April 30 1967 Minnesota-Iowa Tornado Outbreak
by Jonathan D. Finch

Brief Overview

                        An outbreak of tornadoes occurred on April 30, 1967 in northern Iowa and southern Minnesota.  These tornadoes resulted
                        in 13 deaths in Minnesota. While tornadoes were wreaking havoc, a blizzard was raging across the northern plains. Some
                        details of the most prominent tornadoes on this day are given below.

Major Tornadoes

The Alden-Matawan Tornado

                        A tornado moved north-northwest from just northwest of Alden, MN at 605 pm to near Matawan. Farm damagewas near F4
                         at the beginning of the path. Homes and barns were destroyed. Two people were killed.

The Hartland-Waseca tornado

A tornado developed near Hartland around  615pm and moved due north into the town of Waseca. This funnel was in contact
                        with the ground 90% of the time. After hitting Waseca the tornado moved north-northeast and ended 7 miles nne of Waseca.
                        The tornado followed highway 67 into town and destroyed farm buildings on both sides of  the highway. The tornado cut a
                        4-block path into town, destroying 16 homes, 6 of which were leveled. Twenty-five other homes were heavily damaged. This
                        tornado is rated F4 in "Significant Tornadoes" by Tom Grazulis. Six people were killed near Waseca.

                        Another tornado paralleled this tornado about 4 miles to the east--moving from west of Lemond at 615 pm to west of
                        Meriden. Barns were destroyed. It is not known if this was the same storm that produced these tornadoes. Based on the
                        times, the 2nd tornado seemed to have lagged behind the first tornado and may have been produced by a different storm.

The Manly-Mrytle Tornado

                        A tornado moved slightly east of due north from 2 miles southeast of Manly, IA(620pm) to near Myrtle, MN. This tornado
                        destroyed 10 farms, levelling some of them to the ground in near-F5 fashion. Ten other farms, mostly in Iowa were
                        extensively damaged. There is conflicting  information about the time of this tornado. Were there 2 tornadoes back to back,
                        one at 530 and another at 630 pm or is storm data in error?                       


The Albert Lea-Owatonna tornado

                        A tornado moved north-northeast from southwest of Twin Lakes(623 pm) to the western suburbs of Owatonna. Farms were
                        leveled at 6 locations along the path. There was $2,000,000 damage in Albert Lea where 26 homes were destroyed
                        and 64 badly damaged. Two people were killed close to Owatonna near the end of the path with 5 deaths total.

The London tornado

                        A tornado moved north(628 pm) from south of the Minnesota state line to near London, MN. Six farms were extensively                   
                        damaged and at least 2 farm homes were destroyed.


Other Tornadoes 


                    A tornado touched down around 4 pm east of Gruver, IA and moved north to near Huntington. One barn was destroyed
                        and 6 others were damaged.                       

                    A tornado moved northeast(410 pm) from 1 mile west of Crystal Lake, IA to west of Forrest City. Buildings were damaged
                         or destroyed on 8 farms. Three farms lost all the buildings except the homes.                      

                    A tornado moved north-northeast(410 pm) from 8 miles north of Emmetsburg. Homes were unroofed near Halfa and barns
                         were destroyed east of Gridley.                         

                        A tornado moved northeast near Vincent, IA around 350 pm. 

                        A tornado touched down near Hollandale, MN and moved N, lifting east of Geneva. 

                        A tornado touched down(715 pm) on a farm 1.5 miles southeast of Austin, MN and moved north for 6 miles.  At least 2 barns
                        and 1 farm home were unroofed and torn apart.

                        A tornado touched down around 810 pm and moved north from near Marion to northeast of Eyota. A trailer andbarn were



Synoptic Sequence of events 

                        At 12 UTC April 30  1967, a very strong upper level trough was beginning to eject northeast across the southern high
                        plains. A 700mb warm pool stretched up and down the plains from north Texas to Omaha, NE. The 700mb temp.
                        at Omaha was +9C which is very warm by late April standards. However, mid-level cold advection was noted
                        across the southern high plains and southern Rockies. The 700mb temps. were down to 5C at Amarillo and 3C at
                        North Platte. A 850mb moist tongue extended from eastern Oklahoma into central and eastern Iowa with 850mb
                        dewpoints at least 12C.
                        The 18 UTC surface map showed a deep surface low in central South Dakota with a cold front stretching from eastern
                        Nebraska to north Texas. As is common with strong and developing storm systems, several areas of low level
                        frontogenesis were present across northern Iowa and southern Minnesota. A nearly stationary boundary(#1) stretched
                        from south of Mankato, MN to south of Green Bay, WI. Air north of this boundary was much too stable for surface
                        based convection. Another surface boundary(#2) stretched from north of Sioux Falls, SD to south of Waterloo, IA to
                        north of Moline, IL. Air north of this boundary was only marginal unstable with fairly cool temperatures and modest
                        temperatures and modest dewpoints. A warm front(#3) extended from south of Sioux Falls, SD to near Des Moines, IA to
                        north of Kirksville, MO. The airmass along and north of this boundary was extremely unstable with low LCL heights.
                        South of this boundary the LCL heights were much higher but it was still very unstable due to the warmer temperatures.
                        By 21 UTC the northern most boundary was still in roughly the same position. The southern boundaries had progressed

                        The 23 UTC surface map showed the surface cold front charging into southern Minnesota and north Central Iowa.
                        The 3 aforementioned boundaries intersected near a surface low just southwest of Mankato, MN.

                        By 00 UTC May 1  1967, a very intense upper system was centered just north of North Platte. This system obviously
                        underwent development since 12 UTC as the 500mb height near the center of the upper low dropped from 540dm
                        to 528dm and was centered near Valentine, NE. The 500mb wind at Omaha was 110kts so a very strong jet
                        streak was associated with this system. The 700mb chart showed cold advection acros the central and southern
                        plains. The 700mb temp. had dropped from 9C to -4C at Omaha in 12 hours and from 9C to -1 C at Topeka.
                        The leading edge of the 700mb cooling was across central and western Iowa at 00 UTC or roughly coincident
                        with the surface cold front. The 850mb moist tongue had shifted east and extended from Illinois north-northwestward
                        into central and eastern Iowa and southeast Minnesota.                  

                        The following sequence of "zoomed in" surface charts from 18, 21 and 23 UTC show the different airmasses in places
                        across northern Iowa and southern MN on April 30  1967.

                        21 UTC
                        23 UTC

                        00 UTC
                        High temperatures(6pm to 6 pm) from cooperative observers were used to help locate boundary positions and help
                        in the determination of instability. The high temps in the Waseca/Owatonna are were in the 63 to 66F range. Since there
                        was the possibility that the max temp for the day occurred after 6 pm and before the storms hit, I also checked the
                        next day max temp to make sure it wasnt higher than the April 30 maxes. Since the cold front passed immediately
                        after the tornadoes hit, it seems logical that the max temps at the coop sites of Owatonna and Waseca were close   
                        to the temps that the storms experienced. In other words, as the storms approached Waseca and Owatonna, the
                        storm inflow was fairly cool (< or + 66F). The max temp at Albert Lea was 68F but the dewpoint was probably
                        not too far behind the temperatures(mid 60sF).


Instability approximation 

                        Surface based instability(SBCAPE in this study) was approximated for several areas. The first approximated
                        sounding is for areas immediately north of the southernmost warm front. Surface based CAPE in this area
                        was over 3000 /kg. The second sounding was made for areas along boundary #2 where dewpoints were very
                        high and temperatures fairly cool. Surface based CAPE was around 2400 j/kg. This sounding is probably
                        a good approximation of the conditions near Albert Lea near the time of the Albert Lea tornado. The third
                        sounding is probably a good approximation of the conditions near Waseca and Owatonna around the time these
                        towns were hit by tornadoes. The low levels were just too stable north of these towns for continued tornadic activity.
                        The CAPE in this third sounding was around 1800 j/kg. 

                        The above finding show that the most violent tornadoes did not occur in the area of highest surface based instability.
                        Tornadoes did occur in northern Iowa, but these were not near as violent as the ones further north.

                        Just in case anyone is curious, I modified the Feb 12  2007 12 UTC Glasgow, MT sounding to obtain the soundings
                        above. This may seem very odd but I have a very good reason for this method. This sounding happened to the one
                        sounding that I could find in the local AWIPS database that had a starting pressure around 940mb. 940mb matches
                        the station pressure on April 30, 1967 in southern Minnesota. But how is this possible one might ask since Glasow is
                        2100 ft ASL. This is 900ft higher than the terrain around Albert Lea Minnesota and 1000ft corresponds to about
                        33mb assuming 200ft ~ 6.5mb for elevations between 1000 and 2000ft. But the sea level pressure on Feb 12 2007
                        was about 1020mb at Glasgow while the slp was about 986mb at Albert Lea, MN on April 30, 1967. In other words,
                        the effective elevation at Albert Lea was much higher on April 30 1967 due to the very low pressure on that day.
                        Thus, instead of the sounding starting out at 970mb(slp 1016mb), the sounding started out at 940mb(slp 986mb).