A Look Back at the Historic July 28, 1949 Marquette County Flood

A cold front associated with a low pressure system moving through the Upper Great Lakes during the early evening hours of July 28, 1949 led heavy rain to fall over portions of Marquette County. This heavy rain, which accumulated up to 5.35 inches in Ishpeming in about 2 hours, lead to flooding in Ishpeming, Negaunee, and Marquette.

Meteorological Setup

Southwesterly flow ahead of a low pressure system centered in the Dakotas (Image 1) moved warm and moist air over the Upper Great Lakes region in the days leading up to the event. In Upper Michigan, high temperatures rose in the middle and upper 80s over much of the area during the afternoon hours on July 28th (Image 2). In fact, the city of Marquette was 87 degrees at 3:30 pm, before dropping to 65 degrees after the thunderstorms at 8 pm.


Image 1: Surface Chart from 07/28/1949 at 1:30 am (Click for larger image)

Image 2: High Temperatures for July 28, 1949

As this low moved north and then east over Lake Superior during the late afternoon and evening on the 28th of July (Image 3), showers and thunderstorms developed along the cold front and moved east into central Upper Michigan. At the same time, the hourly precipitation data (Image 4) indicated that thunderstorms developed ahead of the cold front and was the main cause of the heavy rainfall in the Marquette County area. Although the exact cause is unknown, efforts to recreate this event with numerical models (more information below) has led us to believe that a lake breeze contributed to the heavy rainfall event.

Image 3:Surface Chart from 07/29/1949 at 1:30 am Image 4: Hourly Rainfall Amounts from 7pm to 8pm on July 28, 1949

How Historic Was This Event (Precipitation Amounts)

While rainfall occurred over much of Upper Michigan on July 28-29, 1949, the heaviest rainfall occurred over a small area of Marquette County (Image 5). In fact, there was a very sharp cutoff to the precipitation to the south-southeast from Ishpeming, with Gwinn only receiving 0.05”, Escanaba had 0.02”, which was same as Iron Mountain (they also had some power outages from thunderstorms).

Taking a closer look at Marquette County (Image 6), the highest amount was 5.35” recorded by the Ishpeming Cooperative Observer (Cliffs Power and Light Co) between 7:30 and 9:45pm. Around the same time, the weather office in the city of Marquette recorded 3.96” (a Top 10 daily rainfall amount) and Big Bay received 2.44” of rain.

Image 5: Rainfall Amounts across the Upper Great Lakes on July 28-29, 1949 Image 6: Rainfall Amounts for Marquette County on the evening of July 28, 1949

To put the 5.35” of rain received in Ishpeming in perspective, the city of Ishpeming normally received 3.35” of rain during the month of July. Thus, it received 2 inches more than their normal monthly amount in just 2 hours and 15 minutes. The 5.35” of rain in Ishpeming ranks as the 10th highest 1 day rainfall total in Western and Central Upper Michigan (as taken by NWS Marquette Cooperative Observers).

Another way to look at the potential for this event to occur is with precipitation frequency data. This data gives the probability of a precipitation amount occurring in a certain amount of time during the current year. For north central Upper Michigan, the probability of seeing 5 inches of rain in a single day during the year is 1% (or once every 100 years). In the case of a 2 hour rainfall, there is only a 0.1% chance (once every 1000 years) of seeing around 4 inches within 2 hours. Since Ishpeming received even more rainfall than that, the potential for it to occur again in Ishpeming is even lower.

Impacts of the Heavy Rainfall 

As you would expect, the heavy rainfall caused numerous issues across portions of Marquette County. The image to the right (click to enlarge) shows all of the different impacts the heavy rainfall had on Marquette County (based off accounts reported in The Mining Journal on July 29-30, 1949). The main issues were flooding and power outages, although there were a couple reports of trees down in the Negaunee and Ishpeming areas. As for the flooding, it was reported that most of the businesses in the Ishpeming/Negaunee area had their basements flooded, along with water 3 feet deep on US 41A between Ishpeming and Negaunee at Partridge Creek. In the city of Marquette, a washout at the corner of Spring and Lake Streets damaged several buildings and the railroad tracks. Also on Lake Street, a washout caused a gas and oil spill at the Michigan Gas and Electric Co when a fuel oil tank was knocked over and gas line was broken. In addition, frequent lightning caused numerous power outages, especially in the city of Marquette. You can see several images from The Mining Journal below. For more personal accounts of the July 28th, 1949 Marquette County Flood, see the book written by Karl Bohnak: “So Cold A Sky: Upper Michigan Weather Stories”.

Attempts to Recreate the Event

Using North American Reanalysis data and the Weather Research and Forecasting (WRF) model, we attempted to recreate the events during the evening of July 28, 1949. Although the models didn’t recreate the events that unfolded over Marquette County on that evening, it did give some insights on what happened. Though most of the model runs that we performed failed to adequately handle the development of the thunderstorms along the cold front (generally too far to the west), they did indicate that lake breeze development was possible. Some runs even developed showers and thunderstorms along that lake breeze. Combining that information with the limited hourly precipitation and temperature data would lead to some support that lake breezes played a role in the heavy rainfall.

Image 7: Simulated Reflectivity from a WRF model run starting on July 28, 1949 at 00Z and valid at 8pm.


Pictures from the Event (From the Mining Journal on July 29-30, 1949) 









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