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Historic flooding hits Iowa

By: Dr. Jeff Masters , 5:07 PM GMT on June 13, 2008

Truly extraordinary flooding has hit the Cedar River in the town of Cedar Rapids, Iowa. Rainfall amounts in excess of 12 inches have fallen in the past ten days over the Cedar River watershed, which extends to the northwest of Cedar Rapids into southern Minnesota. The rains that fell during the weekend of June 7-8 were fueled in part by moisture from Tropical Storm Alma/Arthur, which affected Central America May 29 - June 2. The Cedar River is expected to crest today at 31.8 feet, which is an amazing 19.8 feet above the flood stage of 12 feet. During the historic 1993 flood, the worst in recent history, the river hit only 19.27 feet, 7 feet above flood stage. Nine rivers in Iowa are at all-time record flood levels, and Iowa Governor Chet Culver has declared 83 of the state's 99 counties state disaster areas. Additional heavy rainfall is not expected over the Cedar River watershed over the next two days, so today should mark the peak of this year's historic flooding.

Figure 1. Total rainfall for the period June 2 - June 12, 2008, as estimated by NASA's TRMM satellite. An additional three inches fell over portions of eastern Iowa in the 24 hours since this image was created.

New way to track river flooding on wunderground
Wunderground has added a way to track local river forecast levels and assess flood risk at www.wunderground.com/wundermap/rivers. Using data from the USGS (the U.S. Geological Survey), the product plots river data and forecasts on top of our interactive "WunderMap". Users can scroll across the country and zoom in and out to view in-depth observations from all major rivers in the U.S. Alternatively, one can click an option to view only the rivers with current flood alerts. Each river observation is color coordinated to reflect its dry/wet percentile and users can click on each observation point to view data and graphs that display Flow Rate, Percentile, Current Stage, Forecast Stage and Flood Stage. Flood Alert symbols will appear on every river icon whenever a river is in danger of flooding.

The WunderMap™ also allows one to choose from a variety of layers including current conditions, animated radar, severe weather and tornado warnings, live webcam images and animated infrared or visible satellite imagery showing cloud coverage. WunderMap™ is available as a link on every U.S. forecast page, just under the small radar image.

Tornado outbreak update
The tornado that stuck the Little Sioux Scout Ranch Boy Scout camp in western Iowa Wednesday night, killing 4 and injuring 48, was rated an EF-3 on the Enhanced Fujita scale. The tornado that hit Manhattan, Kansas the same day, causing major damage at Kansas State University, has been rated an EF-4. This is the tenth violent (EF-4 or EF-5) tornado this year, the most number of violent tornadoes since 13 were observed in 1999.

The Storm Prediction Center is calling for a "Slight" risk of severe weather across the Midwest today, from Michigan to Oklahoma. We can expect a few more tornadoes today in the affected region, although the primary severe weather threat will be damaging thunderstorm winds and large hail. The "Slight" risk of severe weather continues Saturday and Sunday across a large portion of the Midwest.

It's quiet in the tropics. There is some disorganized thunderstorm activity in the southern Gulf of Mexico associated with a surface trough of low pressure, but this activity is not likely to develop. None of the models are forecasting tropical storm formation in the next seven days.

Jeff Masters

Sandbagging (Bubbly)
Great volunteer work on sandbagging in Coralville
Flooding in Coralville (Bubbly)
Roads closed and houses evacuated; today multiplied both of these with floodwaters still rising and more rain coming.
Flooding in Coralville
Mammatus Clouds at Sunset (RCPlains)
Mammatus Clouds at Sunset

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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979. guygee
4:04 PM GMT on June 16, 2008
I suppose I could have created a blog and linked to it... otherwise it is an original composition, so there is nothing else to link to.

If people are not interested in my posts please put me on ignore, that will solve the problem.

I tend to put up long posts.
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977. guygee
4:02 PM GMT on June 16, 2008
Re:975. 69Viking

A link to what?
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976. Drakoen
4:00 PM GMT on June 16, 2008
New Blog.
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975. 69Viking
10:56 AM CDT on June 16, 2008
972. guygee

Why not just post a link?
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974. melwerle
3:53 PM GMT on June 16, 2008
Wow - first time I have seen a child abduction emergency on weather.gov...

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11:52 AM EDT on June 16, 2008
A watched pot never boils.

CIMSS 200mb vort Atl
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972. guygee
3:50 PM GMT on June 16, 2008
Re: 164. TexasGulf 2:32 AM GMT on June 14, 2008
Re: 179. Skyepony 3:29 AM GMT on June 14, 2008
Re: 189. atmoaggie 4:48 AM GMT on June 14, 2008

Although the terrible flooding in the Midwest is continuing, I wanted to respond to some open questions on this blog regarding how flood recurrence intervals are computed, how often they are updated depending on changing conditions, and how the corresponding FEMA floodplains are determined.

The FEMA Guidelines and Specifications for Flood Hazard Mapping Partners page contains links to most of the documents describing the procedures and technical specifications and requirements for determining recurrence intervals and floodplains. Quoting from Volume 1: Flood Studies and Mapping,

"An increase in the length of a stream gage record may also affect the flood discharge estimate. If the effective discharge was estimated by conducting a frequency analysis of a relatively short record of stream gage data, the base flood discharge estimate may be changed if newly available data are added. If stream gage data with a relatively long record(50 years or more) were used in the effective analyses, however, a few additional years usually will not cause significant changes in the base flood discharge estimate, unless a large-magnitude event occurred since the analyses were conducted. All frequency analyses are to be performed in accordance with the methods specified in Bulletin 17B, Guidelines for Determining Flood Flow Frequency (Interagency Advisory Committee on Water Data, 1982). The effective flood discharge shall be revised only if that discharge is outside the 90-percent confidence interval (higher than 95-percent confidence limit or lower than 5-percent confidence limits) of the newly computed flood discharge. [February 2002]"

The Bulletin 17B mentioned above is available from the USGS Guidelines for Determining Flood Flow Frequency page.

From reading the documents my understanding is that in general updates may be required by the FEMA Director, but the decisions to update are usually left to the FEMA regional offices. Updates are completed for different subregions every year. A search of updates may be performed by going to the Federal Register EPA Impact Statements site. A search using the words "change" and "elevation" seems to bring up all of the updates.

Although the updates are normally local and ongoing, FEMA is currently engaged in a national update effort called the "Flood Map Modernization Program". Here is FEMA's Map Modernization page with links to all of the documents. The program will involve digitization of many paper products, improved on-line access of data, and widespread updates of current FEMA maps. Quoting from the FAQ,

Q: What is Flood Map Modernization?
A: Flood Map Modernization (Map Mod) is FEMA's approach to updating the Nation's flood hazard maps. Map Mod transforms flood maps into reliable, easy-to-use, and readily available digital products. As a result, communities across the country can more easily obtain flood risk information to help make sound construction and mitigation decisions.

Q: Why do flood maps need to be updated?
A: Reliable information about flood risks is the first step in preventing and reducing losses. Today, more than two-thirds of the Nation's flood maps are more than ten years old, and therefore may not represent the true flood risks. Up-to-date flood hazard data and maps support an actuarially sound flood insurance system, enable wise floodplain management, and increase the Nation's flood hazard awareness.

A good short tutorial on calculating flood recurrence intervals is available courtesy of Dr. Eric M. Baer, Geology Program, Highline Community College via Carleton College: Teaching recurrence intervals.

A very good description of how FEMA's standards for hydrological and hydraulic modeling are translated locally into operational mode is given in Knox County Tennessee Stormwater Management Manual Section 8.4 Floodplain Management Regulations. For example,

" Hydrologic Modeling - Determining Peak Discharges
Peak discharges shall be determined for the 2-year, 10-year, 25-year, 100-year and 500-year
storm events. The peak discharges shall be determined for pre-development and post-development land use conditions, and shall be utilized as input to the hydraulic model that is used to determine floodplain elevations and other floodplain data.

Four methods are considered acceptable for determining peak discharges for the purpose of
floodplain data development, as follows:
1. gage analysis using statistical hydrologic methods;
2. Clark Unit Hydrograph;
3. the use of Tennessee Valley Authority (TVA) regression equations; and,
4. the use of a hydrologic model, such as USACE's HEC-1 or HEC-HMS.

The Director shall select the method that will be used on a case-by-case basis. The selection is based on the availability of existing hydrologic models and/or gage data in the same area as the proposed development, a history of flooding in the same area as, or downstream of, the proposed development, FEMA standards and requirements, and engineering judgment."[...](more)

The U.S. Army Corps of Engineers hydrological and hydraulic modeling software is available on the Hydrologic Engineering Center page.

Interesting to note that FEMA specifies USGS regional regression equations that are used in the National Flood Frequency program (see Program Documentation for V3), but Knox County has substituted TVA equations... apparently an exception in areas where the TVA exists. The differences between the USGS and TVA equations are outlined in the Knox County Tennessee Stormwater Management Manual, Volume 2 (Technical Guidance) Chapter 3.1 Introduction to Hydrologic Methods.

Finally, for a short and fairly non-technical research paper showing how a group in Croatia integrated the USACE hydrological and hydraulic models together with a meteorological model to determine flood recurrence intervals, see "HYDROLOGIC AND HYDRAULIC ANALYSIS OF LESS STUDIED WATERSHEDS" (pdf).
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971. Drakoen
3:45 PM GMT on June 16, 2008
Good morning everyone. Not much to talk about. King SAL rules...
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3:39 PM GMT on June 16, 2008
Anybody know when this High will move out of Texas? It's just burnin' up HOT here.
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968. ShenValleyFlyFish
11:36 AM EDT on June 16, 2008
965. jphurricane2006

We in Human Psychology still have you beat.
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967. sporteguy03
3:35 PM GMT on June 16, 2008
Good Chance of Strong to Severe Storms today 60%-70% chance
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966. ShenValleyFlyFish
11:34 AM EDT on June 16, 2008

SWAG: scientific wild @ssed guess
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964. smmcdavid
10:33 AM CDT on June 16, 2008
Good morning all. I see the tropics are still quiet.

Busy today, but will check back in when I can....
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963. ShenValleyFlyFish
11:22 AM EDT on June 16, 2008
957. DestinJeff

That's why we call it weather. You never know whether it will turn out the way you expect.
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3:28 PM GMT on June 16, 2008
960. presslord

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961. Weather456
11:24 AM AST on June 16, 2008
957. DestinJeff 11:17 AM AST on June 16, 2008

Very well said!

The best we can do is use climatology as something as the norm. We have to look at the situation operationally and objectively (as it is happening now) to gauge whether these conditions are the norm.
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960. presslord
11:25 AM EDT on June 16, 2008
the quote from stormtracker.com bears repeating...

"...meteorology is an attempt to approximate chaos..."

it's as much art as science.....
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958. HadesGodWyvern (Mod)
3:17 PM GMT on June 16, 2008
Tropical Cyclone Outlook (0900z 16Jun)
At 14:30 PM IST, Morning's Depression over north Bay of Bengal off Bangladesh coast moved in a westerly direction and lays centered at 21.5N 89.5E close to Bangladesh coast and about 170 kms southeast of Calcutta, India. The system is likely to move in a northwesterly direction and cross Bangladesh coast between 89.0 and 89.5E by today evening.

Tropical Cyclone Bulletin for Coastal India
Under its influence, rainfall at most places with heavy to very heavy rainfall at a few places and extremely heavy falls (>25cm) at isolated places is likely over gangetic West Bengal and north Orrisa during next 48 hours. Fairly widespread rainfall with isolated heavy to very heavy falls is also likely over south Orrisa and Jarkhand during the same period.

Squally winds speed reaching 45-55 km/h are likely along and off north Orrisa and West Bengal coasts during next 24 hours. Sea condition is rough to very rough along and off these coasts. The Fishermen are advised not to venture into sea.
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955. Nolehead
3:06 PM GMT on June 16, 2008
think the NHC better get used to looking at these "different" areas of concern... the way this year's weather has gone...nothing is a shocker anymore it seems.
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954. Weather456
10:54 AM AST on June 16, 2008
This feature has alot to overcome if its going to development. Stratocumulus near a tropical disturbance especially in the path of motion is an unfavorable factor.

Blob Watching

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953. HurakanPR
10:38 AM AST on June 16, 2008
My humble opinion is that the reason NHC is ignoring the atl wave is simply climatology, which rarely fails. But having said that, this mid June wave is "pretty" healthy. Wonder what will be their reaction if the so call"sickly little wave" surprise us.
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951. TampaSpin
11:02 AM EDT on June 16, 2008
949. cchsweatherman 11:01 AM EDT on June 16, 2008

Should this not be on YOUR on personal blog. Instead of a post....wow
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950. weatherfromFlorida
3:02 PM GMT on June 16, 2008
Morning everyone! I see the wave came back pretty good in DMAX.
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949. cchsweatherman
10:39 AM EDT on June 16, 2008
Tropical Update for Monday, June 16, 2008
Written at 11AM

Right now, the Tropical Atlantic remains rather quiet with just one feature that I'm watching for possible tropical development. The Tropical Atlantic remains rather quiet due to very fast upper-level winds occuring over the most climatologically-favorable area for tropical development for June - the Caribbean - but over the past week, the upper level winds over the region have begun to relax. I will continue to watch this trend as this could be an ominous sign for the upcoming months.

As previously mentioned, there is one feature I'm monitoring for possible tropical development. Over the weekend, there was a very impressive tropical wave that emerged off Africa which now is moving across the Central Atlantic. On the Tropical Atlantic satellite loop above, this tropical wave has just appeared into the view at around 30W. There is a very well-defined circulation, although not at the surface yet. For right now, I cannot determine whether this feature will develop into a tropical system since there are factors going for (very low upper-level winds, very warm water temperatures, and a developing circulation) and going against (very dry air surrounding the system, new dust surge from Africa, and climatology) tropical development. I will know much more about this feature tomorrow as I will be watching for the convection to maintain itself and increasing organization in order for me to determine that this will develop.

Going away from this main feature, we may have to watch the Gulf of Mexico as a frontal system will stall in the Northern Gulf this week. During June, there have been tropical systems that have developed from dying frontal systems when they reach the Gulf of Mexico. Right now, the upper-level winds are quite favorable for tropical development there and water temperatures are warm enough to support tropical development, but it will all depend on what happens with this approaching frontal system once it reaches the Gulf of Mexico.

Overall, no tropical development is expected within the next 24 hours, but I cannot say that definitively for within 48 hours. Stay tuned for further updates.
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948. extreme236
2:58 PM GMT on June 16, 2008
946. I agree, but I think the latitude has something to do with why the NHC isn't talking about it. Also its embedded in the ITCZ too and that is probably a factor as well.
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947. Nolehead
2:54 PM GMT on June 16, 2008
anyone notice that slight spin off the yucatan...probably not anything, but a spin is a spin...just wondering..
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945. catastropheadjuster
2:46 PM GMT on June 16, 2008
Floodman- thanks and Mail call back at cha.
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944. extreme236
2:52 PM GMT on June 16, 2008
850mb vorticity map shows some defined vorticity has formed with the wave, but still low in latitude.
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943. extreme236
2:45 PM GMT on June 16, 2008
There really isn't anything in the Caribbean right now.
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942. Nolehead
2:45 PM GMT on June 16, 2008
morning all...well looks like that nice convection in the Atl....kinda early for this time of the year, but heck the way this year is going...no telling what will happen next..
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941. Chicklit
9:44 AM EST on June 16, 2008
Would the low shear indicate neutral conditions are beginning?
(ie, no more El Nino?)
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940. Weather456
10:45 AM AST on June 16, 2008
Member Since: December 31, 1969 Posts: Comments:
938. TampaSpin
10:40 AM EDT on June 16, 2008
934. cchsweatherman 10:39 AM EDT on June 16, 2008
Tampa - When I work on my Tropical Update, I'll take a look into that area and give you my opinion since it seems that you are dead-set that there will be tropical development in the Southwest Caribbean.

CCHS it just my opinion.....your sarcasm is not needed.......thank you.
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937. IKE
9:42 AM CDT on June 16, 2008
936. weathersp 9:41 AM CDT on June 16, 2008
Anybody noticed a WNW turn in the wave over the last 6 or so hours..

I agree.
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936. weathersp
10:38 AM EDT on June 16, 2008
Anybody noticed a WNW turn in the wave over the last 6 or so hours..

Don't look at the cloud tops look at the "green mist" the circles it and look in which way it moves on the easten side of the wave.

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934. cchsweatherman
10:38 AM EDT on June 16, 2008
Tampa - When I work on my Tropical Update, I'll take a look into that area and give you my opinion since it seems that you are dead-set that there will be tropical development in the Southwest Caribbean.
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933. IKE
9:37 AM CDT on June 16, 2008
931. 305st0rm 9:35 AM CDT on June 16, 2008
Good Morning.....it seems that none of the reliable model runs pick up the wave in the EATL. The only model picking it up is the CMC

The latest GFS has it...it just doesn't develop it into a storm...

Then again, I've seen the GFS not develop systems that do develop....
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932. TampaSpin
10:25 AM EDT on June 16, 2008
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931. 305st0rm
2:28 PM GMT on June 16, 2008
Good Morning.....it seems that none of the reliable model runs pick up the wave in the EATL. The only model picking it up is the CMC
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930. Floodman
9:33 AM CDT on June 16, 2008
Mail call catastropheadjuster!
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