National Weather Service Des Moines, IA National Weather Service Des Moines, IA Iowa Spring Flood Outlook March 5, 2010 Jeff Zogg, Senior Hydrologist

National Weather Service Des Moines, IA TopicsTopics Outlook at-a-glanceOutlook at-a-glance DefinitionsDefinitions Current conditionsCurrent conditions Latest spring food outlookLatest spring food outlook QuestionsQuestions

National Weather Service Des Moines, IA Outlook at-a-glance High risk of significant flooding continues in many areas. Has gone even higher in the Des Moines River basin above Saylorville Reservoir.High risk of significant flooding continues in many areas. Has gone even higher in the Des Moines River basin above Saylorville Reservoir. –Highest risk areas include the Des Moines, Raccoon and Little Sioux River basins, as well as the Mississippi River from Davenport downstream and including its tributaries. –At least near to above normal risk of flooding statewide. Time period when flooding is most likely extends from the middle third of March into late April for most streams.Time period when flooding is most likely extends from the middle third of March into late April for most streams. –Slightly later for the Mississippi and Missouri Rivers.

National Weather Service Des Moines, IA Outlook at-a-glance Above normal risk of flash flooding especially from ice jams.Above normal risk of flash flooding especially from ice jams. –Ice jam flooding is not included in this outlook. Risk of flooding and flash flooding will be higher than normal after the snow melts.Risk of flooding and flash flooding will be higher than normal after the snow melts. –Will remain higher than normal at least into late spring.

National Weather Service Des Moines, IA National Weather Service Des Moines, IA DefinitionsDefinitions

National Weather Service Des Moines, IA DefinitionsDefinitions Stage / Gage heightStage / Gage height –The level of the water surface of a stream above an established datum at a given location. The established datum may be a local elevation or sea level. ReachReach –A section of stream between an upstream and downstream location, for which the stage or flow measured at a point somewhere along the section (e.g., gaging station or forecast point) is representative of conditions in that section of river or stream.

National Weather Service Des Moines, IA DefinitionsDefinitions Bankfull stageBankfull stage –An established gage height at a given location, above which a rise in water surface will cause the river or stream to overflow the river bank somewhere in the corresponding reach. Flood stageFlood stage –An established gage height for a given location at which a rise in water surface level begins to create a hazard to lives, property or commerce. The issuance of flood (or in some cases flash flood) warnings is linked to flood stage. Not necessarily the same as bankfull stage.

National Weather Service Des Moines, IA DefinitionsDefinitions Minor floodingMinor flooding –Minimal or no property damage, but possibly some public threat. Moderate floodingModerate flooding –Some inundation of structures and roads near stream. Some evacuations of people and/or transfer of property to higher elevations. Major floodingMajor flooding –Extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.

National Weather Service Des Moines, IA DefinitionsDefinitions Record floodingRecord flooding –Flooding which equals or exceeds the highest stage or discharge observed at a given site during the period of record keeping. The highest stage on record is not necessarily above the other three flood categories – it may be within any of them or even less than the lowest. Stage – flood category relationship

National Weather Service Des Moines, IA National Weather Service Des Moines, IA Current conditions

National Weather Service Des Moines, IA Winter average temperatures

National Weather Service Des Moines, IA Winter precipitation

National Weather Service Des Moines, IA Snow depth—now

National Weather Service Des Moines, IA Snow depth vs. normal—now

National Weather Service Des Moines, IA Snow water equivalent—now

National Weather Service Des Moines, IA Snow pack—historical (2009)

National Weather Service Des Moines, IA Snow pack—historical (2008)

National Weather Service Des Moines, IA Stream levels—now 14-day average flow

National Weather Service Des Moines, IA Ground frost Observed frost depth

National Weather Service Des Moines, IA Soil moisture—now Percentile key ~1: near record low <10: much below normal : below normal 25-75: normal 76-90: above normal >90: much above normal ~99: near record high Soil moisture percentiles

National Weather Service Des Moines, IA Soil moisture—recent Percentile key ~1: near record low <10: much below normal : below normal 25-75: normal 76-90: above normal >90: much above normal ~99: near record high Soil moisture percentiles— December 2009

National Weather Service Des Moines, IA National Weather Service Des Moines, IA Latest spring flood outlook

National Weather Service Des Moines, IA Assumptions / notes This outlook is biased toward normal temperatures and precipitation (i.e., climatology) during the outlook period.This outlook is biased toward normal temperatures and precipitation (i.e., climatology) during the outlook period. –If conditions are not near normal then the probabilities in this outlook may not be valid. Ice jamsIce jams –This outlook does not take into account flooding from ice jams. Flooding from ice jams would be above and beyond the flooding potential indicated in this outlook.

National Weather Service Des Moines, IA 50% flood category—now

National Weather Service Des Moines, IA 50% flood category—second outlook

National Weather Service Des Moines, IA Risk of minor flooding—now West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

National Weather Service Des Moines, IA Risk of minor flooding—second outlook West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

National Weather Service Des Moines, IA Risk of moderate flooding—now West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

National Weather Service Des Moines, IA Risk of moderate flooding—second outlook West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

National Weather Service Des Moines, IA Risk of major flooding—now West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

National Weather Service Des Moines, IA Risk of major flooding—second outlook West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)

National Weather Service Des Moines, IA Finding river forecast information

National Weather Service Des Moines, IA Finding river forecast information

National Weather Service Des Moines, IA Finding river forecast information

National Weather Service Des Moines, IA National Weather Service Des Moines, IA Final thoughts

National Weather Service Des Moines, IA Final thoughts Most homeowners’ insurance policies do not cover flood-related losses.Most homeowners’ insurance policies do not cover flood-related losses. –To cover flood-related losses, flood insurance must typically be purchased. This is in addition to homeowners insurance. –Disaster assistance, if it’s available, is typically a loan that you must repay with interest. –In most cases, flood insurance requires a 30-day waiting period before it becomes effective. –Visit for more information.

National Weather Service Des Moines, IA Final thoughts Will we see another “2008”?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.

National Weather Service Des Moines, IA Final thoughts Spring flood outlook scheduleSpring flood outlook schedule –1st Outlook: Friday, January 29, –2nd Outlook: Friday, February 19, –3rd Outlook: Friday, March 5, –4th Outlook (Optional): Friday, March 26, 2010.

National Weather Service Des Moines, IA National Weather Service Des Moines, IA QuestionsQuestions Contact information: