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Rainbows form when it rains… but do they form when it snows?

We’ve all seen rainbows during rain showers, but do rainbows form during snow showers? This was a very interesting question posed to me by a viewer, so I thought I’d share the answer with all of you.

First, let’s go over the formation of rainbows. Three conditions must be met before a rainbow can form:

1) It must be raining.

2) The sun must be shining.

3) The observer needs to be standing in between the sun and rain, with their back to the sun.

 

When rain falls from the sky, it falls in a spherical or drop shape (they get the drop shape from gravity pulling on them as they fall to the ground). When a ray of sunlight reaches the raindrop, some of that light enters that drop and refracts (or changes direction/bends as it enters the raindrop). White light (sunlight) is made up of all the colors of the rainbow (red, orange, yellow, green, blue, indigo & violet). These different colors of light refract in slightly different directions, which causes them to seperate and become the stripes of color you see in the sky.

Now, snowflakes on the otherhand are a different story. The biggest reason we don’t see rainbows when it snows is because snowflakes have a very different shape compared to raindrops. Snowflakes are six-sided and flat, in contrast with raindrops which are spherical.

When sunlight shines on falling snow, the fact that the snowflakes have so many different surfaces causes the light to be refracted and reflected in many different directions. This causes the sunlight to become TOO scattered and a rainbow is unable to form.

Though full, bright rainbows don’t form in snow, there are other special times when we do get optical illusions through snow or ice crystals. Parhelion, or more commonly known as ’sun dogs’, are bright spots that appear on either side of the sun. They form when rays of light refract through thin, flat snowflakes (falling through calm winds) or cirrus clouds (high clouds made of ice crystals). These parhelion can often look like parts of a halo and can show some colors of the rainbow. There is usually a reddish shade on the inside of the ring that shifts to blue on the outside.

 

-Michelle Poedel

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Cold Winter + Cold Spring = Cold Summer?

Those of you longing for a hot and humid summer after what felt like a never ending winter and a pretty much non-existent Spring…. you may not get your wish. If the Climate Prediction Center is correct in their thinking, then this summer we will see cooler than average temperatures. Here is the latest outlook for June, July and August of this year.

Now, this probably isn’t a surprise to many of you since the first half of this year so far has been cooler than normal. Let’s look at each month so far this year:

January: High temperatures all averaged together were 2.6°F below normal

February: 1.7°F below normal in terms of high temperatures.

March: High temperatures all averaged together came out 1.3°F below normal.

April: High temperatures averaged 3.5°F below normal

And through May 15th: We are 4.4°F below average

Now, just because we are predicted to be below normal, this does not mean that we are going to see high temps in the 50’s and 60’s all summer. During June, July and August we average temperatures in the 70’s and 80’s. Maybe this just means we will see more 70’s than 80’s? I guess we will just have to wait and find out.

A little piece of good news: The Climate Prediction Center predicts an average summer when it comes to rainfall across most of the country.

The discussion for June-July-August has yet to come out, but to give you a better idea of their reasonings, here is a link to the Climate Prediction Center’s discussion for May-June-July: Climate Prediction Center Discussion.

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Why the quiet weather and sunshine this week?

Its something we haven’t seen much of in a while around the Coulee Region: A stretch of dry weather and sunshine. Well its here this week and its all thanks to what us meteorologists call an “Omega Block” or an Omega blocking pattern.

This is when a strong area of high pressure sits over the central part of the country for days or even weeks with areas of low pressure on either side, as pictured below.

It gets its name because the upper air wind pattern resembles that of the Greek letter Omega.

When this pattern is in place, here in the Upper Mississippi Valley we usually get pretty lucky with a few days (or weeks) of straight sunshine and quiet weather. Though we enjoy getting a lot of use out of our sunglasses, areas to our east or west have to deal with days (or weeks) of stormy weather due to this stagnant pattern.

Though the dry weather is a nice change, if the pattern were to stick around for weeks on end it can lead to some extreme weather conditions across the country such as drought, flooding, and above/below normal temperatures.

Enjoy the weather while its here this week because it looks like the pattern will break just in time for the weekend bringing back the chance of rain and storms.

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Weather Folklore: Fact or Fiction?

I was sitting at work one quiet weather afternoon trying to come up with an interesting topic to write about in a blog. I was having a hard time coming up with any new ideas so I decided to turn it over to our Facebook Fans (hey, we do write these blogs for YOU the viewer! If you haven’t checked out our Facebook page you can find us at www.facebook.com/news8stormteam) and asked what they would want to know more about. Well, the accuracy of old weather sayings or folklore came up as one of those topics. This is a great topic and I must say that I have enjoyed doing the research (Thanks Facebook Fans!). Here is some of the information I found on the more popular weather folklore:

“Red sky at night, sailors delight. Red sky in the morning, sailors take warning.”

This is one of the more famous ones, and it has some pretty good reasoning behind it. Now, remember that this saying was developed way before satellites, radars and the modern knowledge we have in the science of meteorology. A couple things to keep in mind: 1) This saying only applies to locations in the middle latitudes (that would include us)   2)  The sun rises in the east and sets in the west. Something that will never change.   3) Most storm systems in the mid latitudes move in a west to east fashion.  4) Upper level clouds (especially cirrus clouds) are known for giving the sky a reddish hue during dusk or dawn.

Though this saying does have a few flaws, it actually does make a lot of sense. The first part: “Red sky at night, sailors delight”. Since most storm systems move from west to east and the fact that you can see the sun set in the west, this would mean that the storm system is moving away from you. The red color of the sky would be the sun’s rays reflecting off of the departing clouds. If a storm system is approaching at night the sky would not appear as red because the sun would be setting behind the clouds.

The second part: “Red sky in the morning, sailors take warning” is just the opposite. If you can see the rising sun in the east and the sky is reddish this means the sun is shining on clouds to the west, which would imply an approaching storm system.

Now, as I stated above, there are a few flaws with this folklore. 1) Whether there are clouds in the sky or not, the sky can look reddish at both dusk and dawn thanks to the angle of the sun.  2) Storm systems do not always move straight west to east. As we have seen many times, they can move southwest to northeast, south to north, northwest to southeast, or can even sometimes retrograde (move backwards, so for example east to west).  3) Cirrus or any other type of cloud can be present anywhere in the sky without a big storm system approaching or leaving.   But all-in-all, if you can see the sunrise, but it looks dark out to the west, there is a pretty good chance that stormy weather is approaching. If you can see the sunset, the weather will be quiet.

Other sayings and reasonings that are similar to that above: “Rainbow in the east, sailors at peace. Rainbow in the west, sailors distress.” & “Rainbow in the morning, shepherds take warning; rainbow at night, shepherds delight”.

“No weather is ill, if the wind is still”

This saying applies to calm conditions when skies are clear during the day. These calm conditions are usually the result of high pressure. When there is a high pressure system sitting over us, winds are calm due to a weak pressure gradient (pressure gradient is what helps create wind and the gradient is considered strong or tight when you are sitting between two systems or with a strong low pressure system… this causes very windy conditions). Plus, the air is sinking under high pressure, so we usually will not see much in the way of cloud cover (you need rising air to produce clouds).

But there are some flaws to this saying…. 1) When there is a high pressure system sitting over us during the nighttime hours, especially in the middle of winter, this can cause for very frigid conditions. Though there may not be any “weather” like rain or snow, clear skies and light winds are the perfect combo for a very cold night (this allows the warmer air at the surface to escape into the atmosphere). 2) I’m sure you know the saying “The calm before the storm”. Many times thunderstorms will develop when winds are calm.

“Clear Moon, Frost Soon”

This saying is pretty accurate, but only when temperatures drop below freezing. “Clear moon” means that there will be clear skies at night. That along with light winds and a cold air mass, is the perfect set up for frost formation. This usually will happen when we have high pressure sitting over top of our region at night. This allows all of the warmer air from daytime heating to rise up into the atmosphere away from the surface. Again, this will only apply when temperatures are below freezing. You won’t get frost under clear skies with light winds when the temperature is 50 degrees, for example.

“A sunshiny shower, won’t last half an hour”

We’ve probably all experienced it: It will be raining, but the sun is still shining. This saying that indicates the shower won’t last long only applies when it happens at the end of a storm or when a storm system is decaying or pushing away. The clouds will begin to break up, sun may start to shine through, but some of the exiting clouds will still be producing rainfall. When does this not apply? When the sun is shining and it begins to rain. This could indicate that a storm system is moving towards you and that clouds will thicken and rain will intensify.

“Halo around the sun or moon, rain coming soon.”

 A ring or halo around the moon or sun can be an indication that a low pressure system is approaching. The sunlight or moonlight will refract ice crystals at higher altitudes leading to the formation of a halo. This extra moisture in the air will most likely be descending to lower altitudes where it will form clouds or precipitation. Studies have shown that this saying is more relevant in warm months, rather than cold ones.

 

Again, all of these sayings have some flaws to them because Mother Nature can throw us some curveballs every once in a while so they will not be right 100% of the time.  It is pretty interesting to see that many of these have a good amount of truth to them, since most were made up before we had any of our modern forecasting technology or theories. It just goes to show what a huge part observation plays in forecasting our everyday weather. If I have missed any that you’d like to know more about let me know and I will see what I can dig up! -Michelle

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Dear Mother Nature, Where is Spring??

We are winding down to the last few days in April and I have heard many comments and concerns from people saying “Is Spring EVER going to arrive?”… my thoughts exactly. We’ve had a few nice days here and there, like yesterday for instance: We reached 67°F under sunny skies for most of the day. Well, that was the first time in 12 days that our temperatures have been above normal.

Meteorological Spring starts March 1st and lasts through May 30th, so really we only have about a month left in our “Spring”. Well, I did a little math and a little research and here are some of the numbers for March and April so far:

-March High Temperatures:

     *Normal Average High: 44.6°F

     *Actual Average High: 43.3°F

So we were about 1.3°F below where we should have been

-March Precipitation:

     *Normal Snowfall: 7.1″

     *Actual March 2011 Snowfall: 5.6″

Hey, we were BELOW normal on that one! :)

    

     *Normal Total Precip: 2.0″

     *Actual March 2011 Precip: 2.86″

Above normal thanks to the heavy rain we saw on March 22nd… we actually broke a daily record for rainfall on that day!

-April High Temperatures:

     *Normal High Temp through 4/26: 56.3°F

     *Actual High Temp Average through 4/26: 55.1°F

That’s actually only 1.2°F below average! But this is because we’ve had a few really warm days well above average, and then more cool day that were well below average. Remember that 81°F we had on April 10th? Yeah, it seems like eons ago…

-April Precipitation:

     *Average Snowfall: 2.0″

      *Actual April 2011 Snowfall through 4/26: 4.7″

2.7″ above average. If the ACTUAL reading was taken up on the bluff at the NWS, our numbers would be much higher. Our last big snow on the 19th, they had over 8″!

     *Average Total April Precip: 3.38″

     *Actual April 2011 Precip through 4/26 2:18 PM: 5.08″

As you can see we are WAY over in the precip department! And this is as more showers continue to fall outside right now… And with April ending on Saturday, there is definite potential to keep adding to this number. The only completely dry day looks to be Friday.

 

So will we EVER warm up? Well, in one word: Yes. But will it be as warm as we’d like? Maybe not. Here are the 3 month outlooks for the nation for May-Jun-July:

May-June-July Temperature Outlook

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The top image is the outlook for temperatures for May-June-July. The Climate Prediction Center forecasts cooler than average temperatures. Now this doesn’t mean we won’t have hot days, it just means that when all the numbers are averaged together, we will probably come out below normal.
The second image is the precipitation forecast. And we are on the wet side of things again for the next 3 months.
So will these outlooks pan out? I guess we will just have to wait and see.
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