Aggressive cold snap on the way

Impressive Cold Air Mass To Slowly Engulf the Region By Early Next Week

Longer range forecast models continue to advertize that a strong cold air mass for mid October will gradually glide over the Great Lakes Region during the Columbus Day weekend and after. This air mass originates from the Polar region could bring the first wet snowflakes of the season and likely a widespread killing freeze (earlier than on average) but this still depends on cloud cover overnights. While many areas have seen temperatures in the upper 20s to lower 30s with frost and patchy freezes, a widespread killing freeze /<=28f/has yet to occur (see map below) . This risk of the vegetation killing cold comes right at the time past analogue October’s strongly suggested in the local Fall Outlook.  The median date found for widespread frosts was October 5th in the analogue years while widepsread freezes averaged around the 14th.  Keep abreast of the latest forecasts regarding this mid October cold snap.

 

From the Outlook…
Earlier Frost and/or Freeze?

Every Outlook I scan each year for similarities and trends relating to the present. Probably one of the most anticipated trend I expected to find was the likelihood of an earlier frost and or freeze this year. Why? Simply put, the aggressiveness and persistence of the Polar Jet stream this past summer over Eastern Canada can’t be ignored. This pattern is also reflected in the dominant negative NAO seen this summer (and last winter). So then, when did this set of data project the frost and freeze estimated dates? Where they earlier than average?

Generally, it was found the frost and freezes occurred roughly about a week earlier (or by the second week of October). At the same time, late September frost and freezes popped up enough to get our attention. Some areas had freezes when reading at Detroit was around 35-34, so it’s location location. I’ve also added the snowfalls for October and November each year for Detroit. The snowfalls also reflect the colder than normal weather late fall and in some years /three/ over seven inches fell in November /normal 2.7/.

                                                                   FROST/FREEZE            SNOW
Y
frost
freeze
YEAR
Oct
Nov
1896
20-Sep
23-Sep
1896
T
T
1911
27-Oct
28-Oct
1911
0.0
7.0
1918
1-Nov
Nov-14
1918
0.0
T
1925
9-Oct
10-Oct
1925
2.0
7.8
1957
28-Sep
12-Oct
1957
T
1.7
1965
27-Sep
5-Oct
1965
T
0.2
1972
9-Oct
9-Oct
1972
T
7.1
1976
24-Sep
16-Oct
1976
T
1.4
1986
7-Oct
16-Oct
1986
T
3.3
1991
27-Sep
28-Sept
1991
T
2.2
2002

13Oct

14Oct

2002
0.0
1.6
  
snow
T          3.6
 
 
 
 
 
 
 
 

 

 

 

The average freeze dates run roughly during the second to third week (or 10/11-21) of October

Check out the projected cross polar jet aloft /200 MB/ for Columbus Day. This is similar to the pattern seen since last winter with the blocking highs in western Canada and Greenland. At the same time, the jet over the Pacific has also become quite pronounced as El Nino revs up this fall. The development of these patterns through the fall will definitely be watched for the upcoming Winter Outlook (due in early November).

 

-Deedler 10/8/09

 



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