Monday, 11:30 A.M.
So far the winter season has been a little more like winter than the winter of 2011-12. There at least has been some snow, and in the past week or two, there's actually been some legitimate cold. Not necessarily a bitter cold outbreak (yet), but at least something that felt like real winter cold. That's all about to change.
Look first at the latest snow cover analysis, clearly down from its peak a week ago:
I promise you that by the end of the weekend, there will be a lot less snow on the ground in most places from the central Plains to the Northeast. Some will call it a January thaw. I know in my backyard, the temperature exceeded 33 degrees once from the day after Christmas until yesterday, I'll consider that a thaw. For others, it's only been nominally below normal for a handful of days in that window, as most of the arctic air has been held at bay to the north. Either way, there is no denying the fact it's going to get warmer, and in short order.
Just look at today, for example. Even with a cold front sliding off the Northeast coast, the air is hardly cold. And what little cold air slides by the Great Lakes into New York and New England is already being beaten back throughout the Midwest, with temperatures easily more than five degrees above normal in Chicago this afternoon, and even more so the farther west you go. And that's WITH a snowcover. Image how far above normal it can get with no low-level cold air around any more, and no snowcover!
The short explanation of this is that the jet stream is about to undergo a major buckling, with cold air suddenly returning to the West on Friday, while a massive upper-level ridge building off the Southeast coast will promote strong south to southwest winds that will carry warm and increasingly moist air far to the north over the eastern half of the country. And those warm, moist winds will act like a giant eraser, wiping out the early season snowcover.
And before you start throwing things at your computer screens or calling me the anti-cold monger, look at the details! Here's the 500 mb forecast for Thursday evening from the 12z NAM forecast:
Compare that to typical heights:
And then look at the forecast temperature anomalies on Friday:
All I can say is "wow." That's a massive area forecast to be more than 20 degrees above average on Friday. And that's an area currently blanketed by snow. Talk about a dramatic turnaround.
One storm that you see on the NAM 500 mb forecast will roll across Texas tomorrow into Wednesday, and do so at a slow enough pace there may be some severe weather over southeastern Texas and Louisiana along with a risk of flash flooding. This could also extend up into eastern Oklahoma and Arkansas before those risks begin to diminish downstream Wednesday night and Thursday. Still, some rain will make it into the Lakes and Ohio Valley, then, to a lesser extent, into the mid-Atlantic and New England. (Watch it melt, watch it melt, watch it melt!)
With the upstream trough sharpening, another disturbance will drop down the western flank of this trough Wednesday night and Thursday, lowering snow levels throughout the Northwest and into California and Nevada and Idaho. I'm pretty certain it will then spit out at least a couple of disturbances that will head from the southern Plains toward the Lakes and Northeast this weekend and into the beginning of next week. Ahead of them, it will feel more like March and April in many areas. Behind them, though, colder and colder air will spread from the West into and through the Rockies out onto the Plains. It will take some time for that cold air to fully reach the East Coast. Indeed, the kind of temperature anomalies the West will see Friday through the weekend are NOT likely to be repeated along the East Coast and in the Southeast when the cold air arrives. Remember, the current snowcover will be gone, with little of it being replaced by any of those waves.
Call it a January thaw or not, but a massive warm up is underway, one that will last into the beginning of next week.
A deep upper-level trough of low pressure is caught in between two strong upper-level ridges, locking cool weather into Plains to the Appalachians and beyond.
A much cooler air mass will expand from the northern Plains this weekend to the Deep South and into the East by Tuesday, pushing temperatures much below normal.
Intense heat and oppressive humidity surging out of the central Plains will cause severe weather from the Midwest to the Ohio Valley in the next 72 hours, followed by much cooler weather next week.
Despite the heat and humidity in the East today and a surge of intense heat and humidity coming out of the central and southern Plains for a brief period of time, cool air will dominate the pattern through the end of July from the Plains to the Appalachians.
A pattern of extremes is once again unfolding across the country over the next week, with two shots of cool air interspersed with intense heat.
Despite the heat over the central and southern Rockies this week, an amplified pattern means cool air will dominate in much of the country for the rest of July.