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December 2020 Outlook…

The way modeling has been “forced” to correct colder over the past week to 10 days to open December has been staggering. Without question, the initial driver of this change has to do with the strongly positive PNA. Note how this is forecast to remain strongly positive over the upcoming week before trending neutral by mid-month.

This favors a trough over our part of the country and into the Deep South through the better part of the upcoming couple of weeks. We’ve been posting about how the strongly positive PNA could lead to other teleconnections aligning in a manner that could lead to the possibility of more “meaningful” or longer lasting cold beyond mid-month. The trends of the AO, EPO, and NAO have been towards this colder direction over the past few days and it’ll be interesting to see if these trends continue.

Perhaps more importantly has to do with the MJO. While the majority of guidance keeps the MJO in the “null” phase (meaning we’ll lean heavier into the teleconnections above) into and through mid-month, it’ll be worth keeping a close eye on this. The one outlier is the Canadian taking a highly amplified MJO towards the cold phases (after blasting through the warm phases quickly) by mid-month. Again, we’re not throwing our eggs into the MJO basket right now and prefer to lean heavier on the tele. trends.

The latest CFSv2 has been trending colder for December with each model update- especially over the Southeast and TN Valley:

The latest European Weeklies are somewhat similar, but colder across the West.

The JMA Weeklies want to put the ‘mean’ trough (and associated cooler pattern) over the Southeast for December:

Consensus of longer range, monthly products places an area of widespread drier than normal weather across a good chunk of the country:

While there are obvious reasons for a lower confidence forecast around mid-month, thinking here is that we’ll maintain a seasonal to slightly colder than normal regime for our immediate region into the Southeast this month. This is quite different than the recent December torches we’ve been dealt and may seem much cooler than normal as a result. I believe the strongly positive PNA will “force” those other pattern drivers towards a manner that will drive the cooler pattern for the better part of the month before potentially trending milder around Christmas and New Years.

No Comments Client, Long Range Discussion, Monthly Outlook

Client Brief: “System” Snow Transitions To Lake-Effect…

Type: Impactful Wintry Weather

What: Accumulating Snow/ Wind

When: Today through Tuesday Morning

Temperatures: Upper 20s to lower 30s

Wind: NW 15-20 MPH; Gusting to 35 MPH

Blowing/ Drifting: Moderate, especially with late afternoon-evening lake-effect snow band.

Pavement Impacts: Salting required; plowing required within lake-effect snow band.

Summary: We’ll undergo a transition from “system” snow (mostly light) this morning into early afternoon to a more localized, but robust lake-effect snow event late afternoon and this evening. At least for central portions of the state, this is the better opportunity for accumulating snow. As temperatures continue to fall and the wind direction becomes better aligned, a band of lake effect snow is expected to develop initially across northwestern Indiana late morning. It’s this band of snow that should continue to get better organized and heavier as we move into late afternoon and the evening hours and be driven well inland. Eventually, this lake snow band should reach areas as far south as Indianapolis (and surrounding ‘burbs) by late afternoon, potentially including the 5 o’clock rush for parts of the city. Snowfall intensity within this band is expected to be heavy enough to whiten roadways and create slick spots. For most this will only last an hour or two before the band pivots east and impacts east-central Indiana for a longer period of time into the overnight and early Tuesday morning. If you find yourself under this lake effect snow band, a quick 1″ to 2″ can be expected

Confidence: High

Next Update: Tonight (video package)

No Comments ClientBrief, Lake Effect Snow, snow, Windy

Client Brief: Sunday Night – Monday System…

Type: Impactful Wintry Weather

What: Accumulating Snow/ Wind

When: Sunday night and Monday

Temperatures: Low-Mid 30s

Wind: N 15-20 MPH; Gusting to 35 MPH

Blowing Drifting: Minimal to Moderate in lake enhanced zone, as well as east-central IN

Pavement Impacts: Salting required; plowing likely required in lake enhanced zone, as well as east-central IN

Summary: While not nearly as robust as what guidance earlier this week printed out, the season’s first widespread wintry event looms Sunday night into Monday. This is a byproduct of phasing between the southern and northern jet stream (initially set off by the evolving strongly positive PNA), but there are important differences in the speed of the initial vort. max being a bit more progressive that will keep this from bombing out like earlier guidance showed. Consequently, this will result in a much further east system (may still not have seen that eastward trend finish). While our forecast specifically focuses on Indiana, if you have travel plans east of here into Ohio early next week, please pay special attention to the local National Weather Service products as impacts will be greater from heavy snow and strong winds.

Locally, we anticipate precipitation overspreading central Indiana (from southwest to northeast) around, or just after, midnight Sunday night. Initially, this should be in the form of a cold rain before precipitation transitions to wet snow prior to sunrise. Moderate snow should be falling across east-central Indiana from the mid morning hours Monday into early afternoon. Additionally, by this point, a more organized band of lake-effect snow should be firing up off Lake Michigan. This is a bit of a wild card as a combination of ingredients favor a pretty robust lake snow band making it further south than typical. As the wind direction veers towards more of a northwesterly flow late Monday afternoon and evening, it’s possible this lake effect snow band pivots into the Indy metro and surrounding ‘burbs. We’ll keep a close eye on this as time draws closer. Within this snow band, heavier accumulations are possible. Snow showers will continue into Tuesday morning before diminishing.

Confidence: Medium

Next Update: Tonight (video package, including longer range update).

No Comments ClientBrief, snow, Windy