The featured image has been shown since the mid summer highlighting Des Moines probability of 2012 being the warmest year on record. The red line is 2012 and the blue line is the warmest year on record (1931). If we consider all previous years as scenarios to finish out this year, then roughly 89% of the previous years would put 2012 in the warmest spot to end the year. The chart would indicate that we should still have the lead going into December, but our margin may be much closer than it is now. The forecast to start November keeps us around average.

Having water available in the soil for plant use is obviously important during the growing season. Different plants require different amounts of water to thrive. Potential evapo-transpiration (PET) is an estimate of the amount of water that a plant could transpire given always available soil water and observed air temperature, humidity, and solar radiation conditions. This is sometimes expressed in a unit like how we measure precipitation (depth of liquid water) and represents an upper bound on the amount of water a plant could utilize. The featured chart presents the daily accumulation of PET for this year and past years since 1987 for the Ames ISUAG station. The two recent big drought years of 2012 and 1988 appear with the larger values. This may seem counter-intuitive that drought years have the highest potential water use. Drought conditions often include less humid conditions and hot temperatures, both of which promote water usage by plants when soil water is available. The availability of soil water is the key to how much PET is actually materialized into evaporation and transpiration. Unfortunately ET is difficult and expensive to measure, so we are stuck with PET estimates to provide insight into water usage by plants.

The featured map is a simple analysis of lowest observed temperature so far this fall season from the airport weather sensors. This map would indicate that the entire state has seen below freezing temperatures this fall. While some locations have barely breached 32 degrees, other parts of the state have been well into the teens. Low temperatures are strongly influenced by local affects and terrain, so observation stations relatively close to each other can often report much different temperatures. The analysis technique does not consider terrain, so the map can have unrealistic blotches.

Being a swing state, Iowa gets an inordinate amount of attention this time of year for the presidential election. While the Washington Redskins seem to have skill predicting the result of the election, is there some aspect of Iowa's weather that predicts the election here? The featured chart presents the presidential election day averaged temperature and precipitation in Iowa since 1900. The color of the bars indicate the party voting record for Iowa and the U.S at large. There does not appear to be a predictor based on this chart and a number of other charts generated that are not shown here. 2008 saw the warmest day and 1932 the wettest. This year will have around average temperatures and a bit of rain over the northern part of Iowa.

The featured chart displays the maximum daily river flow as measured by the gauge on Squaw Creek in Ames at Lincoln Way for each year since 1991. The chart has a logarithmic y-axis to help show the low flows. The flow this year has been on the dry side and non-existent (not measured by the sensor) for many times since July. The flood years of 1993 and 2010 are highlighted for comparison. We continue to desperately need rain and rain while the ground is still not frozen. This rain would help replenish ground water and provide a reserve for crops to use for next year.

The past few days have seen mostly cloudy conditions here in Iowa. The noticeable visual effect for us is a lack of sunshine during the day and not seeing stars at night! Besides visual effects, clouds are an important component of the surface energy budget (which drives weather variables like near surface temperature). During the daylight, clouds reflect energy from the sun back out into space and act like a mirror. For all 24 hours of the day, clouds are absorbing and re-emitting energy from the ground back down to us, acting like a blanket. The featured image illustrates the effect of significant cloud cover by comparing hours with clouds against all available hours of observations from the Des Moines Airport sensor. The plot shows the primary effect of keeping temperatures cooler during the daytime and keeping temperatures comparatively warmer during the nighttime. The strongest effects are when solar heating of the ground is most efficient in the late summer / early fall season (drier/warmer soils, plenty of potential sunshine for surface heating) and during the early morning hours in spring and fall (peak radiational cooling due to lower humidities). Restating, these times are when clouds have the most influence. So while clouds have been helping to keep us recently cool during the daytime, they have kept overnight temperatures higher than they would be with clear skies at night.

The US Drought Monitor is released weekly and provides an analysis of drought conditions. The featured image displays the week to week change of the drought monitor product over Iowa since January 2000. Drought is classified from a D0 to D4 category. The length of the arrow represents the areal change in combined drought categories. For example, if the entire state went from a D0 to D1 category then the arrow would be one unit long and in red. In this case, the unit length is shown on the y axis as one year. The bottom row of arrows are those for 2012 and clearly show the degrading drought situation that occured during July. The last three weeks of October 2012 have seen some improvement, but there is still a ways to go.

Very warm air is surging into Iowa this Saturday with numerous record high temperatures being set. Des Moines set its record high today by reporting 78 degrees at 12:35 PM. Is it unusual for a record high to be set just after noon? The featured chart provides an estimate of the time of day record high and record low temperatures occurred at. The daily records are from a different dataset than the hourly temperature archive, so some estimates were done and a constraint that the extreme hourly temperature was within 4 degrees of the record temperature. Having a record high near 1 PM has happened previously, but that won't put a damper on today.

The lone blue dot (record low) shown at 5 PM on 25 Sep 1942 appears to be legitimate estimate.

The record high temperatures on Saturday have given way to much colder temperatures and even some snow on Sunday. The past day and a half has seen a temperature swing of 45-50 degrees. The featured chart presents the maximum computed 12, 24 and 36 hour temperature change based on hourly observations from the Des Moines weather sensor. The temperature swing experienced this past weekend is about typical for an extreme temperature swing this time of year. The largest values on this chart are in the springtime when the contrast in air masses are the strongest. The summertime has the longest values as humidity helps to temper potential temperature swings and artic air masses do not survive the trip south.

With the current taste of winter fresh in our mouths, it seems a long time ago that temperatures soared to record levels on Saturday. Not only was it warm, it was some of the warmest weather we have seen in November on record. The featured chart presents the hourly temperature observations at the Des Moines Airport along with the most recent date with such warm weather for that hour in November. For a few of the hours, one has to go all the way back to the 1930s for warmer weather! The immediate term forecast keeps temperatures reasonable for this time of year with mostly dry conditions.

On Monday, Cedar Rapids had its first day of the season with a high temperature below freezing (a frozen day). This was the earliest such day since 1996 as shown by the featured chart. Does an early first frozen day provide any insights into the winter season ahead? Based on average temperature for the winter season (Dec - Jan - Feb), the bottom chart would indicate that the answer is no. The next 7-10 days have daily highs in the 50s, so our next frozen day will have to wait for a bit.

Des Moines has yet to report snowfall this year, which extends the streak of days since the last reported snow during the first week of March. The featured chart shows period between the last snowfall reported in the spring and the first snowfall of the fall. Only two other years have seen a longer stretch without snow (2001 and 2004). The black line shows the average last and first date. Our first snowfall for Des Moines should happen before the end of the November, but the forecast keeps temperatures above freezing until at least Thanksgiving.

The featured chart displays the precipitation departures over three trailing time windows. The 30 days departures have recently turned positive for the first time since May, but dry conditions for the past few days have reverted us back toward zero. Deficits are much larger on longer time scales and we are eight inches short of average for the past 365 days. It will be difficult to make up the longer term deficit during the cold months of the year as the total precipitation is much less than the warm months. It will take heavy rainfalls in March and April to give us a chance to have recovered soil moisture prior to the growing season next year.

The cold weather and reality of a coming winter season for October has given way to rather warm weather for November. The featured chart presents the accumulated streaks of days above or below high temperature average for Des Moines this year. Our current streak looks to continue until at least Thanksgiving with highs even pushing 70 degrees on Wednesday.

Those of you in eastern Iowa getting an early start to Grandma's house for Thanksgiving are experiencing very dense fog this morning. The featured image is an analysis of reported visibility from automated weather sensors. This fog will go away later this morning thanks to an increasing wind and arrival of some warmer air. Two more days of very warm weather is left until the shock of much colder temperatures arrives on Friday.

Some very warm weather again last week prior to Thanksgiving helped to push 2012 into the lead for most days over a number of high temperature thresholds for Des Moines. The featured chart displays the record number of days per year at or above a given high temperature with bars labelled in blue denoting the record being set this year. 2012 now owns the record for most days for nearly all thresholds between 50 and 85 degrees. The 61 degree threshold is a lone hold out, but perhaps we could push that level once or twice before the year ends! It is remarkable to think that nearly half of the days this year were at or over 70 degrees.

Our weather has taken a remarkable change after Thanksgiving last week. The featured chart shows that for the 6 days prior to and including Thanksgiving, Des Moines has the warmest average high temperature for that period this year. Cold air has since replaced the pre-Thanksgiving warmth and high temperatures have been struggling in the 30s. The forecast has a slow warm-up this week with highs back near 50 degrees by the weekend.

Temperatures dropped quickly Monday evening thanks to clear skies and calm conditions. Our saving grace was ground temperatures which are still warm for this time of the year and the lack of snow cover, which prevented temperatures from dropping even further. Snow cover is a game changer when it comes to the surface energy balance during the day and night time. It acts to mostly seperate the exchange of energy from the sun to the soil and back to the air. The featured chart presents the frequency of having snow cover at a given daily low temperature (blue line) and the overall frequency of that temperature (red line). The main point is to show that the coldest temperatures are increasing associated with the presence of snow cover. For example, a low temperature of zero degrees also had snow cover present 90% of the time. The chart also had an interesting (but unexplained here) aspect of having the lines cross at the 50% probabilities for both y-axes around 18 degrees. It is difficult for near surface soil temperatures to get cold enough to support very cold air temperatures, so snow cover is increasing necessary for the coldest temperatures.

While the recent election was uneventful, Thanksgiving marked a major regime change with our weather as daily highs in the 60s for six days were replaced with highs in the 30s for Des Moines. How extreme was this 30 some degree change between two periods? The featured chart presents the largest change in average high temperature between two consecutive periods of days of a given length. The month during which this extreme drop occurred is presented as well. Almost all of the most extreme drops are in February. The largest values are brief warm air masses that are replaced by snow and very cold air. Our forecast is a slow warm up with highs back to around 60 this weekend.

Drought is a complex interaction of short and long term precipitation deficits producing impacts on various time scales as well. If you consider the past 365 day precipitation departure, Iowa is about 6.5 inches below average currently. How soon can this deficit be made up? The featured image considers the scenarios provided by the previous 119 years of climate record when appended onto our current condition. The lines trace out the 365 day departure to date. When considering this long term deficit, the chart clearly shows that no improvements will be made this winter season. Short term deficits could be eliminated though. More disturbing is that we will likely still be below normal to start the growing season as only six years shown provide a scenario were we even get to some level better than negative four inches.

After finally getting a slightly cooler than average October, November has quickly reversed the recent cooling trend and will finish today well above average. The featured chart presents the monthly temperature departures for Des Moines along with the El Nino 3.4 index since Jan 2007. This index is used for the commonly heard terms of "La Nina" and "El Nino". Sometimes our weather is associated with the phase of this index, but it is not a simple relationship. The forecast to start December looks remarkably warm and will give that month a head start on being above average as well. It also looks to push 2012 far enough ahead to finish the warmest year on record.