Record Flood Risk: St. Paul, Shakopee, Fargo, Delano

The flood picture got a little clearer Thursday with the latest NWS Spring Flood Outlook. You may want to look away if you’re sqeamish.

The headlines that jump out from the latest outlook include:

Major flooding is likely along most area rivers this spring.

Here’s the (somewhat alarming) text from the latest NWS Spring Flood Outlook.

PROBABILISTIC HYDROLOGIC OUTLOOK

NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN

358 PM CST THU MAR 3 2011

…SPRING FLOOD AND WATER RESOURCES OUTLOOK…

…THE POTENTIAL FOR FLOODING ALONG THE COTTONWOOD…MINNESOTA…CROW…MISSISSIPPI FOR ST PAUL AND DOWNSTREAM AND THE ST CROIX…IS MUCH ABOVE NORMAL…WITH MODERATE TO MAJOR FLOODING LIKLEY AND CONCERN IS INCREASING FOR RECORD FLOODING…

One of the remarkable features in the outlook is that area rivers may not just flood, or hit “major flood stages” but the high percentages of record flooding.

Again, here is the text from NWS:

SEVERAL LOCATIONS HAVE AN INCREASED RISK OF 20 PERCENT OR MORE OF EXCEEDING THEIR FLOOD OF RECORDS. THE LOCATIONS INCLUDE

*COTTONWOOD RIVER

– NEW ULM

*MINNESOTA RIVER

-NEW ULM

-MANKATO

-HENDERSON

-JORDAN

-SHAKOPEE

*SOUTH FORK OF THE CROW AND CROW RIVER

– MAYER

– DELANO

– ROCKFORD

*MISSISSIPPI

– ST PAUL

– HASTINGS

– RED WING

And here are some numbers.

Risk of reaching record flood stage:

Mississippi River:

St. Paul 48%

Hastings 25%

Minnesota River:

Henderson 25%

Jordan 38%

Shakopee 40%

Red River: (Latest outlook here.)

Fargo-Moorhead: 33%

St. Croix:

Stillwater 18%

South Fork Crow River:

Delano 33%

Potential Effects: So what does it all mean?

Numbers are eye catching, but don’t always bring much meaning or perspective to a story.

The potential effects of record flood levels described by NWS in the outlook are sobering, to say the least.

(Click for bigger, easy to read images with (my) highlights)

For the Mississippi:

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A 10 2100 225 10 1 flood ms.jpg

For the Minnesota:

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A 10 2100 225 10 1mn flood.jpg

For the South Fork Crow & St. Croix:

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A 10 2100 225 10 1 crow stcx.jpg

Digging Deeper: Why such a high risk of record flooding this year?

The bulk of narrative from the NWS Spring Flood Outlook tells the story in greater detail. My highlights in bold.

DUE TO THE SEPTEMBER RAINS…WATER LEVELS AND SOIL MOISTURE WERE STILL ABOVE NORMAL AS WE WENT INTO THE WINTER FREEZE IN MID TO LATE NOVEMBER. THIS SET THE STAGE FOR AN INCREASED THREAT FOR FLOODING WITH A SPRING MELT.

IN ADDITION TO THE WET SOILS…PRECIPITATION FOR SEPTEMBER THROUGH

MID EARLY MARCH HAS REMAINED ABOVE NORMAL FOR CENTRAL AND SOUTHERN

MINNESOTA AS WELL AS WEST CENTRAL WISCONSIN. LIQUID AMOUNTS FOR THIS PERIOD RANGE FROM 11 INCHES IN CENTRAL MINNESOTA TO 18+ INCHES IN SOUTH CENTRAL AND SOUTHEAST MINNESOTA FOR THIS PERIOD. AMOUNTS HAVE AVERAGED BETWEEN 15 TO 17 INCHES IN WEST CENTRAL WI. THESE AMOUNTS ARE 125 PERCENT OF NORMAL FOR THE UPPER MISSISSIPPI VALLEY AND WEST CENTRAL WISCONSIN TO OVER 200 PERCENT OF NORMAL IN PARTS OF SOUTHWEST MINNESOTA.

SINCE THE LAST SPRING FLOOD OUTLOOK IN THE THIRD WEEK OF

FEBRUARY…WE HAD ONE SIGNIFICANT SNOWSTORM THAT IMPACTED CENTRAL AND SOUTHERN MN AND PARTS OF WESTERN CENTRAL WI. THE FAR UPPER SECTIONS OF THE MISSISSIPPI RIVER HOWEVER MISSED THE BRUNT OF THIS STORM. LIQUID AMOUNTS FROM THIS STORM AVERAGED FROM 0.75 INCHES TO APPROXIMATELY 1.25 INCHES ACROSS MUCH OF CENTRAL AND SOUTHERN MINNESOTA AS WELL AS WEST CENTRAL WISCONSIN. FOR THE TWO WEEK PERIOD THESE PRECIPITATION AMOUNTS ARE 150 TO 200 PERCENT OF NORMAL.

SNOW WATER EQUIVALENTS IN THE RIVER BASINS ARE QUITE SIGNIFICANT. RECENT SNOW CORE AND REMOTE SENSING MEASUREMENTS SHOW THAT THERE IS ROUGHLY 3 TO 5 INCHES OF WATER IN THE UPPER MISSISSIPPI AND WISCONSIN CHIPPEWA BASINS. FOR THE UPPER MINNESOTA BASIN…5 TO 7 INCHES OF WATER IS PRESENT IN THE BASIN. FROM A COMPARISON PERSPECTIVE IN THE PAST 60YEARS…THIS IS IN THE 90TH PERCENTILE OF THE RANKINGS FOR SNOW WATER EQUIVALENTS. SO…WHILE WE DID LOSE SOME WATER DURING THE BRIEF WARM UP DURING THE THIRD WEEK OF FEBRUARY…MOST OF THE WATER IS STILL CONTAINED IN THE SNOWPACK…SOILS OR THE SMALLER CREEKS AND STREAMS.

Right now I see the likely timing for the onset of flooding to begin in earnest the week of March 20th, with river levels possibly reaching peak around the first week of April. That could change depending on how the weather unfolds over the next 2-3 weeks.

It’s going to be a wild ride this spring on area rivers.

Stay tuned!

PH