Temperatures soared on Thursday well into the 90s. Dew point temperatures were in the mid to upper 70s as well making for a miserable time outside. The featured chart presents some details on the days when the temperature has reached 100+ degrees for Des Moines. The top chart shows the morning low temperature on the days when the temperature topped 100 and the bottom chart shows the times during the afternoon that 100+ degrees were reported. Low temperatures are typically in the mid to upper 70s and the warmest temperatures occur during the mid afternoon.

The featured chart presents the daily temperature time series for each day the Des Moines Airport sensor was over 100 degrees. The blue lines in the plot indicate days on which rainfall was also reported. Having rainfall on 100 degree days is rather rare, which is probably an indication of having very warm air overhead that prevents thunderstorms from forming while helping to rapidly warm our temperatures.

The fourth of July has been a spectacular day in Iowa with warm temperatures and pleasant humidities. The featured satellite image only shows a few clouds over southwestern Iowa. Looks to be a great evening for fireworks in Iowa.

This growing season has seen its share of warm and cool weather, but the result has been an average accumulation of growing degree days. The shortened work week ahead looks to be about average as well with a good bit of sunshine. Have you taken the opportunity to go listen to and watch the corn grow? :)

A severe thunderstorm developed over northcentral Iowa Tuesday afternoon and marched mostly south. This storm motion is not what we typically expect in Iowa of west to east moving storms. When the NWS issues severe thunderstorm warnings, they include a storm motion. The featured chart summarizes these storm motions issued by NWS offices with jurisdiction over Iowa. The upper chart presents a comparison between storm direction and date of year. It shows the favored direction of travel from the southwest in June to more west- northwesterly in July. The bottom chart compares storm speed with direction of travel. The fastest storms are clearly from the southwest with the largest concentration around 30 knots from the west. So our storms from the north-northwest on Tuesday are a bit rare, but not nearly unheard of like storms travelling from the east to west!

Following up on yesterday's feature, today's looks at a comparison of tornado warned storm motion versus the severe thunderstorm warnings near in both space in time. Sometimes the sign of a storm that can produce a tornado is when the storm's path deviates from others around it. Typically, this deviation is a slight turn to the right (called right turners). Based on forecasted storm motions, just slightly more than half of the storms exhibit some bit of right turning. Another aspect to "right turners" is a decrease in speed as the storm's circulation strengthens. Again, just over half have forecasted speeds below those of warned severe thunderstorms around it. This is by no means an exhaustive look at this topic, but hopefully an interesting chart nonetheless. The bottom chart does contain an interesting dual maximum (25kts and 40kts) that may be a sign of a separation between isolated supercells (slower speeds) with linear convective complexes (typically faster moving).

The past five days have seen not much wind to speak of with daily average values for Ames in the 2-4 mph range. The featured chart presents the daily average wind speed since the first of June. The third of July was one of the least windy for the entire year. The forecast does increase our wind speeds along with more chances of rain.

The damage reports are rolling in after a powerful storm system plowed through Iowa early this Monday morning. The hardest hit areas are from north of Des Moines to Dubuque as shown by the summary of local storm reports from the NWS. Some of the damage reported this morning is significant from winds probably upwards of 100 mph.

The featured chart presents an analysis of averaged surface wind speed and direction over the domain of a Storm Prediction Center issued tornado watch that was centered over Iowa. The wind values are for a period near issuance. The symbols represent the number of tornadoes reported within the watch box. The plot nicely shows that winds from the southeast to southwest are the most common with a sharp cutoff at the southwest direction. Tornadoes form in environments of wind sheer where wind speeds and/or direction change with increasing height in the atmosphere. So having surface winds out of the southeast and upper level winds out of the west provide the sheared environment in Iowa.

The cleanup continues from the high wind event on Monday morning. The featured title typically refers to having the radar beam hitting objects on the ground, but in this case the actual radar hit the ground. WHO-TV (of Des Moines) had their radar blown off its tower by the storms Monday morning. The photo is of their RADAR radar dish on the ground. Earlier this year, WAFF-TV's (of Huntsville, AL) radar was destroyed by storms there.

The featured chart presents daily precipitation totals and the departures from average for the Cedar Rapids Airport sensor. Rainfall this month has been not been widespread and most of eastern Iowa has missed out on the heavier events. There are more chances of rain in the forecast, but this weekend looks to start a very hot and dry period in the state.

The big story is the forecasted upcoming hot weather to begin this weekend and last into at least next week. The featured chart presents the number of hours per year that the heat index was observed to be at or above 100 degrees at the Des Moines sensor. The 2011 total is already above four of the past seven years. This weather will be right on time for the climatological warmest week of the year as well.

Heat index values soared to well over 100 degrees this past weekend thanks to highs in the 90s and dew point readings in the upper 70s and lower 80s. The featured chart presents frequency of having a 100+ heat index by hour and week of the year based on observations from the Des Moines sensor. The bullseye is right about now, the third week of July which is also the warmest week of the year. The very hot weather looks to continue this week.

Yesterday was another very hot day in Iowa with high temperatures nearing 100 degrees. It was the fourth day in a row with a high temperature over 90 for Ames. The featured chart presents the yearly maximum daily streak over 90 degrees for high temperature for Ames. Some years, like 2004, the temperature never got that warm for the entire year! Our current streak has a chance of being the longest we have seen in around 20 years.

The featured chart presents an hourly climatology of temperature, heat index, and humidity (mixing ratio) in July for Ames along with the observations from Monday. The mixing ratio is a measure of the amount of water within a unit mass of dry air. The top chart shows average mixing ratios in the 12-14 range, whereas observations on Monday were in the 19-24 range (blue line). Notice what happens in the last afternoon around 6 PM. While the air temperature was flat for the afternoon, humidity levels kept rising and pushed the heat index well above 110 degrees. This effect was probably heavily influenced by all of the corn transpiring water throughout the day. The hot and muggy weather will continue today.

Our recent stretch of extremely hot and muggy weather has gotten Iowa a bit of publicity as some of our automated stations have calculated heat indexes that exceeded 130 degrees! Typically, this is blamed on the abundant transpiring corn crop in the state, but that is not the entire story. The primary source of automated weather data in the state are located at airports, but there are two classes of instruments. The federally administered ASOS sites have higher quality and sometimes different sensors than their state run AWOS counterparts. Unfortunately, their data is typically thrown together in the same pot and reported as such. While the ASOS sites did indicate gaudy heat indexes exceeding 110 at times, they were not as high as the AWOS sites which got all the headlines. The featured chart presents a comparison of an ASOS and AWOS site separated by 30 some miles and both surrounded by farm fields. The bottom plot raises the most doubt as even while visibilities were at 2-4 miles, relative humidity was just 75% at the AWOS site and near 100% at the ASOS site. This is probably an indication that the AWOS air temperature has a warm bias. The second plot shows another issue of having the AWOS dew point rise dramatically during the morning hours at a much higher rate than the ASOS site. It is hard to imagine a natural process that could be putting that much water into the atmosphere in the early morning hours. The first plot of the ASOS site shows a reasonable depiction of transpiring corn (slowly rising dew point throughout the day peaking late afternoon coinciding with plant transpiration), but the dew point temperature barely gets to 80 degrees which keeps the calculated heat index at reasonable values. The moral of the story is that not all automated sensors are alike and while heat indexes over 110 surely were felt in Iowa these past days, the high end values over 120 are questionable.

With budget deficit talks in Washington dominating the news, some in Iowa are dealing with their own deficits in the form of lack of rainfall. The featured chart presents the four month departure of rainfall from average. The northeastern quarter has been the driest portion of the state. These totals do not include the heavy rainfall falling this Friday morning. This rainfall is coming just in time with corn at pollination stage.

Friday's rainfall was a very welcome relief to some areas of the state that have been on the dry side this year. It also came at a perfect time for the pollinating corn crop in the state. The featured chart looks at how proportional the rainfall was over areas that needed it the most. Indeed, the heaviest amounts fell more proportionally over the areas with the deficits. The top chart shows the portion of the area with a deficit that got over an inch of rain. So over half of the area with a 3 inch deficit since March got over an inch of rain! The bottom chart is simply the average rain over the area with a given deficit.

Our atmosphere has been loaded with water recently. When storms form in this environment, they can become very efficient rain producers and dump extreme amounts of precipitation quickly. During just Saturday morning, the weather sensor at the Chicago O'Hare Airport recorded their largest daily rainfall total on record. The featured chart presents the one minute interval precipitation data from the weather sensor and shows computed rainfall rates measured over various intervals of time. The rates over 1 and 15 minute intervals are extrapolated out over the hour for comparison. The actual hourly rates are shown in red. For a minute by minute basis, rainfall rates once exceeded 8 inches per hour (0.14 inches reported in one minute)!

This July has been one of the warmest we have seen in a very long time. As measured by average daily low temperature, this year comes in second behind 1936 based on IEM statewide estimated data as shown by the featured chart. Years above average are shown in red and the 1930s really stand out. One reason why overnight lows have been so warm is the vast amount of moisture in the air this month (more on this tomorrow). The warm weather is expected to continue until the end of the month.

This month has seen a remarkable amount of humidity in the area as shown by the featured chart comparing average mixing ratio for July since 1951 at the Des Moines Airport. Last year had been the previously most humid for July, but this year has soundly beat it by a full gram! Of course, there is still a few days left in this July, but judging by the forecast, the sticky weather looks to stick around until the end of the month.

The warm and muggy July rolls on with low temperatures again in the mid to upper 70s this Thursday morning. The featured chart presents the daily high and low temperature percentiles so far this month. The low temperatures really stand out with most of the days this month shown well average and near the 100th percentile. The forecast for the rest of July continues this trend with only slightly cooler overnight temperatures expected until this weekend.

Just a few days ago, the Chicago O'Hare weather sensor set a local record for daily rainfall total. This time it is Dubuque's turn. The featured chart displays the one minute interval precipitation data from the Dubuque Airport weather sensor. The hourly rainfall rates are presented looking over various windows of time. On a minute by minute basis, the extrapolated hourly rates exceeded 10 inches per hour (0.19 inches in one minute)! Needless to say, this amount of intense rainfall caused a lot of problems in the area. Other (non-official) weather sensors in the area reported upwards of 14 inches of rain from this event!