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.

Sunday, November 20, 2016

Storms lining up over the Pacific Ocean

Weather systems are lining up over the Pacific Ocean that have the potential of impacting central Indiana through the Thanksgiving holiday weekend.

As of Sunday night, there are three that I am tracking three on satellite imagery.
  1. This one will bring rain to Indiana as early as Tuesday night and continue through Wednesday.
  2. Computer models are still working the calculations on this one.  Saturday the data suggested the upper-level energy could pass through the Midwest as a clipper – bringing rain and then cold air to Indiana, changing some of the rain over to snow – for Black Friday.  Sunday’s run of computer models suggest an area of low pressure in the Rocky Mountains and it will move east through the central United States.  In this scenario, rain for Black Friday would be the primary issue as temperatures look to stay warm enough to keep everything in liquid form.  However, on the tail end of the rain, there could be wintry mix.
  3. Long range computer data brings this system in to the Midwest late next weekend/early the following week.
Looking waaaay out, computer models are indicating a strong signal for a larger storm to impact the United States November 28 through December 1.

To trace the origin of this storm, you have to look off the northern Siberian coast over the East Siberian Sea.  So far north, it is more difficult to get satellite imagery.

As with most long-range forecasts, we will continue to monitor trends and see if whether or not some of these storms – especially #3 and #4 – happen or not.


Over the last 40 years, the average high temperature in Indianapolis for Thanksgiving is 47°.  Coincidentally, we are currently forecasting 48° as the high temperature Thursday.

Through Saturday, November 19, this November ranks the 9th warmest in the previous 145 years of records.  As we go through the remainder of the week, temperatures are forecast to be near normal if not slightly below.

Sunday, November 13, 2016

From near record highs to to winter in hours; BIG changes coming this week!

Sunday night we are watching a weather system over the Gulf of Alaska.  This system will have big impacts on the weather in central Indiana.  We'll go from mild, and even near record breaking warmth, to December-like temperatures in the matter of hours.  All over the upcoming week.

An area of low pressure is spinning and will send pieces of upper-level energy through the United States.
Satellite imagery Sunday night. (click image to see larger version)
The low will send pieces of upper-level energy to the lower 48.  The below animation is a computer model projection of the upper-levels of the atmosphere Tuesday through Friday afternoon.  The areas of yellow and red indicate enhanced areas of spin/energy.

Computer model projection of upper-level energy Tuesday through Friday. (click image to see larger version)
A "dip" in the white lines indicate a trough of low pressure moving onshore by Wednesday.  An area of low pressure will eventually develop in the lower, mid and upper-levels of the atmosphere.  At the end of the animation, an upper-level low is over Minnesota.

A cold front will develop and extend from the surface low, moving through the Midwest Thursday and Friday.  A line of showers and thunderstorms may develop and move through Indiana Friday PM.

Ahead of the front, winds will increase out of the south and southwest.  Early indications point to temperatures climbing in to the lower 70°s in central Indiana prior to rain developing.  This would allow temperatures to approach record levels.  The record high temperature for Friday, November 18 is 73° set in 1941.
Computer model projection of temperatures Friday through Sunday. (click image to see larger version)
After the front passes sometime Friday/early Saturday, temperatures will start to fall.  At this early view, high temperatures Saturday will occur early Saturday morning.

From the above animation, you can see cooler air filtering in throughout the day Saturday and Sunday.  It is still early, but it appears temperatures may struggle to get out of the 30°s Sunday afternoon.

There are a lot of details to be ironed out over the coming days.  Will there be rain Saturday?  Could upper-levels be cold enough to support a few snow showers (over northern Indiana)?  If the wind moves from a direction that could produce lake effect snow showers?

One of the BIG details to work out is whether or not the cold air will move south as aggressively as computer models suggest.  As has been the case over the previous two months, computer models hint at shots of cold coming to Indiana only to back off on the strength of the cold air.  Stay Tuned!

(click image to see larger version)

Wednesday, August 17, 2016

Thoughts After a Storm Chase; We Need to Keep Advancing Warning Technology

Monday evening I saw a tornado developing on radar on the west side of Brownsburg. The storm was moving northeast and not far from where I live. I decided to drive over and watch it pass by.

The wall cloud ended up passing directly overhead.  At the time, there was no funnel; however there was rapid horizontal rotation.  I could see a developing horizontal tube.  This was very reminiscent of a storm I chased near Sitka, Kansas in 1999.  Because of this, I knew there was a high likelihood the storm would tornado soon.

I traveled north on Lafayette Road from northwest Marion County in to Boone County.  I turned east on Whitestown Parkway in the Anson area. As I drove on the overpass, over I-65, I finally got a better view of the base of the wall cloud.  It was at this time, I could see dark clouds beginning to drop below the wall cloud.  I remember describing what I was seeing via the phone on CBS4.  Then I said I could see a tornado.  It was approximately 1-2 miles northeast of my location.

I tried to keep up, but at that point there was no chance as it had passed me by. I was having to navigate tree limbs in the road, full trees down covering the road and other drivers.

During the chase, I was on the phone with the control room and I was on-air describing what I was seeing with Chief Meteorologist Chris Wright, Bob Donaldson and Debby Knox.  While I was on the air with them, I kept hearing them talk about seeing a tornado on traffic cameras but the area they were talking about wasn't near where I was located.  I didn't think about it too much at the time.

While on the phone, I also heard my phone ding in my ear, notifying me I had a new text message. I subscribe to a service that sends me a text message every time a watch and/or warning is issued in central Indiana.  At the time, I thought they were new warnings for the current storm I was chasing so I didn't take time to read the full text of the warning.

I also received a couple Wireless Emergency Alerts (WEA) via the cell phone network. These are automated alerts sent by cell phone carriers when a life threatening alert is issued for your location. Again, I assumed they were for the storm I was watching and I didn't read the detailed information (I.e. where the storm was located.)

Radar imagery from Monday, August 15. Two tornado
warnings for two storms.
Little did I know that a second storm had developed south of the storm I was on.  The storm had produced a tornado south of Brownsburg and was traveling north along Highway 267.  It wasn't until Tuesday night, when I watched recorded video of our coverage on CBS4, that I realized Chris and Bob were showing live video of a tornado developing in Hendricks County.

This is a situation I have not personally encountered before.  Yes, in my previous 16 years of being a television meteorologist, I've had a storm producing a tornado followed by another storm producing a tornado, but this is the first time I have been out in the elements when this has happened.  You might have found yourself in a similar scenario.

This identifies a problem with the weather community's warning process.  If you are not watching tv, how can you easily and quickly assess that the new warning is not for the storm that just passed?

Right now I don't have an answer.  What I can say is that the warning process is constantly being evaluated by the National Weather Service and we at CBS4 also continually evaluate how we get important, lifesaving warning information to you.

Tuesday, January 19, 2016

Overnight snow for southeast Missouri, southern Illinois and western Kentucky

The National Weather Service has issued Winter Storm Warnings for much of southeast Missouri, southern Illinois and western Kentucky in advance of a fast moving weather system that will bring snow and sleet to the area Tuesday night and early Wednesday morning.

Keep in mind, potential exists for sleet to develop near the Missouri/Arkansas/Kentucky/Tennessee border which could cut in to snow totals.


2"-4": South of a line from Farmington to Harrisburg
3"-5": South of a line from Cape Girardeau to Karnak, IL
4"-6": south of a line from Wappapello, MO to Paducah

One thing that could hamper snow totals is sleet formation. It will be possible to have sleet mix in along Missouri/Tennessee/Kentucky border.

Should be noted the National Weather Service in Paducah has mentioned there is the potential for a few locales seeing up to 8". I think that is entirely possible.

FREAK-OUT-METER: (Scale 0-10 with 0 being less, 10 being highest)

Cape Girardeau - 4
Carbondale - 3
Farmington - 3
Mayfield, KY - 5
Metropolis - 4
New Madrid - 5
Paducah - 5
Poplar Bluff - 5
Sikeston - 5

- Posted using BlogPress from my iPad

Wednesday, November 18, 2015

Understanding the "Freak-Out-Meter"

Since my beginning of professionally forecasting weather, I’ve noticed how much people “freak out” over a simple four letter word that starts with the letter “s” - snow.  I’ve tried to find other ways to describe the word to try to keep people calm to no avail.

Every time snow would be in the forecast there would be mass runs on bread, milk and eggs at grocery stores.  Everyone knows it happens.  There are always jokes about the local weatherman having side deals with grocery store to bring in more business.  While it would be nice to make an extra buck, I’ve never had any such deal.

In my opinion, no one should freak out over storms, but I know people will.  So, in 2007 I had enough of seeing it happen.  I wanted to come up with a way to convey how big of a deal the storm would be and suggest how much they “freak out”.  I also wanted to have fun with it because for many - myself included - winter storms are “fun”.  That is when I came up with the idea of the “Freak-Out-Meter”.

The “Freak-Out-Meter” is a number given to a location in regards to how big of deal a storm is going to be.  The scale runs from 0 to 10.  0 being the lowest (non-existent).  10 being the biggest of all big storms.

The “Freak-Out-Meter” is not a number indicating how much snow, ice or rain is going to fall.  It actually has nothing to do with the amount of anything.  It is more about how much the storm will impact the locale.

Normally, the further out a weather event will happen, the lower the number because there is still much variance in what will ultimately happen.  As we get closer to the event, the number gets more tuned - sometimes going higher, sometimes going lower.

This year I have decided to make a few additions to the “Freak-Out-Meter”.  Along with the assigned number, which is the most important part of the meter, I’ve added some descriptions.  The descriptions are meant tongue-in-cheek to have some fun with the storm.
Click image to see larger version.
Let me know what you think in the comment section of the blog.  I enjoy hearing feedback about the “Freak-Out-Meter”.

Saturday, October 31, 2015

Amazing data from the Europeans

The European Center for Medium Range Weather Forecast's computer models are world-renowned for their forecasting ability.  You likely hear it mentioned in current-day weather forecasts from meteorologists.  It gained a lot of attention during the days leading up to "Super Storm" Sandy.  Personally, I've been using the European computer model (ECMWF) since I first started to learn to forecast in 1997.  Since that time, it is the model I most lean on when putting together my forecasts.

It is pretty amazing the resources the European forecast office puts towards the computer model.  It is miles and miles ahead of what the United States puts towards its global forecast model, the GFS.
  • There are 21 member states and 13 co-operating states involved in the project.
  • The office has an annual budget of approximately $88-million.
  • Their system collects 40-million observations a day by more than 50 instruments.
  • Their medium-range computer model runs twice a day (morning and evening).
    • For the medium-range computer model, over 3-million points of data are ingested in to the computer model before it begins running calculations.
    • The supercomputers used operate with a sustained speed of 200 trillion floating point operations per second.
Here's a closer look at the data ingested in to just one computer model run.  Specifically, this is from the 0z June 3 run.
  • 69,627 surface observations
  • 9,296 buoy observations
  • 136,603 aircraft observations
  • 234,543 Infrared atmospheric motion vectors
  • 259,629 Water Vapor atmospheric motion vectors
  • 110,560 Visible atmospheric motion vectors
  • 1,314 Polar Infrared atmospheric motion vectors - Northern Hemisphere
  • 3,205 Polar Infrared atmospheric motion vectors - Southern Hemisphere
  • 348 Polar Water Vapor atmospheric motion vectors - Northern Hemisphere
  • 7,791 Polar Water Vapor atmospheric motion vectors - Southern Hemisphere
  • 638 balloon soundings
  • 3,340 Pilot-profiler soundings
  • 37,517 Microwave imager points
  • 700,651 AMSU-A Satellite soundings
  • 309,580 AMSU-B MHS Satellite soundings
  • 534,853 HIRS Satellite soundings
  • 511,896 SCAT Scatterometer points
  • 64,450 IASI Temp/Humidity profiles
  • 29,164 OZONE points
  • 424,882 GRAD Clear Sky Radiance points
  • 71,307 AIRS Atmospheric IR Sounding points
  • 80,789 GPSRO Precipitable water soundings
  • 57,023 Ground-based precipitable water soundings
TOTAL = 3,658,997 pieces of data

Thursday, October 29, 2015

Early look at what could come in November

I had some time to look over some loooooong range computer model data and make a few observations of what could come between October 28 - November 26 to central Indiana and the Midwest.

One thing to remember, you should take all of the thoughts with a MAJOR grain of salt. This is only one computer model's view over a long period of time and not reality. You should not get too hung up on details. Things can and likely will change.
  • We appear to be moving in to a pattern of upper-level storms coming off the Pacific Ocean and setting up show in the southwest United States before eventually moving east
    • Data suggests 5 of these upper-level storms affecting the Midwest November 2, 8, 10, 19 and 22.
  • Temperatures in the Midwest turn warmer November 3-7.
  • We have a period of above normal temperatures in the Central United States November 12-18.
    • Indiana could see above normal temperatures November 14-21.
  • Colder air arrives in Great Lakes (including Indiana) November 23-24.
  • Above normal temperatures in Indiana November 25-26.

Keep in mind, the model is just that. A computer model. The farther out the model looks, the higher the possible error rate. The key to look at this kind of data is not to look at specifics but instead trends and long wave patterns.

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