National Weather Service“Spring” 2014 Flood

Update

March 28, 2014

Craig Schmidt, Service Hydrologist

Winter 2013-14 Sixth coldest in Minnesota history – five consecutive months below normal

50 days below zero at MSP; 77 days below zero at DLH

100+ inches of snow at DLH; most of the state 1-2 feet above normal; even more in northern WI

IN SHORT… we haven’t dealt with a winter like this in over 30 years.

Flood Outlook Summary

Overall, the spring flood threat over Minnesota remains near historical average…with a catch

Mississippi slightly above average

St. Croix above average

Minnesota R average to below average

In the Wisconsin basins (Eau Claire and Chippewa), the threat is rising to above average as we hold onto snow and move further into spring.

MOST IMPORTANT POINT: the true threat lies in how April temperatures and rainfall hit us. We’re holding onto a lot of water in some basins later into the spring than we normally do. This makes us more susceptible to snowmelt combining with warm spring rain as we move later into the spring.

Background: Snowfall

Good portion of MN above normal this season, well above normal north and into WI

Water Year to date (inches) Percent of normal

Background: SnowfallSnow Depth

Snow mostly gone southwest of I-94; still plenty to melt further north and east.

Background: PrecipitationSnow Depth change in last week

Snow depth decreased over southern and central parts of area; actually increased far north

March 19 March 27

Background: SnowfallModeled Snow Water Equivalent (SWE)

Mostly gone over southwest half…still 1-2 inches around the Twin Cities; 3-5 inches in northern WI and MN.

Soil Moisture (0-72 inch layer)

Near to above average over much of the state, except Minnesota River basin and parts of the far north.

Once thaw occurs, there is some room for soil to absorb water

Frost Depth: Generally 20 to 40 inches over the area, except 10 to 20 inches around the Twin Cities. Much deeper still under pavement and roads.

River Ice: Thick layers of ice on most rivers; breakup jams will be a concern

Other Factors

Flood outlooks posted in the coming slides include known conditions up to that point, and use climatology as the forecast weather conditions.

Significant deviations in our weather pattern from climatology would result in different results. Thus, it will pay to watch our weather patterns closely through April…

Flood OutlookClimatologically based

For St. Cloud…a 30% chance of minor flooding, just above historical average. Near average chance of moderate flooding (12%).

Flood Outlook – Mississippi at St. Cloud

For St. Paul…historically average chance of minor flooding, about 30 percent.

Flood Outlook – Mississippi at St. Paul

Less than 5 percent chance of flooding, well below average

Flood Outlook – Minnesota at Mankato

For Stillwater… about a 60 percent chance of reaching flood stage, well above the 25 percent average. About a 40 percent chance of reaching moderate flood level, 20 percent chance of hitting major flood level.

Flood Outlook – St. Croix at Stillwater

For the Eau Claire… about a 45 percent chance of reaching flood stage, above the 25 percent average. About a 20 percent chance of reaching moderate flood level, just above average.

Flood Outlook – Eau Claire River at Fall Creek

For the Chippewa (WI)… about a 75 percent chance of reaching flood stage, above the 45 percent average. About a 30 percent chance of reaching moderate flood level, above the 15 percent historical normal.

Flood Outlook – Chippewa River at Durand WI

Threat Factors

Main things to watch for that would increase flood threat…

Extended period of well above normal temperatures (60s, for instance), staying above freezing at night

Moist air melts snow much faster than dry air, so look for dewpoints well above freezing when the air is warm

Any major rain or snow event that adds a significant amount of water to wet snow (2 inches of water or more)

Things to watch for that keep the flood threat manageable…

Temps in the 30s and 40s, dropping below freezing at night

Below to average precipitation – light to moderate snow or light rain is fine

Dry air – dewpoints in the teens and 20s.

So, with that said…what’s the forecast?

Weather OutlookShort term forecast – through the next week

Melting over the weekend, then cooler again. Another storm on the horizon early next week. Potential significant snow north of the Twin Cities

Weather OutlookSeven Day Precipitation forecast

One to two inches of liquid possible over much of the area by the end of the week; snowpack will increase again over northern/central MN and northern WI

Weather Outlook8–14 Days – April 4 through 10

Temperatures: below normal trend continues through at least early April

Weather Outlook8–14 Days – April 4 through 10

Precipitation: equal chances of above, below, or normal

Temps: Cool trend expected to continue thru April

Precipitation (not shown): no clear indication

Weather Outlook30 days – April

Temps: Cool trend expected to continue thru April, then moderate

Precipitation (not shown): no clear indication

Weather Outlook90 days – April through June

Weather forecast effect on flood threat

Next week’s storm could be crucial…pay close attention to forecasts on precipitation amounts next week. Likely to add to the snowpack to the northern MN and WI basins, further priming the threat for later in the spring. It could enhance short term runoff around the Twin Cities and in central WI.

After that…temperatures remain cool, melting slows again. This could be a beneficial trend to reduce flood threat.

Our flood threat is becoming more susceptible to late spring rains, as peak runoff will be later than normal. Stay tuned…

NOTE:

RFC daily forecasts will start in early April; some maybe by this weekend if forecasts show significant rises.

Yeah, we can dream…

For the Dreamers…10 month forecast – Dec/Jan/Feb next winter

*WebpagesWeather info: www.weather.gov/twincities

River info: http://water.weather.gov/ahps2/index.php?wfo=mpx

Text version of this outlook:

http://forecast.weather.gov/product.php?site=NWS&product=ESF&issuedby=MSP

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More Info? How to reach us…

*Facebook: US National Weather Service Twin Cities

*Twitter: @NWSTwinCities

*Contact: - Craig Schmidt, Service Hydrologist, at

craig.schmidt@noaa.gov / 952-368-2542

- NWS Chanhassen Operations at 952-361-6671

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