textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion was updated for the 12Z TAF issuance.

KEY MESSAGES

1. Scattered showers and some embedded thunderstorms will remain possible through daybreak as a weak front crosses the area. Behind the front, quiet weather is expected through Monday. 2. A backdoor cold front should arrive late Monday, but confidence is limited on what the impact will be as it moves through and what happens during the middle part of the week.

DISCUSSION

Key message 1: Scattered showers and some embedded thunderstorms will remain possible through daybreak as a weak front crosses the area. Behind the front, quiet weather is expected through Monday.

The latest satellite imagery shows the mid-level moisture gradient accompanying a short wave axis moving slowly east from east TN to the western Carolinas late this evening. A broken band of showers with a few thunderstorms, mainly east of I-77, was moving off to the east along with a plume of deeper moisture associated with a weak low level jet. Until the moisture gradient crosses the region, it remains possible that persistent showers with high precip rates could produce enough rain in a short period of time, resulting in flooding. However, that window was closing steadily. The radar trend is definitely downward in coverage and intensity. We continue to monitor, particularly over the urban areas. Meanwhile...precip probs will steadily drop from the west and end around sunrise with the passage of the short wave axis. The widespread rain in the past 24 hours and the remaining low level moisture suggest that it will remain murky through sunrise. Patchy dense fog looks like a decent bet, but whether or not coverage improves to the point where a Dense Fog Advisory will be needed remains to be seen.

In the wake of the wave, it should be relatively quiet on Sunday as slightly drier air moves in, but the environment will be unfavorable for deep convection with no forcing, a weak cap, poor lapse rates, and a lack of buoyancy. There could be a few ridgetop showers, as per usual, particularly on Monday as the situation gets a bit more favorable over the mtns. A weak front to the north is not expected to reach this far south before late Monday. Temps will warm up to five degrees over normal both days, but nowhere near enough to heat advisory criteria.

Key message 2: A backdoor cold front should arrive late Monday, but confidence is limited on what the impact will be as it moves through and what happens during the middle part of the week.

A strong short wave is expected to pass by to our north on Monday, driving a back door cold front southward and across our region, but probably not until the evening hours. As it stands right now, the model guidance shows little in the way of response, which is not a surprise given the weak cap and lack of buoyancy across the region Monday evening as it passes. The more interesting part of the forecast happens behind the front starting on Tuesday. An upper anticyclone drifts in from the west but remains centered over the TN Valley region. The upper ridge will support sfc high pressure moving slowly from the lower Great Lakes to the Canadian Maritimes from late Monday through Tuesday, then ridging down from the northeast into Wednesday. There are some indications of weak cold air damming developing on Tuesday, though without the benefit of precip or a light easterly flow of moisture, temps might still climb a few degrees above normal. We only mention this because if some moisture were to move in from the east, the temp forecast could be several degrees too warm. For the time being, the NBM indicates that temps are likely to reach at least normal (mid-80s) east of the mtns both Tuesday and Wednesday. As we get into the second half of the week, moisture lingers over the mtns each day, suggesting a chance of diurnal showers and storms each day Thursday through Saturday. As we get into next weekend, confidence is very low owing to the presence of a cutoff low near the Southeast Coast indicated by the GFS, so all bets are off.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Widespread low stratus and fog will impact all TAF sites through daybreak with IFR/LIFR cigs and locally dense fog possible. Mountain valley fog and low stratus will keep restrictions at KAVL as well. Fog will mix out shortly after daybreak, while low stratus will lift and scatter during the same time frame. Expect VFR conditions to prevail through much of the daytime period as a result. Light winds will be out of the south to southwest or variable through daybreak with a shift to the west to northwest by the morning hours. A few low end gusts are likely at KAVL during the afternoon. Guidance hints at another round of mountain valley fog and low stratus, which could impact KAVL overnight tonight.

Outlook: Quiet conditions are expected to persist through early Monday. A second round of showers may develop on Monday afternoon and evening, but confidence is low, and coverage may only be isolated.

GSP WATCHES/WARNINGS/ADVISORIES

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