The most recent winter storm dumped an inch or so of snow over most of Iowa, but combined with bitterly cold temperatures and strong winds, dangerous conditions were present for a while Saturday evening over northern Iowa. The next winter storm system arrives on Monday with much more snow expected from this system. Even colder air will arrive after this next storm system with highs on Wednesday perhaps below zero for much of the state.

A clipper system was able to dump significant amounts of fluffy snow over much of Iowa on Monday evening. The featured analysis combines NWS COOP and Local Storm Reports to show the swath of 5-7 inches with lesser amounts over northeastern Iowa and no snowfall over southwestern Iowa. Very cold temperatures are now over Iowa with high temperatures tomorrow expected not to breach 0F!

Air temperatures have dropped and winds have increased this morning. The combination of both have conspired to create dangerous wind chills. Many schools have cancelled classes today due to the wind chill. The NWS has issued a Wind Chill Warning for today until noon for much of Iowa. The featured chart presents the frequency of when during the day a wind chill warning is active for Story County (Ames). Rewording, when a wind chill warning is active, what is the frequency during the day that the warning was active. The afternoon hours are the least favored time, which makes sense as it will likely be the warmest portion of the day. Products like these are issued on a 3 hour increment of time, which is why there is a rapid cut off at noon.

If you have sensitive sinuses, yesterday was probably not a very pleasant day for you as air pressures were near the largest values ever recorded in the state. The featured table displays IEM computed pressure records (as expressed by the pressure altimeter reading). There are a number of caveats to this chart as locations in the state have different periods of record and the maximum daily high pressure is something not commonly reported, so this table simply lists out the maximum hourly value reported. Extreme high pressures like this are found with dense areas of very cold air during the winter time.

Active winter weather has been the case for this week with strong winds driving a ground blizzard over northern Iowa on Thursday afternoon. The featured chart presents the headlines issued by NWS Des Moines since 3 January for their forecast area of responsibility. The bars represent the time period that the headline was valid for at least one forecast zone in the state. The have only been brief periods in the past seven days that no headline was active.

While the vast majority of impacts from the most recent winter storm system were felt to Iowa's south and east, a swath of snow did fall over extreme southeastern Iowa with totals approaching 2-3 inches as you cross into Illinois. Cold air behind this system has arrived this Monday morning and bitter cold sticking around into Tuesday. Warmer weather is in the forecast for the upcoming weekend.

It is always a good idea to check in on how we look from space. With clear skies overhead on Monday, the Terra MODIS satellite true color image shows the snow covered landscape over Iowa. Just the southwestern corner of the state is free of snow at the moment. After cold conditions today, temperatures are forecasted to approach 40 degrees by the weekend.

The featured chart displays the frequency of having an air temperature within a given range for Des Moines based on long term hourly temperature records. For January, about 75% of the time is spent at temperatures below freezing. In July, we spent about 75% of the time at temperatures above 70. You can generate this plot on this website and pick the intervals you are interested in for the station of your choice.

On Monday morning, the low temperature for Waterloo was -16 while just a few miles east at Oelwein it was 8 degrees warmer at -8. The featured chart looks at differences in morning low temperature between the two sites over the course of a year (top plot) and against the average wind speed at Waterloo. The difference in temperature is due to micro climate effects are that are much more common during low wind conditions. Near surface winds help to mix the lower atmosphere and keep temperatures more evenly distributed. When winds relax, local effects happen and rapid cooling may occur at night time. The lower plot clearly shows the difference are most noticeable at low wind speeds. As wind speed increases, the average difference in low temperature approaches zero. This creates a forecasting issue when local weather stations can have large differences in low temperature as compared with their nearby neighbors.

Our current rebound in temperatures to levels well above freezing are certainly a nice break from the recent few weeks of cold weather. Climatology says that the middle of January is the coldest time of the year, but climatology can be computed different ways. The featured chart presents three daily temperature climatology metrics. The National Climatic Data Center (NCDC) produces 30 year normals which are updated every ten years. The chart shows the most recent two iterations of that product as well as the simple daily average of long term observations. The 1971-2000 product was provided in whole degree Fahrenheit, so that is why it jumps up and down on the plot. It is interesting to note the difference between the 1981 product and the other two metrics.

Gusty winds on Saturday prompted the NWS Des Moines to issue a Wind Advisories for portions of northern Iowa. The featured chart looks at how common the Wind Advisory is issued by week of the year. The top chart displays the number of years with at least one Wind Advisory for that week and the bottom chart displays the total number of advisories. The plot shows a peak number of events in April with near no events during the July- September period. Strong sustained winds are driven by temperature contrasts and during the summer months, these strong contrasts are difficult to find over the central US.

The featured chart displays the frequency of the monthly precipitation total being at least 80% of average or higher for the past 20 years. The average is computed from the period of record data. The chart shows that January has been one of the least reliable months to get close to or above average precipitation totals. This month's total has yet to breach this level, but there are a number of days left and a few chances of precipitation to come.

Highway frost was a major issue over Iowa on Tuesday morning. The featured chart presents the combination of RWIS air, dew point, and pavement temperatures for US Highway 30 near Jefferson along with the reported road condition by the Iowa State Patrol. The clear issue shown in the chart is having the road temperature below the dew point, which causes deposition of water vapor onto a frozen surface. Once the road temperature raises above the dew point, the frost was gone and the road reported as dry.

Des Moines has seen three days so far this January at or above 50 degrees. The featured chart presents the number of 50+ degree days in January for Des Moines. The long term average is 2 days, so our total this year of 3 is doing very well. The forecast has warmer weather returning with a chance of a few more days over 50.

The featured map plots season snowfall total departures for primary climate sites tracked by the National Weather Service. Much of the Midwest is below long term average including locations in Iowa. The near term forecast is not optimistic for accumulating snowfall for Iowa, but there is still plenty of winter to come. Our largest snowfalls come in late winter and early spring anyway.

Our most recent clipper winter storm system brought just an inch or two to portions of southeastern Iowa. This storm system is now approaching the east coast and merge with other energy to grow into a massive storm that is expected to bring blizzard conditions to the northeastern US. Much of this snowfall for Iowa did not survive until Monday and warm temperatures today will help to melt the rest of it.

The featured chart looks at the accumulation of snowfall events and totals relative to the season average of each. For Des Moines, today is about the half way point for accumulating both snowfall metrics. This means that typically we have seen half of our total snowfall events and half of our total snowfall by this date in the winter season. There is a subtle difference in the plot between the two lines, which is interesting to note. The events accumulate faster initially and then the snowfall total catches up. The reason is that the snowfall events during the first half of the winter are of lesser magnitude, on average, than the events that happen during the later part of the season.

The featured chart displays the warmest January high temperature for Ames for each of the past years on record. This year has seen temperatures above 50 degrees, which is just slightly above average for maximum temperature for the month. The chart shows that while each of the past four years has seen a 50+ temperature, the prior five years did not. The amount of snow pack during January makes a big difference to how warm we can get. Temperatures today are expected into the 50s for Ames, so get outside and enjoy it before winter returns!

Our recent stretch of January weather has seen very pleasant temperatures for most of Iowa. Some consider winter as a constantly frozen and harsh time in the midwest and it is certainly like that at times, but the featured map shows that on average, high temperatures are often above freezing for the period of December to February. A considerable gradient exists in the midwest with frequencies dropping by about ten percentage points for every climate district you travel north. The forecast has a return to daily highs below freezing and some chances of snow.

Today's featured map presents the frequency of having a daily high temperature above freezing with the daily low temperature being below freezing for the winter months of December, January and February. Yesterday's feature showed that just about half of Iowa's winter days have a high temperature above freezing. This map shows slightly smaller values, but again about half of winter days have a high above freezing with a low below freezing. The largest frequencies are shown over western Nebraska and Kansas with just under 80% of days meeting this criteria.