textproduct: Columbia

WHAT HAS CHANGED

Extreme Cold Warning is now in effect for Saturday evening into Sunday morning as gusty winds and very cold temperatures will likely lead to wind chills around 0 degrees. Snow forecast has changed little with this package with increasing confidence in a major winter storm for portions of the area as we enter range for higher resolution model guidance.

KEY MESSAGES

- 1) A major and potentially historic winter storm will impact the area beginning early Saturday morning.

- 2) Extremely cold air moves in with this weekends system, likely continuing into the early week. An Extreme Cold Warning is now in effect from 7PM Saturday through 10AM Sunday.

DISCUSSION

KEY MESSAGE #1: A major and potentially historic winter storm will impact the area beginning early Saturday morning.

Overall synoptic pattern remains generally the same with the digging 500mb trough already visible on water vapor satellite imagery this afternoon and an evident highly amplified flow pattern. There is remarkable consistency among global models in the overall progression of this upper low over the next 24-36 hours, not completely unexpected as we get into the near term. This pattern matches climatology for some of the more significant snow storms in central South Carolina and east central Georgia. As a result, we can be reasonably confident in the overall snow footprint over the area as moisture is pulled in from the Atlantic and strong lift contributes to developing precipitation. This trough ushers in a much colder air mass both at the surface and aloft so while there may be a bit of mixed precipitation at the onset before the very cold air moves in aloft, it will quickly transition to all snow. As a result, very confident that Winter Storm Warning criteria of 2 inches will be met across the entire forecast area and high confidence in greater than 4 inches across the northern portion of the area. The question is some of the upper bounds due to mesoscale features that models with typically struggle to specifically resolve. High resolution guidance gives us a good look at the potential for heavier banding with frontogenesis in the 850 to 700 mb level with HREF mean indicating heaviest snow associated with this as this increased lift will line up with the snow growth region. The result will be the potential for high snow amounts, especially in the northern half of the area generally Saturday afternoon into the evening. This, along with a very cold column leading to high snow to liquid ratios, will lead to a fluffy snow that will accumulate more efficiently with chances for greater than 8 inches is around 30 percent for areas north of Columbia. Bottom line is this has the potential to be the most significant snowfall event (especially for the Midlands) in over ten years.

Impacts: Snow will likely start early Saturday morning with guidance favoring heaviest snow rates developing during the afternoon. Travel conditions will quickly deteriorate through the day Saturday and winds will likely increase into Saturday evening, especially as low pressure off the coast deepens and strong winds aloft move in on the back side of an 850mb low. This may lead to some blowing snow as well, further lowering visibilities and creating treacherous travel, especially in northern areas.

KEY MESSAGE #2: Extremely cold air moves in with this weekends system, likely continuing into the early week. An Extreme Cold Warning is now in effect from 7PM Saturday through 10AM Sunday.

Another night with temperatures dipping into the 20s is expected tonight as the incoming winter system begins to move in, but values are expected to remain above Cold Weather Advisory criteria. Temperatures on Saturday likely barely reach above freezing across much of the area as the winter storm moves through before very cold air, moves in overnight and into Sunday morning. Wind gusts between 25-35 mph are expected Saturday evening through Sunday morning with temperatures that bottom out between 12-16F, thanks to fresh snowpack and the cold airmass behind this system. Wind chills near 0F with spots dipping into the negative single digits are likely overnight Saturday into Sunday morning and due to this, the Extreme Cold Watch has been upgraded to an Extreme Cold Warning with this forecast package. It is worth mentioning that in these wind chills, frostbite can occur in the matter of 30-40 minutes to exposed skin. Temperatures during the day Sunday may only reach 32-35F, leading to only minor melting of snow, thus keeping a snowpack Sunday night with high pressure ridging into the area should allow temperatures again to bottom out in the lower 10's to mid teens. NBM probabilities for temperatures less than 15F have reached 60-80%, but luckily little wind is expected overnight, keeping wind chills near the air temperature. Air temperatures will likely be near or exceed Cold Weather Advisory criteria into Monday morning, thus the need for one will continue to be monitored in the coming forecast cycles.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR conditions continue before a winter system begins to move in tonight and through the end of the TAF period with ceiling restrictions possible tonight before snow moves in Saturday morning.

High clouds continue to stream into the region with some mid clouds also nearing parts of the CSRA. Winds are currently fairly variable around 3-5 kts, but should become a bit more easterly to southeasterly this afternoon and into this evening. This evening and tonight, MVFR ceilings are expected to develop as the next winter system begins to move in with winds shifting out of the northeast at 5-8 kts. Some model guidance indicates isolated to scattered snow showers could be seen after 03-07z and thus a PROB30 has been added to account for this, but the main snow is expected to move into all TAF sites after 12-14z generally. With this system, visibility restrictions will be possible as well as periods of IFR ceilings in any heavier snow. These conditions are expected to last through the end of the TAF period at this time with winds remaining out of the northeast, but picking up to 7-11 kts.

EXTENDED AVIATION OUTLOOK...Impactful aviation weather is expected to continue much of the day Saturday as this wintry system moves through the area. Restrictions may improve come Sunday as the system departs with chances for restrictions lowering early in the week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Winter Storm Warning from 10 PM this evening to 10 AM EST Sunday for SCZ016-018-020>022-025>031-035-037-038-041-115- 116-135>137. Extreme Cold Warning from 7 PM Saturday to 10 AM EST Sunday for SCZ016-018-020>022-025>031-035-037-038-041-115-116- 135>137. GA...Winter Storm Warning from 10 PM this evening to 10 AM EST Sunday for GAZ040-063>065-077. Extreme Cold Warning from 7 PM Saturday to 10 AM EST Sunday for GAZ040-063>065-077.