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April Climate Summary and 1965 Tornado Anniversary

Preliminary April Climate Summary:

Despite some ups and downs most observers report a mean April temperature that ranged from 1 to 3 degrees F warmer than normal.  The month started and finished on the warm side, with some very cold days in the middle.  April Fool’s Day (April 1st) produced a great deal of wind (50-60 mph gusts in the western counties) and warmth, with over 40 communities reporting daytime highs in the 80s F, and Luverne setting a new statewide record high for the date of 86°F. A few days later many observers reported only single digit low temperatures over April 3-5, including the lowest reading of the month, 2°F at Camp Norris ( Lake of the Woods County) on April 5th.  Minnesota reported the nation's lowest temperature only once during the month, April 23rd, with a reading of 10°F at F Fosston and Embarrass.  In addition a new low dew point record was set at MSP Airport on April 23rd with a reading of 1°F, and a relative humidity of just 12 percent.

Most observers in northern, western, and southwestern counties reported a drier than normal month, and in some cases just 50 percent of normal precipitation fell.  As a result by the end of the month an area of northwestern and west-central Minnesota was designated to be in severe drought by the US Drought Monitor.  Many lakes and streams in northern and central counties are at very low levels for this time of year.  Although many observers also reported snowfall during the month, it was generally of little consequence.  Only Ely, Orr, Gunflint Lake, and Isabella reported over 6 inches of snow for the month.  Some portions of central, south-central, and southeastern Minnesota benefited from normal or above normal precipitation during the month.  Albert Lea, Austin, Grand Meadow, Preston, Rochester, Spring Valley, Winona, and La Crescent reported over 4 inches for the month.

As noted in the WeatherTalk blog last week, April was an exceptionally windy month, with most observers reporting average monthly wind speeds from 12-14 mph, and several days of wind gusts over 30 mph.  In addition the month brought a number of exceptionally sunny days with near record-setting solar radiation values on the 14th, 23rd, and 27th.  On April 26th a new record high value for solar radiation was set at the St Paul Campus Observatory with a reading of over 650 calories per square centimeter.

50th Anniversary of Twin Cities Worst Tornado Outbreak:

Next Wednesday, May 6th is the 50th anniversary of the most destructive tornado outbreak in Twin Cities history, written about in the Allen Taylor book "The Night the Sirens Blew."  Several communities and organizations are commemorating the event with special public programs, news releases and web-based recollections, including the National Weather Service Forecast Office in Chanhassen and the Minnesota State Climatology Office in St Paul.  You will find interesting accounts at their respective web sites.

Some of the important points that are evident from studies of this dramatic weather event, also recounted in my book (Minnesota Weather Almanac) include:
-Twin Cities dew point record was set that day (May 6, 1965) with a reading of 66°F
-Of the six tornadoes (all essentially between 6pm and 9pm), four were rated F-4 (winds 207-260 mph), a remarkable geographic concentration of severe storms over approximately a 50 mile perimeter.  To the best of my knowledge this concentration of F-4 tornadoes has never occurred in Minnesota before or after.  Even for the worst single day tornado outbreak in state history, June 17, 2010 when 48 tornadoes were reported statewide, only 3 of these were EF-4 intensity (winds 166-200 mph) and those affected the widespread communities of Leaf Valley (Douglas County), Wadena (Wadena County), and Mansfield (Freeborn County).
-The National Weather Service Forecast Office (under the supervision of Joe Strub and Phil Kenworthy) performed heroically during this storm, providing residents with up to 20 minutes of warning and sounding all the warning sirens in the area.  WCCO radio announcers Dick Chapman and Charlie Boone also provided terrific service to the public in issuing real-time on air reports and relaying warnings from spotters.
-Weather was quite unsettled over the first 10 days of May 1965, with rainfall on 8 days, and another six tornadoes across the Minnesota landscape on May 5th, the day before the Twin Cities outbreak.
-The destruction of over 200 trailers in the community of Fridley prompted widespread conversation about making robust storm shelters mandatory for trailer park residents in Minnesota.

Independent Book Sellers Day:

Saturday, May 2nd marks Independent Book Sellers Day across the nation.  I will be at Common Good Books in St Paul (38 Snelling Ave South) from 4pm to 5pm talking weather and sharing stories from my new book, "2nd Edition Minnesota Weather Almanac."  Please stop by if you are interested.

Weekly Weather Potpourri:

USDA veterinarians suggested this week that the outbreak of avian influenza which has produced the loss of millions of turkeys in Minnesota and other states may be related to the cooler than normal weather spells of March and April.  Further, as warmer spring temperatures prevail fewer new cases of avian influenza should be reported.  The University of Minnesota researchers are engaged on this outbreak and hope to discover the reasons behind it and if there is indeed a weather connection that relates to the spread of the disease through wild ducks, geese and other waterfowl.

One of the changing features of Minnesota's climate is more frequent very heavy rains.  This type of change is also occurring in the northeastern states.  Recently NOAA Climate.Gov web site featured an article about considering the new extreme rainfall analysis when designing the right size culverts. This task is challenging and the article offers an example from the state of New York.  

Speaking of heavy rainfalls, NOAA's Storm Events Data Base is now accessible online using a search engine. 

Tropical Cyclone Quang was bringing high seas, strong winds, and rain to portions of western Australia heading into the weekend. With winds over 100 mph and sea waves greater than 30 feet it was expected to rapidly weaken as it made landfall Friday and Saturday.

Weekly drought highlights from the USDA's Brad Rippey:
-drought spread across the USA during the month of April, especially from the Pacific northwest to the upper Midwest.
-moderate drought in Minnesota continues, but severe drought expanded to include nearly 32 percent of the state landscape, mostly in the northwestern counties.
-extreme to exceptional drought covers two-thirds of California and is expected to significantly reduce that state's agricultural output in 2015.

MPR Listener Question:

I have seen water sprites/low grade tornadic winds on a body of water twice, once in July, 2006, at the West end of Lake Nokomis (heading from the Northwest to the East) and again yesterday, April 27, 2015 on a beaver pond on a branch of the East Fork of the Beaver River in the Finland State Forest in Lake County, Minnesota (heading from the North Northeast to the South).

My questions are: How frequent do water sprites occur in Minnesota?  How often can they be expected to occur on a beaver pond in Lake County, Minnesota?  What meteorological/geographic/topographic conditions govern the formation of water sprites?


I think another name for what you witnessed is a water devil, brought about by the surface converge of winds into a rotating funnel over the water surface which sucks up some of the water into a spiraling vortex.  The atmosphere required for this to happen is unstable, usually under sunny skies and with a good deal of surface winds (often gusting to over 30 mph).  These water devils (sprites) are relatively short-lived and spiral aloft for only a few seconds, unlike water spouts which often descend in a vortex from the base of a thunderstorm and then pick up water as they touch the surface of a lake or pond.  Water devils are relatively rare, especially on small bodies of water like beaver ponds.

Twin Cities Almanac for May 1st:

The average MSP high temperature for this date is 63 degrees F (plus or minus 13 degrees F standard deviation), while the average low is 43 degrees F (plus or minus 9 degrees F standard deviation).

MSP Local Records for May 1st:

MSP weather records for this date include: highest daily maximum temperature of 91 degrees F in 1959; lowest daily maximum temperature of 33 degrees F in 1909: lowest daily minimum temperature is 24 degrees F in 1909; highest daily minimum temperature of 64 F in 1934; record precipitation of 1.26 inches 1983; and record snowfall is 3.0 inches in 1935.

Average dew point for May 1st is 36 degrees F, with a maximum of 66 degrees F in 1948 and a minimum of 8 degrees F in 1918.

All-time State Records for May 1st:

The state record high temperature for this date is 100 degrees F at Beardsley (Big Stone County) in 1959. The state record low temperature for this date is 4 degrees F at Pine River (Cass County) in 1909.  State record precipitation for this date is 3.83 inches at Winona (Winona County) in 1936; and the state record snowfall for this date is 8.0 inches at Hinckley (Pine County) in 1909.

Past Weather Features:

A winter-like storm brought snowfall to many parts of the state over April 29 to May 1.  In some cases the snowfall was very significant.  Park Rapids, Walker, and Sandy Lake reported over 13 inches, while Hinckley reported nearly 20 inches of snow.  It was relatively short-lived as the first week of May brought a spring like warm up.

By far the warmest May 1st in state history occurred in 1959, when over 50 climate observers reported an afternoon high of 90 degrees F or higher.  The early May Heat Wave ended with abundant thunderstorms on the 3rd which dropped temperatures back into the 60s and 70s F.

The coldest May 1st historically occurred in 1966 when nearly every corner of the state saw overnight temperatures fall into the 20s F.  It was just 29 degrees F at Winona, normally one of the warmest spots in the state.  In northern counties a few observers even reported single digit low temperatures, but by May 5th temperatures climbed into the 70s F and spring planting resumed.


Warmer than normal weekend coming up with increasing cloudiness later on Saturday and a chance for showers and thunderstorms in the north and central counties.  On Sunday there will be a chance for showers and thunderstorms mostly in the south and east.  Cooler Monday, then warming up again next week with increasing chances for showers and thunderstorms late Tuesday through Thursday. 

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