May Was Second Wettest On Record As The Rains Keep Pouring Down

Green areas are parts of the nation that were wetter than normal
in May. The darker the green the greater departure from
nornal rainfall. 

It seems as if every day, floods capture the attention in weather news.

Yesterday, it was Louisiana and the Oklahoma City metro area that suffered through damaging, dangerous floods. It's just been a continuous drumbeat for it seems like a couple years at least now.

As if to prove that point, NOAA's National Centers for Climate Information released their summary for the month of May, which showed the month was the second wettest on record for the United States.

If you average it out. 4.41 inches of precipitation fell across the nation. Only May, 2015 was wetter and just barely - that month four years ago had 0.03 inches more rain than May, 2019.

The only dry areas of the nation during May, 2019 were in parts of the Southeast, western Washington and along the immediate Canadian border in Idaho, Montana and North Dakota.

Three states - Kansas, Nebraska and Missouri - had their wettest Mays on record. Twelve other states had one of their top 10 wettest Mays. (Here in Vermont it was the 18th wettest May out of the past 125 years, so pretty soggy, but not record breaking.)

Also, the 12 month period ending on May 31 was the wettest such stretch on record. The period ending April 30, 2019 (this year) was the previous wet record holder for a 12-month period. Records go back 125 years.

During that 12 month period, an average of 37.68 inches of precipitation fell across the nation, which is a whopping 7.73 inches above average.

This wetness is consistent with climate change. A warmer atmosphere can hold more water vapor that cooler air. That added water vapor in the toastier air leaves the potential for heavier downpours.

The atmosphere in general has gotten warmer across the globe. It's interesting to note that six of the top ten wettest 12 month periods in the United States have been since 2016 and all of them have been since 1974. Remember, these records go back to 1895.

That said, month to month precipitation in the United States is highly variable. With or without climate change, a given month for the nation can be very wet, very dry, or just average.

But the overall trend has for wetter months overall, especially in the eastern half of the United States.

It's hard to say whether the rest of the year will be wet, but the first half of June is not proving to be particularly encouraging.

There were those floods yesteday in parts of the South. A slow moving collection of weather systems threatens quite a bit of flooding and heavy rain over the next several days in the Southeast. Many areas from Florida to Virginia could see five or more inches of rain over the next seven days.

Long range forecasts into the third week of June suggest that larger areas of the United States will be wetter than normal compared to those that will be drier than normal. (For the record, Vermont is forecast to be overall cooler and wetter than normal into the third week of June, despite an expected warm, dry weekend coming up.)  

Flash flooding in Tulsa, OK
Thursday. Photo via Twitter by
Jonathan Torrio

This next part will get confusing, but bear with me. The overall temperature for the nation as a whole was a little cooler than average during May.

This, after I just got done explaining that a warmer atmosphere holds more water, so that might help explain why we had such a wet national month.

Storms are at least in part a clash between warm and cold air. Although final numbers aren't in yet, May, 2019 was almost certainly in the top 10 warmest for the world as a whole. Warmer air feeding into the storms that affected the nation might have increased rainfall somewhat. Some of this warm air came from outside the nation.

And note the heaviest precipitation was in the middle of country. The Southeast was warmer than average in May, and that's where much of the humid air was coming from to feed the precipitation in those Midwest storms.

However, parts of the United States was on the cool side, bucking a worldwide trend in May, because the weather patterns during the month favored cool air flowing into the middle of the nation.