Wisconsin Weather

La Nina Pattern Evolving

Dec 14 2017 10:00 AM CST| 0 Comments | Wisconsin | Weather Forecasting

The long range forecast favors snow and storminess across the eastern half of the country, much like a classic La Nina weather pattern. We are early in development of this winter pattern and it will be a multiple week process that continues this weekend.


Missing a few 10" data points in northeast Wisconsin.
That was not your average Alberta clipper, yet we(I) fell into that mentally. I learned a few things yesterday; one that yes being conservative is GOOD, but being too conservative is not. Sort of like the stubborn guy riding out the volcanic eruption and impending 30 ft mudflow in his house lol. The last thing you want is to overhype and dilute your audiences response, but how much better is ignorance? There needs to be balance between human interpreter and forecast model. Inevitably it always comes down to the choices the forecaster makes. Models clearly showed the potential for 6-10" snows, despite the location changing by 70 miles in the last 12 hours. I'm actually not that upset and the impact was virtually nothing. I create my own forecasts and I expect them to be perfect, therefore I am responsible. Next time I know I will be better prepared.


Right now our pattern has blocking in the west which is helping to drive cold air masses into the great lakes. We are getting clippered alive on the western edge of the cold upper trough centered over eastern Canada. It hasn't been record-breaking cold like December 2012, this year has been slightly below average. For snow lovers like me this feels a good place to be.

Current 500mb wind direction and temperatures showing cold dome across northeast NOAM

The northwest flow weather pattern is colder, drier than average for the great lakes. The jet stream pushes gulf moisture south towards the equator. The stormiest place is off the northeast coast of north america as systems don't become phased and moist until they exit the country. The block encourages low development on the southern edges, but the lows that develop here often get crushed to the south. Aside from the frequent light snows which I like, it's actually a bit boring across Wisconsin.

Ridge Flattens, Westerlies Increase

Early next week our weather pattern will go through some changes. Nothing ground breaking or massively different, but enough to show some life and evolution to the 2017-18 winter and foreshadow were we might be heading.

Next week the blocking ridge will be beaten down somewhat. The cold dome shifts west slightly and it warms up a little since we are not getting crushed from the north. We're taking a break from the highly amplified northwest flow into somewhat zonal westerly flow. This is symptomatic of a changing pattern. This low amplitude pattern is not very good at producing big storms and most of what happens across the eastern half of the country is a little underdeveloped. This pattern would still favor frequent light snow or mix for the great lakes. FINALLY gulf moisture can begin sneaking into the southern US. Baby steps. This is really a small change in a parade of changes we will see during the winter.

Blocking Returns but....

This time the cold dome is larger and centered farther west. Once amplitude of the long wave pattern increases it will set the stage for big storms and cold blasts across Wisconsin and the Great lakes. This simulation is for Christmas weekend and things will probably change, but maybe it won't. 12Z 12/14 GFS is showing harsh cold late next week into Christmas weekend with a system that reminds me of the annual WI/IL border rider. We'll see if that sticks. It helps to have consistent cold early in the season so that we can build the cold dome across Canada and draw from it later. I mentioned Dec 2012 earlier because that year was so cold that we couldn't get storms systems to focus in on Wisconsin. Perhaps a balanced, or more seasonable temperature trend will be more favorable for big storms? I've seen big storms here and there in the long range forecast into January, but not enough confidence to pick out when or where. They will come.

Storm track across eastern US

This feels like the gradual progression/ life cycle of the typical La Nina winter. By the time we reach January, Feb, and Mar we will be in the heart of the season. Right now it's mostly about getting the pieces together to make the run. In case you need more convincing, here is a look at the 500 mb anomalies for the 8-14 day period straight from the folks at the CPC:

Cold anomalies at the 500mb level across central north america. This typically means storminess for the great lakes or northeast US.

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