textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes to forecast thinking over the next week.

Confidence increasing for near-record or record high temperatures Friday and for generally insignificant precipitation, followed by a dry weekend.

Still low confidence on possible precipitation Monday and beyond, but increasing confidence on a warming trend in that timeframe.

KEY MESSAGES

1. Cloudy but dry weather continues through Friday morning, and temperatures continue their warming trend. 2. Record high temperatures possible Friday ahead of another cold front. The front brings a chance of showers late Friday and Friday night. 3. Cool, dry high pressure is expected to bring a precipitation free weekend, and freezing temperatures to some of the mountains and foothills Saturday and Sunday mornings. Very low relative humidity is likely to worsen fire weather conditions. 4. Warm and somewhat more humid conditions return Monday through the middle of next week.

DISCUSSION

Key message 1: Cloudy but dry weather continues through Friday morning, and temperatures continue their warming trend.

Weakly diffluent NW upper flow continues across the Carolinas on the periphery of a blocking ridge centered over northern Mexico and the Desert Southwest. Ripples of moisture are evident on water vapor imagery and delineate a stream of weak upper forcing rounding this ridge. As of around 6 AM, a bank of thick altocu had developed across the Upstate within SSW flow curling around off of the Atlantic.

Little change is expected to this pattern overnight, or by day Thursday. However, the steady WAA in the low levels will continue to increase sfc-to-850mb thickness values...resulting in afternoon highs creeping into the upper 70s, or even isolated low 80s. Through Thursday night, stronger upper forcing within a broad confluent zone aloft will drive a cold front south across the Mid-Atlantic. Operational guidance is in decent agreement that by daybreak Friday, it'll be positioned to our north...extending from the Cumberland Plateau to the Delmarva Peninsula. This should keep winds elevated and more or less due westerly overnight, resulting in a degree of downsloping even during the overnight and keeping Friday morning lows some 15 degrees above climo.

Key message 2: Record high temperatures possible Friday ahead of another cold front. The front brings a chance of showers late Friday and Friday night.

Cold front will push thru the southern parts of the Ohio Valley Friday, driven by a broad but amplifying shortwave digging over the northeastern CONUS. Though heights will begin to fall during the day, owing to the flat but strong ridge centered over the Rio Grande, the lower troposphere will be exceptionally warm for this time of year. Low to midlevels have a dry/subsident look on prog soundings over our area and immediately upstream in the hours prior to the fropa. We are still forecasting a record high at CLT and GSP with KAVL only off by a couple of degrees, and if winds are slightly more backed than currently expected the record could be in jeopardy there also. Flow preceding the front will be westerly and appreciable moisture return is not expected prior to its reaching the northwest CWA Friday afternoon, but the soundings briefly saturate once cooling occurs aloft. We will continue to advertise likely PoP along the TN/NC border in late afternoon. Downsloping appears to consume some of the moisture and synoptic model and CAM output does not carry the QPF response much east of the mountains. A brief window for deep convection is however suggested when the front reaches the Piedmont via cooling temps aloft, though SB/MUCAPE are still rather unimpressive at only a few hundred joules at most among guidance members; CCLs/LCLs will be rather high. Can't entirely rule out a rumble of thunder, but overall thunder chance is too low to mention. The convective signal is strongest east of I-77 after sunset Friday evening, and the peak PoPs for that area are at that time.

Key message 3: Cool, dry high pressure is expected to bring a precipitation free weekend, and freezing temperatures to some of the mountains and foothills Saturday and Sunday mornings. Very low relative humidity is likely to worsen fire weather conditions.

Rapid cooling will occur Friday night following the front, particularly in the mountains. Moisture in the upslope layer diminishes too fast to expect precip to change from rain before ending. A freeze is likely in high elevations and across lower elevations of our northern mountain zones; mins east of the mountains will return to only slightly above normal. It probably will be too dry for any frost. Wind gusts within a few mph of advisory criteria are possible across the mountains; certainly gusty but well below criteria otherwise. Gusts will taper off during Saturday morning as gradient begins to relax. Max temps Saturday are expected to be on the order of 25 degrees cooler than Friday, a few degrees below normal. Surface high should center north of the CWA Saturday night leading to light winds and strong radiational cooling. A freeze again appears likely for portions of the mountains and possibly including some of the NC foothills; with low-level flow turning southeasterly some moisture may return and frost is somewhat more possible where temps fall into the mid 30s. The first group of zones in the spring frost-freeze program (GA/SC zones outside the mountains and southern tier of NC Piedmont zones) do not activate until April 1, so any frost/freeze Fri or Sat nights would not warrant watches/warnings/advisories. Temperatures and dewpoints both will rebound somewhat on Sunday owing to the developing southerly flow, but RH still is expected to dip below 25 percent over most areas.

With diurnal mixing in the dry post-frontal airmass, RH should easily fall below 20 percent Saturday afternoon, but as of now it appears the lowering RH is not likely to overlap with enough wind to objectively justify a meteorologically based Fire Danger Statement or Red Flag Warning. We are aware some fire officials are expressing concern about drying fuels, and for example the SC Forestry Commission has already issued a Red Flag Fire Alert to enhance public awareness of critical fire weather conditions. With significant precip looking unlikely Friday, similar or worse conditions to those now are expected to linger through the weekend across all parts of our service area.

Key message 4: Warm and somewhat more humid conditions return Monday through the middle of next week.

Surface high drifts off the East Coast late Sunday, and heights rise aloft from then through Tuesday as upper ridge axis pivots over the eastern CONUS. Temps trend back several degrees above normal Monday, with a warming trend continuing through the middle of the week as the upper ridge migrates to the western Atlantic. Dewpoints will trend higher via southwesterly return flow, and afternoon RH values are not expected to be as low as over the weekend. Rainfall still looks fairly unlikely, however. Wave train will continue across the Upper Midwest and Great Lakes thru this time, with the Gulf open to that area via flow around the ridge. Models are in poor agreement as to where fronts and precip might set up in this pattern, but some ensemble members bring the first weak cold front close enough to our area to result in slight-chance 15-20% PoPs in our far north Monday; similar PoPs expand across more of our mountains on Tuesday, with some members bringing warm-sector convective activity to our western periphery that day as cyclogenesis occurs in the upper MS Valley at that time. This trend continues Wednesday as that system advances, and 20-30% PoPs return to all areas.

AVIATION /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Generally VFR conditions expected to continue through the 06z TAF period. SCT to BKN altocu is in place across the Upstate and southern Piedmont, with some lower bases - as low as MVFR - observed in the western Upstate, at KAND and KCEU. Steady 4-7kt SW winds at most locations tonight will become increasingly W/SW after daybreak...and feature gusts of up to 20kts in the afternoon Thursday. Afternoon shallow cu field is expected east of the NC mountains. Intermittent VFR cloud cover likely Thursday night. Cloud cover will increase over the NC mountains after 12z Friday, but any restrictions won't develop until after mid-day.

Outlook: Still a limited case for showers and associated flight restrictions on Friday evening as a cold front pushes across the area. Breezy NW winds will linger through Saturday afternoon. Dry and VFR conditions return behind the front over the weekend.

CLIMATE

RECORDS FOR 03-27

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 85 2020 32 1955 60 1921 11 1955 1894 KCLT 85 1950 40 1894 62 1949 19 1955 1944 KGSP 86 2020 45 2011 60 1921 15 1894 1947

RECORDS FOR 04-01

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 83 1974 40 1919 60 1927 20 1923 KCLT 86 1986 40 1887 64 1998 24 1923 KGSP 85 2010 45 1965 64 2024 24 1900 1986 1910

GSP WATCHES/WARNINGS/ADVISORIES

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