textproduct: Columbia

WHAT HAS CHANGED

No major changes in the potential for an impactful winter event this weekend. Updates to aviation.

KEY MESSAGES

- 1) Well below average temps continue through mid-week with morning lows in the upper teens or low 20's.

- 2) The trend continues towards a potentially significant winter storm this weekend.

DISCUSSION

Key Message 1: Well below average temps continue through mid- week with morning lows in the upper teens or low 20's.

A very cold airmass is forecast to overspread the area during the day today in conjunction with an anomalously strong surface high just to our west. As a result, high temps Tuesday are only expected to be in the mid to upper 40s despite plenty of sunshine. Overnight lows look to be very cold as calm winds, clear skies, and very dry air foster ideal radiational cooling conditions across the area. Look for lows in the 18F-24F range tonight and Wednesday morning. This is range when we typically start seeing impacts with freezing pipes and such.

Key Message 2: The trend continues towards a potentially significant winter storm this weekend.

Overview: The forecast thinking has not changed much for the weekend system with potential for an impactful winter storm continuing. The overall synoptic pattern is quite consistent across all guidance with a deep digging trough in the NE CONUS, strong confluence and an associated strong surface high in the central CONUS, and an ejecting cutoff shortwave in the SW CONUS. This patterns sets up a broad overrunning scenario as the arctic high digs southeastward presenting an all-hazards winter storm potential for much of the southern and eastern US, including GA and SC as strong cold air damming sets up.

Trends and Possible Impacts: Guidance remains in above-typical agreement over the potential impacts from this system, with historic analogs and climatology concurring; this setup distinctly favors mixed precip with snow-sleet-freezing rain potential. While in good agreement for a 96+ hour forecast, there is a spectrum of impact potential in the guidance. The GEFS and ECE favor a stronger CAD scenario, with notably colder surface temps and much longer duration. The Canadian Ens along with much of the AI guidance favors weaker CAD and warmer surface temps throughout the potential event; it should be noted that even these warmer solutions would still yield some impactful wintry precip in parts of the area. So currently, the spectrum of potential ranges from a "typical" low- moderate impact ice event for parts of our area to a much more widespread and highly impactful system.

Forecast Challenges: While there is good agreement in the overall setup, a few of the players in this game are notoriously tricky. The first being the extent and intensity of the surface high, which then directly impacts CAD over our area. The second being the SW CONUS ejecting shortwave and associated cyclogenesis which would impact precip location and therefore p-type. The GEFS and Canadian ensemble handle these features in opposite fashions and their associated p-type and surface differences result from that.

Summary: Guidance continues to be in above-typcal agreement over much of this forecast but subtle differences result in a range of impact potential. Confidence is already fairly high that some areas of SC and GA will see winter weather this weekend. Concerningly, unlike many southern winter events, the ceiling for this event is very high with significant impact potential.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

VFR conditions expected through the 24 hr TAF period.

Very dry conditions continue today with only FEW-SCT high cirrus through the period. A 15-20 knot low level jet may keep surface winds elevated around 5 to 7 knots for another hour or two, but then speeds should diminish to light and variable to near calm through dawn. Winds pick back up from the northwest at around 5 to 8 knots after 15z-16z as high pressure builds into the region.

EXTENDED AVIATION OUTLOOK...VFR conditions likely continue through at least the mid week, possibly into Thursday. The next storm system late this week into this weekend will likely bring a return of restrictions.

CAE WATCHES/WARNINGS/ADVISORIES

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