Thursday, August 17, 2017

How the eclipse may affect temperatures

It will be interesting to see what happens with temperatures on the afternoon of the eclipse.

Forecasters at the National Weather Service in Indianapolis pulled up data from the last annular eclipse to take place in 1994.  The temperature dropped 4° in an  hour when the maximum eclipse occurred over Lafayette.  The moon appears smaller in an annular eclipse, so it does not cover all of the sun.  So it is conceivable the temperature may drop 5° to 7° during the peak of the eclipse.

Right now we are forecasting a high of 90° for Monday.  Since the eclipse is happening during the peak heating of the day I'm curious to see if that keeps the temperatures from reaching their full potential.

Wednesday, August 16, 2017

Solar Eclipse: Closer look at cloud cover projections

We are now less than five days away from the much anticipated Solar Eclipse.  In the Weather Department our eyes are focused on what the weather will be like for the day.

As we get closer computer models usually come in to better agreement as to what cloud cover and precipitation will be.  So far, the two medium-range computer models we use are at odds.
GFS's cloud cover and precipitation rate projection at 2pm ET Monday.

ECMWF's cloud cover and precipitation rate projection at 2pm ET Monday.

The two computer models we are looking at is NOAA's global forecast model (GFS) and the European Forecast Agency's global forecast model (ECMWF).

The best viewing of the solar eclipse will be with less cloud cover.  For that we want to the total cloud cover percentage as close to 0% as possible.  While you may be able to see some of the eclipse through the clouds, the more clouds overhead, the less you will see.

As you can see in the images above both computer models project clouds around in the Midwest on the afternoon of the 21st.

Here's a more specific look at the projected total cloud cover percentage at 2pm Monday, August 21 around central Indiana.

Bloomington, In:
  • GFS - 78%
  • ECMWF - 40%
Cape Girardeau, Mo:
  • GFS - 45%
  • ECMWF - 64%
Carbondale, Il:
  • GFS - 56%
  • ECMWF - 34%
Columbus, In:
  • GFS - 79%
  • ECMWF - 66%
Farmington, Mo:
  • GFS - 83%
  • ECMWF - 39%
Indianapolis, In:
  • GFS - 79%
  • ECMWF - 81%
Kokomo, In:
  • GFS - 98%
  • ECMWF - 52%
Lafayette, In:
  • GFS - 95%
  • ECMWF - 78%
Muncie, In:
  • GFS - 90%
  • ECMWF - 58%
Paducah, Ky:
  • GFS - 43%
  • ECMWF - 83%
St. Louis, Mo:
  • GFS - 99%
  • ECMWF - 29%
Understand that there are another 35 computer model runs to go before the eclipse gets here.  And that's just for these two computer models.  Once we get within 72-hours of the event, additional computer models will chime in with what they think will happen with the weather conditions.

Sunday, August 13, 2017

Updated cloud cover projection for Solar Eclipse

I continue to look over computer model data for the Solar Eclipse coming Monday, August 21.  Specifically, I'm watching how much cloud cover could be in the sky for the eclipse.

This morning's computer model runs are on two ends of the spectrum for cloud cover.  NOAA's global forecast model (GFS) continues its bullish run on clouds.  The European forecast agency's ECMWF keeps skies much more clear.

It is interesting to note that the GFS has been very consistent suggesting clouds over much of the Midwest for several days.

Remember, for the best viewing experience we want less clouds.

Total cloud cover projections for 2pm ET/1pm CT:

Bloomington, In:
  • GFS - 98%
  • ECMWF - 38%
Cape Girardeau, Mo:
  • GFS - 89%
  • ECMWF - 36%
Carbondale, Il:
  • GFS - 93%
  • ECMWF - 18%
Columbus, In:
  • GFS - 90%
  • ECMWF - 51%
Farmington, Mo:
  • GFS - 94%
  • ECMWF - 27%
Indianapolis, In:
  • GFS - 97%
  • ECMWF - 52%
Lafayette, In:
  • GFS - 100%
  • ECMWF - 29%
Muncie, In:
  • GFS - 98%
  • ECMWF - 58%
Paducah, Ky:
  • GFS - 76%
  • ECMWF - 20%
Peru, In:
  • GFS - 100%
  • ECMWF - 20%
St. Louis, Mo:
  • GFS - 92%
  • ECMWF - 3%
Terre Haute, In:
  • GFS - 99%
  • ECMWF - 34%
It just so happens I will be in Missouri the day of the eclipse.  Better yet, where I am going to be is in the area of totality.  Here's hoping the cloud cover projections keep going lower and lower!

Saturday, August 12, 2017

Early look at sky conditions for the 2017 Solar Eclipse

The buzz around the Solar Eclipse on August 21 is starting to increase as we get closer to the day.  While it is still many days away, computer models are beginning to take a stab at what sky conditions will be for the day.

There are two computer models that can reach far enough in to the future to project cloud cover for the 21st.  The National Oceanic and Atmospheric Administrations global forecast model (GFS) and the European forecast agency’s global forecast model (ECMWF).

For several days the GFS has suggested there will be a lot of clouds and rain in the Midwest for the 21st while the ECMWF is more bullish on sunshine.

Sunday morning’s computer model total cloud cover projections* at 2pm ET:

Bloomington, IN:
  • GFS - 99%
  • ECMWF - 45%
Cape Girardeau:
  • GFS - 100%
  • ECMWF - 31%
Carbondale:
  • GFS - 98%
  • ECMWF - 36%
Columbus, IN:
  • GFS - 100%
  • ECMWF - 24%
Farmington, MO:
  • GFS - 98%
  • ECMWF - 19%
Indianapolis:
  • GFS - 100%
  • ECMWF - 40%
St. Louis:
  • GFS - 95%
  • ECMWF - 18%
*Higher number equates to more clouds obscuring the sky/sun.  The lower the number the better for viewing the solar eclipse.
Between those two computer models there are 55 more computer models runs to go before the solar eclipse happens.  The cloud cover projection will likely flip flop many times between now and then.  With luck we'll see the numbers drop to 0%.

Do you plan to view the solar eclipse?  If so, let me know where you'll be watching it by leaving a comment on this post!

Thursday, February 23, 2017

Baking cakes and severe storms

A friend who teaches middle school science asked me to send him something about Friday's severe weather threat he could discuss with his students.  I thought it would also make a good blog post, so here you go.

While severe weather is possible Friday, it is far from certainty.  There are several things needed to create an environment supportive of thunderstorms becoming severe thunderstorms.

I often describe it like baking a cake.  You have many ingredients needed to make one.  However, if one ingredient isn't there, it doesn't come out of the oven looking like a cake.

Some of the ingredients needed for severe weather:  fuel for thunderstorms, a trigger/lift in the atmosphere, instability, turning of the winds through the atmospheric column.

TRIGGER:  The trigger for this event will be a cold front projected to sweep through the state Friday night.  As colder air is more dense, it remains close to the ground.  Think of a cold front as a moving wedge.  As it moves through the state, it will take warm, moist air and lift it as cold air undercuts it.  We can put a check mark next to this ingredient.

FUEL: Fuel for thunderstorms is already present.  Moisture.  For that, we look at dew point temperatures.  In basic terms, the dew point is a measure of the moisture in the air.  You may have noticed Wednesday and today it feels a little more humid outside.  Dew points are in the 50°s.  This is usual moisture for May leading in to June.  Dew points are projected to be in the middle to upper 50°s Friday ahead of the weather system.  We can put a check mark next to this ingredient.

INSTABILITY: Instability is needed to keep things churned up in the atmosphere.  It adds some explosion to the atmosphere as air/moisture is lifted.  When it is cloudy, there can be instability, but it is dramatically held back versus having sunshine to "bake the atmosphere".  That is why you often hear meteorologists say "If we see sunshine today, that is a bad thing if you don't like severe weather."  I've seen a number of potential severe weather days bust due to cloud cover.

TURNING OF THE WINDS:  For this, you need to think of the atmosphere in 3D.  What happens at the surface, where we live, is affected by what is going on overhead.  When we forecast, we look at several layers of the atmosphere.  The surface, 5,000ft above the surface, 15,000 feet above the surface, and 30,000 feet above the surface.  All the layers play a part in what we get down at the ground.

Winds at the surface are projected to be out of the south/southeast (160°) much of Friday.  Go up to 5,000ft and the winds will be out of the south-southwest (200°). Go up to 15,000ft and the winds will be more southwest (230°).  Winds at 30,000 will be out of the southwest (250°).  If you step back and look at the directions in a 3D sense, you can see there is turning of the winds .  This sets up an environment in which a parcel of air will begin to rotate.  Thunderstorms that rotate often become severe thunderstorms.

One of the key things I look for when putting together a forecast for tornadoes and storm chasing, 500 millibar divergence.  500mb is approximately 15,000 feet above the ground.  I look for areas at that level where the wind direction leaves a void (divergence).  Its similar to creating a vaccum.  When there's a vacuum what happens?  Air rushes to fill the "emptiness".  When there is a void at 15,000ft, and lift is in place, air rushes to fill the void.  That air comes from lower levels.  It aids pulling thunderstorms higher in to the atmosphere.

I like to use 500mb divergence because a thunderstorm is like a car engine.  For a car engine to work, you need to have air flowing in, but also need exhaust flowing out.  If you cut off the exhaust, it kills the engine.  By having that void 15,000 ft up, it acts as the exhaust, to help pull air out of the thunderstorm, giving it somewhere to go.

There will be areas of divergence present over Indiana Friday, however, it is not perfectly aligned with some of the other ingredients.

So we now know about the ingredients. What we have to watch for at this point, is whether the ingredients will be lined up and interact all at the same time.  At this point, I'm not convinced they are going to be.  It might be slightly out of line.  But since the ingredients are all there, that is why we are talking about the potential for severe weather Friday.  We won't know for sure it will happen until a few hours before it happens.

BOTTOM LINE:  Potential does exist for severe weather in central Indiana Friday but it is not certain.  It is an afternoon/night to keep an eye on the weather and be ready to act if a warning is issued.  Right now I have the Freak-Out-Meter at a 3 out of 10 for central Indiana.

Be sure to follow me on Twitter (@johndissauer) for the latest on the situation.

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