Tropical Depression Cristobal Drenches Southeast Minnesota, June 9, 2020

Minnesota's first known direct encounter with a tropical cyclone produced heavy rains and flooding in southeastern Minnesota on June 9, 2020.

Tropical Depression Cristobal formed in the far southern Gulf of Mexico on June 1, and headed south into Mexico, before re-tracking northward towards Louisiana as a Tropical Storm. It made landfall on June 8, weakened to a Depression again, and continued heading northward, traveling near and roughly parallel to the Mississippi River.

Copious moisture followed Cristobal northward, and radars displayed a large mass of rotating precipitation, hundreds of miles across, as the storm passed into the region.

When the center of the storm reached eastern Iowa, it began turning northeastward, following the northwest side of a large high-pressure area. This path centered the heaviest precipitation in far southeastern Minnesota and Wisconsin, with the edge of the rain shield reaching into the Twin Cities area, where the rain was generally light.

In southeastern Minnesota, the rain was anything but light, beginning in the early afternoon, and generally lasting 5-8 hours, with bands of intense rain wrapping into the system. Mudslides near Lanesboro, Goodview, Whitewater State Park, Whalan, and Winona spilled onto roads, knocking over power poles in some cases.

Fillmore and Winona Counties received the most rain, with CoCoRaHS observers near Lewiston, Stockton, and Minnesota City reporting 4.19 to 4.62 inches, and the automated DNR gauge at Lanesboro reporting 4.54  inches. The area southeast of a line from Albert Lea to Red Wing generally received 1 to 3 inches of rain, including a total of 1.83 inches at the Rochester International Airport.

Cristobal was still a tropical depression when it began producing rain in Minnesota, making this the only known instance of a tropical cyclone affecting Minnesota directly. Its "eye," or what was left of it, passed just southeast of the state, but the almost solid shield of rains associated with it stretched into the southeastern 1/4 of Minnesota.  Other tropical systems have influenced our weather, usually by providing additional atmospheric moisture to the region and enhancing precipitation--sometimes dramatically. It appears, however, that the arrival of the primary tropical precipitating system into Minnesota may be a first. Additionally, according to analyses by the National Weather Service in La Crosse, Cristobal's track made it farther northwest than any other tropical cyclone in at least 120 years.

Following are a few basic answers to questions Minnesotans may have regarding this rare event.

What is a cyclone, and what is a tropical cyclone? A cyclone is any weather system that rotates around a center of low pressure. In the northern hemisphere, that rotation is always counter-clockwise, when viewed from above.  Minnesota experiences dozens of cyclones per year, most having strong warm fronts and cold fronts, leading to dramatic temperature changes from one side of the system to the other. Cyclones in the Upper-Midwest produce the majority of our precipitation, snowstorms, and hazardous weather. They are most common and most intense in the fall and spring, but occur throughout the year. The more common term, "low-pressure system," also refers to cyclones.

Tropical cyclones form over warm oceans, usually at latitudes of 10-25 degrees (Minnesota is centered on near 45 degrees north latitude), and get their energy from the ocean and its warm water. Tropical cyclones do not have cold fronts or warm fronts associated with them, so temperatures are not that different from one side to another. A Tropical Depression is the formal term forecasters use for tropical cyclones with sustained winds of 38 mph or less. If the winds increase to 39 mph or more, the system becomes a Tropical Storm, and is given a name. Cristobal would not have been named if it had not reached this threshold. A tropical storm becomes a Hurricane when its winds reach 74 mph.

How was the rainfall from Cristobal different from other heavy rain events in Minnesota? The rainfall amounts from Cristobal certainly were impressive, but they were not extraordinary. Minnesota has had much larger rainfall events. What was extraordinary, however, was how the rain fell. Most of Minnesota's flash-floods have come from thunderstorms that form repeatedly over the same areas. During the height of Cristobal's rains in southeastern Minnesota, there was virtually no lightning or thunder. It was instead a steady rain, just much heavier than we normally experience. Note the broad, smooth appearance of the radar echoes on the animation above. Compare that to more rigid and focused appearance of the large thunderstorm cells during an extreme rainfall event in central Minnesota. 

Why doesn't Minnesota see more tropical cyclones? Tropical cyclones require warm ocean moisture and very light winds aloft for survival. Minnesota is over a thousand miles from the Gulf of Mexico, and is often near the position of the jet stream, where winds aloft race through the region, creating and steering our non-tropical weather systems. Most tropical cyclones simply cannot survive these conditions, and so we rarely see anything but their residual moisture make it this far north. Cristobal was able to drift northward with almost no disruption from winds aloft until late on Tuesday, June 9th.

The following flooding and rainfall reports were gathered by the La Crosse office of the National Weather Service.

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE LA CROSSE WI
747 AM CDT WED JUN 10 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..
0821 PM     FLASH FLOOD      1 W WHALAN              43.74N 91.95W
06/09/2020                   FILLMORE           MN   LAW ENFORCEMENT

            MUDSLIDE REPORTED ON HIGHWAY 16, 3 MILES
            EAST OF LANESBORO.

0830 PM     FLASH FLOOD      ELBA                    44.09N 92.02W
06/09/2020                   WINONA             MN   LAW ENFORCEMENT

            MUDSLIDE NEAR ELBA AND WHITEWATER STATE
            PARK. MUDSLIDES ALSO REPORTED NEAR WINONA
            BRINGING DOWN POWER POLES.

0849 PM     FLASH FLOOD      1 S LEWISTON            43.97N 91.87W
06/09/2020                   WINONA             MN   EMERGENCY MNGR

            HIGH WATER OVER ROAD AT CO HWY 29 AND CO HWY
            106 NEAR LEWISTON.

0924 PM     FLASH FLOOD      2 S GOODVIEW            44.04N 91.72W
06/09/2020                   WINONA             MN   EMERGENCY MNGR

            REPORT OF A MUDSLIDE AND TREE DOWN ON HWY 14
            BETWEEN WINONA AND STOCKTON.

0948 PM     FLASH FLOOD      1 ESE WHALAN            43.73N 91.92W
06/09/2020                   FILLMORE           MN   LAW ENFORCEMENT

            REPORT OF MUDSLIDE.


Public Information Statement
National Weather Service La Crosse WI
822 AM CDT Wed Jun 10 2020

...24 HOUR RAINFALL TOTALS...

Location                     Amount    Time/Date       Lat/Lon
...MINNESOTA...

...Dodge County...
Hayfield 0.3 SSE             1.86 in   0730 AM 06/10   43.89N/92.85W
Hayfield                     1.69 in   0747 AM 06/10   43.89N/92.85W
Wasioja (IFLOWS)             1.61 in   0348 AM 06/10   44.07N/92.82W
Mantorville 1.9 ESE          1.26 in   0600 AM 06/10   44.05N/92.72W

...Fillmore County...
Lanesboro                    4.54 in   1230 AM 06/10   43.72N/91.98W
1 S Peterson                 3.68 in   0543 AM 06/10   43.78N/91.83W
Mabel                        3.34 in   0630 AM 06/10   43.52N/91.76W
Chatfield 9.0 ESE            3.31 in   0700 AM 06/10   43.79N/92.03W
Preston 3.2 NNE              2.85 in   0630 AM 06/10   43.71N/92.05W
3 ESE Canton                 2.34 in   0922 PM 06/09   43.52N/91.87W
2 S Pilot Mound              2.02 in   0700 AM 06/10   43.78N/92.03W
1 NNW Fillmore               1.90 in   0700 AM 06/10   43.76N/92.27W
Wykoff 3.1 NW                1.80 in   0700 AM 06/10   43.74N/92.31W
Preston Airport              1.50 in   0735 AM 06/10   43.68N/92.17W

...Houston County...
Houston                      3.11 in   0746 AM 06/10   43.77N/91.58W
Spring Grove                 3.00 in   0800 PM 06/09   43.56N/91.64W
Caledonia                    3.00 in   0800 PM 06/09   43.63N/91.50W
Mound Prairie                2.71 in   0600 AM 06/10   43.78N/91.45W
La Crescent 5.4 SW           2.51 in   0700 AM 06/10   43.78N/91.39W
Hokah 4 NW                   2.28 in   0700 AM 06/10   43.80N/91.43W
La Crescent                  2.25 in   0800 AM 06/10
2 NE Mound Prairie           2.09 in   0730 PM 06/09   43.80N/91.43W
1 NNE Houston                2.07 in   0730 AM 06/10   43.77N/91.57W
La Crescent 1.0 WSW          2.01 in   0700 AM 06/10   43.83N/91.32W
1 SSE Brownsville            1.61 in   0915 PM 06/09   43.69N/91.27W

...Mower County...
Austin 3 NW - Turtle Creek   3.22 in   0700 AM 06/10   43.65N/92.98W
Austin 2.7 W                 2.53 in   0700 AM 06/10   43.68N/93.03W
Austin 2.4 W                 2.45 in   0700 AM 06/10   43.67N/93.02W
Austin 1.5 WSW               2.36 in   0700 AM 06/10   43.67N/93.00W
Ostrander 5.1 WNW            2.32 in   0700 AM 06/10   43.65N/92.52W
Austin 3S - Cedar River      2.28 in   0630 AM 06/10   43.64N/92.97W
4 WSW Austin                 1.50 in   0820 PM 06/09   43.64N/93.05W
Lansing - Cedar River        1.02 in   0600 AM 06/10   43.75N/92.96W

...Olmsted County...
Elgin 5SE                    2.59 in   0700 AM 06/10   44.08N/92.19W
Eyota 2NE                    2.47 in   0700 AM 06/10   44.02N/92.20W
1 W Chester                  2.39 in   0616 AM 06/10   44.00N/92.38W
3 ENE Rochester              2.26 in   0630 AM 06/10   44.03N/92.43W
Rochester 1.5 WSW            2.20 in   0700 AM 06/10   44.00N/92.50W
2 NE Rochester               2.20 in   0600 AM 06/10   44.04N/92.44W
3 N Rochester                2.19 in   0715 AM 06/10   44.06N/92.47W
Rochester                    2.14 in   0745 AM 06/10   44.04N/92.44W
Rochester-Beltline Bear Cree 1.97 in   0600 AM 06/10   44.01N/92.45W
Rochester                    1.96 in   0130 AM 06/10   44.04N/92.44W
Elba 4.7 SW                  1.86 in   1030 PM 06/09   44.04N/92.09W
2 NNW Rochester              1.84 in   0600 AM 06/10   44.05N/92.49W
Rochester International Airp 1.83 in   0746 AM 06/10   43.90N/92.50W
Rochester 5.8 ENE            1.75 in   0700 AM 06/10   44.06N/92.38W
Rochester 2.0 NNE            1.69 in   0700 AM 06/10   44.04N/92.47W
Rochester 4.2 N              1.68 in   0600 AM 06/10   44.08N/92.49W
Mayo Helipad                 1.50 in   0735 AM 06/10   44.02N/92.48W
Byron                        1.15 in   0830 PM 06/09   44.03N/92.65W

...Wabasha County...
Wabasha                      2.65 in   0748 AM 06/10   44.30N/92.00W
1 N Kellogg                  2.52 in   0530 AM 06/10   44.32N/92.00W
Plainview                    2.13 in   0746 AM 06/10   44.17N/92.17W
Zumbro Falls 3.5 SSW         1.37 in   0644 AM 06/10   44.24N/92.46W
3 SSW Lake City              1.20 in   0723 AM 06/10   44.40N/92.30W
Mazeppa                      1.19 in   0700 AM 06/10   44.27N/92.55W
3 ESE Mazeppa                1.11 in   0700 AM 06/10   44.26N/92.49W
Lake City                    1.09 in   0745 AM 06/10   44.44N/92.28W

...Winona County...
Winona 3S                    4.79 in   1200 AM 06/10
Lewiston 0.2 NW              4.62 in   0700 AM 06/10   43.99N/91.87W
Winona 5.1 WSW               4.54 in   0700 AM 06/10   44.03N/91.77W
Stockton 1.2 W               4.36 in   0608 AM 06/10   44.03N/91.79W
Minnesota City 1.1 SE        4.19 in   0700 AM 06/10   44.08N/91.73W
Winona                       3.50 in   0805 PM 06/09   44.05N/91.66W
4.2 N Rollingstone           3.40 in   0600 AM 06/10   44.16N/91.81W
Winona Dam 5A                3.20 in   0600 AM 06/10   44.09N/91.67W
Goodview                     3.20 in   0930 PM 06/09   44.07N/91.71W
Winona 12.0 ESE              3.13 in   0700 AM 06/10   43.99N/91.44W
Dakota                       2.90 in   0700 AM 06/10   43.91N/91.36W
Winona 2SE                   2.87 in   0800 AM 06/10
Whitewater State Park        2.35 in   0700 AM 06/10   44.05N/92.05W
La Crescent Dam 7            2.30 in   0600 AM 06/10   43.87N/91.31W
Beaver                       2.30 in   0500 AM 06/10   44.15N/92.00W
1 WSW Elba                   2.23 in   0700 AM 06/10   44.09N/92.03W
3 SW Elba                    2.10 in   0630 AM 06/10   44.06N/92.05W
Saint Charles                1.30 in   0750 AM 06/10   43.97N/92.06W  

Observations are collected from a variety of sources with varying
equipment and exposures. We thank all volunteer weather observers
for their dedication. Not all data listed are considered official.

Modified June 10, 2020