May 2019: Wet and Cool

May 2019 featured predominantly cool temperatures, anywhere from 4 to 7 degrees below normal, thanks to a jet stream pattern that kept the area on the cold side of several storm systems. Several locations ranked in the top 10 coldest Mays on record: Kennebec 10^th, Sisseton 8^th, Timber Lake tied 6^th, and Pierre 3^rd. Record cold daily low temps were recorded at Aberdeen and Sisseton on the 7^th (24° and 26° respectively), and numerous record cold daily max temps were recorded from the 18^th through the 22^nd: Pierre on the 20^th, 21^st and 22^nd (49°, 47°, 53°), Aberdeen on the 19^th (46°), Mobridge on the 22^nd (53°), Sisseton on the 19^th (44°), Wheaton on the 20^th (48°), Kennebec on the 19^th, 20^th, 21^st and 22^nd (47°, 52°, 46° 52°), and Timber Lake on the 18^th and 22^nd (45° and 48°).

Very wet weather accompanied the cooler temperatures, and a couple days of accumulating snow resulted (not unheard of in South Dakota). Portions of central South Dakota picked up a couple inches on May 6^th and portions of Deuel County followed suit on May 8^th, where an estimated 4” fell at Astoria. Above average total precipitation for May was observed at all locations, but the greatest departure was across central South Dakota where an impressive 4 to 8 inches of surplus rain fell. This May will go down as the second wettest on record in Pierre (7.24" in 1982) and the wettest on record in Kennebec (9.54”, surpassing the old record of 7.2” in 1942). This averages out to just over 0.30” per day. Year-to-date, Watertown has had 12.58” of moisture which ranks as the 4^th wettest start to the year on record, Pierre has had 13.85” of moisture which ranks as the wettest start to the year on record, and Kennebec 15.28” which also ranks as the wettest. For perspective, Pierre averages 20.01” of total moisture each year, and Kennebec averages 19.63 inches. Daily record rainfalls this May occurred at: Pierre on the 21^st (1.54”), Sisseton on the 18^th (1.17”) and Kennebec on the 27^th (4.03”).

Unfortunately, all this moisture exacerbated issues associated with already wet/nearly saturated soils which carried over from April. River flooding remained an issue throughout May as round after round of rain impacted the area, and numerous county roads were impassable at one point or another. While widespread 0.5” to 1” plus rainfall events took place on the 7-8^th, 17/18^th and 21/22^nd, the climax rain event, at least for central South Dakota, took place on the evening of May 26^th. Slow-moving thunderstorms dumped heavy rains in excess of 4” in some cases across Jones/Lyman counties, including 4.34" at Murdo. Kennebec in particular observed flooding in response as Medicine Creek swelled well past its banks. Pierre/Fort Pierre also observed street flooding on the 31^st after about an inch of rain fell in an hour’s time due to a passing thunderstorm.

Climatologically, May is an active month for severe weather across central/northeastern South Dakota and west central Minnesota, but there was a distinct lack of it this year. Only two Severe Thunderstorm Warnings have been issued by NWS Aberdeen this May (16^th for Marshall/Roberts Counties and again on the 31^st for Hamlin/Deuel Counties). Finally, of note, smoke from Canadian wildfires spread across the Northern Plains May 29-31^st due to northwest winds aloft which transported the smoke southeastward. Hazy skies and red sunrises/sunsets resulted.

May 2019 average temperature departures from normal, from the Midwestern Regional Climate Center

May 2019 total precipitation, from the Midwestern Regional Climate Center

May 2019 precipitation departures from normal, from the Midwestern Regional Climate Center

A wider perspective from https://water.weather.gov/precip reveals just how staggeringly wet much of the country's mid-section has been this May. A pattern of continuous low pressure system after low pressure system produced rounds of thunderstorms and upwards of 20" of rain across portions of Kansas and Oklahoma.

The first image below displays multi-sensor precipitation totals for May 2019, and the second is of precipitation departures.