Wednesday, 11:50 a.m.
No, I'm not going political on you, in obvious reference to the current government shutdown and the sharp division between political factions on how to resolve some serious matters! Instead, I'm talking the growing temperature divide from the western half of the country to the eastern half. A vigorous upper-level disturbance is about to move into the Northwest today, and it will be the impetus for change in the West the rest the week.
Here's what that looks like at the 500mb level from the 12z Oct. 2 NAM forecast for this evening:
This feature will generate showers across the Northwest this afternoon and tonight then in the northern Rockies later tonight into tomorrow. By the time we reach Friday morning, this trough will be notably deeper.
During the course of tomorrow night and Friday morning, low pressure will redevelop on the western Plains to begin its northeastward trek toward the Midwest later Friday and Friday night. As the storm deepens, colder air will be drawn swiftly in behind it, and precipitation will expand greatly across the northern Rockies, then across the northern Plains, and it won't all be rain.
It is quite conceivable that parts of northern Colorado, Wyoming, southern Montana and western South Dakota will end up with more than a foot of snow by the time the storm moves away on Saturday. And if it is going to be cold enough to snow, that means it will be much cooler than normal. Here are the projected temperature anomalies for Friday.
Notice that while all of the West is turning dramatically colder, the exact opposite will be taking place ahead of the storm. It already IS warm, but it will get arguably warmer in some communities before any cold front attached to the storm cutting across the Plains can swing across the Mississippi Valley and bring much cooler air to bear. Part of the large temperature anomalies will be tied to a warm night Thursday night into Friday throughout the Mississippi Valley and Plains, as well as across the Ohio Valley and Great Lakes to the mid-Atlantic and parts of New England.
The warmth won't end there. It will last through Saturday across the Great Lakes and Ohio Valley, and through the weekend east of the Appalachians. The storm will slice across the Midwest to the upper Lakes Friday night and Saturday, bringing the cold front eastward. The storm will weaken over the weekend, and as the front runs into a building ridge off the East coast, it, too will lose some of its punch. By the time we get to Monday, with the front finally coming into the Northeast and eastern Seaboard, it will still be milder than normal in the East, while the cold air weakens greatly coming across the Plains:
With signs of a new trough digging into the West later next week, it's likely to mean temperatures will again go way above normal from the Midwest to the Northeast and mid-Atlantic states later next week.
Two systems will delay the onset of warm weather in the Ohio Valley and the East over the next week or so, but then it should get warm all across the country heading into the Memorial Day weekend.
A turn to much colder air over the Northeast and mid-Atlantic states will set the stage for a rain and snow storm later this weekend before it turns much warmer later next week.
It's warm now, but will turn much colder this weekend, with a storm threat later Saturday into Sunday. Warmth will return by the second half of next week.
Though it is cold now east of the Mississippi, with a couple of opportunities for snow into the weekend, a blast of warmth is due for much of the country east of the Rockies next week.
Warm air will once again surge eastward from the Plains to the East Coast this weekend and early next week. A strong storm next Tuesday and Wednesday will then be followed by colder air later next week.
A storm in Southeast Texas will generate severe thunderstorms this afternoon and tonight, and some wet snow on its western flank as it heads into the Ohio Valley tomorrow.