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  • Tim McGill

Light Weekend Snow Then Arctic Air Around The Corner?

On & Off Snow Through Sunday

This is day two of the second half of winter. A trace of snow fell officially on day one at O'Hare Thursday. It was the 11th day this winter with just a trace of snow. We have had only four days so far with more than a trace of snow reported. The total snowfall so far this season (not including today's snowfall) is 4.7". That is 8.5" below the average to date of 13.2".

We should put a minor dent in that deficit today and tomorrow. More on the snowfall below.

Today will be the 22nd straight day with above average temperatures. Highs should top out in the middle to upper 30s.

December is now running nearly 8° above average. We may actually slide just below average by Tuesday with highs in the 20s. That would be the first day in over three weeks with temperatures below average. Temperatures bounce back for the middle of next week then fall on Friday. That is when a shot of Arctic air arrives. It could be followed by another shot the following week. More on that below.

Light Snow & Flurries For Now

Anywhere from a dusting to over an inch of snow fell last night into early today. The GFS model cloud cover and precipitation meteogram shows more light snowfall or flurries possible through early Monday morning. We get to dry out next week and then another round of light snow is possible for the end of next weekend.

The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. Most of the snow forecast in that first bump (.3" to 1.3") has already fallen for today. Snow early Saturday will taper to flurries and then some steady light snow on Sunday could add more accumulation. The models are suggesting up to another half inch to possibly an inch of additional accumulation is possible tomorrow.

Grand Totals For The Weekend

The GFS model forecast spits out a grand total of about 1" to nearly 3" for most of us through Monday morning. Keep in mind we have already seen about a half inch to an inch of that total. The higher end of that range is well southwest of the city and in north central Indiana where some lake effect will add to their totals.

The European model is calling for similar snowfall overall during the same period. It spits out about 1" to nearly just over 2" in total.

Colder Air Coming?

The temperature anomaly forecast for next Friday morning shows northern Illinois anywhere between 5° to 10° below average. That would mean lows that morning possibly dipping down into the single digits.

As I mentioned yesterday, the GFS model brings in even colder air in about ten days from now. Look at the forecast temperatures for the morning of January 26th. The updated forecast isn't quite as cold but still shows Arctic air arriving. It now has northern Illinois plunging to anywhere between single digits to -3°. Those numbers will continue to change but this model has consistently been calling for a more colder pattern by then.

Colder Air Coming Before February

The longer range temperature probability forecasts once again have us trending from about average overall to below average overall. The 6-10 day temperature probability forecast has the Chicago area outlooked for about average temperatures overall from January 21st through January 25th. The longer range 8-14 day forecast all of northern Illinois outlooked for below average temperatures overall for the period from January 23rd through January 29th. These longer range forecasts lately have been consistent in increasing our chances for colder than average air arriving by the end of January.

One place for us to look for a forecast of temperatures here is actually way up north in Alaska. Many times a warm up there means a turn to a colder pattern here. The jet stream pattern that supports above average temperatures for our 49th state usually means a mild southerly wind flow towards them with the jet stream buckling further downstream and turning south, carrying colder air towards the Midwest.

Alaska is favored for above average temperatures overall in both the 6-10 day and the 8-14 day forecasts. An example of the type of jet stream configuration this can produce is shown below.

Active Pattern For End Of January

I commented yesterday about the amount of green on the long range precipitation probability forecasts. This seems to be suggesting a more active pattern for the end of this month. The 6-10 day forecast from January 21st through January 25th has us outlooked for above average precipitation overall. The 8-14 day forecast keep us outlooked for above average precipitation from January 23rd through the 29th. If this verifies and the colder air does indeed come, a lot of this moisture would be in the form of snow. Stay tuned.

Here is my 7 day forecast:

Today: Light snow early then cloudy with on & off flurries (up to 1" accum.) High: 37

Sunday: Cloudy, light snow or flurries (up to 1" accum.) Low: 28 High: 32

Monday: Partly to mostly cloudy Low: 24 High: 31

Tuesday: Mostly cloudy Low: 20 High: 28

Wednesday: Partly to mostly sunny Low: 19 High: 33

Thursday: Partly to mostly sunny Low: 27 High: 35

Friday: On & off light snow, breezy Low: 15 High: 28



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