Saturday, July 19, 2014

'Death Ridge' to Make First Appearance This Summer

The infamous ridge of high pressure which frequently forms over the Plains in the summer months, nicknamed the 'Death Ridge', will be taking up position this week for the first time this season.

The above image shows forecasted 500mb height contours, wind barbs, and wind speeds in the shaded colors. The forecast image comes from the ECMWF model, and is valid on Wednesday evening. Here, we see a body of strong high pressure originating in the Four Corners region, at a strength of about 597dm, as the contour shows. We see the ridge extending well into Canada, setting up sustained northwest flow over the Midwest and Great Lakes in the process.

Model guidance agrees that we will see multiple disturbances traversing the northern fringes of this ridge, swinging up into Canada and eventually down into the Great Lakes, towards the Ohio Valley. As the systems swing down into the Great Lakes, I expect we will see opportunities for severe weather. These opportunities could be plentiful, depending on the number of disturbances expected to rotate along the perimeter of this large high pressure system.

The GFS model's forecast of the Lifted Index, shown above, also valid on Wednesday evening, gives a good idea of where we might expect some active weather to form. The Lifted Index gives forecasters the ability to see how unstable the air is. Negative LI values indicate increasingly unstable air, and values below roughly -6 can indicate the potential for some substantially active weather. In this forecast image, we see LI values in portions of Ohio and Indiana exceeding -12, highlighting the presence of extremely unstable air. Considering this is a low-resolution model, it could very well be exaggerating how unstable the air will be. Nevertheless, this is a testament to what we may see next week, when some parts of the Central US may be affected by severe weather.

Lastly, we see the GFS forecast for temperatures just a few thousand feet off the ground on Thursday evening. This image gives one example of the areas expected to be hit the hardest by this hot weather, with portions of the Rocky Mountains into the Plains on the receiving end of the worst weather. If you live in the aforementioned regions, prepare for this hot weather by stocking up on water for you and your pets, as well as limiting outdoor activity and making sure your air conditioning unit is up to par.