Our recently finished month of March has rewritten the record books in the Upper Midwest and in some respects, was relatively warmer than the iconic months during the dust bowl era! The featured chart presents the monthly record temperatures for Des Moines. The top chart presents the record temperature along with the year it occurred and the sigma departure the value was from current day average. The bottom chart presents the amount the current record is warmer than the second warmest month on record. The value of 3.5 sigma is shown for March 2012, which is larger than any of the other months. The sigma value represents how far the observation is away from the mean distribution of climatology. It provides a simple, but not complete, means to compare different months of the year. Regardless of that comparison, the bottom chart shows another exceptional aspect by besting the previous record by over four degrees! In this regard, this month is the most exceptionally warmest as well! Amazing to think about what we just experienced in the context of climatology for Iowa!

While this past March was easily the warmest on record, it was not the most humid on record as shown by the featured chart. The top chart presents the average near surface mixing ratio which is the ratio of water to dry air. By this metric, 2012 comes in a close second place to 1998. The bottom chart is the simple maximum reported dew point value for the month. In this case, 2012 ties 1990 at 63 degrees. The near term forecast has us back closer to reality with highs in the 60s and upper 50s.

The past few days have seen some remarkable differences in high temperature over Iowa. The featured chart presents the daily high temperature correlation coefficient between a handful of sites in the state. A value of one indicates a positive correlation, but not necessarily that their daily high temperatures are equal. A short physical distance comparison is shown for Ames versus Des Moines to compare against the cross-state pairs. In all cases, the lowest correlations are during the summertime as high temperatures are often guided by the effects of clouds and rain from small scale processes. Looking SW to NE or SE to NW over the state does not appear to yield a significant difference in this crude comparison.

Our remarkable stretch of warm weather continues to set interesting records. The featured chart shows the daily high and low temperature departure from average for Des Moines since the first of March. The past 26 days have seen a high temperature ten or more degrees above average. This is easily the longest streak on record for the site and bests the previous longest streak of 17 days back in Jan-Feb of 1931. Much cooler overnight low temperatures are set to arrive this evening with chances of sub freezing temperatures over the northeastern half of the state.

Sub freezing temperatures have returned to Iowa this Friday morning after a month long stretch above freezing. The featured map presents an IEM computed analysis of the number of days since the last freezing temperature was observed prior to today. The freezing temperatures this morning may do considerable damage to the some of the temperature sensitive plants, who got an early start to the growing season. There are most frost chances in the forecast.

Today's feature is contributed by Chris Karstens. After persistent mild weather the past few weeks, a cool-down to more seasonable values is in store this week. The featured chart presents an ensemble forecast of 2 meter above ground surface temperatures for Mason City, with most models suggesting below-freezing temperatures a good possibility on both Tuesday and Wednesday morning. A return to above average temperatures are expected toward the end of the week.

The featured chart is an attempt to illustrate differences in over night cooling rates by showing a composite profile of temperature for a three hour period prior to reaching a freezing temperature. The airport weather sensor in Des Moines is in a very urban area, while the Waterloo sensor is on the edge of town. The slope of these two lines is slightly different showing a faster cooling rate for Waterloo. This is an illustration of the "heat island" effect that is caused by having lots of heat retaining buildings and pavement nearby the weather sensor.

With temperatures near freezing, many anxious folks were wondering what the low temperature was on Tuesday for Ames. The answer is: "depends on who you ask!" The featured chart presents observation time-series for various weather stations near or within Ames. The Airport sensor is the official temperature for Ames and was much colder than any of the other sites. The hourly observations are presented on the chart and the site actually reported a low of 23 in-between the hourly reports. Other sites hovered just above freezing. This chart will be updated later today once the minute interval data from the airport sensor becomes available. Also, the NWS COOP site reports once daily and is represented by the short line. Temperatures are colder this morning, so we will have to see how much damage these two days cause the vegetation

Update: Sorry, the one minute interval data from the airport came in mostly missing for this time period.

Cold nights typical of this time of year have taken a toll on the vegetation in the state these past three days. The featured chart is of minimum reported temperature from the airport sites since our recent cold stretch began. Temperatures have dipped well below freezing over the entire state. Normally, this weather would not be of concern as our growing season would be starting a few weeks from now. The record warm winter and March got everything growing much earlier this year and put our vegetation in a very vulnerable position.

The Storm Prediction Center has a rare high risk of severe weather forecasted for Saturday with portions of Iowa included in a moderate risk. This risk is due to the combination of springtime instability and strongly sheered wind profiles (winds changing direction and/or speed with increasing height in the atmosphere). This environment supports classic and long-lived supercell thunderstorms. Besides the severe weather, Iowa is also expected to pick up some much needed rain with many locations expected to get much more than an inch of rain.

Storms this past weekend brought damaging winds, hail, heavy rainfall and even tornadoes to Iowa. The weather sensor at the Des Moines Airport reported its second largest daily rainfall for the month of April. The featured chart presents the one minute interval rainfall observations from the site. These values are extrapolated to rates over an hour period showing peak intensities over 12 inches per hour! Of course, these most intense rates do not last that long with actual hour accumulations reaching just over 2 inches per hour (red line).

The past two days have seen quite a bit of wind with high wind warnings and wind advisories issued by the National Weather Service. The featured map presents a crude calculation of the amount of air that passed by an observation station as expressed in miles of wind. As in your car, the distance traveled is simply the product of your speed and the time you traveled at that speed. This calculation is shown in the featured map with some locations over 1,000 miles in the past two days. More gusty winds are expected today.

Yesterday was yet another day this year with the high temperature above average for the date, which made for the 84th day this year above average. The featured chart presents the day which was the 84th day above average for each year since 1900. For 1993, it took until the October to have this many above average days! For the past five years, this total was not reached until June! Just another way that this year has been exceptional.

Now that we are in a stormy springtime pattern, most people know that night time is best time for thunder storms in Iowa. Of course, this is also the time when most of us are trying to sleep! The featured chart presents the climatology of thunderstorm reports from the Des Moines Airport partitioned by hour of the day and week of the year. The highest frequencies are clearly during the night time hours in the spring and summer seasons. Prior to about mid April, there does not appear to be much of a night time signal with all hours of the day having about the same frequencies.

Your Thursday's weather experience in Iowa depended greatly on your location as a warm front bisected the state with lots of rain and cold conditions over the north and warmer conditions to the south. The featured chart compares air temperatures for five locations in Iowa on Thursday. For Mason City and Algona, temperatures did not warm at all during the daytime. The warm front lifted just far enough north to help Ames reach the 60s, but them quickly retreated back south. High temperatures today will be in the 50s with warmer weather expected next week.

The featured chart compares the average Ames temperature for March with the following April for each year since 1893. For Ames, each April has been warmer than its preceding March. After our record setting March this year, there may have been some doubt if April would be warmer as well. The forecast has temperatures warming back up this week, but cooler weather expected again next weekend.

Back in March, our soil temperatures were well above average thanks to our record warm conditions. Since then, we have cooled around ten degrees and are hovering at the critical value of 50 degrees needed for corn crop development. While the next few days will be warm, another cool period is expected into the weekend with highs back in the lower 50s and low temperatures in the 30s and 40s. The warm weather in March will be mostly for naught as our growing season gets off to a slow start.

Temperatures warmed quite nicely on Tuesday and to record levels for places like Sioux City. The featured map presents high temperatures for Tuesday showing that not everyone enjoyed having temperatures into the 80s. Forecasted highs today are expected to be slightly warmer with a chance of severe weather over eastern Iowa.

An interesting phenomena called a heat burst appeared to happen to folks just to our south in Springfield, Missouri. The featured chart presents the one minute interval observations from the airport sensor showing the typical rise in temperature and increase in wind speeds associated with these events. They are caused by rapidly descending air often from decaying thunderstorms that warms thanks to the ideal gas law. Some of the more extreme events have caused plant damage and other damage related to high winds.

The featured map is forecasted probabilities for an inch or more of snow on Saturday from the Hydrometeorological Prediction Center. While most of Iowa looks to avoid the best chances of seeing snow, the temperatures will certainly be plenty cold for this time of year with high temperatures this weekend struggling in the lower 50s. The good news is that warmer weather is expected next week, but chances of rain will be with us for most days.

High temperatures struggled this past weekend in Iowa thanks to cloudy and rainy conditions. The featured map presents a simple analysis of the difference between the high and low temperature on Sunday. Only portions of extreme eastern Iowa saw high temperatures much above their low. Having a difference of less than five degrees is rare for this time of year happening a return period of once every 75 years or so. Warmer weather is set to arrive this week along with plenty of chances of rain.