iowa spring flood outlook
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Iowa Spring Flood Outlook. March 5, 2010 Jeff Zogg, Senior Hydrologist. Topics. Outlook at-a-glance Definitions Current conditions Latest spring food outlook Questions. Outlook at-a-glance. - PowerPoint PPT PresentationTRANSCRIPT
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Iowa Spring Flood OutlookIowa Spring Flood OutlookIowa Spring Flood OutlookIowa Spring Flood Outlook
March 5, 2010March 5, 2010
Jeff Zogg, Senior HydrologistJeff Zogg, Senior Hydrologist
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
TopicsTopicsTopicsTopics
• Outlook at-a-glanceOutlook at-a-glance• DefinitionsDefinitions• Current conditionsCurrent conditions• Latest spring food outlookLatest spring food outlook• QuestionsQuestions
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Outlook at-a-glanceOutlook at-a-glanceOutlook at-a-glanceOutlook at-a-glance
• High risk of significant flooding continues in many High risk of significant flooding continues in many areas. areas. Has gone even higher in the Des Moines River Has gone even higher in the Des Moines River basin above Saylorville Reservoir.basin above Saylorville Reservoir.– Highest risk areas include the Des Moines, Raccoon and Little Highest risk areas include the Des Moines, Raccoon and Little
Sioux River basins, as well as the Mississippi River from Sioux River basins, as well as the Mississippi River from Davenport downstream and including its tributaries.Davenport downstream and including its tributaries.
– At least near to above normal risk of flooding statewide.At least near to above normal risk of flooding statewide.• Time period when flooding is most likely extends from Time period when flooding is most likely extends from
the middle third of March into late Aprilthe middle third of March into late April for most for most streams.streams.– Slightly later for the Mississippi and Missouri Rivers.Slightly later for the Mississippi and Missouri Rivers.
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Outlook at-a-glanceOutlook at-a-glanceOutlook at-a-glanceOutlook at-a-glance
• Above normal risk of flash floodingAbove normal risk of flash flooding especially from ice especially from ice jams.jams.– Ice jam flooding is not included in this outlook.Ice jam flooding is not included in this outlook.
• Risk of flooding and flash flooding will be higher than Risk of flooding and flash flooding will be higher than normal after the snow melts.normal after the snow melts.– Will remain higher than normal at least into late spring.Will remain higher than normal at least into late spring.
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National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
DefinitionsDefinitionsDefinitionsDefinitions
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
DefinitionsDefinitionsDefinitionsDefinitions
• Stage / Gage heightStage / Gage height– The level of the water surface of a stream above an The level of the water surface of a stream above an
established datum at a given location. The established datum established datum at a given location. The established datum may be a local elevation or sea level.may be a local elevation or sea level.
• ReachReach– A section of stream between an upstream and downstream A section of stream between an upstream and downstream
location, for which the stage or flow measured at a point location, for which the stage or flow measured at a point somewhere along the section (e.g., gaging station or forecast somewhere along the section (e.g., gaging station or forecast point) is representative of conditions in that section of river point) is representative of conditions in that section of river or stream.or stream.
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DefinitionsDefinitionsDefinitionsDefinitions
• Bankfull stageBankfull stage– An established gage height at a given location, above which a An established gage height at a given location, above which a
rise in water surface will cause the river or stream to rise in water surface will cause the river or stream to overflow the river bank somewhere in the corresponding overflow the river bank somewhere in the corresponding reach.reach.
• Flood stageFlood stage– An established gage height for a given location at which a rise An established gage height for a given location at which a rise
in water surface level begins to create a hazard to lives, in water surface level begins to create a hazard to lives, property or commerce. The issuance of flood (or in some property or commerce. The issuance of flood (or in some cases flash flood) warnings is linked to flood stage. Not cases flash flood) warnings is linked to flood stage. Not necessarily the same as bankfull stage.necessarily the same as bankfull stage.
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DefinitionsDefinitionsDefinitionsDefinitions
• Minor floodingMinor flooding– Minimal or no property damage, but possibly some public Minimal or no property damage, but possibly some public
threat.threat.• Moderate floodingModerate flooding
– Some inundation of structures and roads near stream. Some Some inundation of structures and roads near stream. Some evacuations of people and/or transfer of property to higher evacuations of people and/or transfer of property to higher elevations.elevations.
• Major floodingMajor flooding– Extensive inundation of structures and roads. Significant Extensive inundation of structures and roads. Significant
evacuations of people and/or transfer of property to higher evacuations of people and/or transfer of property to higher elevations.elevations.
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DefinitionsDefinitionsDefinitionsDefinitions
• Record floodingRecord flooding– Flooding which equals or exceeds the Flooding which equals or exceeds the
highest stage or discharge observed at highest stage or discharge observed at a given site during the period of record a given site during the period of record keeping. The highest stage on record is keeping. The highest stage on record is not necessarily above the other three not necessarily above the other three flood categories – it may be within any flood categories – it may be within any of them or even less than the lowest.of them or even less than the lowest.
Stage – flood category Stage – flood category relationshiprelationship
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National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Current conditionsCurrent conditionsCurrent conditionsCurrent conditions
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Winter average temperaturesWinter average temperaturesWinter average temperaturesWinter average temperatures
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Winter precipitationWinter precipitationWinter precipitationWinter precipitation
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Snow depth—nowSnow depth—nowSnow depth—nowSnow depth—now
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Snow depth vs. normal—nowSnow depth vs. normal—nowSnow depth vs. normal—nowSnow depth vs. normal—now
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Snow water equivalent—nowSnow water equivalent—nowSnow water equivalent—nowSnow water equivalent—now
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Snow pack—historical (2009)Snow pack—historical (2009)Snow pack—historical (2009)Snow pack—historical (2009)
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Snow pack—historical (2008)Snow pack—historical (2008)Snow pack—historical (2008)Snow pack—historical (2008)
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Stream levels—nowStream levels—nowStream levels—nowStream levels—now
14-day average flow14-day average flow
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Ground frostGround frostGround frostGround frost
Observed frost depthObserved frost depth
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Soil moisture—nowSoil moisture—nowSoil moisture—nowSoil moisture—now
Percentile keyPercentile key
~1: near record low~1: near record low<10: much below normal<10: much below normal10 -24: below normal10 -24: below normal
25-75: normal25-75: normal
76-90: above normal76-90: above normal>90: much above normal>90: much above normal~99: near record high~99: near record high
Soil moisture percentilesSoil moisture percentiles
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Soil moisture—recentSoil moisture—recentSoil moisture—recentSoil moisture—recent
Percentile keyPercentile key
~1: near record low~1: near record low<10: much below normal<10: much below normal10 -24: below normal10 -24: below normal
25-75: normal25-75: normal
76-90: above normal76-90: above normal>90: much above normal>90: much above normal~99: near record high~99: near record high
Soil moisture percentiles—Soil moisture percentiles—December 2009December 2009
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National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Latest spring flood outlookLatest spring flood outlookLatest spring flood outlookLatest spring flood outlook
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Assumptions / notesAssumptions / notesAssumptions / notesAssumptions / notes
• This outlook is biased toward normal temperatures This outlook is biased toward normal temperatures and precipitation (i.e., climatology) during the outlook and precipitation (i.e., climatology) during the outlook period.period.– If conditions are not near normal then the probabilities in this If conditions are not near normal then the probabilities in this
outlook may not be valid.outlook may not be valid.• Ice jamsIce jams
– This outlook does not take into account flooding from ice This outlook does not take into account flooding from ice jams. Flooding from ice jams would be above and beyond the jams. Flooding from ice jams would be above and beyond the flooding potential indicated in this outlook.flooding potential indicated in this outlook.
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50% flood category—now50% flood category—now50% flood category—now50% flood category—now
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50% flood category—second outlook50% flood category—second outlook50% flood category—second outlook50% flood category—second outlook
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Risk of Risk of minorminor flooding—now flooding—nowRisk of Risk of minorminor flooding—now flooding—now
West 1/3 of Iowa (Missouri River basin)West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)East 2/3 of Iowa (Mississippi River basin)
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Risk of Risk of minorminor flooding—second outlook flooding—second outlookRisk of Risk of minorminor flooding—second outlook flooding—second outlook
West 1/3 of Iowa (Missouri River basin)West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)East 2/3 of Iowa (Mississippi River basin)
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Risk of Risk of moderatemoderate flooding—now flooding—nowRisk of Risk of moderatemoderate flooding—now flooding—now
West 1/3 of Iowa (Missouri River basin)West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)East 2/3 of Iowa (Mississippi River basin)
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Risk of Risk of moderatemoderate flooding—second flooding—second outlookoutlook
Risk of Risk of moderatemoderate flooding—second flooding—second outlookoutlook
West 1/3 of Iowa (Missouri River basin)West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)East 2/3 of Iowa (Mississippi River basin)
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Risk of Risk of majormajor flooding—now flooding—nowRisk of Risk of majormajor flooding—now flooding—now
West 1/3 of Iowa (Missouri River basin)West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)East 2/3 of Iowa (Mississippi River basin)
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Risk of Risk of majormajor flooding—second outlook flooding—second outlookRisk of Risk of majormajor flooding—second outlook flooding—second outlook
West 1/3 of Iowa (Missouri River basin)West 1/3 of Iowa (Missouri River basin) East 2/3 of Iowa (Mississippi River basin)East 2/3 of Iowa (Mississippi River basin)
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Finding river forecast informationFinding river forecast informationFinding river forecast informationFinding river forecast information
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Finding river forecast informationFinding river forecast informationFinding river forecast informationFinding river forecast information
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Finding river forecast informationFinding river forecast informationFinding river forecast informationFinding river forecast information
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National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Final thoughtsFinal thoughtsFinal thoughtsFinal thoughts
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Final thoughtsFinal thoughtsFinal thoughtsFinal thoughts
• Most homeowners’ insurance policies do not cover Most homeowners’ insurance policies do not cover flood-related losses.flood-related losses.– To cover flood-related losses, flood insurance must typically To cover flood-related losses, flood insurance must typically
be purchased. This is in addition to homeowners insurance.be purchased. This is in addition to homeowners insurance.– Disaster assistance, if it’s available, is typically a loan that you Disaster assistance, if it’s available, is typically a loan that you
must repay with interest.must repay with interest.– In most cases, flood insurance requires a 30-day waiting In most cases, flood insurance requires a 30-day waiting
period before it becomes effective.period before it becomes effective.– Visit http://www.floodsmart.gov/ for more information.Visit http://www.floodsmart.gov/ for more information.
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Final thoughtsFinal thoughtsFinal thoughtsFinal thoughts
• Will we see another “2008”?Will we see another “2008”?– A big factor in 2008 was the heavy rainfall from May-June.A big factor in 2008 was the heavy rainfall from May-June.– High-end events such as the 2008 floods typically result from High-end events such as the 2008 floods typically result from
a sequence of additive factors. While one factor by itself may a sequence of additive factors. While one factor by itself may not lead to a high-end event, the combination of factors not lead to a high-end event, the combination of factors elevates the risk of a high-end event.elevates the risk of a high-end event.
– Factors which contribute to significant flooding this spring are Factors which contribute to significant flooding this spring are lining up.lining up.
– This does NOT automatically mean that we’ll have a repeat of This does NOT automatically mean that we’ll have a repeat of 2008 though. We could luck out this spring—the flooding 2008 though. We could luck out this spring—the flooding may be less severe than our outlook indicates.may be less severe than our outlook indicates.
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
Final thoughtsFinal thoughtsFinal thoughtsFinal thoughts
• Spring flood outlook scheduleSpring flood outlook schedule– 1st Outlook: Friday, January 29, 2010.1st Outlook: Friday, January 29, 2010.– 2nd Outlook: Friday, February 19, 2010.2nd Outlook: Friday, February 19, 2010.– 3rd Outlook: Friday, March 5, 2010.3rd Outlook: Friday, March 5, 2010.– 4th Outlook (Optional): Friday, March 26, 2010.4th Outlook (Optional): Friday, March 26, 2010.
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
National Weather ServiceNational Weather ServiceDes Moines, IADes Moines, IA
QuestionsQuestionsQuestionsQuestions
Contact information:Contact information:[email protected]@noaa.gov
515-270-4501515-270-4501http://www.weather.gov/desmoineshttp://www.weather.gov/desmoines