Wisconsin Weather

Chilly Northwest Flow to Begin December

Dec 6 2017 9:45 AM CST| 0 Comments | Wisconsin | Weather Forecasting

The next 14 days will feature cold, dry northwest flow across the great lakes region. Storm systems will move quickly and favor light snow or mixed precipitation.

Pretty strong anomalies

Below Average Temperatures

During both the 6-10 day and 8-14 day models are showing strong signals for blocking upper level high across the Pacific Northwest. The cold dome positioned over Hudson Bay. This is a clear indication of La nina. This pattern is very likely to produce below average temperatures in Wisconsin. Therefore, expect the first half or two-thirds of December to be cold. Precipitation will come in the form of dry, continental clipper systems from Canada.

northwest flow reverses our moisture transport and it smashes gulf moisture in the Caribbean. This is partially why a tendency towards NW flow also happens to be tendency towards dry conditions. With NW flow the main storm track is up and over the blocking ridge. Storm systems are quicker and smaller. I have seen big snow storms with westerly flow, which comes as we change away from NW flow or as the cold dome pushes west. northwest flow can be snowy with frequent light snow events too but we'll see about this one.

Big snow lovers will want to see the ridge weakened or undercut and try to get something to enter in southern California and exit as a Colorado low. Theoretically this would setup return flow and pull everything together for a big storm at some point. The snow cover being built across eastern Canada will make for better cold conveyors in late December and early 2018. It's the consistency now that will benefit snow storm opportunities later. My favorite year for snow was early 2011 when the cold dome was centered across central Canada, so anything that resembles that would great!

PNA Suggests Active End to December

Our weather patterns go through approx. 50 day cycles that reoccur throughout the winter-year. The PNA is arguably the best indicator of storminess across the great lakes region. The pattern we've been in lately is one we've seen before. Quiet stretches coincide with gradually increasing PNA. The stormy and warmer parts of our winter-year pattern should coincide with the tumultuous up & down we had in October. Looks to me that sometime in late December we should enter a October-like pattern. There is a wives tail that suggests a wet October translates to a snowy winter, but not sure how much I believe that yet.

Here are the temperature, PNA, and precipitation superimposed showing it's that PNA chaotic period between late September and November 1 that seems to be the exciting piece. Interesting how the warm spikes that delayed the onset of fall cooling. Once we hit early November the PNA settled into the long gradual increase again and temperatures trends flip-flopped. I bet a warm pattern like this in late December or early January would be interesting, as it would in late February. Frequent precipitation events also occurred with this pattern. No telling what surprises mother nature will throw our way over the next few months.

Temp = Red, PNA = Black, Precip = Green

lake effect

Depending on how cold it can get, where the cold is centered, and how long it lasts; I believe the potential exists for good lake effect snow across upper Michigan and eastward side of the great lakes in December.

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