textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Temperatures have trended a bit warmer for much of the coming week.

The aviation discussion was updated to reflect the 18Z TAF issuance.

KEY MESSAGES

1. One more day of dry weather today, before a cold front brings scattered showers and a few embedded thunderstorms to the area on Monday. Relatively little rain is expected with this system, and severe risk remains minimal. 2. Another weak cold front may bring a few more showers and thunderstorms to the western Carolinas Wednesday into Thursday. Temperatures warm back above normal next weekend.

DISCUSSION

Key message 1: One more day of dry weather today, before a cold front brings scattered showers and a few embedded thunderstorms to the area on Monday. Relatively little rain is expected with this system, and severe risk remains minimal.

It's a beautiful Sunday afternoon across the area, as clear skies prevail beneath weakly-capped and ill-defined surface high pressure extending across most of the Southeast. The upper pattern will remain mostly flat this afternoon and evening, with no good synoptic forcing to break the cap. Little more than some sparse afternoon cu is expected today, then, with no mentionable PoP anywhere in the forecast area. Some of the deterministic guidance depicts a shallow dry layer at around 700mb or a little lower, with some potential to mix into that layer and bring lower dewpoints to the surface this afternoon. Probabilities of falling into critical RH territory look fairly low in the 12z HREF, which barely eeks out a 30% chance of an afternoon RH below 30%, while the 06z REFS is somewhat more bullish with mixing and supports widespread 25-30% RH across the NC Piedmont. The REFS solution should be considered a worst-case scenario given its membership broadly depicts weaker capping and stronger winds in the inversion layer than most of the other ensemble and deterministic models.

Several low-amplitude z500 features will phase together this afternoon and evening and coalesce into a single defined trough axis over the central Great Plains, and then vigorously push eastward through tonight. Guidance agrees well on the placement of a positively-tilted and deamplifying trough axis extending from the Mississippi delta area into the central Ohio Valley by 12z Monday. The associated surface front will approach the western Carolinas tonight and cross the area through the first half of Monday, with a cooler, postfrontal air mass slipping into the area by Monday night.

The CAMs are not impressed with any severe potential associated with the front. Given the timing - with both the strongest upper forcing associated with the trough, and the frontal circulation itself both crossing the area near the diurnal minimum - ensembles depict fairly limited instability, with the most aggressive scenario featuring a slower frontal passage and destabilization across the eastern 2/3 of the forecast area by mid/late Monday morning. Even then, the probability of >500 J/kg sbCAPE is very limited. Ensembles featuring a faster FROPA depict an even bleaker scenario for convection, with less destabilization. Both the 12z GFS and recent RAP cycles depict a developing axis of low-level convergence moving from the upper Savannah River Valley into the southern Upstate on Monday afternoon...perhaps providing some marginally-better conditions for convective intiation there during the afternoon. Still think that the severe threat is minimal, however, given such a feeble convective environment. Some convective rain rates could nonetheless develop within any areas where elevated instability develops as variously featured in forecast profiles, but even then, QPF response comes to a paltry 0.1-0.15" for most of the area, barely a drop in the bucket against a remaining 3-7" of rainfall deficit across the region.

Key message 2: Another weak cold front may bring a few more showers and thunderstorms to the western Carolinas Wednesday into Thursday. Temperatures warm back above normal next weekend.

Broad upper trofing will move off the Atlantic Coast on Tuesday with the backside of the trof getting reinforced on Wednesday and Thursday. At the sfc, an elongated cold front moves east of our area Tuesday as broad high pressure spreads over the region from the north. Another weak cold front will move thru our area Wednesday into Thursday and could produce some sct showers and/or a few thunderstorms, mostly over our northern zones. Any precip amounts will likely be minimal (ie, < than 0.1 inches for most locations). Dry high pressure returns for Thursday and Friday, with the sfc high migrating offshore over the weekend. This will allow for warming SLY return flow to establish itself over the region and help push temperatures back above normal.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

At KCLT and elsewhere: VFR on tap today as high pressure drives clear skies and light winds. Most of the terminal forecast area is SKC, though on satellite imagery, there was evidence of a shallow, sparse cu field beginning to develop south of I-85. A steady N/NE wind presently in place will gradually toggle over to the SSW over the next 1-2 hours...with all sites expected to be SSW by 18-19z. Cirrus will gradually expand across the area tonight as a cold front approaches from the west, and by daybreak Monday, more extensive mid- level (still VFR) cloud cover should begin to form. A broken band of showers, and some embedded thunder, will cross the area from mid- morning through mid-afternoon, with a least VC weather expected at all terminals. Some MVFR ceilings are expected with these showers and storms, but guidance currently depicts a quick return to VFR in the wake of the system on Monday evening.

Outlook: Dry conditions persist through early Wednesday. A clipper- type low may cross to our north late Wednesday, but guidance suggests rainfall will be paltry with this system, and it's questionable whether any flight restrictions will develop.

GSP WATCHES/WARNINGS/ADVISORIES

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