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The United States is now in the grips of what's known as a positive TNH pattern. The +TNH reflects large-scale changes in both the location and eastward extent of the Pacific jet stream which in this case significantly limits the flow of mild Pacific air into North America. At the same time, it enhances the southward transport of cold Canadian air into the north-central United States.

In a nutshell, with a +TNH the axis of prominate ridges and troughs become aligned in such a way that a strong ridge develops along the west coast and a mean trough is established over the plains/Midwest (not the east). There's also a stable southeast ridge near Florida (which keeps the southeast mild).

The surface temperature departures for the +TNH in January are cold central and west.

The +TNH is aided and abetted by a strongly negative EPO (Eastern Pacific Oscillation) which strengthens and expands the west coast ridge.

The negative EPO teleconnects to the west coast ridge and large Arctic highs which deliver cold air intrusions.

Here's what the 500mb pattern is projected to look like February 1st. That is a text book +TNH

The ridge off the west coast and east coasts drives the trough and its cold air into the Midwest. We pay for that with the EURO indicating temperature departures of 30-35 below normal across Iowa and western Illinois February 2nd.

If the EURO verfies, (STILL A BIG IF) those departures translate to lows of 13 to 19 below zero the morning of February 3rd. Daytime highs the 2nd remain below zero in all but my far southern counties.

Serious wind chills would also be a by-product with readings 25-35 below zero.

The GFS is already showing odds of sub-zero cold of 50 percent in the south to 80 percent in the far north. Pretty strong odds a week out from the event. But I stress, strong is not a gaurantee of such severe cold. I will continue to monitor!

The Climate Prediction Center has a large part of the Upper Plains and Midwest in a high risk hazardous temperature outlook February 1st-3rd.

The 6-10 day outlook January 30th -February 4th

The 8-14 day outlook February 1st-7th. The next 2 weeks don't look fun unless you are a polar bear.

If the cold is not enough, there appears to be several chances for snow which in total the next 2 weeks could exceed what we have seen over the entire winter so far. These are the ensemble snowfall forecasts from the EURO, GFS, and Canadian over the next 15 days. There is remarkably good consistency between all three models over the two week period. Sometimes it's hard to get that a day ahead of an event let alone 15 days.



The Canadian

That brings us to today's snow event which is tied to a southern stream storm phasing with the northern branch of the jet. This takes place just east of my area so we clearly miss the heavier snow band off to the SE which could reach 6-9 inches in spots. You can see in pink the winter storm warnings in effect where the heavier snow is expected. Further west in all but my far NW counties winter weather advisories are posted for lighter accumulations as we get grazed by the storm.

A closer view of the winter weather advisories for my area Wednesday.

One unique aspect of this system is that it brings its initial wave of snow to mainly the SE half of my area Wednesday, especially near and SE of the Quad Cities. Totals up to 2-3 inches are expected in this area with and inch or less to the NW. Here's what the GFS shows through noon Wednesday.

After what looks to be a lull in the afternoon, a secondary short wave follows the primary energy Wednesday evening developing another round of light snow. As this swings through the region it could deposit an inch or so of powdery snow. By the time the entire system exits Thursday morning, the GFS indicates storm totals for the entire event of around an inch in the far west to perhaps as much as 4 inches (maybe as much as 5 inches) just east/southeast of the Quad Cities.

Here's what other models are indicating.


The Canadian

The 3k NAM

The 12K NAM

After this system departs another quick moving disturbance arrives late Thursday night and early friday. This has limited moisture and moves so fast snowfall amounts of an inch of less are expected. That brings colder air into the region and sets the area up for a more significant wave of snow that starts early Saturday and could last into early Sunday. This event will accompanied by temperatures no warmer than the teens north to the mid 20s south and brisk NE winds. The snow should fluff up nicely and several inches of accumulation look likely at this point in the game. This event will no doubt be a focal point in coming forecasts.

Even colder air follows this disturbance and with fresh snow cover expected, lows will likely be below zero in most, if not all areas by Monday and Tuesday of next week.

There are indications of another snow chance later next Tuesday into Wednesday and that is when we watch for what could be a significant Arctic outbreak. I will tell you this much, the next 2 weeks look very interesting with the potential for both impactful cold and snow. I'm on board. Roll weather....TS


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