Thursday, July 19, 2012

Storm Prediction Center Highlights VERY Long Range Severe Risk

The Storm Prediction Center has issued the rare Day 7 outlook and the practically nonexistent Day 8 severe weather outlook for the Upper Midwest into the western Great Lakes. Let's take a look at a day-by-day forecast.

DAY 7 (July 25, 2012)

The latest 0z GFS and 0z ECMWF model runs for 7:00 PM on July 25 are in unusually good agreement, as seen in these below pictures of 500mb heights.

ECMWF Hour 168

GFS Hour 168
Notice the unusually strong similarities in low pressure placement on the US/Canada border near Minnesota. It does look like this, and a cold front, will bring a severe weather risk into the region. Let's look deeper into the 0z GFS and see what it's telling in terms of shearing and instability to identify if there even is a threat.

Instability for the evening of July 25

Shearing values for July 25

There is a lot of instability available over the Upper Midwest and Midwest, which could easily provide a lot of action for both regions. However, in order to get any storms going, and keep them going, we're going to need shearing. Surface to 500mb shearing shown in the second image highlight the atmosphere's willingness to provide such storm energy to the Upper Midwest, while not really supporting the Midwest itself. However, given the high instability and deeply negative Lifted Index values (not shown), I can see at least scattered pulse cells originating over the Midwest and Lower Great Lakes.

DAY 8 (July 26, 2012)

We already know that the GFS and ECMWF remain in very good agreement into Day 8, so let's go right into instability and shearing once again.

Instability for the evening of July 26

Shearing for the evening of July 26
I feel like this is where the ECMWF and GFS are beginning to veer off into their own states as the timeframe increases into more uncertainty. The GFS is showing major instability in the Lower Great Lakes and Midwest, but keeps the shearing into the Upper Midwest. Despite this, I do believe that, if this scenario were to verify, there would be enough shearing for the Lower Great Lakes to possibly get more organized convection, while the lower Midwest and Ohio Valley regions would most likely end up with more pop up storms due to lack of organized shearing.



Alice McDonald said...

Hi Andrew. We got rain this morning and a flash flood warning. And some really huge thunder that set off an alarm at work, then a sheriff showed up. We sent him away. He said he was responding to several in the area.
The drought post: It looks like fall in my back yard.
This post: wow.

Eddie said...

Does this mean rain or bad storms for detroit

Andrew said...

Alice: I got some strong thunder myself last night, but setting off an alarm? That must have been crazy!

Eddie: If this were to verify now, Detroit would be in for some strong storms.