textproduct: Columbia

WHAT HAS CHANGED

Models continue to trend toward a potential winter system this weekend, but high uncertainty in specifics still exists.

KEY MESSAGES

- 1) Arctic airmass overspreads the region Tuesday and Tuesday night. Well below normal temperatures are expected, with lows Wednesday morning in the upper teens and lower 20s.

- 2) Model guidance continues to trend towards a potentially significant winter storm this weekend. Uncertainty is high especially with regards to precipitation types, amounts, and duration. However, model consistency is increasing.

DISCUSSION

Key Message 1: Arctic airmass overspreads the region Tuesday and Tuesday night. Well below normal temperatures are expected, with lows Wednesday morning in the upper teens and lower 20s.

Broad low pressure system across the Great Lakes and southeastern Canada is continuing to move northeastward out of the CONUS. This is being driven by a deep trough axis that is shifting eastward, and these combination of these things is forecast to push a secondary cold front through the area tonight and early Tuesday. A cold airmass is forecast to overspread the area during the day on Tuesday in conjunction with an anomalously strong surface high. Highs tomorrow 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 on Tuesday night and Wednesday morning. Be sure to drip your faucets to protect from pipes freezing!

Key Message 2: Model guidance continues to trend towards a potentially significant winter storm this weekend. Uncertainty is high especially with regards to precipitation types, amounts, and duration. However, model consistency is increasing.

The key message for this weekend remains largely unchanged. Model guidance continues to point to a synoptic setup that favors potentially significant winter weather across our forecast area on Saturday and Sunday. Over the last 36 hours, model guidance has uniformly trended towards showing a robust, near climatological max Arctic surface high pressure pushing into the northern Plains and Great Lakes states by Friday of this week. This surface high may be on the order of 1048-1052 mb, with the surface high looking expansive across the OH Valley and Mid-Atlantic region by this time. Physics-based models showed the strength of this first, and now AI guidance is beginning to trend in this direction as well over the last couple of runs. This surface high is likely to be fostered initially by a strong branch of the northern Jet stream & an expansive area of strong subsidence extending from the central plains into the Mid-Atlantic. As we head into the weekend, guidance continues to indicate that a strong cold-air damming event will setup beneath a coupling of the northern & southern streams of the jet stream. Pacific moisture will stream northeastward within the favorable right entrance region of the jet streak, potentially setting us up for a long duration overrunning event atop the very cold surface wedge. There are a couple of things that lend to increasing confidence in a winter event this weekend: the strength of the surface high & the synoptic scale pattern, and guidance across the board is in relatively good agreement on these two features despite this event still being several days away.

There are a lot of failure modes with any sort of winter weather event, especially in the southern and southeastern CONUS. The surface high could be slightly weaker or stronger, the jet streak could amplify faster than is currently forecast, etc. However, from a pattern recognition standpoint, this is a robust signal that guidance is showing and it must be treated as such. WSSI-P values for Minor and Moderate impacts from a winter storm have increased over the last 24 hours, increasing confidence as well. We will need to keep a close eye on guidance trends over the next couple of days as an impactful winter storm could be on tap this weekend.

AVIATION /18Z MONDAY THROUGH SATURDAY/

VFR conditions are expected to continue through the TAF period.

Winds this afternoon are picking up out of the west at 5-10 kts under clear skies. The remainder of the afternoon could see a couple gusts up to around 15 kts before winds diminish overnight with continuing mostly clear skies and minimal fog concerns. Heading into Tuesday, high pressure fully builds into the region with light winds turning out of the northwest. A couple passing high clouds could near at the end of the current TAF period but VFR conditions likely continue through the whole period.

EXTENDED AVIATION OUTLOOK...VFR conditions likely continue through at least the mid week, possibly into Thursday. The next storm system nears late in week and over the weekend, bringing back potential restrictions.

CAE WATCHES/WARNINGS/ADVISORIES

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