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.

Voting:
Good = 23
Bad = 3

Tags:   fall   frost  

So far, Des Moines has had its 12th driest meteorological fall on record. The featured chart presents the precipitation rank to date since the first of September for this year, 1914 (the wettest year) and 1966 (the driest year). If we got no precipitation for the rest of the season, our fall total would still be a bit higher than 1966 and coming in second lowest. The forecast has some chances of rain in the forecast next week.

Voting:
Good = 32
Bad = 7

Tags:   2011   fall  

Yesterday the chances of seeing warm high temperatures yet this year were featured, so naturally it is time to do the opposite and see how cold it will get in the next two and a half months. About 80% of the years since 1893 have seen at least one day with a low temperature around zero and about 7 days at 10 degrees. Thankfully, the near term forecast does not have temperatures approaching anything on the chart.

Voting:
Good = 26
Bad = 5

Tags:   fall  

With our recent few days of temperatures well below average, one wonders how many warm days are left this year! The featured plot presents the observed frequency of having a given number of days with a high temperature at or above a given temperature from now until the end of this year. For example, 80% of the years since 1893 experienced a high temperature of 70 on at least one day, but only 20% of the years experienced a total of 7 days at 70. The forecast puts us back into 60s after a chilly day today in the lower 50s.

Voting:
Good = 16
Bad = 3

Tags:   fall  

Following up on the previous day's feature, today's featured plot presents an IEM computed metric of the climatological duration of the fall season. The number of days presented represent the time between the warmest 91 day period and coolest 91 day period based on daily climatological high and low temperatures. Think of it as the number of days it takes to get from the warmest quarter of the year to coolest. Iowa is shown right around 90 days, which is about what one would expect for having evenly distributed seasons. The plot would suggest that if you like the fall, don't live on the west coast!

Voting:
Good = 47
Bad = 12

Tags:   fall   temp  

Last week saw two days with most of the state below freezing for the entire day. For Ames, this made for the first such day this fall. Having such a day does not mean cold despair for the rest of the year as illustrated by the featured chart. Even after the first frozen fall day, temperatures many times still nicely warm sometime before 31 December. Highs on Sunday were a case in point as values soared into the 50s. The forecast for this week pushes high temperatures back toward freezing.

Voting:
Good = 21
Bad = 6

Tags:   fall  

The fall season is officially here in Iowa eventhough the actual weather feels more like the muggy days of summer. The featured map presents the three week change in climatological average high temperature over the US. The map nicely shows where fall makes its fastest progression (high plains and mountain regions) this time of year. Places like Florida are only slightly affected thanks to the moderating effects of being surrounded by warm water. The corn belt makes a conspicuous appearance in this plot as an area cooling slower than areas to its north and west.

Voting:
Good = 72
Bad = 11

Tags:   fall  

Low temperatures this weekend were in the 40s and even upper 30s in some locations. The featured chart shows the frequency of experiencing a given threshold temperature by a certain date in the fall for Ames. While having a low temperature in the upper 40s by now is common, the 30s are a few weeks away.

Voting:
Good = 16
Bad = 3

Tags:   fall  

The featured chart is a temperature composite of the time period before and after the first sub 32 degree temperature in the fall from the Des Moines Airport. The three lines represent the temperature range and average of the observations 3 days before thru 1 day after the event. The 12 hours before the first event show a rapid cooling which is often the case with clear skies during the night time hours. Those clear skies are then typically around for the next day when temperatures quickly recover.

Voting:
Good = 23
Bad = 4

Tags:   fall   freeze