Ceaseless Wind

Back in September, the official rainfall for Springfield was close to a foot which ranked tied for third on the all-time wettest September list.

October has reversed this pattern, it looks like the month will finish on Halloween night with just over one inch of rain.

The last weekend of the month looks dry and warm and the pattern for the first few days of November is looking dry as well.

A freeze warning is in effect for all of the Ozarks tonight as temperatures plummet into the twenties in some places.

High pressure will settle in Friday morning.  The timing is such that the center of the high will be right over the Ozarks during the coldest portion of the night.

Temperatures will be cold enough to pronounce this a killing freeze for sensitive plants.

The cold air is flowing in as a response to air circulating around the intense low earlier in the week.  Radiational cooling near the ground will finish the temperature fall tonight.

Once this high moves off, the timing of much warmer air appears to be fantastic for the upcoming weekend.  High temperatures on both Saturday and Sunday will be either in or close to seventy degrees!

Temperature Plot. Large differences Friday AM!

It looks like Friday morning will be the coldest of the season so far but how cold and will it be the killing freeze of the season?

This is a radiational cooling freeze meaning the air will be much colder at the ground than it is aloft. Radiational cooling takes place every night as heat radiation escapes from the earth and the air on contact with this colder ground in turn cools off.  Radiation cooling works best under clear and calm conditions.  This describes a high pressure system to a tee and that is exactly what will park itself over the Ozarks Friday morning.

There are differences between the various computer models as to how cold to make the low Friday morning. One has our readings at or just above freezing while another sends our temperatures down into the middle twenties!

With plenty of dry air in place, I’ll split the difference and went with a low in Springfield around thirty.  There easily could be lows in the twenties in the area Friday morning.

Tornadic supercell with a hook echo passes over the northern Richmond, VA area. Tornado report at Mechanicsville, VA.

Very Deep Low 10/26/10 18z

Not since the Superstorm of 1993 has a low pressure system over the United States achieved such a low central barometric pressure!

From the National Weather Service:

“New record set today for the lowest pressure in a non-tropical storm in the mainland U.S. The massive storm system barreling across the central U.S. had a minimum central pressure of 28.24″ or 956 mb (equivalent to the minimum pressure of a Category 3 hurricane). This breaks the old record of 28.28″ (958 mb), set on …Jan. 26, 1978, during the Blizzard of 1978 (aka the Cleveland Superbomb). This is also lower than the March 1993 Superstorm (aka “The Storm of the Century”), or the “Witch of November” storm that sank the Edmund Fitzgerald in 1975, or even the Columbus Day Storm of Oct. 1962.”

Editors note: it looks like 28.21″ is the official lowest pressure of this storm.

Development of "bomb" low! Thanks NSSL!

Such intense lows at the surface of the earth are brought about in this case by a powerful jet stream wind pattern.  For lows at the surface of the earth to deepen, air must be evacuated out of the top of the low faster than it can be replaced from below.  When this is true, air molecules are removed from the column of air leading to less air pressure as measured by a barometer.  This is called hydrostatic pressure or the total weight of the air on the barometer.

Strong jet stream winds high in the atmosphere can set up a path for air to take away from the deepening low leading to a drop in pressure.

Wind at the Jet Stream Level (300mb) 12z 10/26/10

Wind and pressure are intimately related.  The deeper the low, the larger the difference in pressure or pressure gradient observed.  The stronger the pressure gradient, the faster the wind will blow.

This storm had widespread 40-50 mph wind gusts connected to it over areas of Iowa, Illinois, Minnesota and Wisconsin eariler today.  Some of the gusts near shower and thunderstorm bands reached 60-70+ mph.

Also, the storm system has spawed many tornadoes in parts of Illinois (EF2 near Peotone), Indiana and Kentucky.  At  this writing, many tornado warnings were in effect for counties in Tennesee, Kentucky and Alabama.

Link to a great write-up by the Duluth National Weather Service.

Me and the Rapid Scan DOW Radar

The Severe Local Storms (SLS) Conference is held once every two years.  It’s sponsored by the American Meteorological Society (AMS) and its purpose is to bring together scientists, researchers, forecasters and anyone else involved in severe local storms. 

This meeting, held in Denver this time around, comes on the heels of a huge tornado research project.  Vortex 2 was a multimillion dollar data collection extravaganza covering two storm seasons (2009/2010) and involving hundreds of people. 

I traveled here in hopes of learning some preliminary findings from Vortex 2 and also to get a sense for how the project went and whether the goal of a better understanding of tornadoes was realized, at least at this early stage.   There are other topics of research going on as well and I wanted to learn more about these too.

The conference is made up of of sessions in which presenters are given 12 minutes to talk about their subject using Power Point and sometimes video. There are also poster sessions where the information is printed and hung up along with all the other posters.  Attendees can then just walk up to the poster that interests them and at certain times have access to the author(s) of the poster to ask questions.  Finally, there are invited speakers and special sessions to round out the conference.

As is typical when I attend these conferences, there are papers presented which are FAR beyond my understanding.  But what does make it through helps me to understand severe storms just a bit more. It’s also just fascinating!  Researchers are doing some really exciting things in the areas of remote sensing and instrumentation, computer modeling and forecasting techniques.

I’ll blog in more detail here over the next few days as I collect my thoughts and notes and as time permits.