- Sep 22, 2022

THE AUTUMNAL EQUINOX (FALL)...

At 8:04 P.M. Thursday evening, the Autumnal Equinox occurs signaling the official start to fall. It's only one of two times per year when the Earth's axis is tilted neither toward nor away from the sun, resulting in a "nearly" equal amount of daylight and darkness at all latitudes. These events are referred to as Equinoxes. The word equinox is derived from two Latin words - aequus (equal) and nox (night). At the equator, the sun is directly overhead at noon during the dates of the two equinoxes. Tonight's the night it happens in September.

Needless to say we've made a transition to fall-like conditions over the past 24 hours going from record highs in the 90s Tuesday to lows early Thursday in the 40s and low 50s.

The change shows up nicely by way of Tuesday afternoon's temperatures. With the front approaching St Louis readings ahead of it where in the low 90s there. Behind it 50s were in place in northern Minnesota and NC Wisconsin.

In some parts of Iowa, temperatures were as much as 30 degrees colder Wednesday afternoon than just 24 hours earlier.

This is just the first phase of a 3 pronged cooling trend that is likely to result in some places struggling to get out of the 50s Friday. Before that, Thursday promises to be a quiet cool day dominated by very dry air. You can see the dryness in yellow as it builds southward Wednesday night.

That leaves us with dew points Thursday in the 30s and low 40s. No humidity in that air mass!

That should lead to mostly sunny skies Thursday but it will be a crisp day with highs only in the low to mid 60s. That's apple picking weather.

Friday brings changes as an upper air disturbance streaks across the Midwest. Moisture will be sparse but there will be enough lift and warm air advection to kick up some clouds and scattered light showers later in the day into Friday night. Most guidance has them out by daybreak, (early Saturday at the latest). As for amounts, I've seen nothing significant with most amounts under 1/10th of an inch (probably less in most spots). Here's what guidance is currently advertising.

The EURO

The GFS

The 3k NAM

The national model blend

The Weather Prediction Center

Due to a chilly start Friday with lows well into the 40s, the increase in clouds and perhaps some late day showers in the west will limit daytime heating. If the clouds get established soon enough, highs may not get out of the upper 50s, especially in my NW counties. Low 60s are likely elsewhere unless we can squeeze out a little extra sunshine. The EURO shows this for highs Friday.

Both Saturday and Sunday appear dry (just a slight chance of spotty light showers or sprinkles early Saturday). After that partly cloudy skies and dry weather is expected. Highs Saturday should reach the 70s but could dip back into the upper 60s Sunday, especially in the north. The remnants of FIONA (a category 4 hurricane) will get absorbed in the 500mb flow enhancing a Great Lakes trough Sunday. That tightens the associated NW flow keeping temperatures below normal into the middle of next week. Some warming is possible after that but that is not indicated in all guidance and will be dependent on the NW flow deamplifying. I would lean towards the cooler look of the EURO.

One thing that continues consistent in both the EURO and GFS is that we are now in a very quiet pattern that is not conducive to precipitation. Little to none is indicated the next 2 weeks over the entire Midwest. The EURO indicates this for rainfall departures the next 15 days ending October 6th.