September continued the theme of Summer 2012 in Star Valley, Very warm and very dry,.
Here are the stats for the local stations in Star Valley including the dates of the Max/Min temps and the date of the peak wind in MPH.
Max Min Rain Peak Wind # Days 32 F or lower
Thayne ES 85-9 24-13 .17 38-16 15
Etna ES 86-9 26-13 .23 32-2 7
Star Valley Ranch 82-8 35-18 .25 48-2 0
Etna 2NE 86-9 26-13 .44 28-4 7
Alpine 86-9 28-13 .33 33-12 2
Smoot 80-9 27-13 .39 34-12
The most striking data is the number of mornings with freezing temperatures. Thayne ES had half the days of the month with freezing or below. While just about 4 miles northeast at Star Valley Ranch the first freezing temperature has yet to be observed. Thayne ES recorded the first below freezing morning on August 25 with a 31F. The official growing season has been 5 weeks longer at Star Valley Ranch vs the colder valley locations represented by the Thayne ES observations.
While the Thayne ES observations are taken on the roof of the school, there is also the soil sensors for the school. The first of three sensors is located just below the surface and the following graph displays the large diurnal ranges that occur near the surface.
|Soil temperature at Thayne ES just below the surface-Sept 2012|
On a couple days notably the 14th, diurnal ranges were in excess of 75F. Morning minimum of 23F was followed by an afternoon maximum to nearly 100F. This illustrates the environment for near ground crops vs most locations where the regular temperature observations are considerably higher, above the ground..
It was a much different story with sensor #2 which is buried about 2 feet below the surface. It can be seen from the following graphic that a steady decrease in temperature occurs much of the month of September
|2 foot soil temperature Thayne ES -Sept 2012|
This steady downward temperature trend reflects the overall decreasing solar radiation as we go into the Fall and a lower sun angle. The solar radiation graphic at Thayne ES for the month shows this trend.
|Solar radiation at Thayne ES Sept-2012|
While there were a few mostly cloudy days in the third week of the month, overall sunny skies predominated. The slow but steady decrease in radiation can be noted on the graph.
Now a brief look ahead to the coming week. It now seems assured that the first Fall like cold front will sweep across the Star Valley region by mid week. While it appears that the main energy and precipitation will remain from the continental divide eastward, daytime temperatures will drop from near 70F Monday and Tuesday afternoon to not much above 50F the remainder of the week. Snow will likely occur from areas of Yellowstone NP eastward, with much of the affect in Star Valley limited to strong gusty winds and dropping temperatures. By Thursday morning a hard freeze is likely across Star Valley including those areas along the mountain slopes in the trees that have thus far been spared. The remainder of the week will remain seasonably cool with freezing temperatures each night.
Following are the 500MB charts for Sunday evening and the forecast 500MB chart for Wednesday evening, Oct 3rd.
|Sunday evening Sept 30-2012 500 mb analysis|
|500 MB forecast Wednesday evening Oct 3rd 2012|
The surface forecast for Wednesday shows the Canadian high pressure moving southward east of the continental divide with the much colder air mass.
|Surface pressure forecast for Wednesday evening Oct 3 2012|
The only hope for precipitation with the system this far west will be stronger deepening into our area which now the computer models agree will likely not happen.