textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes to the forecast with this package.

KEY MESSAGES

1. Dry with very low afternoon RH expected Friday. Otherwise, unseasonably cool tonight, with near-normal temperatures returning Friday. 2. Above normal warmth returns this weekend into next week, while limited rainfall chances, mainly in the mountains, provide little relief from ongoing drought conditions.

DISCUSSION

Key message 1: Dry with very low afternoon RH expected Friday. Otherwise, unseasonably cool tonight, with near-normal temperatures returning Friday.

Slightly gusty NW winds continue to advect a somewhat cool and quite dry air mass into the region this afternoon. In fact, some areas of critical RH of 20-25 percent have become established...mainly across the western part of the area. Thus, fire danger will be somewhat elevated this afternoon. As the center of surface high pressure settles over the southern Appalachians tonight, diminishing winds under clear skies and low surface dewpoints are expected to result in min temps a solid 10 degrees below climo.

Rising heights responding to a ridge building across the central Conus combined with developing light southerly flow will result in temps warming to near normal Fri afternoon. Dewpoints will begin to gradually rebound, but widespread afternoon minimum RH of 25-30% (if not lower) will again elevate the fire danger above typical mid-May levels in light of the ongoing extreme drought conditions. Fri night's min temps will be a little warmer than tonight, but still below normal due to good radiational cooling conditions/persistent dry air.

Key message 2: Above normal warmth returns this weekend into next week, while limited rainfall chances, mainly in the mountains, provide little relief from ongoing drought conditions.

Above normal warmth expands across the region this weekend into next week as upper ridging strengthens over the eastern United States. High temperatures Saturday will rise to around 4 to 8 degrees above normal before increasing to 7 to 14 degrees above normal Sunday through at least midweek. Most locations outside the higher terrain should see highs in the mid to upper 80s, with a few Piedmont locations potentially reaching 90 degrees as early as Sunday. The latest NBM probabilities of reaching 90 degrees Sunday range from 25 to 50 percent across portions of the Georgia and Carolina Piedmont. Confidence of 90-degree heat increases further Monday, when exceedance probabilities rise into the 40 to 60 percent range across much of the Piedmont and even portions of the northern foothills since they are closer to the core of the upper ridge that is centered near the Central Appalachians and northern Mid Atlantic.

Despite the early season heat, heat impacts should remain somewhat tempered by a relatively dry air mass. Dewpoints are generally expected to remain in the 50s before gradually rising into the lower 60s early next week, keeping heat index values close to actual air temperatures and limiting more oppressive conditions.

Rain chances through Tuesday remain limited and largely confined to the mountains during the afternoon and evening hours. In the absence of stronger large-scale forcing, convection should primarily be driven by terrain circulations and daytime heating, resulting in isolated coverage and limited rainfall amounts. This pattern is unlikely to provide meaningful relief from ongoing drought conditions for most locations.

There is some uncertainty regarding convective coverage Sunday through Tuesday tied to whether weak shortwave troughs or decaying upstream MCS activity can reach the mountains during peak heating. If this occurs, shower and thunderstorm coverage could become somewhat greater than currently forecast. NBM median SBCAPE values Sunday afternoon range from roughly 500 to 800 J/kg, which would support isolated thunderstorms where convection is able to develop.

Confidence decreases somewhat by Wednesday as the ridge weakens and an upstream trough approaches from the Midwest and Great Lakes. Ensemble cluster analysis continues to show spread in both the timing and amplitude of this trough, with faster and more amplified solutions producing greater rainfall coverage across the area. Even so, shower and thunderstorm chances should increase Wednesday afternoon and evening, especially across the North Carolina mountains where PoPs are highest. Rain chances decrease farther south and east into the foothills and Piedmont.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

At KCLT and elsewhere: A dry air mass in the wake of a cold front will result in continued VFR conditions through this forecast cycle. In fact, other than FEW/maybe SCT cumulus in the 060-070 range this afternoon, SKC conditions are expected. Generally NW winds will continue this afternoon...with frequent gusts to around 20 kts at KAVL, and occasional gusts of 15-20 kts possible at other terminals. Winds diminish this evening, eventually becoming light/variable overnight before becoming light SW by early Fri afternoon.

Outlook: VFR and quiet weather is expected from the weekend into early next week, although isolated diurnal mountain convection will become possible early in the new week.

GSP WATCHES/WARNINGS/ADVISORIES

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