One of the big stories this year has been the flooding along the Missouri River. The featured chart presents the river stage observation from one of the automated sites near Sioux City. The river was in moderate flood stage for over 2 months! Among other things, this did a tremendous amount of damage to some the highways and interstates in the area which will require complete reconstruction.

Temperatures soared well into the 90s on Thursday making for the warmest first of September for Des Moines since the 1980s. The featured chart presents the year one needs to go back to for a high temperature that was as warm as the one reported this year. The cool periods stand out as most of the bars only go back to 2010. Speaking of cooler air, it is working into the state this morning and highs early next week will only be around 70!

Labor Day this year looks to be great, if you like lots of sunshine and high temperatures around 70! The featured chart presents the high temperature and daily average wind speed for Labor Days since 1971. The forecasted value for this year is shown in red. The average high temperature for this day is just above 80!

The remnant of Tropical Storm Lee has been causing all kinds of grief over the southeastern US. A number of tornadoes were reported on Monday along with 99 tornado warnings issued. The featured map presents the number of county based tornado warnings issued so far this year. The largest total is 35 for Madison County, Alabama (Huntsville). More tornadoes are possible today over the Carolinas.

The past two mornings have seen rather chilly temperatures with record lows set in Mason City and Ottumwa. The featured map presents the lowest temperature reported since the first of August. While some locations have dipped into the 30s, the major urban centers of Des Moines, Council Bluffs, and Iowa City have barely breached 50 degrees. This is a classic urban heat island effect of having lots of warm buildings and concrete slowing the rate of cooling overnight.

The weather these past few days has been remarkable for cool high temperatures along with mostly clear skies overhead. The featured chart attempts to look at the relationship of having cool days along with mostly clear skies or northerly winds. While the determination of these two criteria was somewhat arbitrary, the signal appears to be reasonable. Having northerly winds is common for these cool days, but least important during the summer time when the air to our north may not be that cold. Clear skies are the least common during May and June, when are surface heating rates are the largest.

The current analysis of drought severity in the state has just over half of Iowa under abnormal or worse drought condition. The featured graph shows the history of drought category coverage over Iowa since the year 2000. The past 5 years have been relatively drought free with 2008 and 2010 being very wet years. The forecast does not have much in the way of rain chances for the next week as our dry weather continues.

The east coast has been hit very hard by extreme rainfalls from tropical storms. Binghamton, New York set their all time record one day rainfall on Wednesday of 7.49 inches. The featured chart shows the one minute interval rainfall data from the observation site there. A similar chart to this was generated for the other daily records set this year for Dubuque, Chicago, and New York City. There is a very big difference shown by this plot with peak hourly rates in the one to two inches per hour range as compared with double or triple that in the other plots.

The past seven days have been a dry stretch for most in the state. The featured chart presents the daily frequency of that day being a part of a seven day dry stretch. This chart has a clear annual signal, bottoming out around the first week of June and maximizing in mid December. The forecast looks to keep us dry for another week with high temperatures today around 90!

Very chilly air for this time of year settled into Iowa over night and morning low temperatures were below freezing for most of those in the northern half of the state. Our bout with cold air will be brief as chances of rain are in the forecast along with lows well above freezing.

Model Output Statistics (MOS) are produced by taking raw numerical forecast model output and comparing it with observations to produce hopefully bias corrected results. Some of the models were predicting very cold temperatures yesterday and actual reported lows ended up being a bit warmer than predicted. The featured chart looks at the range of predicted morning low and afternoon high temperatures by the NAM MOS data along with the actual observation from the Des Moines Airport sensor. This range is produced by looking at the various MOS output from the model runs for each forecast time.

The last five days have seen a remarkable stretch of cool weather with daily high temperatures in the 50s and lower 60s. The featured chart shows the past five days being the coldest on-average for any five day period prior to 19 September since 1903 for Ames! The forecast calls for a warm up to closer to normal high temperatures along with some more chances of rain.

According to IEM estimates, the statewide precipitation departure since 1 May was around an inch for the period up until 1 September. The featured chart compares the departure from 1 May until 1 September and 1 October for years back to 1893. Seven out of 59 years whereby the departure was negative on 1 Sep was the September total able to push departure into positive territory.

Our recent stretch of cool high temperatures was far from where we should be this time of year. One way to measure the distance a temperature is from the average value is to normalize it by the standard deviation for all temperature reports for that day in history. A value of positive two would mean the temperature is two standard deviations warmer than average. By standardizing, we can compare temperatures at most any time of the year. Indeed, the lowest values on the upper air occurred with our recent cool stretch! The bottom chart simply shows the largest and smallest index value per year. The sore thumb in the chart is the -4.3 on December 24, 1983. High temperatures that day were in the negative teens!

Yesterday was a cool and brisk day for mid September with highs only in the 60s making for the 6th day this month with a high temperature below 70 for Ames. The featured chart presents the minimum high temperature and number of days below 70 for the period of 1-21 September. Our minimum high of 53 this year was only exceeded by a few years in the past. High temperatures today will struggle to reach 60 and more cool weather is expected until a warmup next week.

The featured chart presents accumulated growing degree day (base 50) departures from 1 May to 1 Oct for each of the past 10 years for Ames. The number at the end of the line is the reported corn yield by the USDA for Story County (the county of Ames). The total season departure does not tell the entire story for the resulting corn yield. The black line is so far this year, wish to guess the yield based on this chart? :)

The last half of summer was a dry one and according to IEM estimates of statewide averaged precipitation, the driest since 1984 for the period from 1 July to 24 September. Some rain is in the forecast today before another stretch of dry weather begins lasting into next week.

The 2011 corn crop harvest is well underway in Iowa. One of the detrimental factors to this year's crop was a very hot stretch of weather in July during an important crop development stage. The featured chart looks at the number of days between two key stages in the corn development based on accumulated growing degree days from 1 May. Some suggest that longer the crop stays in this sweet spot for development, the more time the plant has to cycle water and nutrients leading to a better yield. The 19 days that it took this year tied the shortest period on record for Ames. Of course, there are caveats galore to this plot as corn could have been planted earlier or later than 1 May, also could have been a shorter or longer maturity variety, and crop physiology / genetics continue to improve.

This year has certainly seen its share of hot weather as compared with recent years. The featured chart presents two measures of heat stress. The top panel is the number of hours where the temperature was at or above 93 based on data from the Des Moines Airport sensor. The bottom panel presents the traditional stress degree days, which is a measure of the exceedance of 86 by the daily high temperature. For both measures, this year has been the warmest since the drought year of 1988. The largest values, by a large margin, on the chart are from the dust bowl in the 1930s.

A strong pressure gradient will exist across Iowa today, and the result will be strong, gusty winds. The featured plot shows a variety of methods that can be used to forecast sustained winds and gusts, using various weather prediction models as well as the NWS forecast compared to observations for Des Moines. Further explanation of these methods may be found here. To view time series forecasts for other cities around the U.S., go here.

Wind gusts on Thursday turned out to be as advertised with peak gusts in Iowa above 50 mph over a good portion of the state. Unfortunately, this helped to fan some grass and field fires. Winds will not be as strong today with another stretch of dry weather expected to start. Dry weather is good in October to help farmers get the crops out.