A very warm and moist air mass resided across southern Manitoba Thursday afternoon, with dewpoint temperatures reaching 25 C. A cold front, in association with an intense upper trough, was forecast to sweep northeastward from North Dakota into southern Manitoba Thursday evening. Ahead of the cold front, severe thunderstorms – with a primary threat of large hail – were a high probability.

I observed a large, isolated thunderstorm developing just north of the International Border around 7:00 PM, moving northeast at 30 km per hour into southern Manitoba. I opted to intercept this storm as it approached highway 75 near Morris, MB.

As I intercepted the storm, it was apparent that it was evolving from an isolated cell into a linear MCS, with intense electrical activity, wind gusts measured to 85 km/h and quarter sized hail.

In summary, this storm was well worth the short trip south of Winnipeg to witness the amazing “anvil crawlers” that lit up the sky in almost every direction. I found a nice vantage point just north of the precipitation to take some memorable pictures of this event that persisted until well after 11:00 PM. Opportunities like this are a rare treat in September.

At first glance, it looked as though Friday would have good potential for severe weather, and possibly a few tornadoes in North Dakota, with plenty of instability in place (3000+ j/kg) and good low level shear. Gulf moisture had been advecting across the central and northern Plains since early morning, aided later in the day by the development of a respectably strong low-level jet (LLJ).

I proceeded to the south part of the state, where temperatures had reached 83 F by just after noon, with dewpoints into the high sixties and low seventies. Everything looked primed for some explosive convection, especially with a 500 mb short wave trough rounding the crest of the ridge over the central CONUS. I was parked in Fargo, ND for most of the afternoon, waiting for things to pop in that blanket of low level moisture.

By around five in the afternoon, nothing was happening over Fargo, or any other part of southern North Dakota. The GR Level3 software was showing a large squall with possible embedded supercells progressing ESE just north of Grand Forks, so I opted to head north on I29 to intercept the band of thunderstorms, which was showing several tornado warned cells and TVS (tornado vortex signature) markers.

When I arrived on the outskirts of Grand Forks around six, the tornado sirens were wailing in the city. The edge of the squall did look impressive, with a prominent shelf cloud, powerful gust front and drenching rainfall. But no tornadoes were in sight, especially in the low level grunge and scud that rolled and boiled beneath the shelf cloud.

I suspect that the tornadoes sighted within the squall line were more than likely gustnadoes, or perhaps a bookend vortex or two in the mix.

All in all, an exciting and fun chase today, but the prize of a high-contrast tornado photo remained elusive.

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.

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