textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion has been updated for the 18z TAF issuance. Chances for rain ahead of the weekend system continue to increase somewhat. The potential for a impactful winter storm remains the largest concern with a wintry mix on Saturday and Sunday possibly leading to hazardous travel or power outages.

KEY MESSAGES

- 1) A potentially significant winter storm is possible this weekend.

- 2) Temps steadily moderate through the end of the week with some rain chances on Thursday night into Friday.

DISCUSSION

KEY MESSAGE 1: A potentially significant winter storm is possible this weekend.

Overview: The synoptic pattern has changed from days past with a cutoff low near the SW US now being favored to phase with the upper trough digging into the central US more quickly. Ultimately this has led to a more northern surface low track on average (and warmer surface temperatures) in ensemble guidance. That said surface temperatures are still anomalously cold for this region and precipitation type continues to be a concern.

Timing and Confidence: Strong surface high pressure will move into the eastern US late this week and this weekend allowing cold air damming (CAD) to develop on the lee side of the Appalachians. As strong moisture advection develops ahead of a surface low we expect precipitation to begin as early as Saturday morning with increasing chances through Saturday continuing into Sunday. The strength of the CAD and how long it holds on to sub freezing temperatures near the surface will ultimately decide the precipitation type for the Midlands and the CSRA. This situation is a familiar one in the Southeast and typically coincides with a fair amount of uncertainty, especially this far out in the forecast. However, the strength of the moisture advection and arctic air mass are quite unusual. Integrated water vapor transport from the NAEFS is at the 99th percentile of climatology and near surface temperatures are at the 99th of the cold end. This puts the event at the fringes of climatology which lends its own set of uncertainties.

Potential Impacts: The highest confidence in impacts from wintry precip will be near the NC/SC border, where even if there is a continued warming trend, there will be at least a portion of the area with subfreezing temperatures over the weekend. The two most likely dominant precip types are sleet and freezing rain, although there may be intermittent periods of snow or rain. As we go further south, chances become increasingly likely that the boundary of the cold air will give way to warm advection leading to rain. It is likely that total precipitation amounts, including rainfall, will be moderate to high given the amount of moisture transport. In areas where CAD hangs on we could see significant freezing rain or sleet accumulations resulting in potentially hazardous travel and power outages.

KEY MESSAGE 2: Temps steadily moderate through the end of the week with some rain chances on Thursday night into Friday.

High pressure moves off the Atlantic coast through the end of the week as upper level flow becomes more southwesterly. This is expected to allow temperatures to warm through the end of the week. Some shortwave energy ahead of the main weekend system is forecast to move over the area, bringing chances for some rain showers Thursday night into Friday. Any precipitation that does fall during this timeframe very likely will fall as rain as temps are forecast to be way too warm to be frozen.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR conditions expected through the TAF period.

High clouds continue to stream over the region this afternoon. Expect these high clouds to continue into this evening. Mid- level clouds are expected to move over the area tonight into Thursday morning. With the expected clouds, fog is not expected overnight despite some increasing moisture. Winds are expected to remain light through the TAF period, generally 5-8 kts or less. While the direction is mainly anticipated to be from the south this afternoon, some variability in the direction is likely due to being under high pressure. Winds are expected to shift more westerly late in the TAF period, but remain light.

EXTENDED AVIATION OUTLOOK...VFR conditions likely continue into Thursday evening. The next storm system will likely bring restrictions as early as Friday, but especially Saturday and Sunday.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Winter Storm Watch from Saturday morning through Monday afternoon for SCZ016-115-116. GA...None.