AND THEN IT WAS FALL...(SNOW FOR HALLOWEEN)
Officially, summer ends today at 2:21 in the afternoon with the arrival of the autumnal equinox. There are only two times of the 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 on these two equinoxes. The "nearly" equal hours of day and night is due to refraction of sunlight or a bending of the light's rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon.
This creates an interesting short term effect in that the days become a little longer at the higher latitudes (those that are a great distance from the equator) because it takes the sun longer to rise and set. Therefore, on the equinox and for several days before and after, the length of day will range from about 12 hours and six and one-half minutes at the equator, to 12 hours and 8 minutes at 30 degrees latitude, to 12 hours and 16 minutes at 60 degrees latitude.
We all know that the Earth makes a complete revolution around the sun once every 365 days, following an orbit that is elliptical in shape. This means that the distance between the Earth and Sun, which is 93 million miles on average, varies throughout the year. During the first week in January, the Earth is about 1.6 million miles closer to the sun. This is referred to as the perihelion. The aphelion, or the point at which the Earth is about 1.6 million miles farther away from the sun, occurs during the first week in July. This fact may sound counter to what we know about seasons in the Northern Hemisphere, but actually the difference is not significant in terms of climate and is NOT the reason why we have seasons. Seasons are caused by the fact that the Earth is tilted on its axis by 23.5°. The tilt's orientation with respect to space does not change during the year; thus, the Northern Hemisphere is tilted toward the sun in June and away from the sun in December, as illustrated in the graphic below.
We did get a little preview of fall temperatures Tuesday with northerly winds behind a cold front dropping highs into the upper 60s north to the low 70s elsewhere. More important, the front produced one of the most widespread rain events the Midwest has seen all summer. Below you can see many areas in green picked up at least a half inch of rain with some 2"+ totals scattered about.
In my local area you can see the banded nature of the rains which were tied to the tracks of stronger convection. A 3" total was measured near Burlington, Iowa. You can also clearly pick out a 75 miles wide swath where amounts were rather meager to the NW of the Quad Cities. As a result, there continue to be some very dry spots in that part of my area.
Prospects for any meaningful rain the next couple weeks look exceedingly low, especially after Friday night. The mean storm track is expected to remain well north or south of the Midwest restricting both moisture and forcing. There is a chance of a few showers (light in nature) Friday night. That's tied to a vigorous upper air disturbance that rapidly swings southeast. The best chances of measurable rain with it is across the E/SE half of my area, maybe some amounts of 1 to 2/10's of an inch. Most areas likely under 1/10th of an inch. The EURO shows this for rainfall Friday night.
The GFS is far less aggressive on potential amounts. I suspect a bit underdone.
Beyond that event, here are the 15 day rainfall departures through the morning of October 6th. Dry!
These are the actual 15 day rainfall departures that the EURO depicts.
The GFS says I'm with you EURO with departures every bit as significant.
Nice early fall temperatures will continue to dominate the region through the weekend. Wednesday may be a bit cooler though as northerly flow aloft increases behind a storm system traveling through the Ohio Valley. With a fresh north wind highs may remain in the upper 60s, certainly no higher than the low 70s. That sets us up for a chilly Wednesday night. The high res 3k NAM even shows a few upper 30s in the valley's of EC and NE Iowa.
That may be a few degrees too cold and I am leaning more toward the low to mid 40s, similar to what the HRRR indicates below.
Readings will warm some Friday before cooling down again Saturday. After that the general idea is for a warming trend next week with above normal highs much of the 6-10 day period. Summer is still kicking.
Just for shock and awe, I was looking through the EURO weekly control which goes out 46 days. It shows this for snow the day before Halloween.
I certainly would not bet on it but the last 2 years there has been snow before Halloween and plenty of it in spots. Last year on October 19th, 50 reporting stations in Iowa measured at least an inch of snow. These are last years monthly snowfall October snowfall totals
293 stations around the Midwest tied or broke records for October snowfall.
October of 2019 was even more impressive for snow. Most of my area had monthly totals between 4 and 8". That's a serious accomplishment.
It's also rare as you can see most every station in eastern Iowa and western Illinois tied or broke records for October snowfall. 325 total records were established around the central U.S.
To be very frank, the odds of having something similar this October to what's happened the last 2 years are very low and I would be quite shocked to see it happen. In fact, I think overall this October has a good chance of being warmer than normal. However, I do see signs that winter will get off to an early start this year mid to late November and carry right on into December. Still working on my winter outlook but that's one of the trends that's currently high on the board. Roll white gold and roll weather...TS
