textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion was updated to reflect the 12Z TAF issuance.

KEY MESSAGES

1. A summer-like pattern will continue through Wednesday, with above normal temperatures and increasing humidity. Chances for mountain diurnal convection increase Wednesday afternoon as a front approaches. 2. A cold front will bring better rain chances Thursday into the weekend, but any drought relief will be limited.

DISCUSSION

Key message 1: A summer-like pattern will continue through Wednesday, with above normal temperatures and increasing humidity. Chances for mountain diurnal convection increase Wednesday afternoon as a front approaches.

We seem to be on track with flattening the mid/upper ridge on the East Coast through mid-week as a powerful system lifts northeast from the Plains to eastern Canada. However, a new wrinkle has appeared in the guidance today in the form of a curious weak upper low drifting northwestward to the north of the Bahamas. This doesn't really appear to have much potential to develop into anything, but it would introduce a weakness in what would have otherwise been a more persistent southwesterly flow aloft that would have been more efficient in moving moisture northeastward from the Gulf. Instead, it splits the ridge between the old anticyclone moving eastward away from the East Coast, and a remnant ridge over the eastern Gulf. This will not do anything to improve our chances for rain or the rainfall amounts should showers develop. For today, the CAMs keep us dry, as expected, but this would have ramifications starting Wednesday afternoon. The new guidance keeps a cold front strung out across the TN Valley to Mid-Atlantic region through Wednesday night, which is to say, to our west and north. The CAMS go out far enough with this cycle to shed some light on coverage for Wednesday afternoon and there are some differences, with the HRRR being the most sparse. Precip probs have been tempered by the HRRR and lowered a bit from what the NBM indicates for now, and generally kept over the mountains. The threat for severe storms appears to be low because of a lack of buoyancy and shear in the latest RAP. Precip amounts would also be modest.

As for temps, they continue to look summery, with highs running 7-12 degrees above normal, which should result in seasonally mild overnight lows and then highs generally in the lower 90s by Wednesday afternoon. This would still be several degrees below records and not problematic with regard to the heat index as the air mass will remain too dry.

Key message 2: A cold front will bring better rain chances Thursday into the weekend, but any drought relief will be limited.

Our weather situation looks unsettled beginning on Thursday and continuing perhaps through the end of the forecast period as the upper pattern keeps a mean trof to our west and ridge over the East Coast that maintains a southwesterly flow aloft and the Gulf open. Details are sketchy of course, but the cold front should move into the area on Thursday and provide the focus for numerous showers and storms. The boundary will drop south of the forecast area at some point Thursday or Thursday night either as outflow from convection or as a weak cold air damming high wedges down from the Great Lakes. This makes the forecast for Thursday uncertain, particularly in terms of high temps which are still forecast to be warm for the time being. It could easily end up ten degrees less than forecast, but the 10-15 degree drop on Friday looks like the better bet as the signal for cold air damming looks a little bit stronger. The weekend is also more up in the air because the new GFS suggests the weak wedge may persist through Saturday and into Sunday, so precip chances remain high and temps might not return to normal as fast as thought. By the time we get into the early part of next week, the guidance shows a southern stream system lifting out of the southern Plains toward the TN Valley region, which would keep some periodic forcing/focus for above normal chances of rain each day. On the one hand, there isn't much of a signal for heavy rain in any of this, so no meaningful drought relief is suggested. On the other hand, this pattern would, at a minimum, keep the situation from getting any worse.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: VFR conditions will prevail at all terminals through the period. Satellite imagery shows an extensive area of fog and low stratus over the Coastal Plain, but it has made little progress and has yet to reach the Fall Line, so it looks like KCLT will be spared. However, there are some low clouds to the southeast, so a FEW035 will be carried first thing this morning. Otherwise, wind will be light from the S to SW again today, with a few high-based stratocu. Persistence looks good for tonight, meaning more light/variable winds and scattered cirrus.

Outlook: Increasing moisture will bring a more active pattern for mainly diurnal convection beginning Wednesday afternoon and then continuing through the end of the week. The potential for overnight fog/low clouds will increase as well.

GSP WATCHES/WARNINGS/ADVISORIES

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