CHANGE OF SEASON...

At 1:00 p.m. Tuesday in Dubuque, I'm looking out the window, and it's 46 degrees with a wind whipped shower. The wind was gusting to 38 mph, and the wind chill sat at 39 degrees. 18 days ago the high was 87 and as recently as 2 days ago it was 68. I think it is safe to say we have turned a corner. Summer is just a sweet memory now. Change of seasons!

The wind driven change is due to an upper level low spinning over NC Wisconsin. At 500mb, it looks like this. That's an energetic little system that you won't see in the summer, indicative of the seasonal intrusion of colder air into the pattern.

From outer space, the GOES satellite imagery depicts the strong spin (vorticity) associated with the circulation.

On the SW flank of the closed upper air low, a tight pressure gradient and vertical mixing caused wind gusts of 35 to 40 mph over much of my area, a few gusts may have it 45. Dubuque and Cedar Rapids, maxed out at 43 mph. Below, you can see reported wind gusts around 5:00pm, most still in that 30-40 mph range.

Not only were the winds bringing in clouds and cold air, enough lift was available for scattered instability showers. Rain totals Tuesday ranged from a trace to .05".

Wednesday, the system will gradual shift east, but strong cyclonic flow remains aloft. Winds will diminish some towards morning, but with daytime heating, will increase again in the late morning and afternoon to 20-30 mph. Temperatures will start in the upper 30s to low 40s before climbing into the low to mid 50s where sunshine emerges. My northeast counties may have a difficult time shaking the clouds until late, resulting in highs remaining in the upper 40s. It will be another very fresh day.

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A VISIT FROM JACK FROST...

Attention then turns to the potential for frost and freezing temperatures Wednesday night and Thursday night. Just how cold we get will be contingent on how fast winds can diminish. By Thursday morning, the 3k NAM has lows north of I-80 in the 30-34 degree category, certainly good enough for frost.

The HRRR is just a degree or two warmer. Either way, frost is likely in many areas, with a freeze possible in the north.

By Thursday night, the proximity to the primary ridge axis should allow less mixing and readings could be a couple degrees colder with another threat of frost and freezing temperatures by daybreak Friday. It is likely that frost or freeze headlines will be issued for some if not all the area between now and Friday. Some are already in effect out to the west, where wind will be less of a factor.

After the frosty starts to both Thursday and Friday, high both days should inch up into the 50s, maybe low 60s in the far SW Friday.

The weekend ahead hinges on a southern stream system ejecting out of the lower Plains. Most guidance keeps the rain making aspect of the storm to the south. However, some passing clouds and a few sprinkles might work their way into the far south Saturday night. Weekend highs are shown holding mainly in the upper 50s Saturday, before surging into the low to mid 60s Sunday.

Early next week we come under the influence of what should be a large slow moving upper air storm emerging from the north Pacific. The energy rolls out of the west Saturday and evolves into a closed low that gets trapped by a strong blocking ridge over Canada next week. How the system comes together is still in the formative stages, but a few showers could develop Sunday night and Monday before the bulk of what rain falls arrives Monday night into early Wednesday.

One of the issues that still makes the intensity and impacts of next week's storm questionable is phasing. Significant changes regarding the merger of the northern and southern branches of the jet stream will be critical in determining the intensity and track of the storm. Less phasing means a weaker system with less in the way of impacts and precipitation. That is possible. More phasing means a stronger, wetter storm. Confidence remains low to moderate on what eventually happens. It will be a couple more days before we can define a more specific solution.

For now, some healthy rain numbers remain on the table. The EURO is showing this for amounts Sunday night through next Wednesday morning.

The GFS for the same period.

While the system initially has us in its warm sector, its passage will no doubt tug in a healthy stab of a cold air on its backside the 28th and 29th. It may be followed by another surge of cold air, November 4th or 5th. In short, after a very mild September and much of October, cold air is on the charts and pressing. I'm seeing more and more of this trend, not surprising considering November is knocking on the door. Roll weather and keep an eye out for Jack Frost the next couple nights. Roll weather...TS