Monday, 11:40 a.m.
We are but 12 days from the summer solstice, and yet there is still a lot of cool air on the playing field. Temperatures slipped to the 40s from Montana into the Dakotas and western Nebraska, as well as in parts of Idaho, Wyoming, Colorado and Utah, with a few 30s sprinkled in for good measure. The cool air was pulled into the northern Rockies behind a rather small but rather vigorous storm rolling across Kansas. It's also pretty windy in the back of the storm, with gusts pushing 40 miles an hour in places like Goodland and Dodge City, Kansas.
This cool air mass will have no trouble spreading across the Plains toward the Mississippi Valley, but as it tries to come farther east, it will moderate, and none of the cool air ever reaches east of the Appalachians later this week. Instead, the cool air simply 'reloads' for another blast late this week into the weekend, targeting the Plains yet again.
Whereas the surface high associated with the early week cool air mass has already split into two pieces, with one staying back over the Rockies, while the other moves across the northern Great Lakes, the one late this week into the coming weekend will stay together much better. As such, we should expect it to yield a broader cooling with more effective cooling. Indeed, the 0z June 9 GFS ensemble 2-meter temperature anomaly forecasts for Friday show this broadly cool air mass firmly in place from the Plains to the Midwest:
Ahead of these cool air masses, it will be relatively warm and humid in the East. Not oppressively so, mind you, but warm enough to feel pretty uncomfortable. The presence of relatively high heights off the East Coast will promote a southwesterly flow aloft that will keep the region from ever seeing the cooler, drier air from the west until this weekend. And even then, it will only be in modified fashion.
One weak upper-level feature is slipping through the mid-Atlantic into New England states today, generating a lot of clouds along with showers and a few thunderstorms, but for the most part, the rain is not too heavy. With whatever sun develops across the mid-Atlantic, there will be a couple of instability showers and slow-moving thunderstorms.
Unfortunately, that sets the table for an unsettled week. The upper-level and surface storm in Kansas now will move eastward this afternoon and tonight, reaching the middle Mississippi Valley by tomorrow evening. The south to southwest winds ahead of it will pull warm and increasingly moist air from the Gulf of Mexico up across the Tennessee Valley into the Ohio Valley, and that moisture won't be kept out of the East. The question will be how warm it will get on any given day, and that may be dictated by the amount of sunshine any given location gets. Some of the computer-generated numbers suggest it could surpass 90 in the mid-Atlantic Wednesday and get awfully close Thursday and Friday. Certainly these days will feel like summer with temperatures a few degree above average, but there's likely to be too much cloudiness around, and a nearly constant threat of a shower and thunderstorm, especially during the afternoon.
After this week, the signs are pointing to much less cool air in the pattern across the country as we reach the final days of spring.
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