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 gradually evolve through early next week, with above normal temperatures and steadily increasing humidity. 2. A cold front moving in from the northwest is expected to bring better rain chances from Wednesday afternoon through Friday, but probably not enough rain to make a dent in the drought. Cooler temperatures return behind the front for the end of the week.

DISCUSSION

Key message 1: A summer-like pattern will gradually evolve through early next week, with above normal temperatures and steadily increasing humidity.

A relatively flat upper pattern to start the weekend will gradually amplify through Sunday and into Monday as a deep mid/upper trof and low dig down across the Intermountain West and a ridge/anticyclone builds along the East Coast in response. Hope you all enjoyed one last cool night. This pattern will support a summer-like Bermuda High that will allow for a warmup with temperatures climbing around ten degrees above normal by Sunday and Monday, which translates into highs in the upper 80s and lower 90s outside the mtns. Seasonally hot, yes, but probably not high enough to challenge any record highs. A corresponding increase in dewpoint will not be especially noticeable for the next few days and the RH should stay low enough that apparent temps will be essentially the same as air temps.

Whether or not the increase in moisture will be enough to fuel any diurnal convection is an interesting question in light of fcst soundings that reveal the presence of a remnant elevated mixed layer...seen as mid-level lapse rates of 7.5-8 C/km during the Sunday/Monday time frame...that would improve our chances at severe weather. At the same time, the fcst soundings show a formidable cap at least on Sunday, so it will be very difficult to get much coverage of deep convection. The most likely place would be southeast facing mountain slopes where differential heating could be enough to break the cap, but it seems more likely that we won't on Sunday. The precip chances might be overdone over northeast GA and southwest NC. The cap looks more breakable by Monday, but the elevated mixed layer is gone for the most part and, oddly, our precip probs actually drop. Widely scattered ridgetop convection is expected again Tuesday afternoon. Shear parameters are forecast to be rather weak, but a few pulse-type strong/severe storms are possible each afternoon.

Key message 2: A cold front moving in from the northwest is expected to bring better rain chances from Wednesday afternoon through Friday, but probably not enough rain to make a dent in the drought. Cooler temperatures return behind the front for the end of the week.

By the middle of next week, the upper pattern will start to flatten out again as short waves lift out of the western trof and flatten the eastern ridge. The main wave will pass well to our north on Wednesday while pushing a trailing cold front down from the northwest across the OH River valley to the western side of the mtns. Meanwhile, the persistent Bermuda High feature off the East Coast will have had enough time to bring some moisture in from the Gulf, leading to an increase in shower chances for the mtns at least on Wednesday afternoon. That day will probably feel very much like a typical summer day with the increased humidity. Uncertainty increases after Wednesday with regard to where the front stalls and when it lifts back northward, if at all, Thursday or Friday. The guidance is divergent, so the model blend more or less smears out above climo precip probs each day. At this time, there isn't much of an indication that we would have any significant chances for severe weather, as the joint probability of sufficient buoyancy and shear is very low in the model ensemble. Unfortunately, in spite of how great the increased precip chances look, the probability of getting more than an inch of rainfall on any given day is too low to mention. That means most people won't get enough rain late in the week to dent the drought, though a few might be more fortunate. Behind this front, temps cool down back below normal for Friday and Saturday.

AVIATION /10Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR at all terminals through the forecast period, with mostly high clouds. Light/variable wind at daybreak will become SW with daytime heating by late morning, and then stay that way through the evening, courtesy of sfc high pressure off the Carolina Coast.

Outlook: VFR conditions expected to persist through the first half of next week, except in mountain valleys, where as moisture increases, the potential for morning fog/low stratus will increase each night. Isolated diurnal convection is possible early in the week, primarily across the mountains. An active cold front may bring restrictions associated with convective precip from Wednesday afternoon onward.

GSP WATCHES/WARNINGS/ADVISORIES

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