TIS THE SEASON...

Some years it's early, others late, but the numbers show it is rare not to have a freeze by mid to late October. Thursday morning, everybody saw frost, but not everyone reached 32 or colder, as evidenced by this plot of overnight lows. Much of southeast Iowa and a bit of WC Illinois stayed in the range of 33-36. Several places in EC Iowa hit the 20s with the coldest in my area 27 in Monticello, Clinton, and Independence.

Here's a little tighter perspective.

Friday morning, temperatures are expected to even be a few degrees colder, especially in my southern counties. By daybreak, the growing season should be over for a lot of the tender vegetation locally.

A freeze warning is in effect until 9:00am Friday. By that time, readings should be above 32 and eventually reach highs in the range of 55 north to 60 south.

One of the reasons it will be so crisp early Friday is the ridge axis will be directly overhead. Below I have a meteogram for De Witt, Iowa. In the bottom panel at 8:00am., it shows winds down around 2mph or less as the ridge passes. In the top panel, it depicts temperatures at or below freezing for at least 6 consecutive hours, reaching their lowest level of 27 at 7:00am., when winds decouple and become virtually calm (ideal radiational cooling occurs). Similar situations often lead to temperatures a little colder than what models indicate. I could see a few of the typically colder spots down to 25 with a more general range of 27 to 31.

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THE WEEKEND AHEAD...

Over the weekend, the area should remain just to the north of a slow moving system that inches across the southern Plains and mid-Mississippi River Valley. While this should produce passing clouds, aside of a brief shower or sprinkle late Saturday afternoon or night, we continue on with dry weather. Highs will generally remain in the mid to upper 50s. If any select spot can squeeze out a little more sun than is currently expected, a few places could reach the low 60s, especially Sunday.

Next week's system has proven to be a challenge for models and a headache for forecasters. It has evolved from a large slow moving dynamic storm, to more of a clipper that should be far more progressive. As such, it will have less moisture and time to generate precipitation. At 500mb you can watch the energy drop out of the Pacific Northwest Sunday where it's absorbed into the mean trough over the east to create a strong storm there next Wednesday/Thursday.

The GFS has a more defined system and organized rain shield. It still shows some nice rains as it passes. I have my doubts.

The EURO on the other hand is significantly weaker and further SW on the track and forcing. Its rain totals are generally 1 to 2/10ths of an inch.

Timing is also an issue, with the GFS about 24 hours faster bringing rain Monday while the EURO holds off until Tuesday. Basically, next week is a low confidence forecast with rain amounts and timing. At the very least there will be some rain, however I suspect amounts will be more on the lower end of the spectrum, somewhere near 2/10ths of an inch or less. We should know more in the next day or so.

The last thing I will say, is that modeling is having a very tough time handling the energetic pattern that's originating over the Pacific. Multiple clusters of energy in the long wave pattern are keeping wave lengths short and faster moving than was indicated several days ago. The abundance of energy is causing fits for guidance when it comes to phasing. That is a known problem in guidance, and I will be cautious going forward in the long range because I'm seeing big flips in trends from run to run.

Just look at the powerhouse jet that's set up over the north Pacific. It's very difficult for models to actually see and handle the pattern in such a loaded storm track.

That fact is manifested in the 2 week meteograms of the GFS and EURO, which don't show much temperature consistency, especially after November 1st.

The EURO

The newest trends also indicate a return to below normal precipitation with a W/NW flow aloft. 4–5 days ago, I would have not expected that. Obviously, beyond the middle of next week, there are some issues that need to be worked out.

Meantime, after a mantel of frost to start the day, Friday afternoon looks bright and crisp. Good stuff, with the fall colors coming on fast. Have a great weekend and roll weather...TS