Most of the state is below zero this Friday morning. The featured chart presents an analysis of the ratio of days above 100 degrees to days below 0 degrees Fahrenheit. Locations with more days below zero have the ratio flipped to keep all values positive. Locations in white are the closest to having equal days above 100 and below 0. Nearly all of the Midwestern US has many more days below zero and there is a large gradient over Iowa. Southwestern Iowa has roughly 10 times as many days below zero than above 100, while Northeastern Iowa is around 100 times as many days! The moral of the story is that the number of days below zero dwarfs the number of days above 100 for most of the region.

Last Sunday, much of the state picked up freezing rain with the heaviest accumulations shown on the featured map over Northern Iowa. A majority of the snowfall produced with this storm was north of the state, but it was a significant winter storm for Iowa and thus the inclusion in the running series on these events. Sorry about including the analysis for storm number six before this one! A number of smaller snow storms have been impacting the state in the past week as well. If reports are generally less than 3 inches, they are not counted in this analysis.

Our recent stretch of winter weather has seen numerous light snowfall events. A big help for clearing off the primary roads in the state is the sun. The featured chart presents a simple average of afternoon pavement surface temperature near Marshalltown and the frequency of having a sub freezing temperature. Solar declination increases each day in the spring, which makes for more energy entering the pavement and warmer temperatures. In February, it becomes increasingly less likely to have freezing temperatures, which means any frozen water on the surface will quickly melt.

Punxsutawney Phil comes out of his den on Groundhog's Day to make an important forecast for the spring season. The featured top chart presents the number of snow days for Ames before and after 2 February each winter season. The bottom chart is simply the yearly total of snow days after 2 Feb. Neither chart appears to show a meaningful trend, but does indicate that we have on average just under 10 snow days yet to go this winter season.

The featured chart displays the running departure from average for statewide precipitation over three windows of time. The short term windows of 30 and 90 days have shown some recent improvement with precipitation totals this winter close to average. The long term deficit over 365 days has deteriorated. How can short term deficits improve while long term do not? The short term improvements this winter are less than what happened last winter, so the net effect is deterioration as slightly drier conditions this year replace wetter conditions last year at this time.

The "IEM Freeze" application shows the combination of RADAR reflectivity, pavement temperatures (dots), and air temperatures (numbers) this morning. Temperatures so far are safely above freezing where it is currently raining the most. In far northern Iowa, temperatures are very close to freezing and some icing is taking place. This system will work its way out of Iowa today, with our next storm system arriving this weekend.

Most of the precipitation that fell on Thursday over Iowa was at temperatures above freezing. Is that rare for the first week of February? The featured chart presents the weekly frequency of hourly precipitation reports from the Des Moines Airport with air temperatures at or above 32°F. A caveat is that frozen precipitation can hit the ground with temperatures slightly above freezing. For the first week of February, the frequency is about 25%. The chances of these mostly rain events dramatically increases by the end of this month with above freezing events becoming the most common in March.

We have seen our share of precipitation producing storm systems this year. These storms are a welcome sight after a very dry 2012. The featured map shows the combination of the past 7 days worth of precipitation and the US Drought Monitor valid on 5 February. The driest areas in the state (shown by the D3 and D4 designations) received the least amount of precipitation in the past week. The next seven days appear to be mostly dry.

Our daylight time gets longer and the sun gets higher in the sky each day in February, but does that make a difference for our day to day high temperature. The featured chart shows the frequency of day to day high temperature changes by month for Ames. While there is a clear annual signal, the magnitude of the cycle is not that large. The annual climatology of temperature is only a gentle tug on day to day changes. Our daily temperatures are dominated by weather systems and the translation of air masses over the state. Our highs this week will creep a bit higher and then be cooler to end the week.

The featured image is a calendar of statewide averaged daily precipitation since the first of the year. After a dry first four weeks of the year, the next two were on the wet side with both snow and rain events. Our current week started of wet, but now looks to remain dry into next week. We are still in the winter season, so the chances of getting large precip events is rather small. The month of March is just a few weeks away and hopefully larger precipitation events as well.

The past two days have been very pleasant for early February in Iowa. Abundant sunshine and warm winds have helped to push temperatures near 50 degrees for some parts of Iowa. The lengthening days and increasing solar incidence angle provide us with much more energy from the Sun than just a few weeks ago. The featured chart is of recent daily solar radiation reports from the Ames ISUAG site. The past two days have totals that dwarf anything we have seen since the first of November. Air masses are still very important this time of year and colder air will arrive this evening with highs below freezing on Friday.

The present for us on Valentine's Day from Mother Nature was a strange combination of sunshine, mild temperatures and brief downpours of snow! The lower atmosphere was able to produce shallow convective like clouds and have snow reach the surface with near surface air temperatures well above freezing. The automated weather reports from the Des Moines Airport included an observation of 40 degrees and light snow! The featured chart presents the combination of reported temperature and day of the year when the site reports falling snow. Having a temperature of 40+ and falling snow is a rare combination and even more rare in February. The overall maximum temperature on this chart is 46 back on 19 Oct 1964.

There is currently a lot of excitement over the upcoming winter storm forecasted for Thursday into Friday. The featured chart looks at forecasted precipitation totals for Des Moines from the GFS model. The chart shows the current storm along with six recent heavy snowfall events. Each bar represents one of the four model runs made per day prior to the event. The general lack of consistency creates a creditably issue for forecasters. The top series shows one model run dumping a huge amount of precipitation and then backing off on the total up until the event. The fifth and sixth chart show going from having no precip to a storm. The caveat not illustrated here is the storm track, by which small displacements can make a huge difference in forecasted precipitation for a fixed location.

Those of you that fervently monitor the NWS forecast may have noticed something interesting this past Sunday. For some locations in the state, the NWS had a near 100% chance of precipitation forecasted for Thursday. Is it common to see a 100% chance forecast at four days out? The featured chart shows the frequency of this confident forecast based on the afternoon zone forecast for Polk County (Des Moines). Based on data back to 1 Jan 2009, this would appear to be the first time it has happened for the day 4 forecast for Polk County. The chart nicely shows that forecasters get more confident of predicting a 100% chance as the event gets closer. Today's forecast for Thursday remains at 100%!

Tuesday was a brisk reminder of the winter season we are still in with wind chill values below zero for most of the state. The featured chart displays the daily frequency of having at least one wind chill reading below zero. Three selected sites are shown for comparison. The frequencies peak out around 60% for most of January and the first few weeks of February. We are on the downward slope of this chart as we creep closer to springtime.

The long advertised snow storm for Thursday is finally at hand. Snow will get going this afternoon and last into Friday. The featured chart presents the air temperature timeseries for Des Moines for the ten most recent daily snowfall totals over six inches. Based on temperature and hourly precipitation, a crude estimate is made of when the snowfall started to normalize the chart. The chart nicely illustrates how temperatures are generally steady during the snowfall event, with warmer temperatures before and colder temperatures after. Temperatures are also generally in the 20-30 degree range with the noticeable anomaly being an event from Feb 2009, when we had once of the largest snowfall events at a temperature near zero degrees. For this event, temperatures will be steady in the mid 20s, but not much in the way of colder air behind the system.

The long awaited snowstorm on Thursday is winding down this morning after covering most of the state with around six inches. The heaviest totals were in western Iowa with up to ten inches reported. Even heavier amounts were over Kansas and Nebraska with locations just southwest of Iowa picking up around a foot.

After a major snowstorm to end last week, another storm is cranking up to our southwest and is expected to bring more snow to the state tonight into Tuesday. Is it common to have back to back snowstorms like this? The featured chart presents the frequency of having a snowfall event within the 2 to 5 day period after a day with or without snow. Day 1 is skipped since it is hard to differentiate two day snowfall events from the same storm. The frequencies are partitioned by the snowfall total. There appears to be an interesting signal in this chart with the frequencies peaking for days after a three inch total. While the blue bars represent all cases, the red bars denote when the subsequent snowstorm produced a daily total larger than the one proceeding it. So when there was an eight inch plus event, the next snowstorm within two to five days was less intense for Des Moines.

Our recent bout with cold weather was about the relatively coldest weather we have seen in the past year as shown by the featured chart of daily average temperature departures. We are now getting closer to March and one wonders if we can come close to repeating what happened last March with persistent and extremely warm temperatures. But first we have to finish February and some snow over southeastern Iowa today.

The snow is still falling this Wednesday morning and the totals are approaching a foot in some locations in the state. A band of moderate intensity snow setup Tuesday much further north and west than expected resulting in the swath of higher totals you see on the featured map between Des Moines and Waterloo. This map will be updated later today as more reports come in and the analysis is improved.

Our most recent snow storm caused great gnashing of teeth as some areas not expected to receive much snowfall got 8-12 inches! The featured chart attempts to explain why this surprise happened. The GFS forecast model is one of the models used by forecasters to predict the weather. The model is run four times daily and each run produces a forecast out the next week or so. The featured chart presents the model forecasted precipitation for a grid cell over the Des Moines Airport. The top bar displays what was observed. If you focus on the third column in the grid where the most intense precipitation fell, you will see that the model went from a dry solution for Des Moines to having a storm to then again dry and the runs made on the 26th ramped up the totals tremendously. These changes are due to storm track differences as the model moved the storm initially south of Des Moines and then brought it back.