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Extratropical storms in stronger (positive anomaly) flows tend to be stronger and move more slowly. This pattern is responsible for most instances of extreme weather including storm intensity and warmth ahead/cold behind the storm. In an effort to project where extreme storm risk is highest for each month of quarter 4 of 2021 for the U.S. and Europe the Climate Impact Company constructed analog forecast used to generate sensible temperature and precipitation anomalies is used.

Discussion: Extratropical storms in stronger (positive anomaly) flows tend to be stronger and move more slowly. This pattern is responsible for most instances of extreme weather including storm intensity and warmth ahead/cold behind the storm. In an effort to project where extreme storm risk is highest for each month of quarter 4 of 2021 for the U.S. and Europe the Climate Impact Company constructed analog forecast used to generate sensible temperature and precipitation anomalies is used.

In the U.S. for October 2021, extreme storm risk is low-to-moderate for parts of Texas, just north of Minnesota and Quebec to Maine (Fig. 1). The Quebec/Maine risk is likely due to a far north-reaching subtropical rainfall event merging with an incoming cold front. The event just north of Minnesota is related to a vigorous storm on a cold front moving through that region. In November 2021, the CIC-CA forecast reveals low risk of extreme weather events with the exception of Southeast Canada (Fig. 2). In December 2021, a moderate risk of an extreme storm is indicated for the Mid-Atlantic Coast (Fig. 3). Based on the December 2021 climate forecast, this storm may propel very cold temperatures into the Central U.S. moderating once crossing the Appalachians.

In Europe for October 2021, moderate risk of extreme storms is present for southern U.K./northern France and northeastward to the Baltic region (Fig. 4). Given the wet climate forecast for Germany to Poland, the rainfall could be heavy. In November 2021, Western Europe is notably quiet (unusual for late autumn) while greatest risk of extreme storms is near the Baltic region (Fig. 5). The December 2021 forecast reveals greatest risk of extreme storms across northern and eastern portions of Europe (Fig. 6).

Fig. 1: Based on a (CIC) constructed analog, the areas of greatest extreme storm risk are identified for October 2021 for southern Canada and the U.S.

Fig. 2: Based on a (CIC) constructed analog, the areas of greatest extreme storm risk are identified for November 2021 for southern Canada and the U.S.

Fig. 3: Based on a (CIC) constructed analog, the areas of greatest extreme storm risk are identified for December 2021 for southern Canada and the U.S.

Fig. 4: Based on a (CIC) constructed analog, the areas of greatest extreme storm risk are identified for October 2021 for Europe.

Fig. 5: Based on a (CIC) constructed analog, the areas of greatest extreme storm risk are identified for November 2021 for Europe.

Fig. 6: Based on a (CIC) constructed analog, the areas of greatest extreme storm risk are identified for December 2021 for Europe.