textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Aviation discussion updated for the 12Z TAF cycle.

KEY MESSAGES

1. Fair and seasonally warm weather through at least Friday. 2. Rain is expected return to the region over the weekend, but confidence on timing, amount, and duration remains low.

DISCUSSION

Key message 1: Fair and seasonally warm weather through at least Friday.

Fair weather should persist across the region for the rest of the work week, courtesy of sfc high pressure. One high center moves off the New England coast today but a chunk breaks off and lingers across the Carolinas through Thursday. The result will be temperatures that climb a category above normal today, but then warm to more like ten degrees above normal on Thursday, while the air mass remains dry. The center of an upper anticyclone moves overhead on Friday while the sfc high gets reinforced from the north with a weak frontal passage early in the day, which should be enough to drop temps back a few degrees, but it will remain warm. The dry weather is expected to persist through Friday night. After that, all bets are off and our attention turns to the Gulf.

Key message 2: Rain is expected return to the region over the weekend, but confidence on timing, amount, and duration remains low.

Our attention turns to events over the western Gulf as we get into the late part of the week, what with Tropical Cyclone Isaias forecast to strengthen and head toward the northern Gulf Coast. Needless to say, there is much uncertainty as to how this would play out. The majority of the guidance has the system moving northward well to the west of the mountains from late Saturday into Sunday. While it is true that a tropical cyclone remnant moving northward from the Gulf on a track to the west of the mtns typically means a lot of rain for the western Carolinas, if the system moves too far to the west it would be a limiting factor for rainfall amounts. Rain confidence is high enough to keep probs in the categorical range Saturday night through Sunday, but the guidance still has some big differences with regard to the amount and timing differences for the onset. The latest NBM shows an area where greater than three inches of rain is likely across the typical southeast upslope favored locations near and immediately upstream of the Blue Ridge Escarpment, mainly centered on Sunday. The likelihood of five inches of rain is very low at this time. Shear would be good, but buoyancy would be poor. Dry air should work its way back into the region after the system moves farther to the north by Monday or so, but the timing of the precip ending is even more uncertain. Bottom line, we have something to keep an eye on now, so continue to monitor the forecast trends while we await additional guidance.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: LIFR/VLIFR conditions will persist at KAVL and KHKY through 13 or 14Z, with some degree of restriction likely lingering through 15Z, especially at KAVL. A brief restriction cannot be ruled out at other TAF sites, but this is becoming increasingly unlikely, and VFR is forecast at those sites through the period. Fog/low stratus should again develop around lakes and mountain/river valleys tonight into early Thu, although the extent of said fog is uncertain at this time, and there is reason to believe that it may not be as widespread or long-lived as this morning. Otherwise, light variable/calm winds through much of the period, with perhaps a brief light southerly winds this afternoon.

Outlook: Mostly VFR through Friday night, except for continued potential for fog and low stratus in mountain valleys and around rivers/lakes each night. The potential for widespread rain and persistent restrictions increases Saturday and remains through the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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