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We have certainly enjoyed the fruits of Indian summer the past few days. Sun-filled skies and comfortable temperatures have obscured the fact that we are a week into November. In fact, Monday's readings in the mid to upper 60s were more in line with early May.

For the most part, highs were 15-17 degrees above the early November norms.


While there's no way to know for sure, it could be many more months before we enjoy the highs we experienced Monday with a major cool-down on the way and the first snowflakes a real possibility by the time the week comes to an end. While the big chill is still 48 hours away, the changes that will produce it are already in progress. The primary culprit is a strong surge of energy that digs into the Pacific Northwest Tuesday and consolidates into a potent closed upper air low at 500mb Friday. Watch the explosive evolution in the animation below.

At the surface, a low pressure forms over the Plains Wednesday and then deepens as it tracks through Iowa and then heads towards NW Wisconsin by Thursday morning. That keeps my area in relatively mild air through Wednesday, although highs do cool into the range of 55 to perhaps 60 in the far south.

Initially the coming system is lean on moisture but eventually a narrow corridor of it surges northward ahead of the low pressure and associated cold front later Wednesday and especially Wednesday night. Available water vapor reaches an inch or more preceding the front Wednesday night.

While there could be a stray shower or sprinkle around Tuesday, the dry air will keep any rain at bay as the atmosphere works to achieve saturation. Thus, the best rain chances hold off until Wednesday night and Thursday morning when the moisture and forcing consolidate ahead of the cold front. Cape is meager but the forcing is significant enough for at least a chance of scattered thunderstorms along the front. K index values will reach near 30, sufficient for convection in scattered locations.

Due to fast movement, rain totals should be light to moderate in my area with the heavier amounts just to the west near the track of the low. The EURO shows this for rainfall.

The GFS came in like this, just a hair further east clipping my far NW counties with heavier amounts.


Once the cold front passes towards daybreak Thursday, strong westerly winds will drive much colder air into the region with temperatures holding in the upper 40s to low 50s. Finally, Thursday night a secondary surge of energy digs southeast sending readings into the low to mid 30s by Friday morning. At that point, temperatures just above the surface at 850mb cool to -6 which will easily supports scattered snow showers during the day Friday. Watch the evolution of the surface low in this animation. It zips up through Iowa into Wisconsin where it's captured by the upper air low at 500mb. That spins it NW into Minnesota where it does a complete loop and eventually crosses Wisconsin into Lake Michigan Friday. That's pretty cool. It matters because that little loop is what creates the instability and forcing for snow showers. Take a look.

Snow from this event is minimal in my area but the EURO spits out amounts that might produce a dusting on grassy and elevated spots, especially across the north. Most of us will just get snow flurries and a reminder of what lies ahead.

The GFS produces amounts that look like this.


Of additional interest is a clipper that rides the upper air flow SE into the Midwest Saturday night. The EURO ensemble control tracks it far enough SE to produce what could be a measurable snow over the NE half of my area (an inch or so). The GFS flipped from a more northerly track to one that's further south and that clips the far NE. Here's the two depictions of snow totals Saturday night.



The key factor in this situation is the depth of the cold air left over from the first system late this week. That and the ultimate strength of the clipper and its dynamics will determine our fate. The latest data shows a weaker system and minimal consistency, particularly with the GFS. Plenty of time to focus on this issue in days to come.


A couple more notes of interest involving the month of December. The U.S. climate based model the CFSv2 is out and it has made a significant change towards much colder temperatures in December than in its previous outlook from a month earlier. It now shows this for December temperatures.

Precipitation is also above normal and plentiful across the nation. Combined with the cold that could make for a mighty fun December with an active storm track and potentially snow. It's just one model but one that I would welcome in a heart beat.

Also, the EURO weeklies are in and the means show this for snowfall from now until December 24th.

The GFS extended out to December 13th also shows this for snow totals.

A cautionary reminder, these model forecasts should never be taken at face value. All they are good for at this distance is showing a trend and the takeaway here is that both are generous and actually in good agreement. I'd rather have this than an inch or two.

That's a wrap for this addition. Enjoy the last of Indian summer, it's fading fast! Thanks for your time and if you appreciate the site please consider a donation by clicking the link below. The future of TSwails is in your kind and caring hands. Roll weather...TS