Tuesday, 11:59 A.M.
We're about two weeks away from the typical peek of the summer heat, a point where the average temperature is as high as it gets for the entire year in the northern hemisphere. The temperature rise between now and then is basically a degree to at most two for most places across the country. Yet here we are staring in the face of another cool air mass invading the northern Rockies and northern Plains, one that will set temperatures will below that normal mid summer heat. A large high pressure area is already settling in across the eastern Rockies and high plains. Since it was just moving into these locations this morning, the early morning minimums were not particularly noteworthy. Look, however, at tomorrow's projected temperature anomalies:
In the heart of that air mass across the Midwest into the Great Lakes, temperatures are being projected to reach 10 to 15 below normal! As cool and comfortable as it was late last week in the northern Plains and Midwest, and over the weekend in parts of the mid-Atlantic and Northeast, this air mass looks to be every bit as cool, if not a touch cooler when all is said and done.
The cooling will persist in the Ohio Valley through Thursday and into Friday morning before the atmosphere begins to rebound later Friday. The recovery will take place over the weekend farther east. The strongest rebound will be over the eastern Rockies and central and southern Plains, with temperatures likely to reach into the 90s in many places, with a few spots getting to 100. Look at the 0z July 8 GFS model projected maximum 2-meter temperatures for Saturday afternoon:
Some of this heat and humidity will have little trouble reaching the Ohio Valley and the mid-Atlantic states - if not Saturday, then almost certainly Sunday into Monday. But then another cold front will blast on through. And to get a better feel for that, I take you to the western Pacific of all places, where Typhoon Neoguri is about to make a turn to the northeast and head for the southwestern tip of Japan. Here's that forecast graphic:
Now why do I show you this? Well, the fact the Typhoon is about to recurve is a strong indicator of the impact it will have downstream in time. We refer to it in house as the 'typhoon rule', though its something pretty widely known in the meteorological industry. Almost like clockwork, once a typhoon recurves in the western Pacific, you will find a downstream upper level trough of low pressure will form somewhere over the eastern third of the country some 6 to 10 days down the road. If Neoguri turns northeastward tonight and tomorrow, that would suggest that by next Monday and Tuesday, there's very high likelihood of an upper level trough coming into the East.
Where specifically will that trough become established? That largely depends upon how far west the recurvature point is. The farther east it happens, the farther east this trough will show up. BY the same token, if the typhoon gets more to the west, then expect the downstream trough to end up west of the Appalachians. It's just that simple!
All of that is a elaborate way of saying that after the weekend warm up, another strong upper level trough is likely to rotate through the Plains and across the Ohio Valley. The GFS and Canadian models are pretty much in agreement with the timing, bringing a strong trough quickly through the flow and driving a cold front to the East Coast on Monday. Here's the GFS anomalies for Tuesday behind it:
You can make the case for this air mass being broader and cooler than the one currently invading the plains. Regardless of the exact timing and exact strength of the cooler air mass, it is coming, and it will continue the pattern of strong cold fronts blasting across the country, even into the heart of summer.
Warmth will expand from the Gulf Coast into the Ohio Valley and mid-Atlantic states by Memorial Day, but the wet and stormy weather will persist in the Plains, and expand across the Mississippi Valley.
Chilly, wet weather will morph into a warm, humid pattern later this weekend into next week, one that will remain unsettled, especially in the Plains and Mississippi Valley.
Severe thunderstorms will erupt over West Texas late tonight and tonight, but they'll become more widespread over a larger percentage of the Plains states later tomorrow and Saturday.
After a brief cool spell, much of the country from the Plains on east will turn warmer Friday through Sunday, but there will also be more clouds, showers and thunderstorms around as well.