textproduct: Columbia

WHAT HAS CHANGED

Dense fog advisory expanded further westward to cover much of the Midlands and CSRA. Aviation discussion updated for 12z TAFs.

KEY MESSAGES

- 1. Areas of dense fog expanding across the forecast area this morning.

- 2. Mostly dry with above normal temperatures expected through Friday.

- 3. Increasing chances for rain this weekend as a front approaches the area.

DISCUSSION

KEY MESSAGE 1: Areas of dense fog expanding across the forecast area this morning.

Latest satellite imagery shows widespread dense fog/stratus across the eastern Midlands and CSRA and continuing to expand westward this morning. The dense fog advisory has been expanded again to cover all but Newberry, Fairfield and northern Lancaster counties. Visibilities of 1/4SM or less are widespread from Cheraw to Camden to Barnwell and eastward to the coast. The dense fog has been building westward but appears to be slowing its westward progress over the past 30 min or so near Columbia. Confidence is lower in dense fog developing across the upper CSRA where stratus has overspread the region but still may develop with time. Visibilities should begin to improve after 10am as the fog/stratus begin to mix out.

.KEY MESSAGE 2: Mostly dry with above normal temperatures expected through Friday.

Upper level ridge axis will shift eastward towards the end of the week leading to above average temperatures as 500 mb heights will rise to near 1.5 to 2 standard deviations above normal based on ensemble means. This will likely lead to highs nearly 10 degrees above normal, in the low 90s as October begins unseasonable warm. With surface high pressure shifting offshore, low level moisture will gradually increase, although forecast soundings indicate a layer of substantial dry air in place that will preclude any rain today. As the ridge begins to break down and the deep layer moisture begins to increase, especially in the south, some isolated showers a possibly a stray storm remains possible in the afternoon but much of the area is expected to remain dry.

.KEY MESSAGE 3: Increasing chances for rain this weekend as a front approaches the area.

There remains a lot of uncertainty as it pertains to the progression of a front through the area this weekend. LREF continues to trend with PWATs greater than 2 inches as deep moisture builds through the weekend. While forcing will be generally weak, especially on Saturday, weaknesses in the ridge and convergence along the front will lead to widespread rain chances Saturday continuing into Sunday. Models and ensembles show large split in total rainfall amounts through the weekend with an axis of heavier rain likely in the area. LREF still continues to show significant spread from around 1" to 2.5" between the 25th to 75th percentile through Monday morning. Model soundings are showing deep-layer moisture especially on Sunday evening into Monday morning when the heaviest rain falls likely due to the approaching front and shortwave trough. Drier air will likely begin to move into the northern area Monday. There is some uncertainty as how deep the trough digs south. At the surface, the cold front is likely to move through Monday morning, but how far south is uncertain. Showers may linger through mid-week in the far southeast FA depending on the front position although drier air will move in place once the front passes.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

IFR/LIFR restrictions all terminals this morning in fog/stratus.

Satellite imagery shows widespread fog/stratus across much of the area impacting all terminals with IFR/LIFR restrictions. Dense fog at OGB should persist through around 13z before improving, while dense fog is less certain at other terminals with lowest confidence at AGS/DNL/AIK. However, all terminals are dealing with cigs at or below 500ft and this will persist through 13-14z before improvements begin with mixing taking place. Near calm winds will pick up from the south by late morning through the afternoon around 4 to 6 knots before diminishing again with sunset.

EXTENDED AVIATION OUTLOOK...Increasing chances of precipitation this weekend may lead to additional restrictions.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Dense Fog Advisory until 10 AM EDT this morning for SCZ016-018- 022-025>031-035-037-038-041-116-135>137. GA...Dense Fog Advisory until 10 AM EDT this morning for GAZ040- 063>065-077.