Tuesday, 11:55 a.m.
On Monday's post, I focused primarily on the two shots of cool air targeting the middle of the country. One is quickly getting modified over the eastern Rockies and High Plains today, and it will be a shell of its former self tomorrow as what remains of it behind the lifting storm is modified even more. That storm, by the way, now sits over northern Arkansas and southern Missouri and will move northeastward this afternoon and tonight to end up in southwestern Michigan late tomorrow. The second cool shot will move into the northern Rockies and northern Plains tomorrow and rapidly expand south and east the rest of the week into the beginning of the weekend. It, too, will be modified rather easily over the weekend as it tries to cross the Appalachians into the East.
Today, I want to focus much more on the expansion of summery weather across the country. First, the heat. And there was plenty of that yesterday in California, as a number of places set records for the day. The nation's high temperature was 120 in Death Valley. A weak upper-level low migrating toward the coast this afternoon will trim some of that heat this afternoon, with a little more the rest of the week as the upper-level ridge migrates eastward and is flattened a bit.
It's not so much the heat in the South as it is the humidity. Look at the current dew point temperatures:
We're finally starting to see a tropical air mass take hold across the Gulf Coast region, and we have dew point temperatures of 60 or better up into central Illinois, much of Indiana, pretty much all of Ohio and Pennsylvania, and even into New York state and central and southern New England. This in combination with a fair amount of cloudiness has kept nighttime lows above average the past couple of nights from the Ohio Valley into parts of the Northeast, and with no real front coming through the flow until late Friday and Friday night, it's a cinch to keep temperatures on the high side of average.
There will be an air mass change this weekend, though, and some of that cool and dry air moving into the Plains tomorrow and Thursday will spill over the Appalachians into New England and the mid-Atlantic states. However, the cooling will not be nearly as great as it will be farther upstream, and it won't last very long, either. Take a look at the upper-level pattern Thursday night:
Note the lack of ridging over the East, with the main upper-level trough swinging across the Midwest into the Great Lakes. Compare that image to Sunday evening:
Now all of a sudden the heights are MUCH higher in the East! The upper-level low? It retreats northeastward into Quebec, and the massive cooling behind it late this week all but vanishes coming to the East Coast. This allows the heat and the humidity in the southern tier of states to expand steadily north and east next week, really, starting this weekend out on the Plains. It looks like Monday through Wednesday and perhaps Thursday will be the three days with the greatest warmth and humidity west of the Appalachians out to the Mississippi Valley and eastern Plains, while it's more Tuesday to Thursday east of the Appalachians, maybe lingering into Friday. This is the projected, 2-meter, six-hour maximum temperature for next Wednesday:
This won't be extreme or record-setting heat, but it signifies a summer expansion in terms of more typical heat and humidity for the ramp up to the summer solstice next Saturday!
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