Chase forecast update 5, for April 21
As we move into the last weeks of April, classic spring tornado season in the Plains and Midwest is still nowhere in sight. The active upper jet pattern has continued to hold too far south to allow sufficient northward moisture return from the Gulf of Mexico. That has kept storm tracks so far confined to the South, bringing a few multi-day severe weather events across "Dixie Alley", but nothing chase-trip-worthy north of I-40. Medium-to-long range models show this pattern or worse continuing for the next 2 weeks, with no sign of plentiful moisture (above 65°F) migrating north into chaseable regions.
This period will not be completely storm-less. The active jet will eke out a few at least marginal severe events here and there across traditional chase alley if some moisture pooling shown in model forecasts can work out. Those are, however, "everything-has-to-come-together-perfectly" days with high chances of failure that likely won't get me on the road westbound for an expedition.
The only mirages of hope showing on any data source were a few recent ultra-long-range CFS chiclet charts that indicated an uptick in severe weather toward late May. But that's not anything to get excited (or worried) about. Even though the CFS has done reasonably well this season so far, a reliable forecast that far out by any model is simply not possible. No model or forecaster has any track record of skill at those ranges, and any spike in activity shown for late May has more to do with climatological bias than anything substantiative.
To summarize, right now the chances of an April Great Plains chase trip look very low. As with all slow early seasons, there is nothing to do but wait and see what May will bring.
The following table charts the probabilities for a Plains chase expedition taking place for the date ranges shown:
|2019 Plains Chase Expeditions - Probabilities as of April 21|