textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Confidence increasing that the remnants of Arthur will track through the forecast area tonight.

The QPF amounts for tonight have trended up slightly.

The aviation discussion was updated for the 12Z TAF issuance.

KEY MESSAGES

1. Rain chances increase this afternoon through tonight as the remnants of Tropical Storm Arthur cross the area. Widespread rainfall and embedded thunder are expected; instances of locally heavy rainfall and damaging wind cannot be ruled out. A cold front will bring an end to the rain by late Friday. 2. Dry conditions briefly settle over the area Saturday, then diurnal rain chances return Sunday and continue through the middle of next week. 3. Increased Fire Danger this afternoon across the NC Piedmont, as strong gusty winds and hot temperatures overlap with critically dry fuels.

DISCUSSION

Key message 1: Rain chances increase this afternoon through tonight as the remnants of Tropical Storm Arthur cross the area. Widespread rainfall and embedded thunder are expected; instances of locally heavy rainfall and damaging wind cannot be ruled out. A cold front will bring an end to the rain by late Friday.

Post-Tropical Cyclone Arthur is now beginning to get steered by westerly flow over the Lower MS Valley. The latest guidance is in decent agreement that the remnants of this system will track east-northeast today and cross the southern part of the forecast area tonight. Ahead of the system, stratus is expected to develop across the southern half or so of the area, then scatter out later this morning, leaving partly cloudy skies. Unusually strong low-level flow for this time of year will be in place. Even shallow mixing will tap into winds around 25-30 kt this morning thru the aftn. The windy conditions combined with ongoing drought will result in increased fire danger for the NC Piedmont (see Key Message 3). Temps will top out in the upper 80s to lower 90s and will combine with increasing dewpts to make it feel more humid today. Heat index values are expected to stay below 105, but could flirt with 100-102 across the I-77 corridor this aftn.

The latest CAMs seem to be a little slower in convective initiation ahead of Arthur this aftn. What does develop doesn't look all that strong or organized, but with up to 2000 J/kg of CAPE, cannot rule out a few strong to severe storms. Damaging wind gusts will be the main threat

The main precip associated with the remnants of Arthur look to come in late this evening. A closed low and circulation is depicted on most of the guidance, and the center tracks near the I-85 corridor or just to the south overnight. The tropical moisture should make for efficient/heavy rain rates, and there still may be a corridor that locally sees 2-3" of rainfall in a 3-6-hr period. That may result in some excessive rainfall, with a Slight Risk now out for the entire area on the new Day 1 Outlook. The system will be moving steadily and the exact locations of any enhanced rainfall are still too much in doubt to warrant a Flash Flood Watch. The system will provide enhanced low-level shear that could result in a non-zero damaging wind and tornado threat. But instability will be weak and the CAMs show little in the way of updraft helicity streaks over our area.

The remnants of Arthur should exit to the east by around 12z Friday, just as a cold front drops in from the NW. The latest CAMs, along with the NAM and Canadian develop a few showers and possibly thunderstorms along the front across our far southeast zones Friday aftn before the front clear the forecast area. Whatever does develop is not expected to be severe. Later in the day, conditions should completely dry out. Min temps will be slightly above normal with the tropical air mass, but top out just around normal Friday with decreasing humidity.

Key message 2: Dry conditions briefly settle over the area Saturday, then diurnal rain chances return Sunday and continue through the middle of next week.

High pressure crosses the area on Saturday, resulting in a dry day. But diurnal convective chances likely return on Sunday, at least in the mountains, as the pattern will remain quasi-zonal with a series of shortwaves tracking thru the middle and eastern part of the CONUS. A stronger wave will cross the area on Monday and bring a weak cold front in from the NW. The front will likely stall over the Southeast Tuesday, and gradually wash out by late in the week. PoPs will be near to slightly above climo in this pattern with temps near normal. Typical summertime isolated pulse severe and locally heavy rain threat will likely exist to some extent nearly every day next week.

Key message 3: Increased Fire Danger this afternoon across the NC Piedmont, as strong gusty winds and hot temperatures overlap with critically dry fuels.

Gusty southwest winds, possibly 25-35 mph at times, are expected across western NC today. While RH values are expected to be mostly over 40% and thus above typical critical thresholds, the ongoing severe-to- extreme drought across the NC Piedmont and exceptionally dry fuels combined with these gusty winds will lead to an increased risk of fire ignition and adverse fire behavior. This risk will be amplified by erratic and shifting winds and gusts in and near thunderstorms late aftn into this evening. After coordination with WFO RAH, who coordinated with the NC Forest Service and their field operations staff, have issued a Fire Danger Statement for the NC Piedmont from 10 am to 6 pm today to address the increased fire danger.

AVIATION /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: MVFR stratus has spread in across the Piedmont as expected. The clouds may take a little longer than previously forecast to scatter out, as guidance has trended more toward 15z. Cannot rule out IFR cigs briefly, as some METARs show cigs near 1000 ft in spots. Will continue to just mention a few IFR clouds in the TAFs.

SW winds expected to become gusty at all sites (if they aren't already) with gusts to around 25 kts expected at most sites during the afternoon. Guidance continues to trend later with arrival/onset of convection late this aftn. Minor tweaks were made to the PROB30 groups. Confidence may increase enough for some of them to be converted to TEMPOs later today.

Still expecting the remnants of T.S. Arthur to cross the area overnight tonight. Expect cigs lower to MVFR as light to moderate SHRA move in from the west, and lower further to IFR overnight. Winds will be tricky, as a closed circulation is expected with the system and may bring winds around the dial from SW to SE to NE, then finally NW before 12z Friday. Cannot rule out some embedded thunder, but will hold off on PROB30s, since we have them for the diurnal convection today.

Outlook: A cold front will push thru the area on Friday, and could trigger some convection around KCLT, but overall, mostly south of the area. Then, dry and relatively inactive weather will return by Fri night and continue through at least Sat night. Diurnal convection is expected to return early next week.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...INCREASED FIRE DANGER from 10 AM this morning to 6 PM EDT this evening for NCZ036-037-056-057-068>072-082. SC...None.