Saturday, July 5, 2014

Wet But Not Thundery

With the June rainfall record having been broken this year in Fairbanks, and with July already in the top 10 wettest on record, it is interesting to consider that thunder has been reported only twice this year at Fairbanks airport (June 8 and 23); and these two events contributed zero precipitation to the June total.  This led me to wonder if very wet summer months are typically lacking in thunder in Fairbanks.  If so, this suggests a very non-linear relationship of thunder to total precipitation, because very dry weather would also tend to be associated with a lack of thunder.

To answer the question, below are scatter plots of the total precipitation versus number of days reporting thunder, for June and July.  Indeed we see that in both months, the highest rainfall totals are not associated with a high frequency of thunderstorms.  Instead, the highest thunderstorm frequency tends to be associated with moderately, but not excessively, above-normal precipitation.  In June it is possible to have quite high thunderstorm frequency with well below-normal precipitation, but it seems that in July the very driest months tend to have reduced thunderstorm activity.

In conclusion, the wettest summer extremes in Fairbanks are not associated with much-enhanced thunderstorm activity, but in fact quite the reverse: thunderstorms are less common in the weather patterns that bring the wettest conditions.  This is evident also in the history of heaviest daily rainfall amounts: of the top 20 one-day rainfall events in June and July (for years with hourly weather reports available), only 5 days reported thunder.

1 comment:

  1. This makes sense to me. The systems like last week that give a deluge don't usually have a lot of convection; lots of flat clouds.

    I wonder if there is a way to easily calculate the lapse rate with standard station data. The lapse rate would represent the convection of the clouds thus thunderstorm potential. Then you could compare lapse rate to precipitation and get an idea how precipitation relates to thunderstorms.