textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 12z TAFs.

KEY MESSAGES

- 1. Above average temperatures and chances for showers and storms this afternoon and evening.

- 2. Cooler conditions expected Wednesday onward, with periods of showers mainly Wednesday and Thursday.

DISCUSSION

KEY MESSAGE 1: Above average temperatures and chances for showers and storms this afternoon and evening.

A weak shortwave approaches the region today along a lingering stationary boundary, continuing to draw moisture northward across the CWA. This disturbance will lift northeastward off the coast later today in response to an upper-level trough progressing through the Midwest. Broader synoptic forcing will yield higher coverage in Pops, as a surface front pushing southward across the Midlands Tuesday night supports widely scattered showers and storms, primarily during the late afternoon and evening hours. A few severe storms are possible as MUCAPE values approach 2000-3000 J/kg with PWATs of 1.7-2", supporting a localized threat for wet microbursts and damaging wind gusts within the strongest storms. However, weak mid-level lapse rates and minimal effective shear will keep the overall organized severe risk limited. Highs will again be in the 90s for one last time (hopefully).

KEY MESSAGE 2: Cooler conditions expected Wednesday onward, with periods of showers mainly Wednesday and Thursday.

Models are generally converging on high pressure over the northeast pushing the wedge front through our forecast area late Tuesday into Wednesday. The ongoing showers and cloud cover Wednesday morning will likely limit daytime heating, especially with cold advection occurring at the surface. There remains some uncertainty regarding how far south the wedge front will go, and it is expected to have a tight temperature gradient setting up somewhere across the southern Midlands Wednesday afternoon. All said, the temperature drop of 10 to 15+ degrees between Tuesday and Wednesday will be very noticeable north of the front. There will also be some breezy northeast winds accompanying this airmass change. Blended guidance struggles in these scenarios, so we have been using the NAM/GFS models to better capture the expected temperatures late this week.

Additional cloud cover and precip suggests Thursday could be our coolest day of the week for high temperatures, with most expected to remain in the low to upper 70s. An upper trough will work to scour out the wedge through some portion of the day, with drier Northwest flow eventually moving in. Highs will rebound a bit closer to normal as precip and cloud free conditions return Friday and into this weekend. Highs will generally reach the upper 70s to low 80s, with overnight lows in the upper 50s to low 60s. Overall, this should provide our first real taste of fall with a refreshing change in temperatures arriving just as astronomical autumn officially begins later today!

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Little change in previous thinking. Possible br/fg this morning. Scattered thunderstorms expected in the afternoon. Ceiling restrictions beginning late it the taf period.

We will be entering a period of a changing weather pattern across the region beginning late in the taf period. A surface front will begin to push southward, but will remain well north of the area through the daytime and early portions of the overnight hours tonight. This means one more day of what will amount to a repeat of the past several days. Some patchy br/fg can not be ruled out this morning, especially the usual fog prone sites of ags/ogb. For this afternoon, another round of scattered showers and thunderstorms is expected to develop, and have generally continued with the mention of Prob30's by mid- afternoon. Will also begin to add mention of vcts for much of the afternoon, and eventually change over to vcsh by 03z as activity begins to wind down. With the approach of the surface front late tonight, guidance continues to showing ceiling restrictions developing from north to south, generally with mvfr ceilings starting around 03z, then ifr conditions developing by 06z-07z.

As for winds, easterly winds will pick up around 7 kts after 15Z. Winds could begin turning more northeasterly late in the taf period, then turn a little more out of the north more than likely after 06z timeframe as the cold front pushes into the area.

EXTENDED AVIATION OUTLOOK...Widespread restrictions and higher rain chances expected Wednesday through Thursday as wedge conditions set up across the region. Drier conditions expected beginning Friday.

CAE WATCHES/WARNINGS/ADVISORIES

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