Days with rain have been hard to come by the past two months. The featured chart presents the observed daily frequency of measurable rain for the period prior to 1971 and for the period after. October is shown has one of the months with an increased frequency of rainfall, but this year has gone against that trend. Rain is in the forecast to start off November.

Voting:
Good = 13
Bad = 1

Tags:   precip  

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!

Voting:
Good = 30
Bad = 14

Tags:   precip  

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.

Voting:
Good = 13
Bad = 6

Tags:   record   precip  

Portions of southwest Iowa picked up heavy amounts of rainfall yesterday morning with totals approaching four inches. For Ames, the largest daily rainfall has been 2.65 inches so far this year, which is about average for the largest total of the year. The featured chart presents the largest daily rainfall total each year and the day of the year on which that highest total occurred. The three highest totals all occurred in August. It is also interesting to have the largest totals for some year occur in late February!

Voting:
Good = 13
Bad = 1

Tags:   precip  

Getting timely rainfalls in July and August are critical for corn and soy production in Iowa. Some places in the southern plains have had crop failures this year because of the lack of rain and blistering heat. In Iowa, most places have seen timely rainfalls so far this summer. The featured chart presents the longest period during July and August in between quarter of an inch and half inch rainfalls for Ames. It is remarkable to note the lack of many above long term average periods during the past 20 years. This year looks to continue this trend of not seeing long periods of dry weather.

Voting:
Good = 14
Bad = 3

Tags:   precip  

Yesterday's feature presented the last four years as being wetter than average statewide. The featured map compares these four years (2007-2010) against the 30 years previous to that. Please note that the units of this chart are inches per year, so a good portion of the state is shown with values in the 10-15 inches range. This means that the past four years have averaged 10-15 inches more per year than the average of the previous 30 years. Some portions of the state have not been as relatively wet and even a deficit appears in far northwestern Iowa.

Voting:
Good = 25
Bad = 2

Tags:   precip   2007   2008   2009   2010  

Based on some preliminary data and IEM estimates, 2010 will go down as the four year in a row wetter than a recent trend of 30 years of Iowa data. The featured chart presents the yearly areal averaged precipitation along with a trailing 30 year moving average. The flood year of 1993 and drought year of 1988 stick out in this chart. The trend line has increased in this chart by roughly 4 inches in the past 50 years (~12%).

Voting:
Good = 20
Bad = 5

Tags:   climate   precip  

A passing storm system brought rains to primarily eastern Iowa on Monday and with temperatures only in the 40s, it was certainly a cold rain. The featured chart presents the temperature at which the Des Moines ASOS sensor reported an hourly precipitation greater than 5 hundredths of an inch (think of it as the temperature during which the precip fell). The top plot shows that during the summer time, these rain events rarely occur below 60 degrees whereas in late November they occur at 55 degrees and less. Getting stuck outside during a rain is certainly more pleasant in July! The bottom plot shows a comparison between the temperature and reported one hour precipitation total. The bottom plot shows an interesting feature whereby nearly all the heavy one hour events occur at temperatures above 60 degrees. Surface temperatures can be thought of as a proxy to the amount of water capable of being held in a column of atmosphere. To get heavy precipitation rates, one needs a warm column capable of holding more water vapour to yield precipitation.

Voting:
Good = 31
Bad = 5

Tags:   climate   precip  

The streak of dry weather ended for some on Tuesday as showers and thunderstorms visited Iowa again. For Des Moines, the streak was 16 days since the last measurable precipitation event. The featured chart presents the longest dry streak per year since 1893. Each year has seen at least one 10 day period of dry weather with the mean being around 3 weeks long. The bottom chart presents the number of dry streaks that last at least 7 days. The 2010 total is the lowest since 1998, but there are still 2.5 relatively dry months to go this year, so the total will probably be added to.

Voting:
Good = 16
Bad = 4

Tags:   precip  

Our remarkable stretch of dry and warm weather continues this October with most locations experiencing no rainfall for the past week or so. The featured chart presents the longest streaks of having little to no precipitation for each day of the year. The lower chart simply presents the maximum daily rainfall. During the summer time, the longest streaks are only 3-4 weeks long, while they can last much longer in the fall and winter time. Our dry weather looks to continue into next week!

Voting:
Good = 19
Bad = 5

Tags:   precip  

Continuing on the series of features looking at where in Iowa extreme daily weather occurs, this image shows the frequency of a site having the heaviest precipitation for a given day. The plot can be misleading as the smallest percentages are in the middle and increase as one approaches the state border. This pattern shows how some storm systems will clip the state, so locations near the border will pick up the most precipitation while others will receive less. Interestingly, this storm system clipping appears to be the most common to the southeast, where Burlington will get the most.

Voting:
Good = 14
Bad = 6

Tags:   precip  

The featured graph presents IEM computed peak rainfall accumulations measured over an hour and two hours. The values are actual totals from the ASOS precipitation sensor. Just over a week ago, the Ames sensor reported 3.52 inches of rain over a two hour period. This value is only topped on the chart by Spencer back in 2005. You may notice that the two hour total is no where near doubling the one hour total. In Iowa, the heaviest of rainfall events will only last 30 minutes or so. It takes training of multiple cells to produce these large totals.

Voting:
Good = 27
Bad = 7

Tags:   2010   precip  

The featured chart presents the frequency of precipitation events as measured by the number of consecuative hours at least one hundredth of an inch is reported by the Des Moines weather sensor. Events lasting 10 or more hours are highlighted with the white crosses. The chart shows that long duration events are extremely rare during the summer time when storms tend to be more isolated and not associated with large storm complexes. The largest concentration of long duration events is in March and April.

Voting:
Good = 51
Bad = 16

Tags:   climate   precip  

Heavy rainfall events have once again been common this July with some locations in northeast and southern Iowa unlucky enough to experience multiple heavy rainfall events. The featured chart presents the number of times per year a NWS COOP site has reported more than 12 inches of rainfall. 1993 shows up very prominently with a total double that of any other year. The 2010 total is only year to date, so perhaps this years total will surpass 2008. Let us hope not!

Voting:
Good = 22
Bad = 3

Tags:   precip  

The forecast for this week looks much drier than previous weeks, which is certainly a welcome break. Interestingly, this break coincides with a climatological relative lull in daily precipitation probabilities. The featured chart presents the daily frequency of precipitation reported for Ames with a seven day smooth applied to remove some of the noise. Notice how the end of July has a smaller frequency before the beginning of August.

Voting:
Good = 34
Bad = 2

Tags:   precip  

The featured chart presents the number of distinct days per year that at least one NWS COOP site reported over two inches of rain in a 24 hour period. The mean value in this chart is close to 40, which means that we have roughly only seen half of the number of heavy rainfall events for the year so far! The flood year of 1993 shows up as the largest value of 61 days. More heavy rainers are in the state this morning with another round expected tonight into Saturday morning.

Voting:
Good = 70
Bad = 14

Tags:   precip  

Based on preliminary data, nearly each of the IEM tracked Iowa climate sites exceeded their average precipitation for June. The featured chart looks at the percentage of these sites that exceed their monthly average since Jan 2007. The chart shows a lot of month to month variability. The April - July period in 2008 sticks out as a period with four months in a row over 80%.

Voting:
Good = 15
Bad = 9

Tags:   precip  

The featured chart looks at the percentage of long term climate sites that observe a greater than two inch rainfall per year. There are 104 sites in Iowa, that the IEM has precipitation data back to 1951, used for this chart. Based on IEM estimates for 2010, roughly half of these locations have seen a 2+ inch rainfall, which is behind the pace set in the past 3 years. The dots represent the final total for the year with 2007/2008 sticking out as almost every location in the state experiencing a heavy rainfall event. Another take home message of this plot is that more heavy rainfall events will occur as summer is only a few weeks old.

Voting:
Good = 57
Bad = 13

Tags:   precip  

The featured chart displays the percentage of precipitation that falls between 12 and 8 AM against the rest of the day. The black line is simply the ratio if precipitation fell equally for all hours of the day. The chart shows a clear annual cycle with the largest relative contribution occurring in August. The actual ratios for 2010 are presented as well with 60% of the rainfall so far in June coming in the early morning hours.

Voting:
Good = 40
Bad = 3

Tags:   precip  

Yesterday's feature highlighted the rainfall recorded at Lamoni. The station reported more rainfall in a day than what on average falls during the entire month of June! The featured chart today displays the frequency of a climate site in Iowa picking up more rainfall in a day than what is average for the month. While the chart may seem counter intuitive, monthly precipitation averages during the winter months are much lower and so a bit easier to exceed than the summer months. More heavy rainfall is occurring this morning.

Voting:
Good = 77
Bad = 41

Tags:   climate   precip  

The featured graph looks at the frequency of hourly precipitation rates over a quarter of an inch (red bars) and the largest amount of precipitation reported during an hour (blue bars) from the Des Moines Airport since 1973. The lowest and less frequent rates occur during the 1 PM hour with maximums in the late afternoon and very early morning around sunrise. The heavy rainfall events tend to occur in the late afternoon forced by peak solar heating and early morning forced by low level jet activity. The middle of the day tends to be a lull in the forcing activity. For Iowa, peak rainfall rates usually do not exceed around 2 inches per hour.

Voting:
Good = 22
Bad = 11

Tags:   climate   precip  

Yesterday, the months of the year battled for the being warmer than the others. Today's feature looks at the frequency of having a month being wetter than another. This time there is no clear winner. The summer months are generally wetter, but fall and spring months can top the summer months.

Voting:
Good = 19
Bad = 8

Tags:   climate   precip  

Building off of yesterday's feature, today's feature looks at the mean amount of rainfall in three different 7 day periods for a given high temperature in June for all sites in Iowa. For a given day, these 7 day periods are the 7 days prior to the high temperature, the 7 days centered on the high temperature, and the 7 days after. The plot indicates an interesting regime change from when we have highs in the 70s versus highs in the 90s. Notice how in the 70s, the centered and after lines mostly track, while in the 90s the prior and centered lines track. One interuptation would be that when temperatures warm up, more rainfall comes in the forecast and effectively knocks temperatures back down into what is shown in the 70s with more precipitation in the prior period. The overall decrease in precipitation for increasing temperatures is also important (the sun can more effectively warm the ground when it is drier [less precip] ). Rain is in the forecast for this weekend with some strong storms possible.

Voting:
Good = 18
Bad = 12

Tags:   climate   high   precip  

The featured graph displays the frequency of rainfall observations a day after a given high temperature for Ames. The three lines are the frequency of given minimum precipitation thresholds. While there are a number of things going on to make this plot appear the way it does, it generally shows that the frequency of rainfall events increases as our temperature increases (more rainfall in the summer). The interesting detail is to note what happens when temperatures reach the 90s. Our chances of rainfall decrease as the temperature gets even warmer. One could speculate that when our temperatures get really warm, the air mass is often drier and soil moisture state is drier as well allowing more efficient warm ups. Rewording, having temperatures in the 90s for Ames is probably associated with a dry weather pattern.

Voting:
Good = 15
Bad = 6

Tags:   climate   precip   highs  

The featured graph shows the contribution of various daily rainfall total amounts to the monthly average for Ames. The red portion of the bar chart represents when an inch plus of rain falls. If you were to eliminate the red (stop daily rainfalls over an inch) portion of this chart, our wettest month would only see a bit over 2 inches of rain. Another interesting part of this graph is this insignificance of less than 0.05 inch rainfalls to the overall totals (can not see the blues). Heavy rainfall is currently occuring in Iowa today with some locations definitely picking up more than an inch.

Voting:
Good = 21
Bad = 6

Tags:   climate   precip  

The featured chart shows the hourly frequency of rainfall observations based on observations from the Des Moines Airport since 1973. The units of this chart are average number of hourly observations per month per year for that hour. Confused? For example, the red square represents a number around 4. This means that during the month of May, approximately 4 days during May have rainfall reported during the 7 oclock hour, which is the rainiest time of the year. According to this plot, the driest time is roughly 5 PM in August. There are many other interesting things in this plot. Compare October and November versus July and August. During the summer, rainfall comes during the nighttime. During the fall, it mostly comes during the afternoon.

Voting:
Good = 42
Bad = 24

Tags:   climate   precip  

The featured chart is the number of days with measurable precip per year for the long term climate sites. This chart would indicate that the number of rainy days is increasing at a rate of roughly 1 day per 5 years. 2008 will continue this trend with more rainy days in the forecast today and this weekend.

Voting:
Good = 41
Bad = 14

Tags:   precip   climate  

The featured bar chart is of monthly precipitation climatology for Ames. The blue bars are the average monthly accumulation and red bars are the average number of days during the month which have measurable precip. So for June, we average roughly 5 inches of rainfall spread over 10 days. In other words, we average 0.50 inches of rain every 3 days. Our recent weather for this month has been rather dry thanks to slow moving ridge that has kept the rainfall west of the state.

Voting:
Good = 12
Bad = 3

Tags:   climate   precip  

The featured graph is the distribution of hourly rainfall observations from the Des Moines Airport for the month of June (red) and for the year (blue) since 1973. The graph shows two clear modes for rainfall in Iowa. The first being around 6 AM due to the night time thunderstorm complexes feed by the low level jet in the summertime. The second being around 7 PM due to storms fueled by the heating of the day. In general, the night time is clearly the rainiest period during June with the other summer months showing a similiar distribution.

Voting:
Good = 13
Bad = 3

Tags:   climate   precip