Below Freezing Snow Melt?

Snow depth Wednesday, January 17. 2018

You might have noticed something outside today. No, we are not just talking about the sunshine. There’s a chance you stepped in a small puddle instead of a snow mound (or maybe just a slightly smaller snow mound). Upon checking the temperature, you see that it is below 32°F.

It is not uncommon that snow melts when the temperatures are below freezing.

Of course, if temperatures are above 32°, the snow will melt. We also see snow melting with sunny skies as the sun’s rays warm the ground. However, when the sun’s rays hit snow (or other light surfaces), most of the energy reflects off of the snow back into the air but some is absorbed and warmed by the sun. The sun’s rays are better absorbed by darker objects like asphalt. Even dirty snow will absorb more solar energy than fresh, clean snow.

Reflection of sun’s rays against varying surfaces. Lightly colored surfaces will reflect more of the sun’s energy (left side) than darker colored surfaces (right side).

If the ground temperatures are warmer than 32, the snow on the ground starts melting.

This concept falls under the idea of “albedo” or the reflectiveness of an object. Every surface has a different albedo value. Albedo values range from 0-1 depending on the percentage of the sun’s energy an object reflects (fresh snow can reflect up to 95% and would have a max albedo of 0.95).



Posted under Weather Trivia, Winter Weather

This post was written by Rachael Peart on January 17, 2018

Daylight Changes

The days have been getting shorter everyday with the nights getting longer since late June. Between the summer solstice in June and the winter solstice in December, more and more daylight is gradually lost.

We are now more than halfway between the summer and winter solstices. Eastern Iowa will lose more than six hours of daylight within the six month period. However, once we reach and pass the winter solstice (also known as the first day of winter), the days slowly become longer and nights shorter.

If you think nine hours of daylight is bad, imagine living in Barrow, Alaska. The northern most point in the U.S. will see the sunset on November 18, 2017 and the sunrise on January 22, 2018. That is over two months of darkness known as “polar night”.

2017 Sunrise and Sunset in Barrow, Alaska. Orange shades show days where sun never rises above the horizon through the end of the year


Posted under Miscellaneous, Weather Trivia

This post was written by Rachael Peart on November 14, 2017

Strong Fall Storms

November is a month known for large storms across Midwest and Great Lakes area. Many producing widespread strong winds. It is not November yet, but we are getting closer to that time of year. A large storm in the Great Lakes today had a central pressure as low as the storm that sunk the SS Edmund Fitzgerald. On November 10, 1975 the SS Edmund Fitzgerald sank in Lake Superior. An approaching low pressure system caused winds to increase and thus prompted wind related warnings. Strong winds faster than 50 mph produced large waves that day.  There were some wave heights near 30 feet reported

The daily map from that date looked like this. Notice the low pressure over Lake Superior with a central pressure of 984 mb.

November 10, 1975

Now jump ahead to today. The map looks very similar, even to the minimum pressure of 984 mb.

October 24, 2017

A buoy reported wave heights a little higher than 25 feet today in Lake Superior, just north of Munising, Michigan.

The chart below shows the wave heights reported in blue and the forecast wave heights in red. The storm strengthened Monday night and Tuesday and resulted in the rapid increase in wave heights.

Wave heights October 24, 2017

For more information on the Edmund Fitzgerald, visit the Marquette, Michigan’s NWS page here.


Posted under Weather History, Weather Links, Weather Trivia, Windy

This post was written by Rachael Peart on October 24, 2017

Wind FAQ

Winds across the state increased behind a cold front that tracked through on Monday. But what is wind?

It is the flow of air as it moves from high pressure areas to low pressure areas.

In real life, air does not typically move directly from high to low pressure centers. It travels clockwise outward away from high pressure and moves counter-clockwise into low pressure.

The lines around the high and low pressure centers in the graphic above are called isobars (lines of equal pressure). The more isobars there are in an area – lets say, across the state of Iowa – then the stronger the winds become in that area.

1PM CDT Tuesday, October 24, 2017 National Observation

Quick bursts of higher wind speeds are called gusts.

The wind direction refers to the direction (north, south, east, west, etc) from which the wind originates.

There are different tools to measure wind:

  1. Wind vane: measures the direction of the wind
  2. Anemometer: measures the speed of the wind. Wind speeds are usually measured in knots or miles per hour.

Anemometer diagram (1880)



Posted under Weather Trivia, Windy

This post was written by Rachael Peart on October 24, 2017

Does “Heat Lightning” Exist?

The answer is simply, no.  It is a common misconception, and don’t worry, even I thought heat lightning was a “thing” when I was younger.

A lot of times in the summer months, we get several pictures of lightning sent to us with the caption “heat lightning”.  People refer to this as heat lightning, because the sky is mainly clear, and they can see flashes of lightning in the distance, and think it is caused from the heat and humidity.

The truth is pretty simple: All lightning is associated with a thunderstorm.  You are simply seeing the tops of the thunderstorm clouds (and associated lightning) from a distance.  The picture above was taken in Cedar Falls, looking southeast toward storms that popped up in the overnight hours in parts of Tama and Benton counties.  You can see the moon in the right hand corner, indicating the clear sky over Cedar Falls.

So why can’t you hear the thunder?  You are only able to hear thunder if you are within 10-15 miles from a storm.  You can see lightning up to one hundred miles away from a storm (the speed of light is faster than the speed of sound).

That being said, if you can hear thunder, you are close enough to the thunderstorm, you are close enough to be struck by lightning.  As the saying goes, “When Thunder Roars, Go Indoors.”


Posted under Lightning, Photo, Weather Trivia

This post was written by Kyle Kiel on July 7, 2017

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“Matthew” and “Otto” Retired as Hurricane Names

Hurricane Matthew

The World Meteorological Organization (WMO) will retire the names “Matthew” and “Otto” for Atlantic tropical systems, meaning they will no longer be assigned to future storms. These will be the 81st and 82nd names retired for the Atlantic basin. This happens when the tropical cyclone was very deadly or causes a devastating amount of damage during its lifespan.

Matthew will be replaced with the name “Martin” and Otto will be replaced with the name “Owen”. These changes will occur in 2022, when the 2016 list of names is reused. There are 6 lists of names, one list for one year. One list is repeated every seven years. For more information on Atlantic tropical system naming, click here.

For more information on Matthew and Otto being retired, click here.

Matthew forecasts and advisories.

Otto forecasts and advisories.

For other tropical cyclones in the Atlantic that have been retired, click here.


Posted under NOAA, Weather History, Weather Trivia

This post was written by Rachael Peart on March 27, 2017

First Day of Summer 2016

The first day of summer is this week.


The summer solstice marks the beginning of astronomical summer and is the time when the earth is farthest away from the sun. The position of our planet in its orbit determines the astronomical (ie, what we see on our calendars) seasons. Those dates change from year to year. The summer solstice is also the longest day of the calendar year.


Meteorological seasons are much easier to remember. For meteorologists, the seasons begin on the 1st of June, September, December and March. Meteorological summer always begins on June 1st and indicates the beginning of the three average warmest months of the calendar year in the Northern Hemisphere – June, July and August.

Not only is Monday the first day of summer, there is a full moon in the morning. The last time there was a full moon on the first day of summer was in 1948 and the next time this happens will be 2062.

Summer Solstice Strawberry Moon


Posted under Astronomy, Education, NASA, Weather Trivia

This post was written by Rachael Peart on June 20, 2016

Weather Trivia Week #2

Which layer of the atmosphere contains the weather?

A) Thermosphere (14.3%)
B) Troposphere (38.1%)
C) Mesosphere (21.4%)
D) Stratosphere (26.2%)

The correct answer is B) Troposphere


Posted under Weather Trivia

This post was written by Schnack on May 3, 2008

Weather Trivia Week #1

Question: Which of the following devices is used to measure cloud height?

A: Anemometer (16%)

B: Psychrometer (7%)

C: Celiometer (76%)

D: Thermometer (1%)

Answer: C: Celiometer

A ceilometer determines cloud height and levels in the atmosphere. The ceilometer (pronounced se-lom’-i-ter) uses invisible laser radiation to detect cloud levels.

An anemometer is the device for measuring wind speed.

A thermometer is the device for measuring temperature.

A csychrometer is a device used to measure relative humidity.


Posted under Weather Trivia

This post was written by Schnack on April 26, 2008