Severe Prospects Heat Up for Late May
PSU Meteorology / Day 8-10 model forecast
With weather patterns projected to shuffle around over the next week or so, the potential is increasing for an uptick in severe thunderstorm activity for late May.
While portions of the eastern U.S. may enjoy warmer than average temperatures for much of this week, that early summer preview will not last. A fairly vigorous trough is likely to dig into the Great Lakes by Friday and Saturday. This will bring an abrupt end to the 80s and 90s that have been making it as far north as the Ohio Valley and portions of the Northeast. In fact, it looks like from this weekend into early next week, the eastern half of the U.S. will see below average temperatures.
Moving forward, it’s the relaxation of that trough that is a signal of another pattern re-alignment. Although it is pretty far out, there is good model agreement at this point that another ridge will develop across the Plains and ease eastward. This sets the stage for a potentially active periods of weather in the vicinity of the Plains with increased severe activity.
Early next week: The GFS and Euro similarly dig a trough into the Pacific Northwest with surface cyclogenesis east of the Rockies. While the target time-frame for severe may be Monday and Tuesday, the window for increased activity could begin as soon as Sunday.
For analog data, 1986 has been discussed and that shows up as the #1 day 6-10 analog from CPC today and also ranks near the top for day 8-14 analogs. The period in mid-May 1986 was active in terms of severe weather and tornadoes across the Plains. Another date that gets my attention is May 5th, 2007. That ranks as another top analog by CPC and the early May 2007 tornado outbreak was significant.
The evolution of this pattern is going to ultimately dictate how much severe weather is realized. I envision the following scenario as being possible right now: A lower-end severe episode evolves sometime between Sunday the 18th and Wednesday the 21st. Then, a potentially more significant severe outbreak could follow that, perhaps by that next weekend. That first event could set the stage by advecting moisture/higher dew-points further north. It hasn’t happened yet this season, but if the setup is far enough north, it could even turn into an Upper Plains outbreak.
Of course, things could play out many different ways being this far out. With a trough digging into the West, while that sounds good at first thought, there are other variables to consider. An ongoing drought across portions of the Plains and desert Southwest has been limiting moisture advection with northward extent so far this season. This has been one factor in the overall limited number of severe events. As such a projected trough advances east, will vigorous shortwaves swing around the base, or will the pattern become more messy or even zonal?
In summary, while it is far too soon to get into specifics with respect to possible outbreaks, it does look like late May certainly has potential. Data and trends in the coming days will be closely monitored to see how the forecast evolves.
