Throughout the first half of May, the positioning of upper-level flow and lack of good surface moisture return into the Plains states has hampered the development of photogenic storms. Yesterday, the swift passage of a trough and associated cold front resulted in a significant severe weather outbreak from central Oklahoma to the Great Lakes states. Most of these storms went linear shortly after initiation, and there were reports of tornadoes in OK and near Kirksville, MO. These tornadoes rapidly became rain-wrapped, and dangerous to chase. Strong forcing and MLCAPE values of near 4000j/kg resulted in mostly linear storm complexes with a few embedded supercells, with widespread reports of straight-line wind events and very large hail.

For this reason, we opted not to chase yesterday’s event, as the probability of intercepting any photogenic storms was too low to warrant travel distance and the risk of equipment damage.

GFS model guidance suggests that adequate moisture returns from the GOM and upper flow characteristic of sustained severe weather events likely won’t return to the Plains states until the final week of May.

Current Status: Standby

May, a month that normally sees ample active weather across the Great Plains, may go down in history for 2009 as one of the poorest on record for supercell storms and tornadoes, which is extremely bad news for the Vortex II research project that began field operations on May 10. No storms equals no data, and wasted time for scientists trying to unlock the enigma of tornadogenesis.

Currently, GFS model forecasts portray a persistent blocking pattern over the central CONUS, and a resulting north west flow regime that will keep most of the moisture from the GOM locked up at least until the end of the month.

The annual northern migration of the polar jet means that any severe weather outbreaks to occur in June will be more likely to occur in the central or high plains areas, assuming that moisture-rich GOM air is able to once again advect northward during the period.