VORTEX 2: Day 11

Posted by pmarsh on 20 May 2009 | 1 comment

Same song, different verse…

After spending the last two nights in Ogallala, Nebraska (west of North Platte on I80), the armada targeted an extremely marginal setup today in the northwest Nebraska panhandle.  This region of the country has an extremely poor road network for conducting tornado research (which is why it is not included in the “official” VORTEX II domain), not to mention that the Nebraska Sand Hills are located in this region as well leaving poor visibility.  Nothing exciting happened meteorologically to the armada today, however they did at least witness several thunderstorms.  The next few days look to be even worse than today.

I wanted to write a few words tonight on just how bad of a weather pattern we are experiencing.  The last severe thunderstorm or tornado watch was issued on 16 May 2009 for New England (it was a Severe Thunderstorm watch).  There has not been a reported tornado in the VORTEX II domain since 15 May 2009, and that was in the Texas panhandle.  It is absolutely unheard of for the Storm Prediction Center to go four days (and it appears it will be even longer) without issuing a watch during May.  This is peak severe thunderstorm / tornado season after all.

The meteorological reasoning for this amazing streak of little to no severe thunderstorm activity is the result of two rare events and one highly unusual event occurring simultaneously.  First, last Friday and Saturday a strong cold front pushed south through the US Plains and into the Gulf of Mexico.  This cold front pushed all the deep atmospheric moisture very far south into the Gulf of Mexico.  While this is certainly not a common occurrence, it is by no means rare or highly unusual.  What happened next, however, is rare.  A tropical low pressure system (known as a TUT, or Tropical Upper-Troposphere, low) moved west across Florida and strengthened as it interacted with the remnant cold front located across the Gulf of Mexico.  This strengthening system resulted in strong northerly winds across most of the Gulf of Mexico that pushed the remaining moisture south, out of the Gulf of Mexico.  This strong low pressure (which is not a hurricane or tropical storm) located over Florida and the lack of moisture across the entire central United States are both extremely rare events for May.  Furthermore, a strong mid-tropospheric high pressure developed in the middle of the US Plains.  This strong high pressure results in calm winds and warm temperatures aloft and sinking air near the surface.  All three of these things are big negatives for severe thunderstorm development.  Couple this with the absolute lack of moisture means that severe thunderstorms will be nearly impossible.

This atmospheric pattern does not appear to change anytime soon.  Numerical forecast models keep most of the stronger mid-troposhperic winds in the far northwestern US and into Canada for as long as they can forecast.  Additonally, most models keep the tropical-like low over the Gulf of Mexico for the next few days…meaning moisture in the northern US will be hard to come by.  It might take until the end of the first week of June to break out of this pattern…if we ever break out of it.  All of this spells big trouble for VORTEX II research.  A lot of tough decisions will have to be made in the coming days about what to do if this pattern continues any longer…