Past IEM Features tagged: fall

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Fall Highs Above Average

04 Dec 2017 05:32 AM
The fall season encompassing the full months of Sep, Oct, and Nov wrapped up last week. The featured chart looks at the percentage of days for the period that had a high temperature above average. The overall average is plotted as well and is slightly different than an even 50% due to asymmetries of the high temperature distribution. Anyway, years above this value are shown in red and below in blue. This fall was near 50% whereas the previous two where much higher for Ames. It has been about 20 years since the last fall season with substantially lower than 50% of the days above average for the fall season.

Voting:
Good: 6
Bad: 2

Tags:   fall  

Fall Season Precipitation

04 Oct 2017 05:25 AM
The featured chart displays fall season (September thru November) total precipitation for Ames. The past three years have seen above long term average precip for the period and this year's seasonal total appears to be on its way with ongoing rain now and still just under two months of time left. A long term trend line is fitted to the data and would indicate little trend with these totals.

Voting:
Good: 6
Bad: 0

Tags:   fall  

First Fall Temp Frequencies

07 Nov 2016 05:35 AM
For the Des Moines Airport weather station, a freezing temperature has yet to be observed this fall season! This is getting very late into the year to have seen such a cold temperature. The featured chart shows the accumulated frequency of having a given temperature observed by the given date of the fall season. For November 7, nearly all years have seen a freezing temperature and even 75% of them have seen 26 or colder by now. The forecast continues the nice weather this week, with slightly cooler temperatures and perhaps a chance at a freeze later in the week.

Voting:
Good: 8
Bad: 2

Tags:   fall  


Freezing Time

21 Oct 2016 05:34 AM
The featured chart presents an analysis of duration and strength of the first fall periods at or below freezing for Des Moines based on one minute interval temperature observations since fall 2000. Each event represents a sequential fall date during which the low temperature reached 32 degrees or colder. For example, event three would be the third day during the fall season at or below 32. The time duration is the period between when the temperature hit 32 degrees and rose back above 32. The maximum duration period for each date was used in cases of multiple periods on a given date. The box and whisker plots represent the spread of duration. A strength metric is also calculated and is simply the temperature difference from 32 multiplied by time. So what is the moral of the story here? The initial dips below freezing are brief (1.5 hours on average) and shallow. Both the duration and "depth" increase with sequential event with more noise than signal appearing after the fourth or fifth event.

Voting:
Good: 7
Bad: 2

Tags:   freeze   fall  

Has Fall Already Started?

29 Aug 2016 05:36 AM
If one considers the summer season to be the warmest 91 day stretch of the year, we may already completed it as shown by the featured chart for Ames. Currently, August 24th is denoted as the end of the warmest 91 day period, but it could change with hot weather pulling the average back up and thus establishing a new high mark for the year. Regardless, the chart also displays some statistics on the start date of fall and how long the season lasts. The length is defined as the period between the end of the 91 day warmest stretch and then the start of the 91 day coolest stretch. The averages show that fall goes by more quickly than spring with an average of 85 days!

Voting:
Good: 14
Bad: 0
Abstain: 2

Tags:   fall  

Fall Season 70s

04 Nov 2015 05:36 AM
Early morning fog put a bit of a damper on an otherwise great November day with temperatures again reaching 70+ degrees for much of Iowa. The featured chart presents the number of days each meteorological fall season that the high temperature was at or above 70. This year's total is the second largest since the early 1960s. Today will be another warm day before cooler weather arrives tomorrow!

Voting:
Good: 10
Bad: 3
Abstain: 4

Tags:   fall   70  

Warm Mins to Date

30 Oct 2015 05:35 AM
So far this fall season, we have avoided very cold temperatures. For Des Moines, the to date minimum has only been 36 degrees. The featured chart displays the fall to date minimum temperature this year along with a climatology of this metric. 36 was also the to date minimum last year for this date. The range of values shows that only a few events have been warmer to date and that value is only 37. If the current minimum of 36 holds until 7 November, it would be the warmest minimum temperature this far into the fall season. A caveat for the Des Moines Airport site, is that there is a clear urban heat island effect there and so its temperatures are often warmer than surrounding areas.

Update: The low this Friday morning dipped to 34, so the 36 mentioned aboved has already been breached.

Voting:
Good: 22
Bad: 23
Abstain: 5

Tags:   fall  


Stepping Down

30 Sep 2015 05:36 AM
Some of the coolest air this season has settled into Iowa overnight with temperatures stepping below previous lows for the fall season. The featured chart presents some diagnostics of these step downs in temperature with the 'step down' representing the setting of a new (since 1 July) cold temperature for the year. The average number of these events is around 19 for Des Moines, which is roughly one out of every ten days for the half year period. The second and bottom charts present histograms of the temperature levels and day of year whereby these steps occur. The increased frequencies at the start of July is an artifact of the algorithm, but there is a clear jump around mid September, which is about the time cooler air masses start arriving. There is also increased frequencies in the 50s, which is a temperature a bit lower than our supporting/typical 60 degree dew points in the summertime. There is also another jump just below freezing. These are levels that it takes a bit of time to push through as dew point and non-frozen soils offer resistance to cooling below those levels.

Voting:
Good: 7
Bad: 11
Abstain: 3

Tags:   fall   spring  

Fall Minimum to Date

09 Oct 2014 05:39 AM
The featured chart displays the climatology of minimum to date temperature for dates after 1 July. The trace for this year is shown as well for Ames. This year saw a very cold temperature arrive in mid September and we have only recently breached that level lower. As it stands now, we are about at average for the minimum temperature to date. You can generate this chart dynamically on the website and plot previous years for comparison.

Voting:
Good: 17
Bad: 6
Abstain: 8

Tags:   fall  

No freeze yet

08 Oct 2013 05:37 AM
This is about the time of year by which much of Iowa has experienced its first freezing temperature. The featured chart presents the year to date lowest temperature after 1 July climatology for Ames. While not strictly the same metric, the intersection of the black line (average lowest temperature to date) and dashed line (freezing temperature) around this time approximately matches the average first freezing temperature of the fall. The minimum to date temperature for this year shows that we are well on the warm side of long term average. The shaded areas represent the percentile ranges of 50% and 95% of the daily data. The red line should remain flat for at least the next seven days with low temperatures well above 40 degrees.

Voting:
Good: 46
Bad: 16

Tags:   fall   freeze   low  


click image for better view

First Fall Hard Freeze Climatology

14 Dec 2011 05:48 AM
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  


Can't catch 1966

28 Oct 2011 05:55 AM
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  


Cold Expectations

21 Oct 2011 03:49 AM
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  


How much warm weather is left?

20 Oct 2011 05:56 AM
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  


check out yesterday's feature as well.

Fall Duration

03 Dec 2010 05:46 AM
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  


Warm weather after frozen day

29 Nov 2010 05:46 AM
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  


Generate This Chart on Website
3 week difference of NCDC 1971-2000 Climatology

Fall's Tug on Climatology

24 Sep 2010 04:59 AM
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  


A bit early for cold

31 Aug 2009 06:06 AM
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  


Based on 1973-2007 data

Before the first 32

09 Sep 2008 06:37 AM
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