Flood Threats

Flood Threats:

Many factors have contributed to the current flood threat on Minnesota rivers this month. Perhaps the three most important at this point in time are:

-a wetter than normal final four months of 2018 (Sep-Dec was 40-50 percent above normal precipitation)
-frost depths in the ground in many areas, ranging from 25 to 45 inches, preventing infiltration of melted snow
-Above normal snowfall for the 2018-2019 season (over 125 climate stations report a seasonal total of 65 inches or greater so far) with widespread water content of 4-6 inches.

As a result of these climate factors the NOAA-North-Central River Forecast Center flood outlook for certain points along many southern Minnesota Rivers including the Redwood, Cottonwood, Minnesota, Des Moines, Crow Wing, Cannon, and Mississippi Rivers (at St Paul and Hastings) calls for moderate to major flooding.

These conditions are similar to those faced in the flood years of 1952, 1965, 1997, 2001, and 2011 on many of these watersheds. Yet, two factors that play an important role in determining the peak flood level are only going to play out over the next 2-3 weeks. These are the pace and persistence of a spring thaw with temperatures that remain above freezing; and the amount of precipitation that falls during the snowmelt time period. In this context, an expected intermittent thaw with temperatures rising above freezing during the day, but dropping below freezing at night will help mitigate the flood threat. Countering that however, there is an chance for above normal precipitation to prevail over the southern half of Minnesota during the next two weeks, so this may increase the volume of flow on some rivers. For those who live in more vulnerable areas with respect to flooding it is wise to check the web site of the NOAA-North-Central River Forecast Center for updates.

Roller Coaster Temperatures:

Minnesota reported the nation’s coldest temperature on March 1st (-23°F at Cotton, MN) , and set or tied over 180 cold daily temperature records (either daily maximum or minimum) during the first week of the month. But temperatures have moderated since March 8th, with a large number of freeze-thaw cycles. Many climate stations have seen afternoon temperatures in the low to mid 50s F this week.

Weekly Weather Potpourri:

NOAA provided a more comprehensive national flood outlook on their web site earlier this week, with notes about flood risks on both the Missouri River and the Red River of the north between Minnesota and North Dakota. Wide geographic regions of the country are facing moderate to major flood probabilities at this time.

According to the BBCWeather Centre, Cyclone Idai which struck portions of Mozambique and Zimbabwe late last week has inundated over 1800 square miles of landscape, caused over 300 deaths, and left thousands homeless. Many relief organizations are working there to help victims of the storm.

Elsewhere in the Southern Hemisphere this week Tropical Cyclones Veronica and Trevor were producing strong winds, churning up high sea waves, and bringing rainfall to portions of northern Australia. Sea wave heights have ranged from 30 to 40 feet this week.

MPR listener question:

I am a truck driver in southern Minnesota and listen every day to Morning Edition. I have noticed around Rochester and Marshall this winter that the snow depths have been especially deep. Have these two Minnesota cities had record amounts of snowfall this winter?

Answer:

No they haven’t, but they certainly have recorded a snowy winter. At Rochester the snow season total for 2018-2019 so far is 78.6 inches, in second place historically to 85.1 inches which came in 1996-1997. At Marshall they have recorded 77.3 inches so far this season, that is 6th place all-time and below the 84.7 inches they reported in 1936-1937.

Twin Cities Almanac for March 22nd:

The average MSP high temperature for this date is 44 degrees F (plus or minus 12 degrees F standard deviation), while the average low is 27 degrees F (plus or minus 10 degrees F standard deviation).

MSP Local Records for March 22nd:

MSP records for this date include: highest daily maximum temperature of 71 degrees F in 1945; lowest daily maximum temperature of 10 degree F in 1888; lowest daily minimum temperature of -14 degrees F in 1888; highest daily minimum temperature of 56 degrees F in 2012; record precipitation of 1.40 inches in 1952. Record snowfall is 13.7 inches also in 1952.

Average dew point for March 22nd is 23°F; the maximum dew point on this date is 60°F in 2012; and the minimum dew point on this date is -10°F in 1974.

All-time state records for March 22nd:

The state record high temperature for this date is 81 degrees F at Pipestone (Pipestone County) in 1939. The state record low temperature for this date is -30 degrees F at Pokegama Dam (Itasca County) in 1888. The state record precipitation for this date is 3.00 inches at Elk River (Sherburne County) in 1865. Record snowfall for this date is 14.6 inches at Fairmont (Martin County) in 1952.

Past Weather Features:

By far the coldest March 22nd in state history was in 1888 when morning lows ranged from the minus teens to minus twenties across the state. The daytime high temperature at Rochester that day was only 6 degrees F. Abundant snow was still on the ground.

The warmest March 22nd in state history was in 1939. Over 20 climate stations saw an afternoon high of 70 degrees F or higher. There was little or no snow on the ground in western Minnesota. March 22-23, 1952 brought a blizzard with heavy snowfall to many areas of Minnesota. Snowfall amounts of 10 to 18 inches were common. Many people were stranded along closed roads and travel was at a standstill for a day or two afterwards. The abundant snow of March that year melted rapidly in April causing spring flooding in many areas.

Outlook:

Generally sunny and warm on Saturday, with temperatures several degrees F above normal. Increasing cloudiness on Sunday with a chance for light rain in the southern regions of the state, perhaps a light mixture of snow and rain in the north. Temperatures will fall back a bit for Monday and Tuesday then rebound with a warming trend for next Wednesday through Friday. There will be a chance for rain towards the end of the week as well.