Spring Flood Outlook

1. Spring Flood Outlook National Weather Service Chanhassen - Twin Cities North Central River Forecast Center March 6, 2014 craig.schmidt@noaa.gov 952-368-2542

2. Summary Up Front • Overall, the spring flood threat west of the Mississippi remains near or below historical average • East of the Mississippi, the St. Croix, Chippewa and Eau Claire basins have a higher probability of flooding (50-60%) • Due to higher water content in the snowpack over WI/northeast MN • As always…the true threat lies in how the spring temperatures and rainfall hit us – currently, long range models show a good likelihood of below normal temperatures and rainfall

3. Background: Precipitationsince last briefing (Feb 19) Since last outlook: added .50 – 1.0 inch of water to the snowpack Almost no melting

4. Background: PrecipitationLast 30 Days About 1 to 2 inches of water equivalent has fallen over eastern MN/ WI during the last 30 days Less than one inch in western MN Shown as percent of normal precipitation Source of map: Regional Climate Centers

5. Background: PrecipitationDec/Jan/Feb Percent of Normal Winter precipitation has been well above normal north and east of MSP (4 to 7 inches) Below normal over western MN (1 to 3 inches) Source of map: Regional Climate Centers

6. Background: PrecipitationSnow Water Equivalent (SWE) SWE on the ground: • < 2 in. west and southwest • 3-4.5 in. MSP area • 4-6 in. WI portion

7. Background: PrecipitationSnow Water Equivalent (SWE) Ranking Summary of graphic: SWE falls in the middle of those observed (30-70 percent) over the past 60+ years for much of our area Some basins in western/northern WI and northern MN near the most seen in 60+ years

8. Weather Outlook8–14 Days • Temperatures: likely below normal, somewhat moderate • Precipitation: No clear signal

9. Weather Outlook90 days – March through May Temps: Likely below normal through the spring Precipitation (not shown): no clear indication of above or below normal

10. Other Factors Soil Moisture: Near to below normal over most of area, but higher than last year at this time Frost Depth: Generally 20 to 40 inches over the area, except well below 6-8 feet under pavement. Depth is greatest where snowpack is light or bare ground, shallower where snowpack has insulated the ground River Ice: Thick layers of ice on most rivers; breakup jams will be a concern

11. Flood OutlookMar-Apr-May 2014 • Orange: 50% or greater chance of minor flooding • Red: 50% or greater chance of moderate flooding (none in MPX area) • In MPX area …the main threats are: • Chippewa at Durand • Eau Claire at Fall Creek • St. Croix at Stillwater • Minnesota at Savage (backwater from the Miss. R.) • Flood threat is greater in the Red River of the North (but fairly typical) Forecasts take into account all current conditions, 7-day forecast weather, and climatological normals for the remainder of the spring.

12. Flood Outlook – Durand WI Black Line is current forecast: shows about a 75 percent chance of minor flooding, compared to about 50 percent chance in a normal year (blue line). About a 35 percent chance of moderate flooding, compared to 15 in a normal year.

13. Flood Outlook – Fall Creek WI Black Line is current forecast: shows about a 55 percent chance of minor flooding, compared to about 30 percent chance in a normal year (blue line). About a 40 percent chance of moderate flooding, compared to 15 percent in a normal year.

14. Flood Outlook – Stillwater MN Black Line is current forecast: shows about a 60 percent chance of minor flooding, compared to about 20 percent chance in a normal year (blue line). About a 40 percent chance of moderate flooding, compared to 17 percent in a normal year.

15. Threat Factors Main things to watch for that would increase flood threat… • Extended period of well above normal temperatures, staying above freezing at night • Normal highs in lower 30s early March, close to 50 by April 1 • Moist air melts snow much faster than dry air, so look for dewpoints well above freezing when the air is warm • Any major rainfall event that adds a significant amount of water to wet snow Things to watch for that keep the flood threat manageable… • Temps in the 30s to mid 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.

16. Summary • Overall, spring flood threat over MPX area of responsibility is near to below historical average, but has increased slightly since late February • EXCEPTIONS are the Chippewa and Eau Claire basins in Wisconsin, and St. Croix in MN and WI • Also the lower Minnesota R around Savage due to backwater from the Mississippi R • As always…the true threat lies in how the spring weather unfolds

17. More Info? • Text version of this outlook available at • http://forecast.weather.gov/product.php?site=NWS&product=ESF&issuedby=MSP • Weather information: • http://www.crh.noaa.gov/mpx/ • River information: • http://water.weather.gov/ahps2/index.php?wfo=mpx • For further information or if you have questions, please contact us at the NWS Twin Cities office • 952-361-6671 (forecaster desk, 24/7) • 952-368-2542 (Craig Schmidt, Service Hydrologist) • craig.schmidt@noaa.gov