951 3 2015 KCLT 76 2014 26 2015 55 1961 8 1958 1939 KGSP 75 2014 30 2015 55 1961 9 1958 1916 1900 1900 1911

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.