Monday, 11:58 a.m.
It would seem that is going to be the case this week once again - unsettled weather will rule, and that seems to just be our normal for the late spring and early summer. And when I use the term unsettled, I mean having a good opportunity for a shower and thunderstorm on any given day. In this case, there will be multiple days with this 'unsettled' or wet weather. And not just in a relatively small area, but over a large one.
Take Chicago, for instance. While there was no rain there yesterday, the previous four days had been wet, and it has already rained today. It is likely to rain at least a little tomorrow and could well be wet again Wednesday. They have a chance for a shower and thunderstorm the rest of the week and into the weekend, as a matter of fact.
Or how about Minneapolis? Already this month they've picked up 10.85 inches of rain. While they may not be as 'unsettled' this week as their neighbors to the southeast, it will rain at least a couple of days and probably more between now and Sunday. And this is common from the eastern Dakotas and central Plains all the way to the East. Many places have been wetter than normal for the first three weeks of the month, and there some locations in the Midwest with two, three, even four times average rainfall.
Why has it been so wet, and why is that likely to continue? For the most part, the jet stream just hasn't configured itself in such a way as to promote large-scale heat and sunshine with dry, warm air aloft. Instead, the jet stream have been relatively flat, thereby limiting how much warmth can get to the northern tier of states. Look, for example, and the 12z June 23 NAM 500mb forecast for Wednesday evening:
No strong ridge there, not even a strong trough. Much like we saw over the weekend, there will be a fairly strong surface high pressure area (by late June standards, anyway) passing north of the Great Lakes Wednesday evening and Thursday, one that will push dry air into the Midwest and Great Lakes and eventually parts of the Northeast. However, the dry air can only go so far south before stalling, as that same jet stream orientation just won't allow it to get any farther south.
So, as any little disturbance comes rolling along, it will help to focus a more concentrated area of showers and thunderstorms, even areas with steadier, heavier rains. One such disturbance will cross the Great Lakes this afternoon and evening, while another comes out of the southern Plains and crosses the lower Mississippi Valley. Still another will be entering the northern Plains. Each of these features will be sufficient to trigger more unsettled weather. Undoubtedly more will follow later in the week and into the start of the weekend.
And it's not like the eastern half of the rain is the only place getting the wet weather, too. While not as prolific, there will be a couple of different features bringing some showers and even a few thunderstorms across the Northwest, and the next couple of afternoons will be active in the Rockies as well. This will persist in the northern Rockies right into Thursday, and there could easily be some showers and thunderstorms on Friday from Montana to the northern Plains.
How does this look in terms of total precipitation? Look again at the NAM model, with its 84-hour total precipitation through Thursday evening:
Some of this will, of course, be biased toward the afternoon and evening hours thanks to daytime heating, but the bottom line is that many areas will have to endue this wet, unsettled weather pattern this week into the coming weekend before there's any potential change in the pattern.
A snow storm affecting the central Plains and Midwest into the Great Lakes this afternoon into tomorrow night will be followed by the first of two arctic outbreaks around the country before Thanksgiving.
Winter is six weeks away, and there will be a couple of signs this week of the approaching season as a storm develops on the western Plains and heads through the Great Lakes.
A warm pattern is setting up for much of the nation next week.
Tropical moisture associated with the one-time Hurricane Patricia will bring heavy rains to many areas east of the Mississippi Valley between now and Wednesday night.
Patricia, the strongest hurricane on record in the eastern Pacific, will make landfall this evening in Mexico. It will spread torrential rains into East Texas, and impact the weather all the way to the Northeast next week.