July has mercifully come to a close. It goes into the record books as one of the hottest and driest July's on record. The featured chart presents three metrics of how warm it was. The top graph displays the number of days each July that the high temperature was at least 90 degrees. For Des Moines, July 2012 saw 27 days, which is the most of any month on record! The middle chart presents average daily high temperature and this year was easily the warmest since 1936. The bottom chart is of average daily low temperature and it comes in second warmest behind last year. You may recall that July 2011 was very humid, which promotes warm over night low temperatures. Will August be a warm and dry repeat of July?

On Wednesday, August started off where July left off as temperatures soared into the upper 90s. This year has seen more than its fair share of hot days. The featured chart presents the number of days during 2012 that were warmer than even the warmest day of a given previous year. For example, there have been 31 days this year in Des Moines that were warmer than the warmest temperature for all of 2004! The overall chart average is 13 days, which is remarkable. The hot weather looks to continue with another wave of really hot temperatures arriving next week.

Rainfall was difficult to come by in July for Iowa. The featured map is an analysis of July total of daily NWS COOP rainfall reports. There are a few zeros on the map north and east of Omaha! To have a dry month is a rare event, but for that month to be in the middle of summer is even rarer. Even the lucky spots in the state that got upwards of four inches were below average for the month. The first part of August and the near term forecast do not hold out much hope for the hot and dry weather to change anytime soon.

An intense cluster of thunderstorms rolled through Iowa on Saturday bringing much needed rainfall to lucky portions of the state. The rainfall was quite intense for some as shown by the featured graph of one minute interval rainfall from the Davenport Airport site. 2.38 inches of rainfall was reported between 1:37 and 2:03 PM on Saturday. The black line shows the one minute intensities extrapolated to an hourly rate. The green line is the same extrapolation, but over a 15 minute trailing window. Unfortunately, intense rains like this probably included significant run-off instead of soaking into the ground. The water did not disappear though so rivers and lakes benefited from this event as well.

Ideal cooling conditions on Monday morning allowed low temperatures to reach the 40s for some locations in the state. These were record lows for places like Waterloo and Mason City. The featured map is a simple analysis of low temperatures reported on Monday. Having temperatures in the 40s for the first week of August is a somewhat rare occurrence. It had not happened in Iowa since 2009.

Tuesday was yet another very warm day this year with high temperatures reaching the century mark for some in the state. This year continues to be much warmer than any previous year on record for Des Moines. The featured chart looks at the possibilities that this year will end up being the warmest on record. The spaghetti of lines represents the combination of this year's data and all previous year's data from today to the end of the year. With these scenarios, 81% of the previous year's data would provide this year with the warmest year on record. A few weeks ago, this same chart was featured and the percentage was only 64%. The chart would indicate that this year will be the warmest on record at least until Thanksgiving.

While much needed rain showers have recently graced much of Iowa, most of this summer has been very dry. The lack of rainfall produces water availability stress in plants and their production of water vapor by transpiration is decreased. The result should show up in decreased air humidities as shown by the featured chart of Des Moines daily mean mixing ratio (the amount of water in the air versus total air). In general, this has been the case for most of the summer with humidity values running near or below long term average. The warm and humid weather we had in March is probably the most noticeable feature in this chart. The initial wet period we had to start May also shows up as an elevated period of higher humidities.

The latest US Drought Monitor released this week shows continued degradation in Iowa with now more than half of the state in "Extreme" drought category. The featured chart shows the weekly areal coverages of drought categories over Iowa. The "Extreme" category has doubled in size during the past week. August has seen near daily occurrences of rain in the state and some heavier totals since the last drought report valid on Tuesday. Unfortunately, this rain is coming very late in the growing season and we still could use plenty more to help the crops that still can be salvaged.

The drought of 2012 for Iowa will certainly go down as one of the more extreme on record. Since most people can remember the drought of 1988, comparisons continue to be made to that year with many wondering which year was more severe. While there is no correct answer, the featured chart provides two metrics for comparison. The x-axis presents the accumulated, from 10 August back to the given date, precipitation departure for both this year and 1988. For the period since 1 January, 1988 had the least amount of precipitation since 1893. The two lines show that 1988's drought started much earlier in the year than 2012, but the intensity of the drought during the growing season has been slightly worse (for this period) in 2012. The chart also shows you how much precipitation we would need to erase a given deficit over some period. For example, at least ~8 inches are needed in order to erase the deficit since 1 May.

Our recent respite from the hot weather has been on the few cooler than average periods this year as shown by the featured chart displaying daily high and low temperature departures from average for Des Moines. The sustained warmth of March and July shows up clearly on this chart as well. The forecast only has a brief warm up this week before highs return to the 70s to end the week. Great weather for the Iowa State Fair!

Sustained rainfall has been very difficult to come by for this growing season. Even getting a seven day period with above average rainfall has been rare for most places in the state and especially the southeastern quarter of Iowa. The featured chart presents the number of days each growing season to date that the previous seven days (inclusive) of precipitation was above average for Cedar Rapids. For this metric, this year has the second lowest total since 1900. The next seven days look to be on the dry side of average as well with only modest chances of rain.

A few weeks back, we featured a plot known as an aridity plot showing the combination of seasonal temperature and precipitation departure from average. This departure is measured in units of standard deviation to provide a closer comparison between temperature and precipitation departures. 2012 still ranks up there with the other legendary years of Iowa's climatological past. A simple linear fit is also shown. While the correlation is a bit low, the implication is that dry years tend to be warm and wet years tend to be cool.

August has seen a few very warm days and then a number of rather cold days for this time of year. The current result is for the statewide average temperature to be below average for August. The featured chart shows recent monthly temperature departures and if this departure holds, it would be the first below average month since September of last year. The extreme warmth of March 2012 sticks out like a sore thumb on this chart. The near term forecast has high temperatures below average, so perhaps August will finish on the cool side!

The featured chart presents yearly time series of USDA reported weekly corn crop condition for Iowa and five nearby states. The charted line represents the total area estimated to be in either "poor" or "very poor" condition. These are the two worst categories that are designated. Each chart contains the time series for each year since 1986. Conveniently, this allows us to compare this year with the last major drought of 1988 in the Midwest. Other significant years of 2005 and 1993 are included for comparison. While 2012 has been devastating in Missouri, Illinois, and Indiana, things have not been all that bad in Minnesota. Compare that with what happened in 1993 where Minnesota got the worst of it. It is not for certain how much some recent rains in the Midwest will help the corn crop as the damage has pretty much already been done in the hardest hit areas.

Since we like to identify ourselves by the state we live in, climate parameters are often provided on a state by state basis. Given that precipitation varies on very fine spatial and temporal scales, how representative are statewide values for a location in Iowa? The featured map presents a simple analysis of the correlation coefficient between the monthly statewide precipitation value and the local site's monthly total. One could think of this map as which location in the state has monthly precipitation that most resembles the statewide areal average. Intuitively (since we are a land locked state), the middle of the state is the most representative. Northwestern and extreme southeastern Iowa show up with the lowest values as they both lie at the extremes of the annual precipitation for the state. Ames shows up with the highest value, so those of us at Iowa State are the most representative of Iowa! :)

Here is the same plot split by seasons: spring, summer, fall, winter

For temperature and precipitation, it has been well established that this growing season has been a lot like 1988 (our previous worst drought year). It is interesting when other metrics, like the one presented in today's feature plot, equal 1988 as well. The featured chart presents the number of days per year with at least one tornado warning issued for somewhere in the state of Iowa. Due to the nature of having severe convection happen over midnight, a day is considered to be a 24 hour period ending at 7 AM. This year has only seen 6 days, which is the smallest total since 1988! The green bar represents the number of days after 19 August until the end of the year. 1988 saw an additional day with tornado warnings issue, will 2012 as well?

During the blistering hot month of July, some wondered just how bad it would be for the state fair in August! Turns out, the weather was some of the coolest seen in the recent decade. The featured chart presents the simple daily average high and low temperature for each state fair period back to 1880. Some of the years are blank due to there being no fair that year. Years above long term average are in red and below are blue. The cool weather certainly boosted attendance and made the week more bearable for the carny folk.

The mostly dry conditions and lack of robust vegetation have lead to very dry conditions for this time of year. Dew points have accordingly been running very low this month. The featured chart presents the maximum and minimum dew point for the first 19 days of August for each of the past years since 1933 for Des Moines. Both values this year are some of the lowest on record and the lowest they have been in quite some time. The red bars are years at or lower than 2012. In order for the first freeze to occur, the dew point has to drop to freezing temperature as well. Could the low dew points be a harbinger of things to come, namely an early freeze?

After the very warm July, we were nearing "metaphysical certaintude" that this year would be the warmest on record for Des Moines. Most of August has been a different story and we have lost some of our lead over the next warmest year on record (1931). The featured chart presents the year-to-date average temperature along with a spaghetti plot of scenarios to finish the year with based on previous year's observations. The number of scenarios that finish this year warmer than 1931 can be thought of as probability. As of today, this probability is near 75% which is down from a few weeks ago. The bottom chart tracks this probability over time showing that July certainly put us on track to be the warmest, but August is slacking off a bit.

The difference in dew point temperature from the air temperature is called the dew point depression. On Wednesday, the dew point depressions in Iowa were over 50 degrees Fahrenheit for some locations with a air temperature in the 90s and dew point in the 40s. For Iowa, this is a very rare event! The featured chart presents the largest dew point depression by year and the minimum dew point observed with an air temperature at or above 95 for Des Moines. The bottom chart shows that having such a low dew point and high temperature is very rare and last happened in 1955 (red bars). The upper chart shows that having a 50+ degree spread has happened in a number of past years, but for August it last happened in 1936 (not shown)!

Thursday was yet another warm day for Iowa and Des Moines had its 50th day with a high temperature at or above 90 degrees. This makes for the largest total of days since 1988 as shown by the featured image. Only five other years than 2012 have had 50+ days over 90 degrees and we still have just over four months to go this year! The bottom chart presents the number of days each year above 90 for days after 23 August. We would need another 10 days to catch 1983 and then a bunch more to catch 1934 and 1936. The forecast has a high very close to 90 on Friday and then more close to 90 weather next week, so we are saying that we have a chance...

The rainfall much of Iowa received this weekend is almost too good to believe! Rainfall totals on Saturday reached 3-4 inches over southwestern Iowa. The featured image is a combination of rainfall estimates and modeled surface water runoff from the storms on Saturday. This model output is from the Iowa Daily Erosion Project found on this website. Areas that are shown picking up 2-3 inches of rain only show less than a half of an inch of runoff. The reason being that the rains feel at a reasonable pace and there is vegetation around to slow down rain drops before they strike the ground. It also helped that the ground was quite thirsty! Heavy rains are continuing on Sunday with Lamoni reporting over 8 inches for the event!

Tropical Storm Isaac continues to under-perform expectations for development into a Hurricane, but remains a great worry for folks along the northern Gulf of Mexico. The featured map is a composite of National Hurricane Center position and max wind forecasts for the past week. The thicker line with a white outline is the actual observation of wind speed and position. Isaac has yet to reach Hurricane strength of 75mph winds, but is a large system that is expected to dump very heavy rainfall. Our weather will stagnate while this system clears out to the east later this week.

Warm and rather muggy weather has returned to Iowa with highs around 90 degrees. The forecast calls for more of this weather for this week to end August. Will the end of August bring the end of 90 degree weather for Des Moines? The featured chart presents the last day each year whereby the high temperature was at or above 90. The black line represents the average last date, which is still in our future this year! The bottom chart is a simple comparison between the last 90 degree date and the average temperature for that year. The really warm years do not necessarily have a late last 90 degree day. With this year set to smash the average temperature record, we will not necessarily see 90 degree weather into October.

The rainfall this past weekend was certainly welcome and helped to put a dent in some of the deficits that have built up this year. The featured map presents an estimate of the past seven days of rainfall along with the drought status valid at the beginning of this period. Most of the heaviest rainfalls fell over southern Iowa in the area currently in D2 (Severe) status. A majority of central and east central Iowa missed out and will probably remain in D3 (Extreme) status for this week's drought monitor update. A ray of hope does exist with Hurricane Isaac as some models are tracking the remnants of the system into Iowa, which would bring a very welcome rainfall.

Tropical Storm Isaac continues to pound the southern plains with heavy rain and strong winds. The size of these storms is sometimes difficult to imagine for those of us who have lived in Iowa their entire life. So what better way to illustrate the size of Isaac than to move the storm here for comparison! The featured map moves Isaac as depicted on RADAR yesterday morning to Iowa with its eye near Des Moines. The size of this storm is certainly comprehensible as nearly the entire state is engulfed by it! The remnants of Isaac may actually make it to Iowa in a few days, but its form will look much different than this.

Thursday was the second of two very warm days for late August in Iowa. Des Moines hit 97 after reaching 96 on Wednesday. This is latest date for two straight days with such a warm temperature since 1990. The featured chart presents the latest date for having two days at or above a given high temperature threshold. For example, having two days at or above 90 has happened as late as the first week of October. While Friday will be slightly cooler, we will stay above average until the middle of next week.