The main weather system on the US maps these days is probably the Lower Mississippi Valley to Southeast ridge because it’s this that’s helping start the Southwest monsoon season and it’s this that’s also contributing to the severe thunderstorms firing on the Northern Plains into the Lower Midwest today.

The position of the ridge is important as it’s far enough west for tropical moisture to get lifted into the Desert Southwest from Mexico and it’s far enough south and west for a series of fronts to push in through the Great Lakes, Northeast and Mid-Atlantic. That’s if you like a fairly changeable, often wet, thundery and cool pattern.

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Here’s the GFS 500mb charts which show the ‘ring of fire’ like action around this hot dome supporting upper 80s and 90s from Texas to Georgia.

This graphic by AccuWeather sums up the national picture quite nicely for the upcoming weekend.

Behind each front which pushes through the Northeast, humidity lowers, making for pleasant days and comfortable nights by July standards.

With that position of ridge, it also leaves an open door for a trough to drop into the Pacific Northwest this weekend and into next week, the GFS shifts the ridge core west more into Texas while the closed low expected to push into Washington state slides eastwards over the N Rockies.

It’s the interaction between the southern ridge and PNW trough that helps draw on Mexican moisture.

As you can see, that PNW system acts like a bowling ball as it moves east becoming a rather potent feature and forces a brief surge of heat up into the Mid-Atlantic and Northeast.

That system is followed by another which pushes into the West Coast and according to the GFS, it carves out an even deeper trough which sends cooler air along with showers and storms deep into California and the Desert Southwest late next week into the weekend.

These systems are acting like ripples in the atmosphere just like you’d find on the surface of a lake. These ripples supress ridge building and therefore truly hot weather is short lived and where wet, greatly supressed. You only have to look at the high dew points over the saturated ground across Iowa, Illinois into Missouri.

Note the model has some 80-degree dew points towards by Sunday.

The widespread mid to upper 70-degree dew points is holding air temperature down by day but holding it up by night. The low in Kansas City and St Louis is struggling to get out of the low 80s because of the amount of moisture holding the heat in the air overnight.

Looks like the GFS has widespread 100s over the central Plains with even an area of 110-115 showing up Saturday over Kansas.

Because of less rain in the pattern and very high evaporation rates, the heat is allowed to build some at the surface now, particularly north of Texas and Oklahoma.

See video for the disc.

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