textproduct: Columbia

WHAT HAS CHANGED

Update to aviation.

KEY MESSAGES

- 1) A long duration stretch of well-below normal temperatures will continue through early next week.

- 2) Guidance continues to show the potential for an impactful snow event this weekend across the forecast area.

DISCUSSION

Key Message #1: A long duration stretch of well-below normal temperatures will continue through early next week.

The synoptic pattern driving our cold weather the last several days will continue into the extended. Persistent, deep troughing across the eastern CONUS is anchored across the Hudson Bay area, with 500 hPa heights well below normal for this time of year. Teleconnections continue to show this persisting into at least early next week, with guidance uniformly showing strongly positive PNA values and strongly negative NAO values. This will favor strong, cold high pressure across the central US, extending eastward and maintaining our cold air that is currently in place. Looking at multi-day temperature means, AI and Physics based guidance shows 7 day temp anomalies in 10F-15F below normal. This will result in multiple days of highs in the 40s and lows in the mid to upper 20s. The 1-5/2-6/3-7 day ECE EFI for mean temps is really robust in this area, with values of -0.8 to -0.9! While we won't be near cold weather advisory criteria until this coming weekend (more on that in the next section), the persistent cold weather could present a compounding problem with poorly insulated pipes around here. Please be sure to drip faucets at night to avoid pipes bursting!

Key Message #2: Guidance continues to show the potential for an impactful snow event this weekend across the forecast area.

The overall message has not changed regrading this, albeit confidence is slowly increasing in the setup as we get closer to the event itself. Over the next 24h, a robust PV anomaly is forecast to rotate around the center of a 500 hPa low between the Hudson Bay and the Great Lakes states. This vorticity anomaly is forecast by guidance to then push southward into the upper Midwest and Great Lakes states by Friday as it is driven southward by increasing upper level ridging emerging out of western Canada. By this point, a broad area of vorticity is forecast to be at the base of the trough in Texas associated with the southern stream of the jet stream, with guidance in good agreement that the parent vort max will begin phasing with this vorticity plume and dig into the southeastern CONUS by this point. Broad, robust lift is then forecast to yield rapid cyclogenesis along the Carolina coastline, with a broad precipitation shield developing between the upper low and the surface low. Cold air across the region, in association with a gelid airmass pushing southward out of Canada, will favor all snow/rain as opposed to the rain/snow/sleet/freezing rain that we typically see.

Model guidance is clustered tighter than it was about 24 hours ago when we were first getting a handle on this and seeing some level of model consistency. Guidance trends (if you can find them) have generally favored a similar pattern that we have anecdotally observed over the last few weeks, which is to slightly amplify the overall pattern as the event approaches. In this case, that means a slightly stronger shortwave, slightly further west, with the upper low taking on a negative tilt somewhere over the TN Valley and Georgia. AIFS/GFSAI/Canadian guidance was the first to really point to this yesterday & has continued to do so, with the physics-based GFS/ECMWF moving in that direction over the last 24 hours as well. As such, the former grouping of models is favored currently because of consistency & the way they've verified recently. Additionally, guidance has had a slow but noticeable uptick in forecast QPF associated with this system.

While all of this is the case, the forecast still contains a good bit of uncertainty. These events are difficult to pin down & as described above, there are a lot of moving pieces to this forecast. As I always tell my friends & family when they ask about snow around here, "it takes a lot of luck and good fortune for us to get decent snow in the deep south because so much needs to align just right". Well, the winds of fortune may be blowing in our favor, at least for snow-lovers, this weekend. Confidence is growing that an impactful, if not significant, snow event could be on tap across the Carolinas on Saturday and Saturday night. It should also be mentioned: the airmass Saturday and Sunday looks downright frigid. Temperatures are unlikely to get out of the low 30s for highs either day, with lows in the teens. A Cold Weather Advisory is likely in this period as well. So please stay tuned to the latest forecast as things are likely to continue changing and adjusting over the next couple of days!

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

VFR conditions expected through the TAF period.

High pressure centered to our west is expected to remain in place through the TAF period, leading to VFR conditions. Satellite imagery shows a cirrus deck is beginning to move into the area. These are the only clouds expected over the next 24 hours. Winds at the surface as well as a low-level jet continue to diminish overnight. As a result, LLWS is not strong enough to be included. Winds pick up out of the west again around 18z, generally in the 8-12 kt range. A few gusts of 15 kts or greater are also possible and may need to be added in the next TAF update.

EXTENDED AVIATION OUTLOOK... VFR conditions likely through early Friday, then impactful aviation weather becomes possible as a low pressure system likely moves somewhere near the region bringing the possibility of wintry precipitation.

CAE WATCHES/WARNINGS/ADVISORIES

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