textproduct: Columbia

WHAT HAS CHANGED

The Winter Storm Watch as been upgraded to an Ice Storm Warning. Winter Weather Advisory issued for the southern Midlands and Burke County in GA.

KEY MESSAGES

- 1) Freezing rain is expected to cause hazardous travel and power outages with greatest impacts north of I-20.

- 2) Behind this weekends winter system, very cold air funnels into the region with values near Cold Weather Advisory criteria possible.

- 3) Isolated showers, not associated with the incoming winter system are possible into the evening.

DISCUSSION

KEY MESSAGE 1: Freezing rain is expected to cause hazardous travel and power outages with greatest impacts north of I-20.

Overview: Freezing rain is expected across the forecast area late Saturday into Sunday. Significant ice accumulations of one quarter to a half of an inch expected along and north of I-20. These areas, including the larger Augusta and Columbia metro areas, are under an Ice Storm Warning. Some warming is expected through the day on Sunday which may limit the overall accumulations in the southern FA. Therefore an Winter Weather Advisory has been issued for the southern tier of counties in the County Warning Area.

Potential Impacts: An ice storm will track across the Southeast late Saturday into Sunday. Significant ice accumulations are expected to cause hazardous travel, power outages and downed tree limbs, with the greatest threat along the I-20 corridor and north. Further south, ice accumulations may be lower but may still cause isolated power outages and difficult travel. As temperatures rise from south to north on Sunday, travel conditions may improve in areas south of I-20, however power outages could still remain.

Forecast Challenges: Light rain or sleet may fall on Saturday afternoon ahead of the system but as strong, warm advection develops above the sub-freezing surface layer we will quickly see a transition to all freezing rain Saturday evening and overnight. Some models try to hold on to sleet p-types longer into the evening however, given the strength of the warm nose, sleet after 06Z seems unlikely. This may lead to slightly higher freezing rain amounts to the north than shown in some models. Another item of note is that weak elevated instability may develop across the southern FA, leading to a brief period of thunderstorm chances from 00z to 06z Monday.

Perhaps the biggest forecast challenge is the extent of the warming expected on Sunday. There is a very large spread in model guidance for temperatures on Sunday afternoon in the southern half of the forecast area. The IQR in the NBM temperature probabilities range from the mid 30s to mid 50s. Typically in Cold Air Damming events, models are too aggressive to erode the cold air. However given the impressive temperatures in the warm nose we should expect some warming as warm rain continues to fall into the cold low levels. The concern is that if the more aggressive models verify then any ice accumulations from Saturday night or Sunday morning would quickly melt. However the effect of downed tree limbs or power outages could already have been realized.

KEY MESSAGE 2: Behind this weekend's winter system, very cold air funnels into the region with values near Cold Weather Advisory criteria possible.

Strong troughing combined with strong surface high pressure are expected to persist across the region much of the upcoming week behind this weekend's winter system. The combination of these two features brings cold temperatures to the area for much of the week, especially Monday night and into Tuesday. Temperatures are expected to be around 10-20 degrees below normal into the mid week period where multiple nights with low temperatures falling into the teens or 20s is possible. Right now, the chilliest night is expected to be Monday night and into Tuesday where LREF probabilities for temperatures less than 15F remain generally between 20-40%, with highest probabilities are north of I-20. Due to this, the need for a Cold Weather Advisory will continue to be monitored, especially once this system has passed. Near Cold Weather Advisory criteria lows/wind chills cannot be ruled out other nights next week as the area hangs onto to this arctic airmass through the end of the current forecast period.

KEY MESSAGE 3: Isolated showers, not associated with the incoming winter system, are possible into the evening.

Persistent southwesterly flow with a weak shortwave moving through could bring a few more showers later this afternoon and evening (this rainfall is not associated with this weekends system). These isolated showers look to mainly affect the eastern Midlands.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR conditions to start the TAF period with MVFR conditions possible at the Augusta terminals.

Generally low end vfr ceilings being reported across the area, with some MVFR ceilings near AGS/DNL. Periodic MVFR ceilings are anticipated at those terminals for the next several hours before more predominant MVFR ceilings arrive. Confidence has decreased for MVFR ceilings for the remaining terminals, so have taken those ceilings out for now, but can't rule it out. Ceilings are expected to raise late in the TAF period. Shower chances have also decrease, but OGB could see some activity between 00z and 06z. Northeast winds between 5-8 kts this afternoon and evening, before increasing after about 06z. Winds pick up more after 12z, gusting to 15-20 kts at times.

EXTENDED AVIATION OUTLOOK...The next storm system is likely to bring restrictions Saturday evening and Sunday as sleet and freezing rain are likely to impact terminals.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Ice Storm Warning from 1 PM Saturday to 1 PM EST Monday for SCZ016-018-020>022-025>031-037-115-116. Winter Weather Advisory from 1 PM Saturday to 1 PM EST Monday for SCZ035-038-041-135>137. GA...Ice Storm Warning from 1 PM Saturday to 1 PM EST Monday for GAZ040-063>065. Winter Weather Advisory from 1 PM Saturday to 1 PM EST Monday for GAZ077.