Temperatures yesterday warmed 37 degrees for Ames after a chilly start in the low teens. Having this large of a daily warm up is somewhat rare for this time of year as shown by the featured chart. The chart presents the frequency of 20+, 30+, and 35+ degree differences between the daily low and high temperature. The spring and fall seasons show up clearly in this chart along with a general annual signal of the 20 degree line. The dip in frequencies for the largest differences in the summer is due to shorter nighttime periods (less time to cool off) and abundance of water vapor to help moderate any temperature moves.

Precipitation totals for November ranged from around double of average over southeast Iowa to around 10% of average over northwest Iowa as shown by the featured map. This pattern did not help the dry conditions that have been worsening over portions of the northern plains. A winter storm is set to arrive this weekend with a dry work week expected after that.

Our second significant winter storm of the season is in the books with snowfall totals upwards of six inches reported. A good portion of the state that didn't see snowfall, saw needed heavy rainfall of around an inch. Unlike the nice warm up that occurred after our first winter storm, very cold air is coming with highs expected below freezing for most of the week.

Ames experienced its first day with a high temperature below freezing on Sunday. The featured chart presents the number of days each winter with a daily high temperature below freezing along with the first day of winter below freezing. The first day this year is a bit later than normal. The bottom chart hints that having the first frozen day in December typically leads to a below average number of frozen days for the winter season. If this were to happen, it would buck the recent trend shown in the middle figure of having above average number of days per year with a high temperature below freezing.

Low temperatures have been quite cold for this time of year with near record low values over northwestern Iowa thanks to a new snowfall and clear skies. The featured map presents an analysis of low temperatures for Tuesday showing a 40+ degree gradient over Iowa. Southeastern Iowa is snow free and had the warm comfort of clouds overhead which help to trap in the earth's heat during the nighttime. The forecast has some hope for slightly above freezing temperatures this weekend.

Those of you that frequently look at weather radar have perhaps noticed a nearly persistent feature showing up over southern Iowa. The featured map presents the frequency of RADAR returns over 0 dBZ for most of yesterday. The red bar you see is coming from the Saint Louis RADAR and is the result of interference, perhaps coming from a nearby cellular phone tower. The map also shows blobs around the Des Moines and Davenport RADAR due to ground clutter (the RADAR beam hitting stuff on the ground and reflecting back to the RADAR). These types of phenomena make RADAR meteorology fun and a challenge to derive reliable products like precipitation estimates from reflectivity data.

The high temperature on Thursday barely breached freezing for Ames putting an end to the streak of four days below freezing. The featured chart presents a comparison between the length of the first period below freezing each winter to the total number of days below freezing and the average temperature for that winter season. The good news is that having an initial streak of four days does not appear to provide a hint to having a bad winter season. Today will be another cold day with a slight warmup expected for this weekend.

While it wasn't much of a winter storm, our most recent bout with winter brought a few inches of snow over portions of southern Iowa. This snow is already gone thanks to warm temperatures on Sunday. More storms are in the forecast for this week, but the chances for rain seem to be better than snow at this point. Some portions of Iowa may set monthly precipitation records for December after this week is over.

The featured chart presents a climatology of winter season snow storms for Des Moines. For this chart, a snow storm is defined as having at least one day with measurable snowfall followed by at least one day without snow. The years with the maximum and minimum number of storms are shown as well. With only a few storms in the books this year, we have plenty more to go.

Yesterday's feature presented the climatology of the number of winter snow storms. The featured chart today presents the total snowfall for the winter season. The years with the maximum and minimum accumulation are shown as well. For the immediate future, our chances of rain look to be better than snow, but technically it is still the fall season and we have all of the winter season yet to go!

Having air temperatures at or below 28 degrees Fahrenheit are often considered to be a 'killing frost' event. It is not an exact science and very small scale processes occur to kill or protect the plant, anyway the featured chart presents the the frequency of having such a cold temperature by a given date in the fall season. For example, Waukon has seen the first hard freeze roughly 70% of the years prior to 1 November. There is a variation of just around a month from the earliest to latest in the state. In fact, Fort Madison made it till 9 December back in 2001 before hitting such a cold temperature.

The featured map presents precipitation estimates for the past two days from NOAA. A portion of southeastern Iowa is shown in the 1.5 to 3 inch range, which is quite large for December! Unfortunately, the areas that need the rain the most over northwestern Iowa largely missed out again. Temperatures on Wednesday were abnormally warm as well with record maximum low temperatures set in some locations. Normal temperatures return today along with not much hope for a white Christmas.

After all of the heavy rainfall events of these past four years, it is hard to imagine having drought conditions in Iowa. The featured chart presents a time series of the areal coverage of various drought categories in the state from the National Drought Monitor. The chart shows conditions recently getting both better and worse (two arrows) with the total area under drought shrinking while the area in severe drought condition expanding. This implies that recent precipitation events have missed the hardest hit areas. These areas are in northwest and northcentral Iowa. The near term forecast does not have much hope for large precipitation events.

A small snow storm clipped portions of extreme eastern Iowa Friday night and Saturday morning. Snow fall accumulations were under four inches for Iowa. This snow will not stick around long with above freezing temperatures expected this weekend. The big question at the moment is if we will have a white Christmas. The chances do not look good at this point.

Temperatures warmed into the 50s for most of Iowa on Sunday with even warmer temperatures to our west. This warm air will be replaced by colder air supporting a major winter storm developing to our southwest. Blizzard warnings are in place for much of the region near the Oklahoma panhandle. This storm's impact on Iowa remains in doubt with the main storm impacts passing just to our south.

The featured chart presents a comparison between the accumulated snowfall prior to and after Christmas. Only a handful of winters have seen less snowfall after Christmas than before. The chart also shows that not having much snow prior to 25 December does not limit the amount of snow after with some of the largest totals coming after just a few inches in the first period. Currently, a large winter storm is just to our southwest, but struggling to bring snow into Iowa. The chances for a white Christmas continue to look rather dim.

This December has bucked the recent trend of the past four years each having cold starts to the month. The featured chart presents the average temperature and wind speed for the first 20 days of December since 1940. The average wind speed is only slightly greater than the minimum shown on this chart back in 1971. Temperatures will be above normal again today with plenty of warm weather expected in the next seven days.

The day with the least amount of daylight is also the start of the winter season. This at first may seem counter-intuitive as the sun is the energy source for heating the ground which then heats the air. We have about another month yet to go before we see the coldest average air temperatures as shown by the featured chart presenting the daily climatologies of air and soil temperatures along with daylight length. You can see that none of these curves exactly line up with their maximums and minimums shifted in time slightly.

The featured chart presents the observed daily frequency of snowcover partitioned by if there was snow cover on Christmas and the overall average is shown. The highlighted area shows the period were these three lines show visual differences, which is a way to show the memory of having a white or brown Christmas. In other words, by mid February the frequency of having snow cover does not relate to if we had snow cover on Christmas. Back to the matter at hand of our snow state for this Christmas, well it will be brown with very warm temperatures in the 40s!

After a very warm Thanksgiving, Christmas does not disappoint with high temperatures well into the 40s. The featured chart presents the daily high and low temperatures on Christmas Day. Having a day with a high temperature above 45 is rather rare as shown by the red bars on the chart. High temperatures look to continue in the 40s for the rest of the year with no snow in sight.

The featured chart presents the number of consecutive days with daily high temperature above 40 degrees to end the calendar year for Des Moines. Our current streak has started on the 23rd and the forecast has a good chance of this continuing until this weekend. Today looks to be the most difficult to reach 40. Interesting to note how the past 20 years have seen most of the longest streaks.

The featured map is of forecasted high temperatures by the National Weather Service for this coming Saturday, the last day of the year. This would end one of the warmest stretches of late December on record. Where has winter gone and does it intend on coming back?

The featured chart presents the accumulated average temperature percentile for Ames for December. Each value represents the percentile for the period from the first of the month to that date. After the first 10 days of December, we were near the coldest 25% of years on record. Thanks to our recent stretch of very mild weather, we are now in the warmest 25% of years. The last few days of this year look to be remarkably warm with highs near 50!

High temperatures on Thursday were almost too good to be true around 50 degrees. How exceptional is it to have 50 degree temperatures in December? The featured chart presents the daily 95th percentile for high temperature (which ~50 in December approximately falls). Using this metric, we can see that our current weather is about equivalent to having 100 degree temperatures in July. The bottom chart shows the distance, as normalized by the day's standard deviation, the 95th percentile is from the daily average.