textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Heat Advisory has been issued for Union County, NC from 11 AM to 8 PM Thursday. Additional counties may be added to the Advisory later today or tonight.

KEY MESSAGES

1. Unseasonably hot and muggy conditions continue through the week. A Heat Advisory is in effect Thursday for portions of the North Carolina Piedmont. Relief is forecast arrive early next week. 2. Showers and thunderstorms are forecast over the mountains each afternoon through the work week, but coverage and intensity should remain limited. Chances for showers and storms begin to increase for all areas over the weekend into Monday.

DISCUSSION

Key message 1: Unseasonably hot and muggy conditions continue through the week. A Heat Advisory is in effect Thursday for portions of the North Carolina Piedmont. Relief is forecast arrive early next week.

The center of a strong upper anticyclone will continue to settle over the southern Appalachians and vicinity through tonight, persisting through at least Thu night before weakening/retrograding in response to northeast Conus height falls late in the week. The result will be unseasonably hot conditions persisting through at least Saturday, with max temps expected to range from 7-10 degrees above normal each day. Having said that, deep afternoon mixing along with gradual/slight drying of the atmospheric column are anticipated, which is expected to allow surface dewpoints to lower to the mid/upper 60s during peak heating. Therefore, while plenty of 100-105 Heat Index values are expected this afternoon and again Thursday afternoon across the Piedmont and portions of the foothills, confidence is modest at best that Heat Advisory criteria will be met in any location. An exception is across Union County-NC, where probabilistic guidance as well as ongoing temp/ dewpoint trends are lending increased confidence that Advisory conditions will be met for at least a couple of hours Thu afternoon. A Heat Advisory has been issued for that county for tomorrow. It's possible that additional counties within the Charlotte metro area could be added this evening based upon how temp/dewpoint trends evolve over the next few hours (as conditions tomorrow should be very similar to today.)

The potential for Heat Advisory conditions may increase Fri/Sat as the atmosphere begins to moisten a bit and mixing becomes more shallow, but residual heat lingers, with perhaps only a degree or so expected to be shaved off max temperatures despite height falls. Even if Heat Advisory criteria are not met late in the week, impact-based considerations will come into play owing to the attritional effects of 4+ days of hot weather as well as it being a holiday weekend. Cooling conditions are finally expected early next week as the upper trough off the East Coast continues to deepen, likely introducing a frontal boundary to the forecast area along with increased convective activity/cloud cover. Near-normal temperatures are therefore forecast from Monday-Wednesday.

Key message 2: Showers and thunderstorms are forecast over the mountains each afternoon through the work week, but coverage and intensity should remain limited. Chances for showers and storms begin to increase for all areas over the weekend into Monday.

Spotty deep convection has been slower to develop this afternoon in comparison to yesterday. However, conditions are unstable...even a little more unstable than Tue afternoon, and satellite imagery depicts congestus over the ridge tops of the southern mountains, so spotty deep convection is still expected to develop over the high terrain this afternoon, but activity will again be limited to the mountains. Generally more of the is expected Thu and Fri afternoons, with perhaps a little more coverage possible Friday as the anticyclone begins to weaken/retrograde and the air mass moistens up a bit. Nevertheless, activity should remain confined to mostly the mountains, as forecast profiles across the lower elevations feature weak capping and/or high LFCs each afternoon through Friday.

By Saturday afternoon, the leading edge of a frontal boundary associated with East Coast height falls is forecast to move into the forecast area, interacting with a quite unstable air mass to produce scattered diurnal convection across the entire CWA. Increased targets of opportunity, robust instability, and increasing deep layer shear along the southern periphery of the westerlies will yield an uptick in the potential for a few strong-to-severe storms Sat afternoon.

By Sunday, the leading edge of the boundary is forecast to be south of the CWA, but moisture and some linger instability on the cool side of the boundary...combined with a developing ESE upslope flow should result in showers and some storms lingering into the early part of the week. By Tue/Wed, sufficient drying is forecast outside the mountains to bring an end to the showers and storms there, but isolated diurnal activity will possible across the mountains both afternoons/evening.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: The weather pattern will remain stagnant through at least Thursday, and aviation weather will therefore be very similar to the past 24 hours. Spotty convection this afternoon is again expected to remain confined to the mountains, with chances being insufficient to mention convection at any site this afternoon/evening. Fog/low stratus will again develop in the mountain valleys after midnight, but will again be most likely to the west and north of KAVL. MVFR conditions are currently forecast at KAVL between 09-13Z, but IFR or worse conditions cannot be ruled out. Otherwise, VFR is forecast to continue. Winds will remain light/variable...perhaps favoring a light S/SE component this afternoon into the evening.

Outlook: Isolated to scattered mountain convection expected through Friday, then expanding to all areas for the weekend. Fog and low stratus will be possible each morning, primarily in the mountain valleys.

CLIMATE

RECORDS FOR 09-02

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 91 2020 65 1928 70 2020 45 1967 2011 KCLT 99 1932 67 1928 74 1993 53 1967 1947 1941 KGSP 100 1912 65 1928 73 2020 50 1887 1947 1932

RECORDS FOR 09-03

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 92 2020 66 1994 70 1993 44 1967 1920 KCLT 98 1925 69 1994 75 1993 52 1967 1990 1941 KGSP 97 1962 65 1994 74 2015 52 1967 1944 1925

RECORDS FOR 09-04

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 95 1954 67 1913 70 1925 45 1952 KCLT 100 1925 70 1974 75 1925 54 1952 1886 KGSP 100 1954 67 1920 76 1925 52 1892 1925 1905

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Heat Advisory from 11 AM to 8 PM EDT Thursday for NCZ082. SC...None.