Evening Sounding

Here is a temp profile of the atmosphere this evening. At the ground it is cold, about 7° F and only about 5,000 ft up it warms to near 32° F

Share

Posted under Education

This post was written by Schnack on January 11, 2018

Sunglint

The new GOES-16 satellite is AMAZING. There are so many things we can see and so much more clear than the older satellites. This afternoon at the bottom of the image below you can see the sunglint.

Share

Posted under Education

This post was written by Schnack on March 30, 2017

Narrow snow band

Friday morning and into early afternoon, a narrow band of snow produced a few inches of snow in western Illinois. The snow developed similarly to the type of snow in areas around the Great Lakes. The first image below shows the band of snow just south of Davenport extending southeast.

KWWL 2015 MAX Storm ED

The visible satellite below shows the snow on the ground from today.

11

 

Andy Ervin, Senior Forecaster at the National Weather Service in Davenport, has more information about this type of situation. The paper below was originally written in 2006.

Click on the text below to enlarge.

9

 

 

Share

Posted under Education, Winter Weather

This post was written by Schnack on January 27, 2017

Precipitation Type

Here is a look at how the different precipitation types form. Way up in the sky the air is below freezing (below 32°F or 0°C). In some cases there is a warm layer closer to the ground. Exactly how thick that warm layer is and how close to the ground impacts the type of precipitation we receive.

I will start with snow (left side of the graphic below). As the snowflake above falls toward the ground, the temperature through out the travel toward the ground remains below freezing not allowing it to melt. So the snowflake stays a snowflake from top to bottom.

Now for sleet. The snowflake falls through a warm layer (above freezing) and the snow melts and turns to a raindrop. The raindrop than falls through a pretty thick layer of cold air. This allows the raindrop to freeze. By the time it reaches the ground it is sleet.

Compare that with freezing rain. That same warm layer is now thicker leaving a very small layer near the ground below freezing. There is less time for the raindrop to freeze and turn to sleet so it falls as rain and freezes on impact to anything on the ground.

Now if that layer is above freezing all the way to the ground it stays as rain and doesn’t freeze. The air closest to the ground is above freezing and the ground is above freezing. The result would be rain.

Precip Type

Share

Posted under Education, Educational, Ice, Winter Weather

This post was written by Schnack on January 12, 2017

First Day of Summer 2016

The first day of summer is this week.

2016summersolstice

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.

NASA-seasonalvariations

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

Share

Posted under Astronomy, Education, NASA, Weather Trivia

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

Fluffy Snow Sunday

Snow still looks likely for Sunday afternoon and Sunday night. Start and stop time, right now, appears to be around noon Sunday to shortly after sunrise Monday. This could adjust as we learn more about the atmospheric conditions…so stay updated on the forecast.

I wanted to take a moment to talk about why I think it will be a fluffy snow. Snow formation is dependent on moisture, temperature and how fast the air is rising. The hardest of those three things to forecast is where the air is rising the fastest. What is easier is the temperature profile in the atmosphere. Snowflakes fall in so many different shapes and those shapes typically happen at different temperatures. The snow flake that produces the most snow is a dendrite. It is a larger snowflake, so as they pile on top each other there is more air between them and the result is deeper snow.

Dendritic Snowflakes

The larger dendrite snowflakes form when the temperatures are between -12C and -18C. The chart below is a forecast sounding (a vertical profile of the atmosphere at a given point and at a given time). The area highlighted in yellow is the -12C to -18C area called the “Dendritic Growth Zone”.  The red line is the temperature and the green line is the dewpoint. When they come close, like they are, it means the atmosphere is saturated…cloudy. Now when the atmosphere is saturated in that zone the chance of fluffy snow is good. And the deeper a saturated atmosphere falls in that zone the chance of fluffy snow increases. The depth, on the chart below, is considered very good for dendrites to grow. This is where we can get large snow ratios of 15:1 or 20:1. That means it does’t take a lot of moisture to produce accumulating snow.

Dec 5 Fluffy Snow

Share

Posted under Education, Winter Weather

This post was written by Schnack on December 5, 2013

Colder than Others

It has been pretty cold around here lately. Temperatures have been well below normal for highs and lows.

Nov 29 Past 7 Days ALO

The low temperature officially Friday morning at the Waterloo Airport was -1. Between 2 AM and 8 AM, it held at 3 degrees or colder. The other reporting stations (not official NWS sites) in town (Waterloo/Cedar Falls) reported temperatures between 6 and 12 degrees.

Nov 29 Waterloo Low

So why such a difference? When forecasting temperatures you have to take into consideration a lot of things. One of the things to look at, especially in Waterloo, is the location of the site. The official Waterloo reporting site for the National Weather Service is at the airport. North of the airport is a more rural area…”country”. South of the airport are the towns of Waterloo and Cedar Falls. The temperature difference from in town to the country on a clear night, with snow on the ground, could be as much as 10-15 degrees different.

Again, the low Friday morning was  -1. If you look at the above temperatures, outlined in blue, you will notice the wind speed and direction to the right of hourly reports. The wind was either calm or a slight breeze from the ENE. The slight northerly component of the wind came from the colder country location. If the wind was from the south it wouldn’t have not reported so cold. It would have been closer to the temperatures in town.

Nov 29 ALO Site Location

 

Share

Posted under Education

This post was written by Schnack on November 29, 2013

NW and SE Wind

Most of the wind so far this month has been either from the NW or SE.

Nov 22 Wind Rose

Click here to learn a bit more about how to read a wind rose.

 

Share

Posted under Education, Windy

This post was written by Schnack on November 22, 2013

Lightning Safety Awareness Week: June 24-30

From NWS:

When Thunder Roars, Go Indoors!

Summer is the peak season for one of the nation’s deadliest weather phenomena— lightning. But don’t be fooled, lightning strikes year round. The goal of this Website is to safeguard U.S. residents from lightning. In the United States, an average of 54 people are reported killed each year by lightning. Click here to learn more about lightning.

 

 

 

 

The below chart shows what type of weather event has caused death.

 

 

 

Share

Posted under Education, Lightning, NOAA

This post was written by Schnack on June 24, 2012

Pella Heat Burst

A thunderstorm moved across Pella last night and created a heat burst. A heat burst is a downdraft of very warm but dry air from a collapsing thunderstorm. Dry dense air high in a thunderstorm accelerates towards the surface at a high speed. As it accelerates, it continues to heat up. Therefore, upon reaching the ground it produces a sudden increase in temperature, decrease in dewpoint and strong wind gusts. In Pella, the heat burst created a sudden 12 degree increase in temperature and an 18 degree drop in dewpoint. Winds gusted over 76 mph.

 Below is a radar image of  the event over Pella taken by Iowa Environmental Mesonet.

 Below is a graphic depicting the sudden increase in temperature and decrease in dewpoint in Pella.

Want to witness the heat burst? Below is a youtube clip capturing the storm as it moved through.

Share

Posted under Education, Severe Weather, Uncategorized

This post was written by Denice Pelster on May 3, 2012