Flood Update: River forecasts raised 1 to 2 feet

Update 4pm:

Updated river forecasts from NCRFC are in reflecting this week’s anticipated rain & snow. The bottom line is that hydrologists have raised (most but not all) river forecast levels about 1.5 feet for most rivers by this weekend.

See the updated forecasts here.

PH

***Original post 9:03 am***

They’re busy crunching some new numbers today at the North Central River Forecast Center in Chanhassen.

As a new storm system rolls into the forecast for Minnesota Tuesday & Wednesday, the potential for heavy rain and snow will likely send river crest forecasts higher. River forecasts through the weekend did not include the latest batch of precipitation.

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Wintery weather makes a comeback this week. (Click to enlarge)

The system will bring rain late tonight into Tuesday morning. Forecast models are cranking out some heavy rain totals with the system, over an inch in some cases. The latest NAM run wrings out 1.23″ of liquid precip for the metro, most of which falls as rain.

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NAM wrings out .50″ to 1″+ precip through Wednesday.

As the system pulls in colder air Tuesday night, rain will change to a wind-driven wet snow from north to south. Winter storm watches are flying for most of the northern half of Minnesota and Wisconsin. A blizzard watch has been hoisted for Duluth and the North Shore.

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Watches posted. (Click to enlarge)

After a rainy Tuesday that could include bouts of thundery rain, It looks like the metro will see a changeover to wet snow late Tuesday night into early Wednesday. It’s still a little early to pinpoint Metro & southern Minnesota snowfall totals with this developing system, but the potential for a few inches of slushy accumulation is there early Wednesday.

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NAM snowfall pastes northern Minnesota with 6″+ but keeps heavy snow north of metro…for now.

Bottom line: Expect rain Tuesday, possibly heavy totals of 1″ in some places… changing to snow by Wednesday.

Flood forecast changes:

Heavy rainfall totals of 1″ will make for some changes in river forecasts this week. As you might guess, most of those changes should be to raise projected river levels later this week.

If the models are right and rainfall totals 1″ or more, that could send a “shock wave” of water with rapid runoff into rivers in southern Minnesota. It may also serve to “flush” some of the moisture still lingering in soils above rivers quickly into river systems, causing more rapidly rising river levels this week.

Here are the main things to watch with regard to river levels and forecasts as this critical week unfolds.

-All creeks & rivers in southern Minnesota are on the rise this week.

-Many rivers and creeks are forecast to reach moderate to major flood levels this week.

-An additional 1″+ of rainfall may create rapidly rising rivers and creeks this week, and the potentially localized nature of heavy rains will be difficult to account for by hydrologists.

-Watch for (rapidly?) changing flood forecasts this week form the NCRFC.

While all rivers will rise this week, the biggies to keep an eye on this week seem to be: These forecasts do NOT include rainfall this week, which could push levels even higher.

The Crow River @ Delano:

The Crow is forecast to rise to “major” flood stage of 18.6′ by this weekend. Latest hydrograph here.

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Impacts: Crow @ Delano -Current forecast 18.6′

24.95 Water begins to flow over the dike on the west side of town.

21.85 Water may begin to flow over the bridge on Bridge Street.

21.05 Water begins to flow over the dike on the east side of the river at Second Street.

20.3 Water seeps through east bank along N River Street/CR 17.

18.95 Sanitary sewers may need plugging at this stage to prevent water from backing up into homes.

18.35 The southwest part of Delano begins to experience flooding.

16.85 Storms sewers may need plugging to prevent river water from backing up into city streets.

15.35 Water begins encroaching on Mill Avenue north of Watertown.

14.85 Minor basement flooding may begin to occur at homes closest to the river.

13.85 Carver County Road 123 between Mayer and Watertown becomes flooded.

The Cottonwood @ New Ulm:

The Cottonwood is also forecast to hit “major” flood stage of 17.1′ by Thursday. Latest hydrograph here.

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Impacts: Cottonwood @ New Ulm: -Current Forecast 17.1′

13 Flood waters begin to impact Cottonwood Street west of the river.

11 Flood waters begin to impact low lying areas…and some roads along the river.

The Minnesota River @ Mankato, Henderson, Jordan, Shakopee & Savage.

Forecasts going into the weekend had the Minnesota rising to moderate flood stage at locations between Mankato & the Twin Cities.

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The forecast river levels (as of early Monday am) would mean top a 10 flood of record on the Minnesota including:

Mankato: 25.5′ (10th highest)

Henderson: 737.6′ (7th highest)

Jordan: 31.5′ (9th highest)

Shakopee: 715.3′ (8th highest)

Savage: 711.7′ (8th highest)

Mississippi River:

The Minnesota feeds into the Mississippi, so any adjustments for higher river levels this week on the Minnesota will affect flow (and river levels) into the mighty Misssissippi.

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Minnehaha Creek:

One (underreported?) aspect of this year’s flood threat is the potential for rising waters and urban flooding on Minnehaha Creek and other metro creeks. The Minnehaha Creek Watershed District has a nifty flood map that shows potential for flood along the creek’s path this spring.

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(Click to enlarge)

You can enter an address and check out flood potential for you neighborhood here.

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You can sign up for flood updates in Carver County here.

Keep an eye out here for the latest changes in river flood forecasts as we move into this week.

PH

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