Past IEM Features tagged: clouds

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Clear Skies Make a Difference

12 Oct 2017 05:36 AM
The coldest temperatures of the season were experienced Wednesday morning over areas that had clear skies overnight. Other locations in the state with clouds were many degrees warmer. The featured chart displays the combined time series of all airport weather stations in the state. When the site was reporting clear sky conditions the dot is blue and for all other sky conditions the dot is grey. A remarkable and pretty contrast is shown by the chart with the coldest areas being clear and warming quickly with the rising sun during the morning hours. The impact of clouds during the daytime can be seen as well to suppress heating by reflecting the sun's energy prior to it arriving at the Earth's surface.

Voting:
Good: 89
Bad: 1

Tags:   clouds  

Opposite Effect

25 May 2017 05:37 AM
The clouds have been somewhat difficult to keep away these past few days thanks to a large storm system spinning now off to our south and east. What sunshine we have seen often goes into self-destructing sunshine mode as heating quickly builds clouds and blocks the sunshine again. The impact on temperatures during the day light hours is clear as clouds tend to suppress temperatures as shown by the featured chart for Des Moines. The chart compares hourly temperatures by week of the year between the case of having mostly cloudy conditions vs all cloud conditions. Values in green indicate cooler temperatures with clouds and red indicates warmer. During the overnight hours, the effect is the opposite than during the daytime. Clouds act as a blanket during the night time by absorbing long wave radiation and emitting it back to the ground.

Voting:
Good: 6
Bad: 1

Tags:   clouds  


Overcast Streak

04 Apr 2017 05:21 AM
Recently, the clouds have been difficult to get rid of. For Des Moines, it has been mostly cloudy for the past 12 days or so. To pick an arbitrary comparison point with the long term archive of cloud coverage at Des Moines, the featured chart presents the longest streaks of having the 10 AM CDT observation indicate overcast. The current streak of 12 days is the longest since 2010 and only a few days shorter than the longest back in late 1979 and into 1980. When will our current streak end? At the moment, it would appear Thursday would have the earliest chance with a more likely chance on Friday. Needless to say, there will be plenty of happy folks to see full sunshine when it returns!

Voting:
Good: 12
Bad: 0

Tags:   clouds  

January Clouds

31 Jan 2017 05:32 AM
A bit of sunshine was able to sneak through the clouds on Monday, which has not been common these past two weeks. The featured chart attempts to illustrate the cloudiness reports by the automated Des Moines Airport weather station. The areas in blue represent clear skies vertically up until a cloud deck is reported or the vertical limit of the sensor is reached. You can generate this chart for other sites in the country by following the 'Generate This Chart on Website' link.

Voting:
Good: 6
Bad: 0
Abstain: 1

Tags:   clouds  

Overcast January

23 Jan 2017 05:25 AM
Seeing the sunshine has been a struggle for much of this January. The featured chart considers the metric of having overcast conditions reported by the Des Moines Airport weather station at noon local time. The total for this January is well above average for the month. The forecast does not have much hope for sunshine until this upcoming weekend. On average, this month and December have the highest frequencies.

Voting:
Good: 5
Bad: 0

Tags:   clouds  

November Clouds at Temp

09 Nov 2016 05:32 AM
Yesterday was yet another pleasant day this November with highs reaching into the 60s for much of the state. This was with mostly sunny skies overhead. The featured chart looks at the observed frequencies of overcast clouds at a given temperature in November for Des Moines. It is interesting to note the three regimes depicted in the chart. For really warm or cool temperatures, it is clear that less cloudiness needs to be present. This makes physical sense as the presence of clouds at night traps heat and during the day, limits heating by the sun.

Voting:
Good: 5
Bad: 3

Tags:   nov   clouds  


Hard Freeze Clouds

14 Oct 2016 05:34 AM
Freezing temperatures finally arrived in Iowa on Thursday with some locations, like Ames, even reaching sub 29 degrees. Cloudy conditions on Wednesday gave way to clear skies overnight, which greatly helped the atmosphere cool off. Do skies always need to be clear on the first fall occurrence of sub 29 degree temperatures? The feature chart looks at the hourly sky coverage as reported by the Ames Airport for the 24 hour period before and after the first sub 29 degree temperature event. All but two years since 1996 are indicated to be clear skies at the time of sub 29 (denoted as 0 hour on x axis).

Voting:
Good: 10
Bad: 1

Tags:   freeze   clouds  

Overcast early morning

25 Feb 2016 05:35 AM
Seeing clear skies, let alone sunshine has been a struggle this month. The featured chart displays the frequency of having overcast conditions reported by the Des Moines Airport weather station. The top chart displays the monthly climatology frequency along with those experienced this year. The bottom chart displays the February values for each year on record. This analysis places three quarters of the 6 AMs so far this month as being overcast and only 1998 was higher for the entire month. Maybe our luck this month will change with the four days we have left!

Voting:
Good: 20
Bad: 12
Abstain: 11

Tags:   clouds  

Gloomy at noon

23 Dec 2015 05:41 AM
While most days have seen warm temperatures this December, clouds have been common as well. The featured chart displays the frequency of having overcast conditions reported by the Des Moines Airport weather sensor for this year and over all the years by month. For this year, only May is shown at a higher frequency of having overcast conditions at noon. More gloomy conditions are in the forecast for the rest of the month.

Voting:
Good: 19
Bad: 9
Abstain: 9

Tags:   clouds  

Overcast and Temps

09 Dec 2015 05:36 AM
Even with overcast sky conditions for much of Tuesday, temperatures were still able to warm into the low 50s for some locations in the state. Is this combination of clouds and warm temperatures typical for December? The featured chart displays the frequency of overcast conditions being reported by the Des Moines Airport by temperature for December. There are interesting things going on within the plot with a clear signal that overcast conditions as less likely as temperatures reach colder values below freezing. This makes sense was clouds help retain heat at night time, which prevents temperatures from cooling more rapidly.

Voting:
Good: 13
Bad: 8
Abstain: 4

Tags:   clouds  

Clouds and Temps

20 Jul 2015 05:36 AM
The presence of clouds has an impact on near surface air temperature, but that impact varies by time of day and time of year. The featured chart attempts to tease out the impact by looking at the simple difference between hours that have significant cloud cover versus all hourly temperature reports. A general summation of the chart is that clouds suppress temperatures during the daytime and support temperatures at night time. There is a day of the year impact as well with the largest differences occurring in the fall season.

Voting:
Good: 15
Bad: 4
Abstain: 5

Tags:   clouds  

Overcast at noon

22 Dec 2014 05:45 AM
If your impression is that it has been exceptionally cloudy this month, you are very perceptive! The featured chart displays the monthly frequency of having overcast clouds reported by the Des Moines Airport weather station at noon. The red bars represent the long term average while the blue bars are the frequencies for this year. This analysis shows 76% of the days this month being overcast at noon while the average is 42%. For this metric, December is the most cloudy month of the year, but it should not be this cloudy!

Voting:
Good: 11
Bad: 3
Abstain: 2

Tags:   clouds  

Clouds this December

11 Dec 2014 05:43 AM
The featured chart is an attempt to show automated cloud reports from the Des Moines Airport ASOS. These cloud reports include up to four levels of cloud coverage. Once the automated sensor reaches a cloud deck that it considers to be overcast, no further reports are possible above that layer. The past week has seen plenty of clouds with ceilings below five thousand feet. You can now generate this plot on the website for other sites the IEM collects data for and for previous months in the archive.

Voting:
Good: 12
Bad: 6
Abstain: 4

Tags:   clouds  


Clouds then Rain

09 Jul 2014 05:41 AM
Skies were mostly fair on Tuesday with even the 4 AM observation reporting "clear" from the automated airport sensor in Des Moines. The featured chart looks at the frequency of having measurable precipitation for the midnight to 8 AM period the day following an hour with a given cloud coverage reported. In general, having overcast skies have more frequent rainfall events than clear skies which makes intuitive sense. Of course you have to have clouds for it to rain, so having overcast conditions later in the day leading up to the next day increases the frequency and having clear skies decreases the frequency. The overall frequency of having rainfall sometime during the 12-8 AM period in July is around 15%.

Voting:
Good: 8
Bad: 4
Abstain: 4

Tags:   clouds   jul  


Influence of clouds

21 Oct 2013 05:36 AM
The featured map displays the combination of morning low temperatures and infrared satellite imagery for this past Thursday morning. The white areas on the map represent the presence of clouds and the warmest low temperatures you can find on the map are underneath these clouds. Clouds play a critical role in the radiation balance by absorbing long wave radiation emitted by the surface and then re-emitting it back toward the ground. This process helps keep air temperatures warmer versus nearby areas without clouds.

Voting:
Good: 23
Bad: 6

Tags:   clouds  

Clouds and Temperature

08 Nov 2012 04:28 AM
The past few days have seen mostly cloudy conditions here in Iowa. The noticeable visual effect for us is a lack of sunshine during the day and not seeing stars at night! Besides visual effects, clouds are an important component of the surface energy budget (which drives weather variables like near surface temperature). During the daylight, clouds reflect energy from the sun back out into space and act like a mirror. For all 24 hours of the day, clouds are absorbing and re-emitting energy from the ground back down to us, acting like a blanket. The featured image illustrates the effect of significant cloud cover by comparing hours with clouds against all available hours of observations from the Des Moines Airport sensor. The plot shows the primary effect of keeping temperatures cooler during the daytime and keeping temperatures comparatively warmer during the nighttime. The strongest effects are when solar heating of the ground is most efficient in the late summer / early fall season (drier/warmer soils, plenty of potential sunshine for surface heating) and during the early morning hours in spring and fall (peak radiational cooling due to lower humidities). Restating, these times are when clouds have the most influence. So while clouds have been helping to keep us recently cool during the daytime, they have kept overnight temperatures higher than they would be with clear skies at night.

Voting:
Good: 36
Bad: 7

Tags:   clouds  


Cloud Sensor Differences

30 Nov 2011 06:02 AM
The airport weather sensors for Des Moines and Ames are typically called 'ASOS' sensors and lumped into the same data pile as they both have similar sensors and maintenance standards. The featured chart presents a summary of reported sky conditions at 6 AM each morning this year. While these sites are only separated by 30 some miles, there are some large differences in the number of clear mornings reported. The difference here is that the Des Moines sensor has augmentors that report cloud ceilings higher (to 25,000 feet) in the sky than the Ames sensor can (to 12,000 feet). This is just one of the data quirks that keeps life fun and various people employed to keep track of this all!

Voting:
Good: 23
Bad: 5

Tags:   clouds  


Cool days and clear skies

08 Sep 2011 05:50 AM
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  


June Highs and Clouds

23 Jun 2011 05:55 AM
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  


Frequency of clouds

01 Oct 2010 05:47 AM
The featured chart presents the hourly frequency of cloudy or mostly cloudy skies by day of the year based on observation data at the Des Moines Airport. The plot has a number of interesting features about the diurnal and annual cycles in Iowa. Firstly, a good number of our clouds are a result of day time heating by the sun. The late summer and fall months show up nicely for having fewer clouds during the night time. The forecast for the next 5-7 days continues to keep most of the clouds away with very pleasant fall weather!

Voting:
Good: 68
Bad: 14

Tags:   climate   clouds  


click image for better view

On a clear day

27 Aug 2010 05:57 AM
Our stretch of sunny days looks to continue today. The featured chart looks at the observed frequencies of having one day (black line) and three days in a row (blue line) of mostly clear or clear skies as observed at the Des Moines Airport. The chart shows September as having the highest frequencies with an interesting dip in the trend during the middle of the month. It is not clear what would be causing that, but this is another chart that would indicate perhaps fall is the best season of the year in Iowa!

Voting:
Good: 57
Bad: 15

Tags:   climate   clouds