textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation forecast was updated to reflect the 18z TAF issuance.

KEY MESSAGES

1. Quiet conditions continue for most of today before a decaying convective line crosses the area Tuesday morning. 2. A storm system and associated cold front will bring rain chances late Tuesday night through Wednesday morning. Another round of precipitation may return over the weekend, but confidence is low at this time.

DISCUSSION

Key message 1: Quiet conditions continue for most of today before a decaying convective line crosses the area Tuesday morning.

Deck of stratocu finally dissipating as deeper afternoon mixing continues. Quiet for the rest of the day, but changes will filter into the region overnight as a strong surface low centered near the Upper Great Lakes will send of a trailing boundary into the area from the west. Hi-res guidance continues to depict a remnant MCS slipping off the boundary and tracking across the TN Valley before reaching the NC/TN border after 06Z tonight. Almost all of the guidance kills the MCS as it crosses into the region overnight into Tuesday morning as the available environmental parameters will not be conducive for sufficient MCS maintenance as it crosses the rugged terrain as well, while eventually moving into the Piedmont around or just after daybreak Tuesday. As a result, the severe threat is near zero, but can't rule out a rogue severe wind gust, mainly along the NC/TN border. Otherwise, any rainfall will be beneficial and lingering convective debris will keep conditions on the cooler side Tuesday with afternoon highs at or slightly below normal.

Key message 2: A storm system and associated cold front will bring rain chances late Tuesday night through Wednesday morning. Another round of precipitation may return over the weekend, but confidence is low at this time.

By tomorrow night, a second in a series of southern stream shortwaves will be sliding across the Mississippi Valley and lifting into the Ohio Valley and Appalachians. Widespread deep convection will be ongoing across portions of the mid south from southern Illinois down to the I-20 corridor across Louisiana and Mississippi. This convection will reside within fairly impressive parameter space with several clusters of severe storms likely. With time, this activity will progress eastward through the evening and overnight as height falls overspread the Tennessee Valley into the Southern Appalachians. The 12z suite of CAM guidance is in rather good agreement that at least some form of QLCS will be approaching the area from the west during the early morning hours Wednesday. Deep- layer vertical wind shear will be supportive of maintenance of organized convection, but the primary limiting factor will be limited instability with generally 100-200 J/kg of MLCAPE progged during the nocturnal instability minimum. While low, this may prove to be sufficient to maintain at least some degree of linear structure into the forecast area with an associated threat locally gusty winds and perhaps a few isolated severe storms. Any severe threat will largely hinge on how upstream convection evolves. A more well established QLCS would likely survive farther into the area. The morning convection should leave a stable airmass in its wake with a good bit of uncertainty as to whether additional precipitation will be able to develop through the afternoon. A few widely scattered showers seem plausible, but confidence is low as to much beyond that.

A frontal boundary finally clears the area Wednesday night into Thursday morning as the longwave trough axis shifts east and a sprawling surface high drops across the Great Plains and into the Mississippi Valley. This should keep dry conditions in place Thursday through at least Friday morning. Forecast confidence quickly wanes by Friday into the weekend as guidance continues to vary notably as to how the synoptic pattern evolves. The frontal boundary is expected to stall to our south as active southern stream flow persists from the Southern Plains across the Lower Mississippi Valley and into the southeast states. A closed upper low ejecting out of northern Mexico and into Texas is progged to slide across the Gulf States Friday into the weekend. The exact track of this feature and placement of the boundary will determine northward extent of rainfall. The GFS has trended farther north with a nice round of rain across the region while the ECMWF solution remains suppressed with a dry forecast. The forecast will continue to follow the national model blend for now and will be adjusted as needed once guidance comes into better agreement.

AVIATION /18Z MONDAY THROUGH SATURDAY/

At KCLT and elsewhere: The stratocu deck from earlier has mostly dissipated, leading to mostly clear skies across the terminals with some lingering MVFR stratocu near KAND, but that should dissipate by 20Z. Continued east to southeast winds for most of the day. A cold front will approach from the west as an area of showers and thunderstorms pushes into the area around daybreak Tuesday. Coverage gradually decreases as it pushes from the mountains into the Piedmont through the morning hours Tuesday. As a result, kept a prevailing mention of SHRA at KAVL and KHKY, while the rest of the sites maintain a PROB30 for rain and associated restrictions. Most of the rainfall should exit the area by Tuesday afternoon, but cloud cover will linger and could take until late in the afternoon for the MVFR cloud deck to lift and/or scatter out.

Outlook: Active weather will continue into mid-week, with another disturbance expected on Wednesday/Wednesday night. Further rainfall is possible by the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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