textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion was updated for the 18z TAF issuance. Corrected Key Message 2.

KEY MESSAGES

1. A cool and dry airmass will remain over our area today. Dry vegetation and low RH values will keep elevated fire conditions in place through this afternoon. 2. Warm temperatures for Tuesday through next weekend with afternoon shower and thunderstorm chances increasing.

DISCUSSION

Key message 1: A cool and dry airmass will remain over our area today. Dry vegetation and low RH values will keep elevated fire conditions in place through this afternoon.

Flow aloft remains rather quasi-zonal today into Monday, while a strong surface high remains parked near the Mid-Atlantic Coast this afternoon. Lingering cool and dry airmass with deep boundary layer mixing has allowed for dewpoints to tank, leading to RH values plummeting to 25% or below for most locations, especially along and north of I-85. Factor in very dry vegetation, this has allowed fire weather concerns to remain elevated and thus, a Fire Danger Statement has been issued for all of the western Carolinas and northeast Georgia through 8 PM this evening in coordination with State Forestry Commissions and neighboring WFOs. As the surface high continues to slip further offshore later today into tonight, the low-level flow turns more out of the south and southeast. In the return flow, dewpoints will rise as better moisture returns across the area. A weak subsidence inversion develops in this regime and allows for low-level moisture to become trapped underneath. As a result, stratocu is expected to develop later this evening, through tonight, and during the day on Monday. Overnight lows will rebound significantly compared to Saturday night as most locations rise into the mid and upper 40s with low 50s possible closer to the Upper Savannah River Valley. With continued south to southwesterly flow on Monday, low-level WAA will be ongoing and help dewpoints return into the 40s and 50s. This will eliminate fire weather concerns for most of the area, but afternoon highs will rise as well which could cause some locations, mainly along and east of I-77 to see RH values dip below 40%. May need another Fire Danger Statements for some of these counties, but will be issued once the Fire Danger Statement for today expires if needed. Monday will be the start of a warmer trend as a afternoon highs reach the low to mid 70s (60s for the higher elevations). Can't rule out a spotty shower during the afternoon in the western portions of the CWA, but confidence is too low for a mentionable PoP at this time.

Key message 2: Warm temperatures for Tuesday through next weekend with afternoon shower and thunderstorm chances increasing.

We seem to slip easily into a late Spring pattern early in the week and the model guidance suggests that it will persist through next weekend, depending on the eventual eastward progression of a progressive nrn stream trof and cold front maybe next Sunday. The upper flow starts out relatively flat on Tuesday but gradually amplifies with a ridge off the East Coast and a trof coming off the Rockies by the end of the week. The East Coast ridge will support sfc high pressure out around Bermuda, which will promote a general SW flow at low levels across the southeast that should bring the dewpoint up into the 50s and lower 60s, which means that afternoon RH will not be critically low like it has been over the past several days. Meanwhile, temps will be on the order of 10 to 15 degrees above normal, with highs and lows close to what would be normal for mid- to late-May. The other end result will be an environment that will support diurnal shower and thunderstorm activity each day, thus the precip chances included in the forecast. Note that the NBM looks a bit enthusiastic on the precip probs each afternoon mid to late week, given our ongoing drought, so one might want to manage their expectations for getting much in the way of much-needed rain. But...at least we're saying there's a chance. As for severe thunderstorm chances, right now Wednesday has the best potential, with the NBM showing a 40-60 percent prob of sfc-based CAPE exceeding 1000 J/kg but all other days having much less potential for decent buoyancy. We shall see what Sunday holds for us with the potential for a progressive cold front adding some forcing/organization potential.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

At KCLT and elsewhere: Dry conditions expected through the period with mostly VFR. Guidance increases cloud cover overnight and cigs will hover near MVFR around daybreak Monday and could potentially linger through the rest of the morning hours before cloud cover scatters, mainly across the Upstate sites where MVFR restrictions would most likely develop. Winds are picking up out of the east to southeast and should favor a southerly trajectory through the afternoon and evening. Some low-end gusts can't be ruled out this afternoon, mainly at KAVL. Light winds expected tonight, while continuing to toggle at a southerly direction. South to southwesterly winds expected for Monday at 5-10 kts, with low-end gusts possible.

Outlook: Dry, VFR conditions are expected to continue through the early part of the week. Moisture will increase Tuesday and Wednesday, leading to elevated chances for showers and thunderstorms with associated restrictions.

GSP WATCHES/WARNINGS/ADVISORIES

GA...INCREASED FIRE DANGER until 8 PM EDT this evening for GAZ010- 017-018-026-028-029. NC...INCREASED FIRE DANGER until 8 PM EDT this evening for NCZ033- 035>037-048>053-056>059-062>065-068>072-082-501>510. SC...INCREASED FIRE DANGER until 8 PM EDT this evening for SCZ008>014-019-101>109.