textproduct: Columbia

WHAT HAS CHANGED

Key Message 1 and Aviation updated

KEY MESSAGES

- 1) Rain increases in coverage and intensity ahead of a cold front, continuing into Wednesday night.

- 2) Temperatures near to slightly below average through the weekend.

DISCUSSION

KEY MESSAGE #1: Rain increases in coverage and intensity ahead of a cold front, continuing into Wednesday night.

A warm front remains draped near the South Carolina-North Carolina border this morning, placing much of the forecast area in the "warm" sector of the approaching surface cyclone now centered in eastern Tennessee. Rain increases in coverage and intensity this morning and periods of moderate to heavy rain are possible, especially across portions of the eastern Midlands and Pee Dee. Amounts should generally range between a half an inch and an inch but could be lighter than that across our northern and western counties where there may be a sharp cutoff to the rain.

Precipitation should taper off Wednesday evening as the cold front moves through and drier air moves in from the north. Hi- res model guidance continues to show the potential for low-level moisture to become trapped under the increasingly dry mid to upper levels of the atmosphere Wednesday night. With surface temperatures cooling, there is a low probability for a period of freezing drizzle across portions of Chesterfield and Lancaster counties. Model soundings also depict a warm nose aloft, reducing the probability of a transition over to snow in the northern Midlands. While any frozen precipitation should be brief, there could be some minor icing on bridges and overpasses and/or black ice development in our northern counties as temperatures are forecast to fall at or below freezing there by daybreak Thursday. Confidence is not high enough to warrant any products with this package, but trends will continue to be monitored as the storm unfolds.

KEY MESSAGE #2: Temperatures near to slightly below average through the weekend.

No changes made to the previous forecast. Overall expect temperatures to be near average through much of the period, quite the change from the significant cold spell for the Midlands and CSRA over the last week or so. The exception will be behind the front Thursday which likely be colder with an upper trough over the forecast area, with NAEFS mean indicating 500mb heights will be below the climatological 10th percentile. Upper ridging late this week into the weekend will begin to build over the central US with blended guidance favoring a quick return to near average temperatures.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

VFR conditions expected to deteriorate to IFR by late morning and persist or lower to LIFR through the end of the forecast period.

Moisture continues to increase across the region ahead of an approaching cold front and upper trough with satellite imagery showing widespread clouds over the region. Cigs have gradually lowered through the predawn hours as the lower levels saturate due to moisture advection and some light precipitation. MVFR cigs expected to expand over the terminals during the 12z-15z time frame before widespread IFR cigs expected to move in after 15z. Rain expected to generally be light and intermittent through mid morning and then become more steady and widespread this afternoon into early evening as better forcing arrives and this should lead to MVFR or possibly IFR vsbys. Generally southerly winds expected around 5 to 10 knots before relaxing a bit after 00z. Winds will then shift to the northwest and north after midnight when the front pushes through the region but IFR/LIFR cigs expected to persist through the end of the period.

EXTENDED AVIATION OUTLOOK...Restrictions likely continue the first half of Thursday and drier air moves in behind the front. Returning dry air should bring low chances for restrictions Thursday night into this weekend.

CAE WATCHES/WARNINGS/ADVISORIES

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