Northern Plains - Midwest: Pattern Shift Could Open the Door to Repeated Severe Weather Mid-June

It's been an active week of routinely photogenic and damaging storms across the Southern High Plains. A building ridge of high pressure over the Central U.S. will quiet the pattern some early this week, while allowing an eventual pattern shift that looks increasingly likely to roll over into an active stretch of severe storms from portions of the Northern Plains into the Midwest and Great Lakes.

Metropolitan areas that are familiar with active, stormy periods in mid-June like Rapid City SD, Sioux Falls SD, Omaha NE, Minneapolis MN, Chicago IL, Des Moines IA, and Indianapolis IN may be included in this upcoming run that will likely span ~ June 15-20, with a potential continuance into late June.

Without getting into daily specifics, this is a rather classic summertime pattern that often fosters localized areas of severe thunderstorm activity daily, with the potential for upscale growth into damaging thunderstorm clusters or MCSs. One or more significant severe weather outbreaks is possible should a well organized storm system or two eject from the Plains into the Great Lakes.

Severe storms may be possible across Montana/Wyoming/Dakotas as early as June 11-14, but a cut-off low traveling from the Southern Plains to the Ohio Valley will temper northward transport of deep Gulf moisture until the weekend of June 14-15 and beyond.

After the Southern U.S. cut-off low evacuates the area, high pressure in its wake will allow the Gulf to open up with a long fetch of deep moisture being transported into the Northern Plains and Great Lakes June 15 and beyond.

The resulting pattern will see deep moisture and seasonally appropriate heat

build across the Central U.S. as a series of storm systems begins to eject from the Pacific Ocean across the Northwest U.S. into the Northern Plains. As these jet stream disturbances traverse the Northern Plains and Great Lakes interacting with a strongly unstable air mass, corridors of intense thunderstorm activity are likely to emerge.

The potential ceiling during this period revolves around getting a more organized storm system to eject into this highly unstable environment. The ECMWF deterministic and ensembles have begun hinting at this potential outcome around the June 18-20 time frame... does a big storm eject into this volatile air mass? If so, watch out...

Daily chances for at least isolated severe thunderstorm activity appear likely across this zone during the June 15-20 time frame, but a few higher end severe weather days may be on the table. Which days? Where? Tornadoes? Derechos? Those are all questions to be sorted over the next week. Patterns like this are notoriously difficult to nail down in advance as the day to day details have major impacts as the pattern progresses. A big storm cluster and surging outflow boundary can scour moisture and instability and delete a big day from the rotation... or a day producing less storms than expected can leave a pristine environment for a big severe weather day the following day.

The bones of the pattern are emerging though - multiple model runs with good agreement on a highly unstable environment from the Northern Plains into the Great Lakes/Midwest with increasing confidence we'll see jet stream disturbances interacting with it producing routine storm clusters and severe weather chances.

Summer storm season is about to commence across the Northern Plains and Great Lakes!