textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion has been updated for the 12Z TAFs.

KEY MESSAGES

1. Very active convective weather is expected to continue through today. A Flash Flood Watch is in effect for portions of the northern NC mountains and northern foothills until 8 PM today. Localized flash flooding will be possible across the remainder of the area as well. Isolated severe storms are also possible across the southern part of the area this afternoon. Otherwise, well-below normal high temperatures are forecast through Tuesday. 2. A return to seasonably hot and drier conditions is expected during the latter half of next week.

DISCUSSION

Key message 1: Very active convective weather is expected to continue through today. A Flash Flood Watch is in effect for portions of the northern NC mountains and northern foothills until 8 PM today. Localized flash flooding will be possible across the remainder of the area as well. Isolated severe storms are also possible across the southern part of the area this afternoon. Otherwise, well-below normal high temperatures are forecast through Tuesday.

Convection has diminished in intensity across the area this morning, but scattered-to-numerous,mostly light to moderate showers persist along and north of I-85. This is spelling a relative lull in the flash flood threat that will persist through the morning, but convection should blossom again this afternoon into the evening, as the air mass modestly destabilizes in continued very moist conditions. The flash flood threat will again ramp up during this time, especially across the eastern escarpment areas of NC, where poor antecedent conditions are expected, and where the ESE upslope flow is forecast to intensify somewhat. By Monday evening, 24-hour rainfall totals of 2-4" are expected across much of the area (lesser amounts closer to the TN border), with locally higher amounts of 5" or more very much in the realm of possibility. For this reason, a Flash Flood Watch has been issued for the northern NC mountains and foothills. Away from this area, flash flooding will certainly be of some concern, but the threat will be more localized in nature...dependent largely upon which basins are primed due to recent localized heavy rainfall.

There is a lesser concern for severe storms this afternoon...mainly across the southern part of the area where the most significant instability is expected. Even there, destabilization is expected to be limited by extensive morning cloud cover, but just enough buoyancy combined with lingering deep layer shear of 20-30 kts may be just enough to allow for a couple of stray severe storms. NE low level flow, cloud cover, and showers/storms are expected to result in high temperatures 10 or more degrees below climo.

NE flow is expected to steadily deepen tonight into Tuesday, as stacked/weak cyclone to our west retrogrades into the Deep South. This will allow for gradual infiltration of lower thete-E/more stable air into the forecast area. Nevertheless, ESE upslope flow will continue into the overnight, with some potential for showers to linger across the eastern escarpment, and perhaps the southern part of the area through the night. The Flash Flood Watch currently expires at 8 PM today, but it's not out of the question that this may need extension into the overnight hours.

Much of the CWA should see the benefits of the advection of lower theta-E air from the NE and extensive low cloud cover on Tuesday, as guidance generally indicates little-to-no destabilization, except perhaps across the southern periphery of the area, and across the higher terrain near the TN border. These areas are where PoPs for diurnal convection will be advertised Tues, but the bulk of the CWA should be largely free of showers and storms Tue afternoon/evening. High temperatures are forecast to remain well below normal.

Key message 2: A return to seasonably hot and drier conditions is expected during the latter half of next week.

Upper ridging is forecast to be the dominant synoptic feature across the East during the latter half of the week. This will result in a modifying air mass/return to seasonably hot conditions by Thursday... with near-to-slightly above normal temps forecast to continue through next weekend. Heat Index concerns could crop up again during this time, with 100+ values forecast across southern areas and Charlotte metro most afternoons...although there is no clear signal for Heat Advisory concerns at this time. Despite the seasonably hot and muggy conditions, the synoptic pattern will be somewhat non- conducive to convective development...and PoPs for diurnal convection are generally limited to near, or even below seasonal levels...with at most widely scattered activity forecast each afternoon across the high terrain, with generally isolated coverage forecast elsewhere.

AVIATION /12Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Showers continue across mainly the NC portion of the Terminal Forecast Area this morning. Showers are expected to gradually diminish in coverage through the morning before redeveloping (along with scattered TS) this afternoon. IFR cigs have been slow to fill in this morning, but they are slowly but surely doing so, and expect all sites...perhaps excepting KAVL...to see IFR settle in by late morning. Once they do fill in, only modest improvement is expected in cigs during the afternoon, but most sites should see MVFR at some point, with perhaps a brief period of VFR possible this evening. Coverage of showers and storms is expected to ramp up from 18-24Z, with Prob30s for TSRA advertised at all sites. Any improvement in cigs is expected to reverse this evening, with IFR likely returning by 06Z Tuesday. LIFR conditions will be possible during the overnight, but confidence is not high enough to include in the TAF at this time. Winds will mostly be ENE at 5-10 kts through the period.

Outlook: Drier conditions should develop Tuesday into Wednesday. Low stratus and/or fog will be possible each morning in the mtn valleys and in locations that receive appreciable rainfall from the previous day.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Flood Watch through this evening for NCZ033-035-049-050- 501>506. SC...None.