textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes to the previous forecast. The Aviation discussion was updated.

KEY MESSAGES

1. Near-normal temperatures with relatively low humidity through Friday, and a near-zero chance of rain. 2. Another frontal system is expected to arrive from the west this weekend, possibly stalling across our area early next week, bringing back high rain chances but also below-normal temperatures.

DISCUSSION

Key message 1: Near-normal temperatures with relatively low humidity through Friday, and a near-zero chance of rain.

The cold front appears to have moved south of the forecast area, but the dry and cooler air has been slow to move in from the N/NW thus far. As a result, the southern parts of the forecast area around the Lakelands may still end up with a hot day with highs in the mid-90s and lingering humidity, while the parts north of I-40 should start to feel the air mass change this afternoon. Deep convection is not expected, but a stray shower will not be completely ruled out close to the TN border where the NW flow upslope could help to overcome any inhibition.

We should feel the air mass change overnight and into Thursday as the sfc high drops in from the Midwest, supported by the upper ridge axis stretching from the southwestern Plains to the Great Lakes. Temps will be on the order of a category on the cool side of normal, but more importantly, the dewpoints will drop back to the upper 50s and lower 60s which should drop the afternoon RH into the 35-40 percent range. Aaahhh. Should be a right nice day. Alas...the air mass will modify into Friday...and temps will creep back to normal or maybe a few degrees warmer. There will be almost no chance of precip through Friday night, unless a stray ridgetop shower develops during peak heating.

Key message 2: Another frontal system is expected to arrive from the west this weekend, possibly stalling across our area early next week, bringing back high rain chances but also below-normal temperatures.

By late Friday, a short wave topping the upper ridge to our west will be moving across the northern Plains. That wave should dive southeast to the Midwest Friday night as an upper ridge axis moves over our area. By Saturday morning, with the ridge axis to our east and sfc high pressure off the Carolina coast, the return of moisture and humidity from the south will begin in earnest. This might not be in the form of a returning warm front, but the effect will be the same. Meanwhile, the short wave will approach from the west. The model guidance shows the development of mid/upper forcing associated with that wave, which arrives over the region by peak heating on Saturday if the timing doesn't slip. So, after a few quiet days, it looks like a quick ramp-up to above climo precip probs. Nothing out of the ordinary thunderstorm-wise for mid-summer, just more of it. There is a growing consensus among the models for this wave cutting off a low over the TN valley region by Monday then lingering into the middle part of the week, in which case we would have another period of numerous showers and storms and perhaps an increasing risk of heavy rain as precipitable water climbs well above normal. The increase in cloudiness and precip coverage would act to keep daytime highs at or below normal.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: With the sfc front well to our south, all terminals are expected to remain VFR through the period as high pressure builds in from the N to NW. Some high-based cu will affect mainly the NC terminals through peak heating. Those clouds should melt away with sunset. Wind should stay N to NW, with occasional gusts at some locations, though maybe not as much as previously thought. The dry air mass will arrive overnight, which means the chances for mtn valley fog are very low. On Thursday, wind will return light from the N or NNE, and a few fair weather cu may form again.

Outlook: Dry and VFR through Friday, with shower and thunderstorm chances and associated restrictions returning this weekend into early next week. Low stratus and/or fog will be possible each morning starting Friday, mainly in the mtn valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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