Tropical Storm Cristobal
A Tropical Depression Crosses Central & Western Wisconsin
Introduction
Historical Wisconsin Tropical Tracks. Image courtesy of the National Hurricane Center.
Tropical Strom Cristobal traveled about 2,500 miles from the Yucatan Peninsula in southeast Mexico into southern Wisconsin in early June of 2020. As Cristobal lifted into southwest Wisconsin, this marked just the 3rd time a tropical weather system's center tracked across parts of Wisconsin. Cristobal was also the furthest north and west tropical system on record. Learn more about tropical systems and their tracks on NOAA's Historical Hurricane Tracks Website . Also, check out NWS La Crosse's local tropical website to see more detailed information on tropical systems that have tracked across the Upper Mississippi River Valley.
Cristobal's Lifecycle
On the afternoon of June 1st, 2020 Tropical Depression Three was analyzed off of the Yucatan Peninsula in southeast Mexico. Over the next few days, the tropical depression was nearly stationary, bringing heavy rain and devastating flooding to parts of Mexico and northern parts Central America. Eventually the tropical depression became more organized and strengthened into Tropical Storm Cristobal.
Satellite animation following Cristobal as it tracked from the Gulf of Mexico toward Wisconsin. Images courtesy of the Weather Prediction Center.
At times, Cristobal was downgraded to a tropical depression as it moved over the Yucatan Peninsula. However, it was projected to re-intensify as it slowly moved north over the Gulf of Mexico. On the afternoon of June 5th, Cristobal had done just that, moved off the Yucatan Peninsula and strengthened back into a tropical storm.
Tropical Storm Cristobal maintained its status as it tracked north across the Gulf of Mexico, eventually making landfall in the United States in southeast Louisiana. Landfall occurred around 5pm on Sunday, June 7th, and brought devastating flooding, heavy rain, and dangerous storm surge. The tropical storm continued its track north-northeast, but eventually was downgraded to a tropical depression on Monday, June 8th.
On Tuesday, June 9th, Tropical Depression Cristobal continued to lift northeast over the Mid-Mississippi Valley and up into southern Wisconsin. As Cristobal lifted northeast, it brought with it heavy rain and flash flooding along the way. It also began to interact with a low pressure system exiting the Central Plains.
Late in the evening on Tuesday, June 9th, Cristobal became extra-tropical across southern Wisconsin, and lost its tropical depression status as it continued to become absorbed by and interacted with the upper-level wave moving into the region.
Tropical Moisture - Extremes!
Leading up to the event, the North American Ensemble Forecast System (NAEFS) was pointing to historical or extreme levels of precitable water (PW) as the remnants of Cristobal lifted into Wisconsin. PW values were progged to approach 2 to 4+ standard deviations, with values essentially maxing out within the database dating back to 1979. Diving a bit deeper, return intervals for PWs also pinpointed values falling well outside of climatological values for early June, with return intervals exceeding 30 years. All that being said, the NAEFS guidance was hinting at a high probability of extreme PW values as the remnants of Cristobal lifted north into Wisconsin.
Interactive swipe showing North American Ensemble Forecast System (NAEFS) precipitable water plots leading up to the arrival of Cristobal. Tied to tropical moisture, projected precipitable water values were at or near the top of the model climatology. Click and drag on the arrow icon to move the slider back and forth.
How Did The Tropical Moisture Pan Out?
Green Bay, Wisconsin sounding precipitable water climatology. Image obtained from the Storm Prediction Center.
The image to the right shows the range of observed PW values with the daily observed maximum values in red and minimum values in blue, based off an archive of upper air soundings from the Green Bay, Wisconsin forecast office dating back to 1953. In between the maximum and minimum values is a black line that shows climatologically where the average or normal PW values typically fall. This data come from the Storm Prediction Center's Sounding Climatology page.
Plotted with the black square is the observed PW value from the 7 PM June 10th upper air sounding observation, where a record 2.2 inches of PW was observed. Thus, the tropical connections and extreme levels of PW did pan out as the extra-tropical system lifted north across Wisconsin.
Heavy Rain
The remnants of Cristobal brought a swath of moderate to heavy rain across the Upper Mississippi Valley. Generally 1 to 3 inches were observed across western parts of Wisconsin. Rises on local rivers and some flooding did occur as the widespread rain lifted across the region, but Iowa was especially hard hit where rainfall amounts were locally higher. Forecast rainfall amounts shown below were spot on when comparing the rainfall observations.
Side by side comparison of NWS rainfall forecasts (left) and observed precipitation (right).
