Wednesday was yet another amazingly warm day in winter for most folks in Iowa. Des Moines hit 60 degrees for the third day in a row. The weather bureau noted that this was the first three day stretch of 60 degrees for Des Moines during the period of 15 Dec to 15 Feb on record! The featured chart presents the warmest three day streak of weather based on the minimum high temperature during that period. The first day of the streak is used to place the three day value for a month. Our most recent streak would be the warmest for January besting the previous streak in 2002 of 59.

Voting:
Good = 11
Bad = 4

Tags:   2012   highs  

Our remarkable stretch of warm January weather came to an abrupt end on Wednesday thanks to a very strong cold front plowing through the state bringing some snow along with it. The high temperatures, before the front passed through, hit record levels over portions of eastern Iowa and with snow falling today, creates the unique situation of having a record high temperature followed by snow the next day. The featured chart presents an IEM computed analysis of the most recent occurrence of having snowfall on the day after a record high temperature for some long term sites in the state. There are caveats galore with this data due to issues with snowfall data quality and the nature of daily climate observation times being at 7 AM (long story). Heavier snowfall totals are expected over eastern Iowa, so the bottom portion of the chart presents the most recent occurrence where the snowfall was four inches or more. In general, these events are rare and getting heavy snowfall is even more rare. Note: the record high temperature was computed up until that date since the beginning of the record.

Voting:
Good = 33
Bad = 6

Tags:   jan12   snow   highs  

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.

Voting:
Good = 32
Bad = 7

Tags:   highs  

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.

Voting:
Good = 16
Bad = 3

Tags:   climate   highs  

After high temperatures soared into the 70s on Tuesday, they will struggle to do any raising at all today with some locations expected to set their daily high temperature at midnight this morning. The featured chart looks at the frequency of having the warmest temperature of the day occur during the midnight hour for Des Moines. For November, these frequencies equate to roughly 4-5 days per year.

Voting:
Good = 13
Bad = 3

Tags:   highs  

The high temperature on Wednesday was more than 20 degrees colder than the high on Tueday making for the largest one day drop in temperature for Ames since early June. The featured chart presents the day to day changes in high temperature for this year along with the daily maximum and minimum value since 1893. Day to day variability is much less in the summer time thanks to the moderating effects of water vapor in the air, warm ground temperatures, and more direct solar angle.

Voting:
Good = 11
Bad = 4

Tags:   highs  

Our recent stretch of cool high temperatures was far from where we should be this time of year. One way to measure the distance a temperature is from the average value is to normalize it by the standard deviation for all temperature reports for that day in history. A value of positive two would mean the temperature is two standard deviations warmer than average. By standardizing, we can compare temperatures at most any time of the year. Indeed, the lowest values on the upper air occurred with our recent cool stretch! The bottom chart simply shows the largest and smallest index value per year. The sore thumb in the chart is the -4.3 on December 24, 1983. High temperatures that day were in the negative teens!

Voting:
Good = 12
Bad = 3

Tags:   highs  

The weather these past few days has been remarkable for cool high temperatures along with mostly clear skies overhead. The featured chart attempts to look at the relationship of having cool days along with mostly clear skies or northerly winds. While the determination of these two criteria was somewhat arbitrary, the signal appears to be reasonable. Having northerly winds is common for these cool days, but least important during the summer time when the air to our north may not be that cold. Clear skies are the least common during May and June, when are surface heating rates are the largest.

Voting:
Good = 8
Bad = 5

Tags:   climate   clouds   highs  

The featured chart presents the frequency of a given day being one of the seven warmest for the year. July is clearly the winner with most days having an one in ten chance of being one of the seven warmest for the year. The red bars indicate the warmest seven days so far this year and given that these days fall outside of the higher probabilities, perhaps we can expect warm days ahead in July with highs well into the 90s? The forecast has highs above 90 on Thursday and Friday.

Voting:
Good = 13
Bad = 2

Tags:   highs   climate  

High temperatures on Wednesday struggled in the 60s and were only a few degrees warmer than the coldest high temperatures on record for the date. This was thanks to a thick cloud cover and cold air brought in from our north. The featured chart looks at a measure of the amount of cloud cover on days were the high temperature was at record minimums and maximums. It makes intuitive sense that the coldest days are typically more cloudy during the spring, summer, and fall months as the sun is effective at warming the ground thanks to its high declination. Clouds are less important in the winter months as temperatures are dominated by organized air masses and the sun is less effective. For the warmest temperatures, having more sunny conditions are the most important in October it appears. Outside of a blip for warmest days in May, the plot has two clear annual signals!

Voting:
Good = 14
Bad = 5

Tags:   highs   climate   clouds  

The high temperature on Monday was 30 degrees colder than the high on Sunday of 82. The featured image presents the extreme day to day high temperature changes based on data for Ames. A 30 degree negative change is near the maximum experienced for early April. The chart nicely shows the annual cycle with a minimum in temperature swings during the summer.

Voting:
Good = 8
Bad = 4

Tags:   highs  

High temperatures are struggling so far today thanks to our recent snowfall and being on the cold side of a departing area of surface high pressure. The featured chart presents the high temperature for a day after snowfall as recorded from the long term stations near Ames. The favored temperature is clearly around or just below freezing, which makes sense with all the newly deposited snow around. The greater the snowfall, the more likely the next day temperature will be below freezing, which makes sense as well. Much warmer air is set to arrive tomorrow and rid us of most of this new snow.

Voting:
Good = 16
Bad = 6

Tags:   snow   highs  

Wow, after being stuck in winter for a period seeming like forever, the warmer air this past weekend sure felt nice and makes spring feel like it is not that far away. The featured chart presents the climatology of when the first occurrence of a temperature happens in the new year. The blue line can be thought of the earliest a given temperature has been observed and the red line would be the latest we have waited for a given temperature in a given year. The green line is the average date of the first observation. So for mid February, we'd expect to have seen at least one day in the lower 50s after 1 January. The turquoise line shows the pain that occurred last year when we had to wait until March to see a temperature above 40.

Voting:
Good = 30
Bad = 4

Tags:   spring   highs  

The high temperature on Sunday in Barrow, Alaska was a balmy 35 degrees whereas Des Moines, Iowa struggled in the 20s. The featured chart presents the daily frequency of occurrence for having Barrow with a warmer high temperature than Des Moines. Given that the chart presents 60 years of data, the chances are still rather slim for having such an occurrence. There have been 251 occurrences overall, so this happens about 4 times per year. The bottom chart presents the actual difference in high temperature on days that Barrow was warmer. The two lone events in September occurred back in 1995 (21 and 22). Temperatures on Monday will come close to accomplishing this rather rare feat with highs in both locations in the low 20s.

Voting:
Good = 26
Bad = 4

Tags:   alaska   highs  

The abnormally cool stretch of weather ended up lasting a full week for Ames with high temperatures not reaching 60 degrees. According to IEM data, this sets a record for consecutive days below 60 in May. The featured chart displays the monthly records for Ames and the most recent year the record was set or tied. During the winter months, a large number of years had the entire month below 60. It is interesting to see that July never has had a high temperature below 60 for Ames since 1893. Temperatures will approach 70 today!

Voting:
Good = 48
Bad = 8

Tags:   may10   highs   may  

Thanks to a slow moving storm system to our south, places like Lamoni (in Southern Iowa) experienced a cloudy and rainy day while locations farther north like Mason City saw the sun and warmer temperatures. The high temperature in Mason City was 9 degrees warmer than Lamoni. The featured chart looks at the frequency of Mason City having a warmer high temperature than Lamoni (north/south comparison) and also Dubuque having a warmer high than Sioux City (east/west comparison). In November, Mason City is warmer than Lamoni about 10% of the time (think of it as 3 days for the month). The chart shows an interesting annual signal and a probable change in the dominate spatial temperature structure between the summer and wintertime.

Voting:
Good = 18
Bad = 9

Tags:   highs  

High temperatures soared on Monday to values above normal for this time of year. The featured chart looks at the largest stretch of consecutive days with the high temperature above average per year for Ames. So far for 2009, the best we did was 11 days. Our current streak stands at a mere one day with today expected to make it two. Rain and cooler temperatures are in the forecast, so the current streak will not last.

Voting:
Good = 17
Bad = 7

Tags:   highs  

After a high temperature of 82 on Sunday, Ames only got up to 64 on Monday which is almost a 20 degree cool off in high temperature. The featured chart looks at the monthly frequency of having a 20+ degree high temperature swing either up or down. In general, these events are somewhat rare with primary direction being a 20+ degree downward swing.

Voting:
Good = 19
Bad = 6

Tags:   highs  

The past week or so has seen high temperatures not vary much for Ames with the range being a mere 3 degrees (78-81). The featured chart looks at the minimum 7 day temperature range for all days of the year. In general, the lowest values are in the summer time when strong temperature fronts are not common. The spikes during the spring and fall months are when we often experience air mass changes via strong fronts.

Voting:
Good = 8
Bad = 12

Tags:   persistence   highs   lows  

The featured graph is a simple plot of the number of days per year that Ames has observed a high temperature at or above 90 degrees. 2008 only saw a handful of days while two years in the 1930s experienced 60 days (dust bowl). While the forecast for this weekend is for warmer weather, we will have to wait a while yet before maybe seeing 90 degrees again.

Voting:
Good = 25
Bad = 7

Tags:   highs  

The featured graph displays the frequency of rainfall observations a day after a given high temperature for Ames. The three lines are the frequency of given minimum precipitation thresholds. While there are a number of things going on to make this plot appear the way it does, it generally shows that the frequency of rainfall events increases as our temperature increases (more rainfall in the summer). The interesting detail is to note what happens when temperatures reach the 90s. Our chances of rainfall decrease as the temperature gets even warmer. One could speculate that when our temperatures get really warm, the air mass is often drier and soil moisture state is drier as well allowing more efficient warm ups. Rewording, having temperatures in the 90s for Ames is probably associated with a dry weather pattern.

Voting:
Good = 15
Bad = 6

Tags:   climate   precip   highs  

Last Friday, we were experiencing low temperatures around our average high for the date. Today, we are on the opposite end with high temperatures near our average lows. The featured chart looks at frequency of having the high temperature below the average low. As with Friday's chart, there is a period in the summertime where this has never occured for Ames. Our actual weather is expected to warm up this weekend!

Voting:
Good = 22
Bad = 3

Tags:   highs   lows  

In some locations, low temperatures on Thursday were warmer than the average high temperature for the date. The featured chart looks into the frequency of this occurance with the bars representing the number of years that this has occurred for Ames. The red line is the record daily maximum low temperature and the black line is the daily average high temperature. Notice that during the summer season, the black line is always higher. In fact, the period of 9 May to 29 Sep has never seen a low temperature greater than the average high for Ames!

Voting:
Good = 35
Bad = 19

Tags:   highs   lows  

The featured chart is the yearly difference between the number of days with a high temperature above average versus below for Ames. Negative numbers represent having more days below average than above. 1932 has the largest positive value while 1993 the lowest. For our recent decade, 2008 was the only year with a considerable number of more days below average. The number thus far for 2009 is a mere -4. Our weather is expected to creep above average later this week.

Voting:
Good = 27
Bad = 4

Tags:   highs   yearly   climate  

The featured image is a scatter plot of next day high temperatures versus snow depth. The plot tries to answer the question how warm can it get the next day after having snow on the ground today. An old forecasting tip is that high temperatures rarely exceed 43 degrees with 4+ inches of snow on the ground. The 4 inch snow depth reference line on the chart indeed shows very few 43+ degree temperatures. With high temperatures forecasted in the 50s today, this will be exceptionally warm given our current snow pack!

Voting:
Good = 44
Bad = 16

Tags:   highs   snowcover  

Last Friday, we featured the favored times of rainfall. Today we featured the favored times of day when the high temperature occurs. This plot has a number of interesting features including the increased chance of the high temperature coming at midnight during the winter season. This is often associated with air mass changes with a steady feed of colder air during the day. Another interesting feature is the shift of high temperature shown between Feb/Mar and Oct/Nov. This is due to the change of daylight savings time. The hourly time axis on the plot is in local (standard/daylight) time depending on the time of year.

Voting:
Good = 27
Bad = 7

Tags:   climate   highs