Mid American Energy Spring Flood Outlook

1. Mid American Energy Spring Flood Outlook February 16, 2010 Jeff Zogg

2. Outlook at-a-glance • High risk of significant flooding in northwest Iowa. • Also concerned about flooding in southeast Iowa—Mississippi River and its tributaries. • At least near to above normal risk of flooding statewide. • Above normal risk of flooding from ice jams. • Higher than normal risk of flooding also in areas that have little to no snow cover. • The flooding potential will be more sensitive than normal to the occurrence and timing of weather events such as rapid warm ups and heavy precipitation.

3. Current conditions

4. Average temperatures since 1/25/10

5. Precipitation since 1/25/10

6. Snow pack—now

7. Snow pack—now

8. Snow pack—now

9. Snow pack—historical (2009)

10. Snow pack—historical (2008)

11. Stream levels—now 14-day average flow

12. Soil moisture—now Soil moisture percentiles Percentile key ~1: near record low <10: much below normal 10 -24: below normal 25-75: normal 76-90: above normal >90: much above normal ~99: near record high

13. Soil moisture—recent Soil moisture percentiles—December 2009 Percentile key ~1: near record low <10: much below normal 10 -24: below normal 25-75: normal 76-90: above normal >90: much above normal ~99: near record high

14. Latest spring flood outlook

15. Assumptions / notes • This outlook assumes near normal temperatures and precipitation (i.e., climatology) during the outlook period. • If conditions are not near normal then the probabilities in is outlook may not be valid. • For example, if above normal precipitation is expected during the outlook period, then the probabilities in this outlook may be too low. • Outlook assumes near normal through late April. • Official temperature outlook  near to above normal. • Official precipitation outlook  no strong trend signal.

16. Assumptions / notes • Ice jams • Any ice jams which do occur may result in locally higher river stages and rapid river rises. This outlook does not take into account potential flooding from ice jams. Any flooding from ice jams would be above and beyond the flooding potential indicated in this outlook.

17. Median (50% chance) flood category

18. Risk of minor flooding West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

19. Risk of moderate flooding West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

20. Risk of major flooding West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

21. Detail—Waterloo Service Center  90-day stage exceedance probability Weekly stage exceedance probability 

22. Detail—Two Rivers Service Center  90-day stage exceedance probability Weekly stage exceedance probability 

23. Final thoughts

24. Final thoughts • Will we see another “2008”? • A big factor in 2008 was the heavy rainfall from May-June. • High-end events such as the 2008 floods typically result from a sequence of additive factors. While one factor by itself may not lead to a high-end event, the combination of factors elevates the risk of a high-end event. • Factors which contribute to significant flooding this spring are lining up. • This does NOT automatically mean that we’ll have a repeat of 2008 though. We could luck out this spring—the flooding may be less severe than our outlook indicates. But, the risk of flooding is elevated so we need to watch things closely.

25. Final thoughts • Spring flood outlook schedule • 1st Outlook: Friday, January 29, 2010. • 2nd Outlook: Friday, February 19, 2010. • 3rd Outlook: Friday, March 5, 2010. • 4th Outlook (Optional): Friday, March 26, 2010.

26. Questions Contact information: jeff.zogg@noaa.gov 515-270-4501 http://www.weather.gov/desmoines