textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Aviation Discussion updated for 18Z TAF issuance.

KEY MESSAGES

1. Another round of precip is expected tonight and early Wednesday, followed by scattered thunderstorms Wednesday afternoon, a few of which could be strong to severe over western NC. 2. After a brief period of cooler and much drier weather Thursday and Friday, another round of rain is likely to impact much of the forecast area Friday night and Saturday. Dry weather returns early next week.

DISCUSSION

Key message 1: Another round of precip is expected tonight and early Wednesday, followed by scattered thunderstorms Wednesday afternoon, a few of which could be strong to severe over western NC.

Lingering cloudiness behind a departing band of precip will help to keep afternoon temps a little on the cool side. Few changes were made to the forecast through tonight. Can't rule out fog developing in a few locations with visibility becoming poor during the pre-dawn hours Wednesday ahead of the next batch of precip, but nothing suggests much dense fog potential. Which brings us to late tonight. The CAMs continue to show the decaying remnants of an MCS moving in from the west after midnight. The agreement is there among the CAMs, which gives confidence to keeping a likely to categorical precip prob. The chances for severe weather or flooding rain thru most of Wednesday morning look very low at this time as the MCS remnants outrun the forcing and instability.

That may not necessarily be the case Wednesday afternoon and evening, assuming the next batch of precip makes steady eastward progress out of the fcst area by midday and we manage to break out. Fcst soundings from the RAP show a mixed layer CAPE upwards of 1500 J/kg late in the afternoon east of the mtns, to go with deep layer shear upwards of 50 kt. So, the Marginal Risk seems perfectly valid in that regard, but could end up being conditional upon being able to maintain storms. The CAMs for the most part appear to struggle to develop anything other than ordinary showers and a few storms scattered about, so hardly anything that appears concerning. We will have to wait for later runs of the CAMs to see if they latch on to anything in the environment and start to depict anything of substance. Otherwise, temps will remain mild overnight and then will get back to five degrees above normal or so for Wednesday afternoon highs.

Key message 2: After a brief period of cooler and much drier weather Thursday and Friday, another round of rain is likely to impact much of the forecast area Friday night and Saturday. Dry weather returns early next week.

An upper low will meander around the border between Quebec and Ontario from Thursday into early next week, with the axis of an associated broad/low-amplitude trough extending south through much of the eastern Conus. An attendant cold front is forecast to push through our forecast area Wed evening, with token PoPs lingering into Wed evening across mainly the southeast part of the forecast area, as well as the NC counties bordering TN...where a developing NW/upslope flow could support shower development through at least Wed evening. Cooler and much drier air will filter in behind the front for Thu, with temps returning to near-normal levels for Thu and Thu night.

Clouds will increase Friday, as a dampening short wave trough ejects from Texas into the base of the eastern trough Fri/Fri night. Frontogenesis will develop along the lingering baroclinic zone over the Southeast Fri night into Saturday, and this will bring the next chance of rain to our CWA, with warranting likely PoPs across the southern half of the area, with more like solid chances across the north. Even across southern areas...this event appears unlikely to put much of a dent in the longer term drought conditions, but every little bit helps. Rain and/or cloud cover is expected to result in Saturday max temps around 10 degrees below climo, with cold air advection developing in the wake of a western Atlantic cyclone resulting in temps remaining 5-10 degrees below normal through Sunday night. A dry air mass otherwise accompanies the cooler air, while temps steadily warm to around normal Monday/Tuesday.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: The precip has moved off well to the southeast, but a lingering low cloud deck east of the mtns will keep an MVFR cig restriction through the mid/late afternoon before it finally scatters out. Some boundary layer mixing will allow for occasional gusts through peak heating in spite of the relatively low clouds, direction SW to S. Our lull in activity should end after midnight as the next batch of clouds and precip arrive with another MCS remnant. This will not be quite the same as there appears to be little support for thunderstorms, but more low level moisture initially, so the restrictions begin as the rain is moving in. Probs are fairly high, so after a short period where the onset time is in doubt, we go straight to prevailing MVFR/IFR restrictions with the precip. The wind direction should stay southerly. Once that batch of rain moves out by mid-morning, we will again have a slow improvement of ceiling, but we may not lose the restriction before the end of the period.

Outlook: Dry and VFR conditions may return Wednesday night into Friday before another disturbance brings rain chances and associated restrictions over the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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