Dry Start to Spring

After a very wet January, mainly thanks to a month’s worth of rain falling in one event, Bermuda has seen a succession of progressively drier months to end winter and begin spring.

Spring itself is typically the driest time of year in Bermuda. The driest month is May with 3.01″ of rain (1971-2000 average). In spring, mid-latitude cyclones start to track further away from the island, yet the western Atlantic hasn’t quite become the warm, humid environment that supports isolated summer showers and tropical disturbances. At the same time, the Bermuda-Azores high extends westward across the Atlantic suppressing clouds and rain.

This April was characterized by a blocking ridge of high pressure over Northeast United States and Southeast Canada. This kept most mid-latitude cyclones away as they tracked northward into Canada rather than westward into the Atlantic. Their trailing fronts found dry and stable air in place leading to them fizzling out on approach.

[See the ridge in 500 hPa height anomalies]

Year-to-Date rainfall for 2017, through 30 April (blue) compared to average for the year (red, dashed) with the range of values each day in the period of record (POR: 1949-2017).

The record wet year-to-date precipitation totals that January’s deluge brought have receded to below average levels as successively drier February and March led to the second driest April since 1949 with only 0.73″ of rain at the airport.

Here’s how April 2017 stacked against some other dry months:

April Any Month
1 Apr 1973 (0.33″) 1 May 1991 (0.28″)
2 *Apr 2017 (0.73″) 2= Apr ’73
& May ’82 (0.33″)
3 Apr 1954 (0.76″) 4 Jan 1950 (0.54″)
4 Apr 1964 (0.79″) 5 May 1993 (0.59″)
5 Apr 2010 (0.84″) 6 May 2011 (0.62″)
6 Apr 1957 (0.94″) 7 Jun 2005 (0.64″)
7 Apr 1955 (1.13″) 8= Jan ’74
& *Apr ’17 (0.73″)

April 2017 didn’t quite make it into the top 5 of any dry month. Prolonged periods without significant rain lead to low water levels in tanks around the island. My unofficial TankRain project seems to capture this decline in tank level quite well. Not much rain is expected through the first weekend of May – mild and dry weather persisting a little longer. See the latest official forecast and observations at the Bermuda Weather Service.


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