textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for 12Z TAFs.

KEY MESSAGES

1. Gusty winds with above average temperatures today, a few isolated to widely scattered showers late today and tonight. 2. Anomalously warm temperatures continue through late this week. 3. Rainfall returns to the area over the weekend and then ushers in significantly colder temperatures for next week.

DISCUSSION

Key message 1: Gusty winds with above average temperatures today, a few isolated to widely scattered showers late today and tonight.

A flat and broad upper ridge extends from Mexico into the Gulf with an active jet stream extending from the Great Basin to the Appalachians. A lead shortwave ridge is currently translating across the Appalachians this morning with a shortwave trough lifting through the Midwest in its wake. The majority of the energy from this wave will be deflected north of the area with high heights within quasi-zonal flow draped from the Deep South to the Carolinas. Thus, while the region will be entrenched within an expansive warm sector, the majority of the QPF response will reside across the Ohio Valley closer to the warm front. Furthermore, forecast soundings are capped around 800mb and will preclude deeper shower activity outside of the immediate Tennessee border area. With time, at least a few isolated to widely scattered shallow warm advection showers will begin to overspread the mountains and perhaps the far western foothills tonight. Otherwise, temperatures will remain well above average with deep mixing up to 800mb. Highs will run from the mid to upper 60s with a few readings around 70 possible across the Savannah Valley. Robust wind profiles within the mixed layer will also support efficient momentum transport to the surface. 25-30mph gusts will be common.

Key message 2: Anomalously warm temperatures continue through late this week.

Long-range ensembles continue to depict broad, flat ridging across the Southeast through the end of the week, with embedded lobes of vort energy making tracks across the Mid-Atlantic and the Carolinas through late Friday. In response, some rainfall is still forecast for Thursday night and Friday, but with the better forcing now displaced a little to our north, QPF response appears muted across most of the area...and later than in previous forecast cycles, with the bulk of what rain does fall doing so during the predawn hours on Friday and into the first half of the day.

A weak cold front should slide through the region from the north-northwest on Friday evening into Saturday, with little fanfare. Temperatures on Thursday and Friday will climb some 20 degrees above normal...into the mid or even upper 70s...possibly breaking records on Friday especially...then trend back toward normal (or at least, not as far above normal) on Saturday.

Key message 3: Rainfall returns to the area over the weekend and then ushers in significantly colder temperatures for next week.

By late Friday night, a cold front should be stalled in or just south of our forecast area, having lost its upper-level steering flow...and as another shortwave arrives from the Deep South early Saturday morning, moist upglide atop the boundary should reactivate it as a warm front. Long-range ensembles variously depict this as anything from weak isentropic ascent, to a pronounced upper wave, to full-blown cyclogenesis...and so QPF response varies quite a bit among ensemble members...but at least some rain appears likely, though totals remain uncertain. Ensembles also can't agree on the timing of the front's northward retreat...which will influence whether any surface-based instability will develop, and thus moderate any potential severe risk. Certainly cannot rule out at least some embedded thunder at this point in time.

Behind this system, a significantly colder continental air mass will work into the region, bringing lows 5-10 degrees normal Sunday and Monday night. The air mass will slowly modify through the end of the week, allowing temperatures to trend back toward normal. Generally dry conditions are expected during this time period.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Increasing moisture into the region has resulted in the development of low stratus, especially along the I- 85 corridor. Ceilings are expected to continue to lower through the morning with MVFR ceilings from KAND to KGMU/KGSP and KCLT. Eventually, all terminals should return to VFR by late morning to early afternoon. Winds will be gusty through much of the day with frequent 20-25kt gusts out of the southwest. Winds will relax tonight along the with the potential for a more widespread deck of low stratus with restrictions and perhaps a few instances of patchy fog as well.

Outlook: Restrictions may return late Wednesday night into Thursday morning as guidance shows a round of patchy fog and low stratus developing. Rain and associated restrictions may return to the area Thursday and Friday but chances are better over the weekend.

CLIMATE

RECORDS FOR 02-19

MAX TEMPERATURE MIN TEMPERATURE 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.