This is an update to the original blog posted on 5/30/2018:

With the NWS forecast not even mentioning rain for the 31st, numerous showers popped up through the Metro area in the afternoon and evening, providing the Portland Airport with an additional 0.02” of rain to add to its earlier monthly total of 0.15”.  With the new monthly total of 0.17”, it was still the 2nd driest May on record. With the now 5 days of measurable precipitation, it drops out of a tie for 1st place, into 2nd place at the airport (and 3rd place in the historical record when including the downtown locations back to 1872 (and prior to 1940, when the airport period-of-record began)).

Top-5 Driest Mays:

1. 0.10” (1992) (PDX)

2. 0.17” (2018) (PDX)

3. 0.45” (1924) (Downtown)

4. 0.46” (1982) (PDX)

5. 0.56” (1994) (PDX)

Temperature-wise, the monthly mean temperature of 63.0° was a +4.7° departure from normal, and 2nd-warmest of all time, just behind the 63.1° mean from 1992. Historically, this current May is also in 2nd place, even when including downtown locations (again, back to 1872 (and prior to 1940, when the airport period-of-record began)).

Top-5 Warmest Mays:

1. 63.1° (1992) (PDX)

2. 63.0° (2018) (PDX)

3. 62.7° (1931) (Downtown)

4. 62.6° (1928) (Downtown)

5. tie 62.4° (1940) (PDX)

5. tie 62.4° (1888) (Downtown)

It’s interesting to note the similarities between 1992 and 2018 with both temperatures and precipitation as they were just 0.1° different in mean temperature as the two warmest on record and also the two driest.

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Initial posting on 5/30/2018:

 

As of this writing in the evening of May 30, 2018, the Portland Airport (PDX) has only recorded 0.15″ of rain for the entire month of May, the second lowest monthly total for May ever recorded since weather records began there around 1940 (the record lowest is the 0.10″ measured in May 1992). When including the historical downtown locations back to 1872, no other month comes very close to the current month as 0.45″ in May 1924 is the lowest prior to 1940.

A record that might be tied is the 4 days of measurable rain (≥0.01“) that have been recorded this month. If this were to be the final total, it would tie May 1947 for the least number of days. Again, looking at the historical downtown records, only 3 days had measurable rain in May 1924, pushing the current May to second place overall.

The current National Weather Service forecast for May 31st calls for no rain on the final day so the above totals should hold.  

The last measurable rain fell 20 days ago on May 10th (a whopping 0.05″), and the last “appreciable” precipitation was 0.34″ 45 days ago (way back on April 15th), causing concern as we are significantly drier than normal as we head into wildfire season. 

 

Cover photo courtesy of Freshwallpapers.net