The latest update of the US Drought Monitor has all levels of drought eliminated from the state and the featured chart shows that the statewide precipitation departure for the past year is now positive! It has taken the wettest spring on record and a wet June to get us back to average for Iowa. The forecast for the first week of July looks to be mostly dry and rather cool. Of course, drought could start creeping back in the state with a dry July and August, but we shall see!

Temperatures were just about average across the state on Monday with the 4 PM temperature at Des Moines of 84 degrees coming in at the long term average for the first week of July at 4 PM. The featured set of pie charts present the percentage of days that the 4 PM temperature was either above or below average when a given condition occurred. For example, when there was no rainfall between 8 AM and 4 PM the temperature was above average about 55% of the time. However, when it did rain, about 75% of the days had a below average temperature at 4 PM. Having an overcast sky at 4 PM also shows a strong signal with 76% of the days also being below average at 4 PM for temperature.

The featured map presents an analysis of the contribution heavy rainfall events have to the overall precipitation total. For this plot, these events are defined as daily precip totals at or above two inches. The map shows the percentage of total precipitation that comes during these events. For Iowa, about 10-15% of the annual precip comes from these intense events. The pattern over the Midwest shows the maximum over southeastern Kansas and minimums over northern Michigan and western North Dakota. The reason being the combination of higher precipitable water (potential for heavy rainfall) the further south (warmer temperatures providing more capacity to hold water vapor) and the favored areas for thunderstorms (clash of air masses providing lift).

Happy 4th of July! The featured image presents the weather condition reported by the Des Moines site at 10 PM on the 4th of July since 1951, which is about the time of legal firework displays in Iowa! If the given year satisfies the condition shown, it gets a star on the chart. The left hand side then presents the number of years out of the past 62 that this condition has occurred and the numbers along the top show how many out of the four were meet for that year. Having rain during the 9 to 10 o'clock hour is the least common among these. This year would appear to have none of these conditions present with a very comfortable dew point, temperature in the 70s, and nearly clear skies.

Thanks to a wet spring and June, Iowa made up its 365 day precipitation deficit from the drought of 2012. The featured chart presents some metrics related to making up this year long precipitation deficit. The top panel displays the daily rate the deficit was made up as measured from the date with the largest deficit to when the deficit was erased. The second panel displays the number of days it took for the given deficit to be erased. The bottom panel displays the depth and time of each period since 1900 with a deficit for statewide precipitation. This year's deficit bottomed out at 9.18 inches on 26 Jan 2013 and was erased on 24 June 2013 (red items on chart). The chart shows that once the long term deficit reaches four or more inches, it will probably take three months or more to recover.

After having plenty of rain during the spring season and June, rain has been difficult to come by for the first seven days of July. The statewide total so far is second driest behind 1940 according to IEM calculations. Some heavy rainfall has fallen in extreme northeastern Iowa this morning and more chances of rain are in the forecast for this week. The black line on the chart shows the normal accumulation of nearly an inch and getting about an inch of rain per week is about normal for most of the summer.

The featured chart presents the yearly maximum heat index and date of maximum for Des Moines since 1935. This year's maximum barely exceeded 100 degrees and would be one the lowest minimums on record if it stood for the rest of the year. But it is only the second week of July and as the bottom chart shows, most years experience its hottest heat index sometime in July and August. Today looks to be a very hot day with heat index values for Des Moines expected in the 100s.

After a very wet spring and a wet June for some in Iowa, July has started off dry. It is hard to believe that we are again worried about precipitation departures, but they are back for much of the state. Extreme northeast Iowa got some very large totals in June and has seen the limited July precip events so far. The forecast for the next week looks very dry and so this situation appears to only get worse. For farmers, we are left with a late planted crop that will be needing rain soon after whatever soil moisture reserves built up from this spring are exhausted. Remember that we came into this spring with very low moisture reserves due to the drought of 2012.

Very comfortable air arrived in Iowa on Wednesday with dew point temperatures only in the 50s. The featured map looks at how common it is to have sub 60 degree dew point temperatures in July. Iowa is analyzed in the 20-40 percent of the time range with frequencies decreasing the further south you go. The benefit of having such a low dew point temperature is that it allows the air to cool to that temperature overnight making for windows-open sleeping weather! Humidity is expected to slowly build back into the state with dew points back into the 60s to 70s next week.

Most are familiar with the old adage; "Red sky at night, sailor's delight. Red sky at morning, sailor take warning." Does this saying apply for us land-locked Iowans? IEM's webcam archive contains an image every five minutes dating back to as far as 2003. For the featured analysis, webcam images approximately 10 minutes prior to sunrise and 10 minutes after sunset were analyzed for amount of red in the sky. The algorithm attempted to differentiate red sky from the red horizon that is common with everyday sun rises and sets. Of 2300 some sunrises and sunsets, 248 red sunrises and 88 red sunsets were identified by an algorithm. For these events, hourly precipitation data from Ames was queried to see if measurable precipitation fell in the 24 hours proceeding the event. The third bar is daily climatology which shows not much of a signal with these events, but there is a slight increase for red sky at morning events. Obviously, a limited sample and computer program does not prove or disprove this adage.

On average, the third week of July is the warmest week of the year as shown by the featured chart. The bottom panel shows the number of years since 1879 that the given week was actually the warmest for that year. The warmest week has happened any time during the summer and even into September. The warmest week so far this year was June 18- 25th at just over 78 degrees. The forecast for this week has some warm temperatures included, but does not appear to be warmer than the current warmest for this year.

Rain has been very difficult to come by this July for most of the state. The featured chart displays an analysis of precipitation percentage of average for the first 15 days of July. Most of the state is shown in the 0 to 20% range with the actual accumulation labeled on the map. Des Moines has only reported six hundredths of an inch, which is the driest start since 1975. The forecast continues the dry weather with temperatures in the 90s for the rest of the week.

The weather pattern earlier this week was a bit strange with the southern plains experiencing a storm system that traveled west! The winds well above the ground surface, that help guide storm systems, were actually from the east. The featured chart looks at the frequency of easterly winds at a height of 200 hPa (millibars), which is about 7- 8 miles above the earth surface. The chart presents 12 wind roses, one for each month for the sounding site near Omaha. The site launches a weather balloon twice per day, providing a vertical profile of temperature, humidity, pressure, and winds. The wind roses provide frequencies of wind direction and speed. Westerlies clearly dominate for all months of the year. Each month is labelled with the percentage of observations that are primarily easterly. The highest percentages (although meager) are in the summer time, which is when the jet stream (very strong westerlies) is furthest away permitting such flow to occur. So while such events are very rare, this is the time of year when they most frequently happen.

The featured map displays the estimated percentage of corn areas per state that are currently tasseled/silking along with the departure from the past 30 years average for the second week of July. The western Corn Belt is way behind with only 1% estimated in both Iowa and Minnesota. The corn crop is behind schedule due to late planting dates because of cold spring weather and wet conditions. These estimates were valid for four days ago and a visual survey of your local corn crops probably shows more acres now tasseling. This is an important time for corn development and it desperately needs moisture. Having hot and dry conditions during this period is not good for the eventual yield.

This week has a warm and muggy one with heat indices pushing 100 degrees in some locations. The popular phrase, "it isn't the heat, its the humidity", means that warm temperatures are bearable unless high levels of humidity exist at the same time. The featured chart presents the frequency of having either a 3+ or 5+ difference between the temperature and heat index when the air temperature is at or above 80 degrees. This "humidity effect" indicates how often the humidity levels are high enough to produce a noticeable difference from the temperature. Long term averages are shown for each value with bars above or below average colored separately. For Des Moines, about 50% of the time when temperatures are above 80 the heat index is adding at least three degrees to the temperature. The average is just below 30% for a five degree change.

A number of severe thunderstorm watches have been issued today by the Storm Prediction Center (SPC). None of these in Iowa though. Anyway, the featured chart presents the daily frequencies of SPC issued watches and the ratio between the number of severe thunderstorm versus tornado watches issued. Both have clear annual signals with their respective peaks happening at different times of the year. The largest number of watches (dots) occur during the strongest battles of the air masses during the spring season. The bars shows the ratio of severe thunderstorm versus tornado warnings. This ratio peaks out during the first two weeks of August as temperatures are the warmest over the United States and the cool air masses are well north leading to less wind shear in the atmosphere.

Rain is at least falling in parts of the state this Sunday, but some locations picked up a bit too much rain in a little time. The featured chart is of one minute interval precipitation from the Chariton SchoolNet site showing 3.5 inches of rain falling in just an hour. The plot also shows extrapolated hourly rates over different periods of periods. For example, the peak hourly rate over an one minute period was over eight inches! Of course, the most intense rates do not last that long.

It actually rained in Iowa on Sunday with the Des Moines Airport picking up eighteen hundredths of an inch! This was the first daily rainfall over a tenth of an inch since 24 June. The featured chart presents the longest stretch of days between 1 May and 31 August each year for Des Moines in between daily rainfalls of at least a tenth of an inch. The simple average of this chart is just over 17 days with the stretch this year being the longest since 1988. All of the years with a longer stretch than this year are labelled on the chart.

Yesterday marked the 10th year of webcam imagery collection by the IEM. This is thanks to our partners (KCCI-TV, KCRG-TV, KELO-TV, and the Iowa Department of Transportation) who allow us to collect and archive images from their respective networks. The featured chart shows the number of images saved per year along with the first image collected from the KCCI-TV webcam in Jefferson back in 2003. These images are valuable environmental data providing easily discernible visual reports of sky and ground conditions. Along the way, over 300 lapses have been uploaded to YouTube, including a very popular Gravity Wave video with over 1.3 million views!

While the rain that fell on Monday evening was welcome, the storms also brought along damaging winds and some hail. The storms also produced a heat burst event, which was nicely captured by the Knoxville AWOS site as shown by the featured chart. Heat bursts are produced behind thunderstorm complexes as warm air is forced to the ground. This air continues to warm as it descends and since no water is being added, its relative humidity drops resulting in warm and dry air at the surface. The classic signature, as shown in the chart, is a rapid increase in temperature and decrease in dew point at a surface observation site. These events tend to be very windy as well with the site reporting a gust over 70 mph. Note that the chart would indicate the gust lasting for a number of minutes, but that is most likely a quirk with how wind gusts are reported by the sensor.

The featured chart presents an analysis of the number of days since the last half inch plus rainfall for a calendar day. The western half of of the state is shown in the 30-45 day range as rainfall events have been difficult to come by. Northwestern Iowa would appear to have a chance of breaking this streak this evening as strong storms are expected. As with our most recent storm, the rainfall is much needed but unfortunately may come with damaging wind as well.

The precipitation gains made this spring to practically eliminate the drought condition in the state are being lost thanks to a dry June and July. The featured chart shows the percentage of the state covered by analyzed drought condition from the National Drought Monitor. The most recent update to this analysis has over 50% of the state now covered by abnormally dry condition (D0). The good news is that there have been recent rains, but the heaviest totals have mostly missed the western half of the state. More chances of rain are in the forecast, but the heaviest totals will be to our south and east.

While rain has been difficult to come by in July for Iowa, Oklahoma has seen plenty of it. The featured chart is of one minute interval precipitation for Oklahoma City ASOS on Friday showing extremely intense rainfall. The 5:16 AM minute accumulation was 0.3 inches of rain, which extrapolated to an hour yields a rate of 18 inches! For a rain gauge with a tipping bucket mechanism, this means a tip every 2 seconds! Sadly, OKC's daily total is more rainfall than most of Iowa has seen this July.

The low temperature dipped to 51 degrees for Des Moines on Sunday morning, which set a record low temperature. How common is this cold of a temperature in July? The featured chart presents a means by which low temperature frequencies can be compared to high temperature frequencies by equating their respective percentiles. A line is shown for each month of the year. So for July, the 51 degree low temperature compares with a high temperature around 104. Restating, Des Moines has about the same number of days at or below 51 degrees for a low temperature as it does for having a high temperature at or above 104. So you could say the weather this morning is as common as a high of 104!

The past few days have been rather remarkable for July with record lows being set over parts of the midwest. Each day the sun heats the ground, which warms the air near to the ground. This warmed air vertically mixes growing what is known as the planetary boundary layer. The air temperature we experience near the ground is a result of the strength of the surface heating and the mixed air down from above. The featured chart shows a climatology of air temperatures at the 850 hPa pressure level for the sounding site near Minneapolis for its 12 UTC (6/7 AM CT). This level is typically included in the planetary boundary layer. For this recent event, the temperature at this level (2.2 centigrade) was the coldest on record for the site in July.

The featured chart presents a time series of trailing 14 day departures of temperature and precipitation for Iowa. The line connects this metric computed every seven days and the points are labelled for the end of the 14 day period. The start of the line is on the first of April and the line ends with today. The chart shows that our past two weeks closely resemble the two weeks ending on 1 April with cool and dry weather. These types of plots often create loops when the variables are correlated. Our next period of weather looks to continue the dry weather, but closer to average temperatures are expected.

The featured chart is an aridity chart showing the combination of temperature and precipitation departure for the month of July expressed in units of standard deviation from average. The total so far for this July is shown on the chart as a red dot and is nearly the same value as 1947! There have been other IEM daily features this year showing 2013 trending like 1947. Extreme dots on this chart are labelled and 1993 certainly stands out (the great flood year). A simple fit is made through this plot showing the inverse relationship as below average temperature is correlated with above average precipitation. This July is a bit unique in the regard of being one of the most extreme in quadrant III (below average temperature and below average precipitation).