FROST ON THE PUMPKIN....
It's that time of year when wild temperature swings are commonplace across the Midwest. It's not surprising with the remnants of summer battling the growing cold of the coming winter. The next 10 days are a perfect example of what early fall is all about. Check out the 10 day temperatures forecast by the GFS for Cedar Rapids.
Highs go from 50 September 28th to 81 October 3rd and back down to 50 October 5th. The max/min range of 37 to 81 is a 44 degree swing. Below is another version of he same CR meteogram only this one shows daily precipitation in the blue bars. Starting Friday the 28th, 5 of 8 days show rain...the total coming to 2.9"
Needless to say with so much thermal bounce and rain potential it's going to be a challenging period to accurately forecast. I like that.
A couple of teleconnections that are helpful in determining long term trends, especially going into October are the EPO (eastern Pacific oscillation) and the WPO (western Pacific oscillation). Look at the wild amplitude of the two compared to the base state of 0. First the EPO.
The negative phase of the EPO correlates to below normal October temperatures in the Midwest.
The positive EPO is just the opposite with an above normal correlation.
The WPO shows a similar situation. The forecast against the base state.
Here's the negative phase temperature correlation for October-cool.
Now the positive phase-mild.
These two Pacific teleconnections fit the coming pattern to perfection. Just look at the dates of the highest and lowest temperatures in the first graphic and see how they coincide with the negative and positive phases of the EPO and WPO. Pretty cool and a real confidence builder if you're a forecaster..
We're also getting to that time of year when frost and freezing temperatures come to the forefront. I mention that because Friday night conditions look ripe for the first real frost threat of the fall. Should it reaching freezing that would be early as most of my area does not see its first 32 degree reading until sometime within the time frame of October 10-20th.
The first hard freeze (28 or below) comes about 10 days later.
That said, here's what the 3k NAM shows Saturday morning.