Thursday, 11:20 a.m.
We're a week out from Thanksgiving, and the days leading up to the holiday are some of the busiest days of the entire year in terms of travel. Given the state of the economy these days, the number traveling may be down, or perhaps the distances traveled will be a bit shorter. Regardless, the weather will impact millions trying to get to their destinations.
And wouldn't you know it, there's a storm brewing for next week. The model guidance is still not in total agreement with the path of the storm, and on its specific timing, but there will clearly be a storm. Right now it is a feature buried over southern California, completely detached from the main flow of the jet stream. Look at the 12z Nov. 21 NAM 500mb forecast for this evening:
That trough coming at the northern Plains this evening will drive a cold front across the Great Lakes tonight, then through the Ohio Valley into the Tennessee Valley tomorrow, then off the New England and mid-Atlantic coast by Saturday morning. It will be followed in relatively short order by an arctic cold front, one that will move into the Great Lakes tomorrow night, then cross the Ohio Valley into the Northeast and mid-Atlantic states later Saturday and early Saturday night. Here's the latest NAM surface forecast for Saturday afternoon:
By the time we get to Sunday morning, the arctic air will be drilling off the East coast and through the Southeast, the coldest air so far this season. However, as that is happening, the upper-level low over southern California will begin to roll eastward into the Southwest deserts:
With the low levels of the atmosphere chockful of chilly air deep into Texas this weekend, the upper-level flow from the southwest ahead of this upper-level low will force warm, moist air back up and over this low-level chilly air, and that's going to mean a cloudy, cool, wet weekend for Texas. Over time, that cloud shield will fan out across the lower Mississippi Valley. In fact, that area may never completely clear this weekend.
By Monday, the upper-level low will roll out of the southern Rockies into Texas. At that point, a surface low should begin to organize over the Texas coastal waters, and the precipitation shield will begin to expand more generously in the lower Mississippi Valley and the Deep South. From there, the storm will track east-northeastward and could dump 2 to 4 inches of rain on the Deep South Monday night into Tuesday. By late Tuesday or Tuesday night, the low will jump to the Southeast coast, with the precipitation shield already fanning out up the Eastern Seaboard.
During this time, the core of the cold air should have had plenty of time to escape east of the Appalachians, meaning the most probable form of precipitation should be rain away from the mountains, even up into southern and eastern New England. What's not as certain is how far north and west the precipitation shield will get with the storm, and that hinges on a couple of things. One is any potential phasing with a northern branch trough that would pull the storm farther north and west. And another is how much cold air catches up to the back side of the storm to change any rain to snow in the mountains and surrounding areas. This would be one of the bigger travel headaches to contend with later Tuesday into Wednesday and could impact areas from West Virginia all the way to upstate New York and northern New England.
One thing is certain, though. Regardless of the storm track, its timing, and who might get snow or not, another blast of arctic air WILL follow the storm for Thanksgiving Day. It may not be quite as cold in the southern Plains and along the Gulf Coast, but it may well be across the Midwest, the Great Lakes and the Ohio Valley into the mid-Atlantic states and New England.
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.
A building upper-level ridge over the southern Plains will escalate the heat, while diverting disturbances with showers and thunderstorms around it through the northern Plains into the Great Lakes.