Tuesday, 11:55 a.m.
Three separate disturbances are moving across the eastern third of the country, though the lead disturbance is the one that has caused all of the trouble over the past 36 hours. It's taking the main storm swiftly northeastward, with the low near Watertown, N.Y., at 989mb. Let's look at the 12z NAM 500mb forecast for 0z this evening to illustrate what I'm talking about:
The second one in the northern branch of the jet stream is driving a cold front southeastward through Ontario into Quebec, and over the course of tonight and early tomorrow, the front will move through the Northeast to pull some chillier, much drier air into the region from central Canada. There will be some rain and snow showers with this front late this afternoon and tonight from parts of Wisconsin to upstate New York and northern New England, but that's it for this feature.
To the south, the third feature is the broad upper-level trough rolling across the lower Mississippi Valley into the Deep South and Tennessee Valley. It's being accompanied by some showers and a few thunderstorms, and temperatures in this area will be much below normal before recovering nicely tomorrow in the wake of this wide feature.
By day's end tomorrow, these three features will have all progressed to the East Coast:
Surface high pressure will build across the Gulf Coast tomorrow, setting up camp in the Southeast tomorrow night. That means a chilly start to the day Thursday throughout the East, but in this progressive pattern, that high will be moving away from the Southeast coast, though it will leave a beach head, if you will, over the Florida Panhandle.
Meanwhile, that next disturbance you see will bring a cold front through the Pacific Northwest late this afternoon into tonight, with just a few showers. This is not going to be a big rain maker for most places from Washington to Minnesota as it flies over the Rockies and through the northern Plains toward the Midwest late tonight and tomorrow. Widely separated showers can pop up from Wyoming into Nebraska and Iowa, but rainfall amounts will be very light.
Much warmer air will surge across the Mississippi Valley into the Ohio Valley tomorrow afternoon and especially Thursday. Temperatures will also jump Thursday afternoon across the Northeast and mid-Atlantic states, and with the front slowing down as it comes into the Ohio Valley and New England, it will remain mild in the mid-Atlantic Friday and downright warm throughout the South and Southeast.
The slowing of the front will give an opportunity for a wave of low pressure to form along it, enhancing the rainfall for a time later Friday and Friday night before the wave pulls the moisture off the New England and mid-Atlantic coast Saturday morning.
Behind all of that, there's not an immediate surge of arctic air for a change! Indeed, if you look at the projected anomalies for Friday, there's not much cold air anywhere in the country!
As you can see from that image, if you're looking for an early hint of summer, head southwest, where temperatures will be in the 90s the next few days across the deserts of southern California and southern Arizona. A few locations will likely top the century mark tomorrow.
Much above-normal warmth is in store for the next week from the Plains to the Northeast and mid-Atlantic states, while it turns much cooler throughout the Northwest.
Despite the current chill, warmth is becoming more certain this weekend and beyond from the Plains to the Northeast, even as Erika threatens Florida Sunday night and Monday.
While Danny has been declared an open wave, the low pressure area trailing it will likely have at least a passing impact on the weather along the East Coast next week.
It may be hot now in the Northeast, but much cooler air is drilling into the Rockies and is heading eastward. An even cooler air mass this weekend and early next week will be followed by a stronger warming trend.
The retreat of the jet stream will lead to more warmth than not in much of the country heading into the second half of August.
More concentrated areas of active weather will be the rule into the early part of next week across the country as weak storms move steadily eastward.