2012 will go down as one of the drier years on record for Iowa as shown by the featured graph of preliminary estimates for the state. This past year was the driest since the drought of 1988 with only a handful of other years drier since 1900. After four of the wettest years on record between 2007-2010, these past two have bucked the recent trend. While the calendar has changed, the drought of 2012 will roll on into 2013 and has near-zero chance of being busted before springtime.

The featured chart attempts to answer the question of what was missing from the precipitation for Des Moines during 2012. The chart divides up the daily precipitation totals into 5 bins that over the long term have each contributed 20% of the total. For example, the first bin of 0 to 0.29 inches on average provide 20% of the yearly total over an average of 134 days. On the high end, there are an average of 3 events of over 1.51 inches providing another 20%. The red bars are what was observed in 2012 along with the contribution to the departure this year in red text. One category clearly dominates and that was a lack of events between 0.92 and 1.51 inches. While the difference in days at the lowest bin looks significant, the actual departure of total rainfall was marginal.

The featured chart displays the daily difference in high and low temperature between the Des Moines ASOS and Ankeny AWOS weather station. Ankeny in a suburb of Des Moines and the sites are separated by only 12 miles. Recently, the daily low temperature has differed by up to 10 degrees Fahrenheit. The bottom chart shows that since June of 2012, Des Moines has almost always had a warmer overnight low temperature. It is not clear what could be causing this phenomena, but local micro-meteorological effects could certainly be at play here. It is somewhat disconcerting to see systematic shifts in this comparison that may be a sign of calibration or sensor issues. The Des Moines site is a part of the federal ASOS network, while the Ankeny site is an Iowa DOT AWOS site.

On Thursday, the temperature at 6 AM was a balmy 31 degrees for Des Moines but then dropped to 18 at noon. The featured chart looks at how common it is for the noon temperature to be colder than the 6 AM temperature for each day of the year. This situation is certainly the most common during the winter months when air masses dominate our temperatures and the sun is the least effective at warming during the daytime. The bottom chart presents the largest difference in temperature between these two hours and for some days in the summer, this situation has yet to happen for Des Moines. Friday will be a different situation with warmer air and sunshine both conspiring to push us to just above freezing!

This past weekend saw some mild temperatures on Saturday and was some of the warmest weather we have seen since the blizzard on 20 December. The featured chart displays the daily high and low temperature for Ames since 1 December 2012 along with the daily climatology. The arrival of snow certainly changed our weather as temperatures have been mostly below freezing since. Moderation looks to be in store this week with colder temperatures arriving for next week.

Above freezing temperatures and sunshine helped to melt some of our snow in Iowa on Monday. The featured chart is of latent heat flux from the one of the NLAE flux sites since the first of the year. Latent heat is a measure of the energy being transferred from the surface to the atmosphere as the result of evaporation or sublimation of water. In this context, a positive number is a transfer of energy to the atmosphere. The large spike on Monday is certainly indicative of the enhanced snow melt, sublimation, and evaporation that was occuring. These processes require heat, so it acts to slow the surface air heating rate as energy is consumed to change the phase of water. This is a big reason why near surface air temperatures can not get too warm with snow on the ground.

The National Climatic Data Center issued a report yesterday placing 2012 as the warmest year on record for the CONUS. While it was the warmest year for Des Moines, it was not the warmest for all sites in the state. The areal averaged temperature for Iowa came in a very close second place behind the year 1931. The featured image presents the year to date average temperature for 1931 and 2012 in the top chart and the monthly average temperature departures in the bottom chart. It is interesting to note how August for each year was similar and both very close to average. The last four months of the year show why 1931 was able to remain number one in Iowa. Please note that these numbers are IEM estimates and do not match the NCDC estimates, but we both have 2012 coming in second for Iowa.

Temperatures are expected to warm nicely on Thursday and again on Friday before crashing into the weekend. The featured chart presents 24 hour temperature traces in between a day to day high temperature change of at least 30 degrees. The zero hour in this chart is after the peak temperature occurred for the first day. These events are almost always associated with cold front passage. The average fit line shows how quickly these events tend to occur with the temperature dropping 30 degrees within the first 8 hours. It remains to be seen if the high temperature on Saturday will be 30 degrees cooler than Friday.

Some of the forecast model runs made earlier this week were advertising a significant rainfall event on Thursday as shown by the featured chart. The chart shows the 6 hour interval forecasted precipitation for Des Moines from the GFS model that runs 4 times per day. Des Moines ended up with just over a tenth of an inch of rain. The forecast looks dry and cold for the next week.

A long standing need of the mesonet project was to clone the primary developer. On Sunday, this need was fulfilled with the addition of Margaret Ann as shown by the featured image. She is doing well and will be in intensive computer programming training with dad for the next few days, so dad may not respond to your emails immediately :)

The meteorological winter season from 1 Dec to 28 Feb is now half over and it has been on the warm side of average so far. The featured chart presents the statewide areal averaged temperature for the 1 Dec to 15 Jan period each year since 1900. Years above long term average are shown in red. The forecast for the next seven days has us starting off on the warm side with much colder temperatures arriving this weekend.

The southern plains have seen a number of bouts with severe weather so far this year. The featured chart presents the number of severe thunderstorm and tornado warnings issued between 1-16 January each year since 1986 along with the total for each year. Active or inactive severe weather starts to the year do not appear to indicate what the yearly total will be. Iowa's severe weather season is still a few months away, but our weather will become severely cold this weekend.

What makes for a brutal winter season? Perhaps having a streak of days below a certain temperature would qualify. The featured chart presents the longest streak of days below a given temperature for each winter season since 1893. A few of the most brutal years are highlighted along with the simple average of the lines plotted. Our upcoming bout with cold air will be intense, but does not look to persist for very long. The lack of snow cover makes persistent cold difficult to come by.

Temperatures warmed nicely on Saturday into the 50s, placing us over a standard deviation from average for the date (called sigma). Temperatures have since crashed and will struggle in the single digits today, which less than negative one sigma from average. The featured chart looks at how often this change of going from at least a positive one sigma high temperature to lower than a negative one within three days. The top chart shows that January is the least frequent month for this event as warm air surges are the least common. The bottom chart presents the yearly total of these events and last year saw the second most at 12 days.

The coldest air in two years for some locations in Iowa arrived on Monday and remains over Iowa today. The featured map presents the low temperature on Monday along with the number of days since as cold of a temperature. For the Des Moines Airport, the -2 was the coldest since February 2011 and the first temperature below zero since then as well. The cold air will stick around this week before warmer air arrives next week.

Our recent bout with cold weather was the coldest of the season. Ames reported negative five for a low temperature, which tied the lowest temperature for the season. Is colder weather to come or is this it? The featured chart looks at the coldest temperature of the winter season and the date on which it occurred. There is certainly plenty of time for colder weather to occur and negative five would be one of the warmer temperatures on record for a winter minimum. Selected warm, cold, and March events are labelled on the plot.

The seasonal total of snowfall for Des Moines is about 34 inches. This is a result of many individual snow storms during the season. The featured chart looks at the contribution of snow storms of various size to the seasonal total. The five bins presented approximately divide up the total snowfall equally. The bar height and number above the bar are the average number of days per season with a snowfall within the shown interval. Roughly 70% of the snowfall events only provide 25% of the total snowfall. Des Moines has only seen a handful of snowfall events this season and is below average so far.

The featured map presents an analysis of the average number of hours per year that the wind chill reading is below zero. The total number of hours is presented in units of 24 hour day periods for easier comprehension. While there are some local poor data effects, the north to south pattern is clear with the nation's ice box around 50 days and the south under 1 day. The gradient over Iowa is fairly strong with northern Iowa near 30 days and southern Iowa around 10. The past week has seen the coldest wind chills over north central Iowa, which makes the preferred region in the state for the most frequent sub zero wind chills.

Our most recent storm brought significant freezing rain to Iowa with the largest accumulations over northeastern Iowa. The featured chart looks at the combination of air temperatures with reported road conditions for two locations along Interstate 35. While both locations received freezing rain, conditions improved significantly for Ames as the air temperature rose above freezing. For Mason City, temperatures are still just below freezing and thick fog is not helping the tricky driving conditions this Monday morning.

It was a struggle on Monday for some locations in Iowa to warm up. Spencer reported a high temperature just four degrees warmer than the low temperature. The featured chart presents the frequency of having such a small temperature difference per month. Overall, these events happen a few times per year with the coldest half of the year being the preferred period. In the summertime, it is very difficult to keep the sunshine from warming us up as extremely optically thick clouds tend not to persist the entire day.

The featured chart displays a time series of air temperature for Cedar Rapids and NWS issued alerts for Linn County since Saturday. We have gone from cold temperatures, to freezing rain, to dense fog near freezing, to severe thunderstorms, to record high temperatures, to a winter storm and finally brutal cold temperatures. "This is Iowa Weather" many proud Iowans exclaim, but this stretch has been unique and certainly not what typically happens most of the time. Wind Chill Advisories are also in effect for portions of Iowa on Thursday as bitter cold air rushes into the state.

The warmer weather earlier this week is now a distant memory and much of the state is now covered with fresh snowfall. The featured analysis of snowfall reports from the event show the highest totals near Waterloo around 8-10 inches. Northwest Iowa completely missed out and totals were much smaller over Southeastern Iowa. While every little bit of snow certainly does not hurt the drought situation, they are not sufficient to make significant impacts to soil moisture recharge. It would probably be better to thaw the soil and get many rainfall events during the early spring. Beggars can not be choosers at this point!