Nice Autumn Takes A Tail-Spin

NICE AUTUMN TAKES A TAIL-SPIN WITH PROJECTIONS FOR A COLDER NOVEMBER NOW LIKELY A REALITY

By: William R. Deedler, Weather Historian NWS White Lake, MI  (11/21/2008)

In spite of a relatively nice autumn through early November, the tables have turned quite aggressively to much colder weather. This was foreseen by our set of analogues falls which called forquite a variable temperature pattern through much of the fall but with a decided turn toward colder than normal ending, in November. This was really the only distinctive trend seen in the fall in an other-wise typical autumn.

In the Autumn Outlook, it was stated that the autumn should be fairly average with normal frost/freeze date occurrences and typical first snow dates. The data also suggested September would have the best chance to average above normal and October normal to below but the data here was quite variable with no distinctive pattern seen.  Not only were the frost/freeze and snow dates projected fairly well by the analogues but so was the likely-hood of one of two Indian summers. While some may argue we had more than one this fall (depending on when you’re killing freeze occurred), all of Southeast Lower Michigan had an Indian Summer which started on Halloween into the first week of November with the beautiful warm core running from November 3rd through the 7th timeframe, when temperatures averaged well above normal (see more in up and coming November climate /CLM/ write-up)

From the Autumn Outlook

Temperatures

Indications are temperatures this fall will be quite variable (even more than usual) but in the end, temperatures should average near normal (or -1.5 to +1.0 degrees of normal). The data in our analogue falls remains quite mixed and looking at that, along with the upper wind projections, suggest end results will be near normal.

Frost/Freezes

Our guidance indicates temperatures are quite variable and most years our frosts and freezes were on schedule and the more widespread freezes occurred by the third week of October.

Indian Summer

Perusing our analogue autumns, the likelihood of a period or two of Indian Summer weather this fall looks promising. Note, most temperature patterns in October and November varied considerably in the analogue years, this is generally a pre-requisite for Indian summer falls.

Checking back on our Novembers in the Autumn Outlook shows that they were dominated by below normal figures and their final averages, skewed down the fall averages.  

Overall, the composite charts for the fall do indicate temperatures averaging a degree or so below normal for Southeast Lower Michigan

As of the 21st, Southeast Michigan’s average November temperature is close to normal being we had the warm start, but that will change some. Check out the temperatures in Novembers in the Autumn Outlook (shaded blue averaged below the norm).

 

YEARS
DETROIT
FLINT
SAGINAW
 
 
 
 
1904
40.1
37.4
38.2
1907
38.2
35.8
37.4
1951
34.6
30.9
29.9
1956
40.9
38.3
37.5
1965
42.7
40.9
40.3
1976
33.5
33.3
33.3
1985
42.4
39.8
38.1
1989
38.2
35.9
34.2
2000
40.2
38.6
38.5
 
 
 
 
Ave
39.0
36.8
36.4
 
 
 
 
Norm
40.7
38.1
38.0
 

Looking ahead to remainder of the month pretty well leaves the area averaging below normal for the most part.  In addition, check out the projected 500 MB maps for late November into early December with the delivery of polar air into much of the eastern two-thirds half of the country.

 

 

The 500 MB Ensemble map is intimating, with time, that the cold core over eastern Canada will get recharged by some Siberian air and then dig south into the US. This is just preliminary (and the particulars will undoubtly change) but it needs to be watched to see if this trend continues the next several runs. This cold air could also back more into the southwest part of the US before shifting east with time. This cold start to the winter does match up with our analogue winters well where mid November into December averaged below normal, we shall see.

 

 



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