textproduct: Columbia

WHAT HAS CHANGED

A Winter Storm Watch has been expanded to areas along the I-20 corridor including the Columbia SC and Augusta GA metro areas. After the system passes, cold air moves into the region to start the workweek.

KEY MESSAGES

- 1) The chance for an impactful winter storm continues, focusing along and north of I-20 late Saturday into Sunday.

- 2) After the weekend winter system, very cold air settles into the region.

- 3) Ahead of the weekend system, mild temps expected with some rain chances into Friday.

DISCUSSION

KEY MESSAGE 1: The chance for an impactful winter storm continues, focusing along and north of I-20 late Saturday into Sunday.

Overview: The greatest concern continues to be freezing rain and sleet beginning late Saturday into Sunday. There has been a model trend in cooler surface temperatures to the south resulting in a greater risk of winter weather for areas along the I-20 corridor. As we move north of I-20, confidence increases that impactful freezing rain and sleet accumulations will occur.

Potential Impacts: The potential remains across the northern Midlands and Pee Dee for an impactful ice storm. Primarily late Saturday and into Sunday, notable impacts remain possible in these locations, with potential for over 0.25" of freezing rain causing very difficult travel, power outages and downed trees. Sleet amounts may also be significant with amounts of around 1 inch possible contributing to hazardous travel. Ice amounts for areas along the I-20 corridor, including the Columbia and Augusta metro areas, are currently expected to range between 0.1 to 0.25 inches. Although there is less certainty in these amounts, freezing rain can quickly cause driving and travel impacts. With the models trending colder this increases confidence in at least reaching winter weather advisory criteria.

Forecast Challenges: Models continue to hold on to dry weather through much of the day on Saturday. This shifts our timeframe for winter weather later than previously expected. Although some light wintry precip may occur earlier, the main threat now appears to begin Saturday afternoon near the NC/SC border and Saturday evening or overnight further south. As strong warm advection develops above the cold surface air, we will tend to stray from a sleet p-type to freezing rain with 850 mb temperatures rising to near 10C by Sunday morning. The sub- freezing cold air will likely hold in the northern half of the FA but WAA and warming from latent heat and mixing will eventually lead to rising surface temps. Temperature are expected to rise to above freezing for the southern FA on Sunday resulting in a change over rain from south to north. A tremendous temp gradient Sunday is consistent in all guidance now, with even some CAPE developing south of the warm.

Summary: Areas along and north of I-20 should be prepared for an impactful winter storm, with freezing rain likely late Saturday and into Sunday. The watch may need to be expanded further south if models continue to trend cooler.

KEY MESSAGE 2: After the weekend winter system, very cold air settles into the region.

Strong high pressure builds into the Southeast under large scale troughiness, leading to very cold air to begin the work week ahead. Monday and especially Monday night are expected to be the coldest of the first half of the week, which could produce a couple of different hazards. One hazard to be aware of is the potential refreezing of any residual water on the roads and surfaces, which would make for tricky travel in spots. The other hazard is simply the cold as forecast lows Monday night are hovering around Cold Weather Advisory criteria.

KEY MESSAGE 3: Ahead of the weekend system, mild temps expected with some rain chances into Friday.

Southwesterly flow over the region into Friday keeps the area relatively mild ahead of the weekend system. A weak shortwave is forecast to move over the region, which is expected to bring periodic isolated to scattered showers this afternoon into midday Friday. Most of the activity is expected in the western Midlands and upper CSRA, gradually moving to the I-20 corridor overnight into Friday.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

VFR conditions expected overnight with MVFR conditions expected to develop by Friday afternoon.

Strong Canadian high pressure centered over the northern Plains will build into the area overnight. Aloft, westerly zonal flow persists and a blanket of mid level clouds continues to move over the region and should continue through the night. Moisture advection off the Gulf should support continued clouds through the period with some lowered of ceilings late tonight through the day Friday. Guidance is mixed on whether MVFR cigs will impact terminals but trends have been increasing confidence in MVFR cigs by mid morning in the AGS/DNL area and by 18z CAE/CUB with lower confidence at OGB. Included prevailing MVFR cigs AGS/DNL after 15z and at CAE/CUB after 18z. Some moisture convergence around 850mb has resulted in some very light showers this evening and this should persist through the period as well but low confidence in vsby impacts so generally keeping VCSH prevailing. Winds should be light and variable to calm overnight then pick up from the northeast around 5 to 6 knots after 15z Friday.

EXTENDED AVIATION OUTLOOK...The next storm system could bring more restrictions Friday night, but much higher confidence on Saturday and Sunday with sleet and freezing rain likely to impact terminals.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Winter Storm Watch from Saturday morning through Monday afternoon for SCZ016-018-020>022-025>031-037-115-116. GA...Winter Storm Watch from Saturday morning through Monday afternoon for GAZ040-063>065.