Two very different cold fronts

1A quick look at a weather map can usually give us a quick idea whether it will produce severe weather. On the left is the scenario for Thursday. A weak cold front will work in from the north. Because of its east-west orientation, there may be just enough convergence at the surface to produce some showers. However, long-lived thunderstorm activity isn’t expected. With east-west cold fronts, the jet stream is almost always parallel to the front. While rain is possible, big thunderstorms aren’t likely.

2However, with thunderstorms that sweep in from the west, there is usually more convergence which leads to higher rain and thunderstorm chances. Southerly winds in advance of the front can bring in higher levels of moisture from the Gulf of Mexico. In addition, there’s usually a strong jet stream perpendicular to a north-south front. This leads to higher wind shear…and a higher intensity of thunderstorms! So as we head through the spring season, be on the lookout for the north-south orientation on the weather map.

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Posted under severe weather, weather, weather geek

This post was written by Eric Sorensen on April 8, 2014

Weird clouds spotted over Northern Illinois

Many of you spotted these weird clouds overhead on Monday. Earlier this evening, I posted one on Facebook and asked if anybody wanted to guess what was going on. Michael Janssen said “Snowing but not reaching the ground.” Joseph Girouard said “Flock of Altocumulus with virga.” You both are exactly correct!

UntitledLet’s examine Lorraine Dyba’s photo from Dixon, Illinois. Here you can see a few cumulus trying as hard as they can to develop. Unfortunately, there isn’t much moisture in the air. And there isn’t enough instability to keep them going. Notice the lack of a discernible updraft. For rising motion, look for hard edges on the top of the clouds. (Think about the cauliflower appearance to Summer cumulus clouds.) Instead, what’s going on here are cumulus clouds that are literally falling…quite literally! Looking closely, you can see some precipitation falling out of the clouds. Instead of a rain or snow shaft falling all the way to the ground, the precipitation is falling into dry air. This is called virga. So if you were under the clouds, you’d stay dry, even though the clouds above you were producing rain and/or snow.

Cool stuff!

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Posted under weather geek

This post was written by Eric Sorensen on March 19, 2014

Magic Number: Two

Capture

There are two different days where 50 degree temperatures are anticipated this week. A broad, southwesterly breeze will allow temperatures to surge right up to that 50 degree mark on Tuesday, even without much sunshine. Some rain will mark the change back to cooler weather Tuesday night into Wednesday morning. Another 50 degree day is anticipated Friday ahead of another weathermaker. This one will bring much cooler temperatures to our region for the weekend. 30s are likely both Saturday and Sunday.

Capture3Two weather systems will bring some light rain or snow to the region this week. The first will bring us about a quarter inch of rain Tuesday night into Wednesday. By Wednesday, as low pressure moves up to our northwest, it could be cold enough for a few wet snowflakes to mix in. No accumulation is expected. A similar stormtrack will affect us Friday into Saturday. Again, little/no accumulation is expected. However, it will turn colder after the passage of each low pressure system. -ERIC

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Posted under weather, weather geek

This post was written by Eric Sorensen on March 17, 2014

Nice car wash weather!


Temperatures have certainly taken a tumble! We’ll drop to 10 degrees as the wind subsides overnight. Thank goodness or we would have below zero chills!

Thursday will give us a fair amount of sunshine. Highs will tick up near that 40 degree mark! But Friday is the day to rejoice in the chance of seeing a 50. The problem is a cold front will come through during the day taking us back into the 30s and 40s for the weekend.

Good news is if you’re thinking of getting your car washed, it doesn’t look like we’re in for many systems to mess it up!

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Posted under weather, weather geek

This post was written by Eric Sorensen on March 12, 2014

Snow to Liquid Ratio

This isn’t snowman snow!

Saturday’s snowfall was very fluffy in nature, thanks to limited moisture in our atmosphere. Our atmosphere lacked moisture because temperatures were well below freezing at the surface and in the lower layer of our atmosphere. As a result, our snow-to-liquid ratios were on the higher end of the spectrum.

A higher snow-to-liquid ratio means a lower snow density.  In other words, the weight of the snow is less when there is less liquid content.  On the ground, there are more air pockets in between the snow crystals, resulting in a “fluffier” than average snow. 

Snow-to-Liquid Ratio

Snow-to-Liquid Ratio

An “average” ratio is approximately 10 to 1 (often written 10:1).  This means that if you melt 10 inches of snow, you will get 1 inch of liquid.  Heavy, wet snow (the kind we don’t like to shovel) typically has a ratio between 5:1 and 8:1. Fluffy, powdery snow can have ratios as high as 30:1.  Saturday’s snow-to-liquid ratio was around 18:1 (definitely on the higher side).

Saturday Totals

Saturday Totals

Snowfall totals were on the higher end of our forecast range of 1 to 3 inches.  A few of our backyards even picked up close to 4 inches of the powdery stuff!  At WREX-TV, I measured 3.1 inches of new snow.  Applying our knowledge of ratios, 3.1 inches of snow with an approximate snow-to-liquid ratio of 18:1 gives us 0.17 inch of liquid precipitation.

Math for the win!

-Joe

 

EDIT: MORE SNOWFALL REPORTS FROM SATURDAY

  • Genoa – 4.8″
  • Elmoville (Jo Daviess Co.) – 4.0″
  • Freeport (Lancaster Heights neighborhood) – 4.0″
  • Freeport (Park Hills area) – 3.2″
  • Machesney Park – 3.0″
  • Woodstock – 3.0″
  • Roscoe – 2.9″
  • Rockford (Highland neighborhood) – 2.8″
  • Winslow – 2.8″
  • Mendota – 2.7″
  • Brodhead – 2.5″
  • Monroe – 2.5″
  • Byron – 2.4″
  • Chadwick – 2.3″
  • Elgin – 2.3″
  • Mount Carroll – 2.3″
  • Ashton – 2.2″
  • DeKalb – 2.2″
  • Beloit – 2.0″
  • Dixon – 2.0″
  • Janesville – 2.0″
  • Shannon – 2.0″
  • South Beloit – 2.0″
  • Williams Bay – 2.0″
  • Edgerton – 1.9″
  • Polo – 1.9″
  • Lanark – 1.8″
  • Steward – 1.8″

*Reports will be updated as the information comes in.

 

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Posted under snow, statistics, weather, weather geek, winter weather

This post was written by Joe Astolfi on February 8, 2014

Rockford, Alaska or Anchorage, Illinois?

ALASKAThe weather is totally out of whack. The LOW temperature in Anchorage, Alaska was 35 degrees. The HIGH temperature in Rockford, Illinois was 6 degrees today. The jet stream continues to bring warm air into Alaska which displaces the cold reservoir of air over Northern Canada, southward. More extreme cold is anticipated in the Upper Midwest. However, this pattern can’t last too much longer because the high latitudes are running out of cold air…literally! Temperatures will begin to moderate by the end of the month as the northwesterly orientation of the jet stream becomes more zonal (west to east).

Here’s the forecast for Rockford, Illinois versus Anchorage, Alaska.

Rockford, Illinois
FRI -13/21
SAT 13/24
SUN 9/24
MON -7/-1
TUE -18/-4
WED -2/11
THU 15-27

Anchorage, Alaska
FRI 38/48
SAT 32/43
SUN  32/38
MON 33/40
TUE 30/38
WED 31/39
THU 32/38

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Posted under climate/climate change, weather geek

This post was written by Eric Sorensen on January 23, 2014

The Polar Vortex

We are slowing pulling out of the deep freeze, but this past week has brought about a catch phrase of sorts that folks are using to describe what has been making the US so darned cold. The “polar vortex” is indeed a real thing, but it might not necessarily be what you might have gathered over the past 4 days. The polar vortex is a counter-clockwise circulating upper air mass that contains the coldest air located near the north pole. This vortex is always present, both in the summer and in the winter. It is also capable of having a piece break off thanks to the jetstream. That is what has happened this past week. Part of the polar vortex shifted far to the south of its typical location, bringing with it the bitter cold.vortex

The polar vortex isn’t something new. It’s also NOT something that exists at the surface of the Earth. It is an upper air mass which we cannot see. It isn’t visible like other weather phenomena like tornadoes, thunderstorms and lightning. Not only can we not see it, it also can’t hurt us itself. It is a circulating air mass, so think of it like this, the polar vortex is like a fence that holds in the cold air. The fence can’t hurt us, but the dangerously cold ait inside can. Hope that clears up the definition a bit! If not, feel free to find me on facebook “Meteorologist Greg Bobos”, and I’d love to chat more! -Greg

p.s. Thanks to our friends at the National Weather Service for the inspiration for the story and graphic.

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Posted under cold blast, weather geek, winter weather

This post was written by GregBobos on January 9, 2014

Rockford, Alaska?

If you’ve ever wondered what Alaska is like in the winter, you don’t have to anymore. And you won’t need to take the 3,000 mile trip! Check out the comparison between Northern Illinois and Northern Alaska! The temperature will likely be warmer up in the 49th state for four days in a row!
FAIRBANKS
61Rockford’s temperature is set to go below zero Sunday afternoon, staying negative until Wednesday afternoon for a total of 61 consecutive hours. On top of that, we’ll have a strong northwesterly wind that could bring our wind chill values into the -45 to -35° range. This would qualify for “Wind Chill Warning” status, enough to cause some delays/closings in schools, and depending on the temperature, could make it hard to start the car Monday-Wednesday morning.

We’ll keep tracking this strange January weather. Bookmark the blog and you’ll have updates at least once a day.

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Posted under cold blast, end of the world, weather geek

This post was written by Eric Sorensen on January 2, 2014

Strange booms startle many in Northern Illinois

The strange booms you heard on Sunday night weren’t the stomps of Bears or Packers fans, they were likely from cryoseismic activity! Lisa Kammes from Sycamore says “My husband went to the back yard to check on [the booms]. My neighbor called police. We heard lots, until we finally fell asleep at 3am. Kelsey Brown of Pecatonica said it sounded like someone “hitting the side of the house.” In South Beloit, Bobbi Bilderback reports that her dogs started barking. And down the road from her in Rockton, Marcie Severson-Haselton said she heard three loud booms. “My son even woke up and came to our room immediately!” At my house in Southwest Rockford, it sounded like someone threw something heavy onto my roof. For me, it was more of a thud. I didn’t put two and two together until I heard about other people who heard the strange sounds.crysoseisms

Some of you on Facebook were correct when I asked what the strange sounds were from: a cryoseism. Because our ground is pretty dry, the warm air on Sunday allowed water to seep deep into fissures and cracks. The water flowed down into and around the rock and limestone. When the Arctic cold front came through during the day, the temperature dropped quickly. We all know that water expands as it freezes (the reason why soda cans explode when they freeze and why a milk jug of water will expand to a ball-shape if it freezes). The water in all of these cracks expanded so quickly, it created mini explosions…explosions of water and ice all over the region. These booms aren’t enough to physically shake the ground, but they are enough to startle livestock and unsuspecting people!

Cryoseisms are a fairly rare occurrence here in Northern Illinois, as the temperature drop has to be fairly quick…from above freezing to very cold, in a short amount of time. If you heard them, chime in on our Facebook page! -Eric

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Posted under end of the world, weather geek

This post was written by Eric Sorensen on December 30, 2013

November: Primetime for “Frost Flowers”

Got your attention with that headline, didn’t I?

This morning I received an e-mail from Dick Roush of Freeport. He writes about the “Frost Flower,” and says “I’ve never seen anything like these in 80 years!” Take a look at this slideshow and see for yourself!

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Here’s how it works. The air temperature must be below 32°F with non-frozen ground. Conner says it’s likely to occur only once per year. “The water in the plant’s stem is drawn upward by capillary action from the ground. It expands as it freezes and splits the stem vertically and freezes on contact with the air.” The conditions for Frost Flowers only happen once because after it occurs, the plant’s stem is either destroyed or the expansion of the ice won’t allow it to happen again.

Frost Flowers are also referred as ice blossoms, ice castles, or crystallofolia.

This is a big reason why it’s great to hike Northern Illinois and Southern Wisconsin in the fall! -Eric

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Posted under news, science, weather, weather geek

This post was written by Eric Sorensen on November 12, 2013