textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion was updated to reflect the 00z TAF issuance.

Confidence remains low on the details of potential precipitation on Friday through next weekend. In general, though, the forecast has trended warmer for the low terrain, keeping snow and/or ice mainly confined to the NC mountains.

KEY MESSAGES

1. Dry weather and a warming trend continues through Tuesday. 2. Next shot of rain expected Wednesday, followed by a brief dry spell and some cooling on Thursday. 3. Active weather returns Friday into the weekend, with a nonzero chance of wintry weather for at least part of the area.

DISCUSSION

Key message 1: Dry weather and a warming trend continues through Tuesday.

A flat upper ridge to our west will continue to build eastward tonight and Tuesday, supporting high pressure that moves off the Southeast Coast this afternoon. The temps appear to be on track for this afternoon, with a nice rebound back toward normal as sky becomes sunny across the region. Dewpoints are not on track, though, and it would appear that deeper mixing was forcing the dewpoint downward late this morning. This trend into the afternoon suggests that our RH values will also drop lower than planned, probably into the mid/upper 20s percent. Fortunately, wind will be light. For Tuesday, we still expect significantly warmer temps than what we've had for the past few weeks, with many locations east of the mtns reaching into the 70s. Won't that feel nice...but not nearly close to records for this time of year. The latest guidance suggests that the leading edge of precip associated with the next system will remain to our west through sunset.

Key message 2: Next shot of rain expected Wednesday, followed by a brief dry spell and some cooling on Thursday.

Scattered light rain is anticipated Tuesday night into Wednesday as a weak cold front pushes south across the Carolinas. Guidance is in good agreement that rain will develop across Appalachia during the predawn hours...albeit with fairly little QPF response...before the boundary slides across the rest of the area early Wednesday. Given the orientation of the front and only prefrontal weak moisture advection, originating over the Tennessee Valley, it's questionable how much moisture will be able to pool east of the mountains as the front arrives. Indeed, the deterministic guidance as well as many of the mid-range ensembles continue to depict low PoP east of the mountains...and so while the Upstate can expect a brief shot of 20- 30% rain chances...portions of the NC Piedmont may receive little more than some drizzle.

The front should sag south of the area by Wednesday evening, and a lower-theta-e air mass associated with broad high pressure over the Great Lakes will slowly filter into the area behind it. As a result, expect markedly cooler temperatures Thursday morning than Wednesday, and for highs to be a category or so cooler on Thursday than Wednesday. In the latest round of 12z guidance, the Great Lakes high is depicted as making little eastward progress through Thursday, resulting in weaker CAA and less drying than in previous forecasts, but given little forcing aloft, Thursday should nonetheless be a dry day for the area.

Key message 3: Active weather returns Friday into the weekend, with a nonzero chance of wintry weather for at least part of the area.

Long-range guidance continues to struggle with the next system, progged to arrive on Friday. There's still not much consistency in the operational models, with the latest runs of the the GFS, ECMWF, and GDPS all depicting a much slower arrival of the upper energy needed for our system to develop. Where prior model runs clearly depicted intensification of a surface low over the southern Great Plains on Thursday night and Friday, resulting in onset of moist upglide over the Carolinas sometime Friday...the bulk of guidance now delays cyclogenesis until well into the day Friday (or fails to depict it at all, as in the new GFS's solution)...resulting in a drier forecast for Friday and onset of precipitation more into Friday night or Saturday, when the surface low really gets going. Even then, most of the European and Canadian ensembles now depict the low tracking across the Deep South but lifting northeastward well before arriving in the Carolinas, resulting in overall warmer profiles aloft than in prior cycles. Pair this with a generally warmer surface forecast for the weekend, and we would be looking at a rainier forecast outside the mountains for Friday through Sunday, with less chance for snow/ice.

The key word here is "would" however - until we start to see some semblance of run-to-run consistency, we won't feel great about what we're seeing. 24 hours ago there was ample support for snow or ice outside the mountains, and 24 hours before that, we were more or less where we are now. The track of the low remains a big question mark, and will need to be monitored closely as we get closer to this event. Confidence is a good bit higher that we will indeed see precipitation, so even if it's warm enough that we get an all-rain forecast for the low terrain...we do indeed expect to get at least a good wetting rain over the weekend. For the mountains, conditions still look more favorable for low-end snow or ice accumulations, mainly on slopes and peaks.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: VFR conditions will prevail through the TAF period at all terminals. High clouds may gradually return to portions of the area overnight into tomorrow, but will be of no impact. Otherwise, winds will be light to calm overnight and generally out of the south. Winds pick up through the morning and shift to out of the southwest. Low-end gusts may become common through the afternoon at most terminals,but should remain at or below 25kts.

Outlook: Moisture will return Tuesday night, which could result in light rain and some ceiling restrictions late Tuesday into Wednesday. A second period of more widespread precipitation and restrictions could return Friday into next weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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