Mid-Atlantic Thunderstorm Frequency

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A comparison between Baltimore, MD and Richmond, VA of number of thunderstorm days during the warm season for 2014-2018 is reviewed. Interestingly, the catalyst to the most active year (2018) was a persistent positive phase of the North Atlantic oscillation.

Mid-Atlantic Warm Season Thunderstorm Days 2014-2018

Discussion: The number of thunderstorm days in 2 Mid-Atlantic U.S. locations during the warm season of the past 5 years is reviewed (Fig. 1-2). Most striking is the 2018 activity towering over 2014-2017 activity featuring 46 thunderstorm days in Baltimore and 36 in Richmond. Secondly, the annual activity in Baltimore is steady with 25-26 days each year of 2014-2017 while Richmond is more variable (a range of 18-30 days). The most active month was August of last year in Baltimore (14 thunderstorm days) and July 2016 in Richmond (11 thunderstorm days).

Fig. 1: Number of thunderstorm days in Baltimore, MD during the warm season 2014-2018.

Fig. 2: Number of thunderstorm days in Richmond, VA during the warm season 2014-2018.

Interestingly, the North Atlantic oscillation stands out in 2018 as a contributor to the unusually active 2018 thunderstorm season (Fig. 3). Last year an intense high latitude polar vortex represented by a persistent strong positive phase of NAO correlated to the very active 2018 thunderstorm season in the Mid-Atlantic. A strong +NAO during the 2019 warm season IS NOT EXPECTED.

Fig. 3: The warm season 2014-2018 monthly North Atlantic oscillation index.