Cloud Shadow but in the Sky

The photo above was taken by Dan Gingerich. It is the Hot Shot photo at 5 pm today. It was taken in Decorah. I was not sure exactly why the shadow looked the way it did in the sky. When it comes to atmospheric optics the #1 source is Les Cowley. He runs a GREAT web page. http://www.atoptics.co.uk/ 

I have asked him questions before and he ALWAYS has the answer. So I went to him again to help me out. Here is what he had to say about the photo above.

Cloud shadows and rays can, like these ones, be very counter intuitive! 

The dark shadows look like they are pointing upwards but in reality they are angled downwards – all shadows cast by the sun must go downwards.      

There is a thin layer of hazy cloud _below_ the top of the towering cumulus.    The sun is casting a shadow of the cumulus cloud onto this lower layer.   We see the shadow through the other side of the lower cloud layer ‘screen’.     The shadow looks above the cumulus cloud simply because the shadow is closer to the camera.   See the diagram here: http://www.atoptics.co.uk/atoptics/rayim13.htm

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Posted under Optics

This post was written by Schnack on January 17, 2013

Weather Hot Shots on Thu. January 17

Click here to learn more about the cloud shadow photo above.

Submit your weather Hot Shot by clicking here.
One photo is shown on the 5 pm newscast and one on the 10 pm newscast.

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Posted under Hot Shots, Photo

This post was written by Schnack on January 17, 2013

Highs in the 40s Tomorrow



UPDATED at 4:40 PM

Tonight: Partly to mostly cloudy with flurries northeast of Waterloo. Low: 15-21. Wind: S 5-15 mph.

Friday: Decreasing clouds, breezy and warm. High: 45-50. Wind: SW 10-20 mph.

Friday Night: Mostly clear. Low: 27-31. Wind: SW 10-15 mph.

Saturday: Partly cloudy and windy (NW 15-25 mph). High: low 40s in the AM….falling temps in the PM.

Sunday: Mostly cloudy and cold with a 20% chance of light snow/flurries. High: near 20.

Monday: Partly cloudy and cold. High: near 10.

Tuesday: Mostly cloudy and cold. High: mid teens.

Wednesday: Partly cloudy. High: low 20s.

Thursday: Mostly cloudy with a 20% chance of rain/snow. High: low 30s.

A warm front currently over the Dakotas will push through eastern Iowa tonight. Here is the current surface map.


Ahead of the front there is a chance of light snow in Minnesota and Wisconsin. Now here in Iowa I am leaning more toward just flurries. Areas northeast of Waterloo will see the snowflakes. I may have to include light snow into the forecast later tonight, but I want to hold off on putting it in the forecast right now. I want to see the trajectory of the light snow in North Dakota (see map below).


It is moving southeast. It will be a close call if the light snow makes it into northeast Iowa compared to just a few flurries. If I do add light snow to the forecast it would be for the 10 pm newscast. The chance of any precipitation would be after midnight anyway.

Friday will be a warm day with clouds clearing in the morning. The wind will increase from the southwest pushing highs into the 40s. As highs reach the mid and upper 40s you might think records. We will be short of any records Friday. Here are the numbers:


An Arctic cold front is forecast to cross Iowa early Saturday afternoon. The HPC forecast map for Saturday morning shows the front northwest of Iowa (see map below).

Temperatures will warm, into the low 40s, before the front arrives in eastern Iowa. The cold front will cross the state dry, but usher in a gusty northwest wind and much colder air.

Here is the WSI RPM model showing where the strongest wind will be Saturday afternoon.

There is a chance for some light snow/flurries Sunday. The coldest day of the next seven is forecast to be Monday with highs near 10. The coldest night will be Tuesday morning with lows near zero and in some locations below zero.

The arctic air does not hang around long as high temperatures slowly warm each day back to the low 30s by Thursday. At that time we are tracking an area of low pressure to bring us a chance of rain/snow.

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Posted under Forecast Discussion

This post was written by Schnack on January 17, 2013

January 17

From NWS
1996
: Unseasonably warm air surged into Iowa ahead of an approaching cold front, bringing temperatures into the 50s across much of the state and lower 60s in the southeast. Many stations broke their daily high temperature record including Waterloo with a high of 54 F and Burlington with a high of 63 F. Other reported high temperatures included 60 F at Fairfield and Ottumwa, 61 F at Centerville and Mount Ayr, 62 F at Keosauqua. Behind the front arctic air blasted into the region, and by the 19th some stations in northern Iowa remained below zero even in the afternoon. A series of reinforcing arctic fronts followed in the subsequent weeks and by the first few days of February, Iowa was gripped by one if its worst cold snaps on record.

 This Day in National/World Weather History …
 17 January 1892 → The lowest temperature recorded in Delaware was -17 F in Millsboro.
 17 January 1982 → A terrific Chinook wind buffeted the Colorado foothills with wind gusts up to 147 mph. It was the most costly windstorm in Colorado history at the time.
 17 January 1999 → Tornadoes swarmed from Arkansas into Tennessee and Mississippi. This was the first outbreak of several that would take place between today and the 22nd from the Ozarks into the Lower Mississippi Valley.
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Posted under Weather History

This post was written by Schnack on January 17, 2013