STATUS: Down

Today gives a nice illustration of the difficulty we face in VORTEX-SE in designating our IOPs (Intensive Observing Periods).

There will likely be an event tonight that includes the passage of storms with rotating updrafts.  The probabilities are much higher in the northwest part of AL where low-level moisture is much more likely to return in sufficient quantities.  Further east, storm outflow should become progressively colder owing to drier low-level air (and more evaporation), and the storm rotation will have decreasing probability of being associated with tornadoes.

But, in VORTEX-SE the size of the grants doesn’t really allow a lot of the scientists to be positioned in northern Alabama for a full two months.  Instead, they must travel on short notice, collect observations, and then return to their home bases.  Because of the time involved in arranging and conducting the travel, we must decide four days (three days makes things uncomfortably tight) before an event that we will conduct an IOP.  This time, there wasn’t a clear enough signal of tornado potential four days in advance for us to pull the trigger.  We only have funds for about four IOPs, so we look a lot at probabilities of certain atmospheric conditions being met, including CAPE (for updraft thermal energy) and shear (for updraft rotation and tornado potential).  This time, the probabilities were much too low to make it reasonable to use one out of our four IOPs.

You might think it’s impossible to make four-day tornado forecasts… you would be mostly right.  But we are not really forecasting tornadoes, but rather the large-scale change in conditions, often associated with a passing atmospheric wave, that would lead to thunderstorms with tornado potential.  That’s a much easier forecast problem… most of these waves are fairly well depicted in our numerical models out to about 6-7 days.

Nevertheless, VORTEX-SE supports certain “always-on” observations.  In the meteorology realm, these include a nice array of instruments, fixed and mobile, operated by the University of Alabama-Huntsville, the CLAMPS atmospheric profiler from NSSL, and the Stesonet array of surface stations that Texas Tech deployed last week across northern Alabama.  Certain other research programs in VORTEX-SE, involving damage and debris studies, treefall analysis, and analysis of forecasts and human response, are also rather independent of our IOPs and ready to go into action if a tornado does occur outside of an IOP (time or region).

Looking down the road… no big change from yesterday’s blog post.  The overall weather pattern should be cool and dry for a while, and we are casting a wary eye toward the Pacific and a possible jet stream approaching North America in about a week.