Thursday 11:45 a.m.
A cold front stretches from Minnesota to southeastern Colorado at midday, and it is separating two distinctly different air masses from one another. Ahead of it, dew points are in the 60s, even to 70 or better in parts of the Midwest, something more typical in the middle of summer, rather than the second half of September! Behind the front, dew points quickly drop into the 40s in the Dakotas and Nebraska back into eastern Colorado. As you might expect with such a contrast in air masses, there are some strong thunderstorms on the prowl across parts of Minnesota. A severe thunderstorm watch is already in effect for southern and eastern counties of the state, as well as northwestern Wisconsin.
Farther southwest, more strong thunderstorms are marching across eastern Nebraska, and these are likely to expand down into Kansas and out into Iowa and northwestern Missouri in the coming hours. Then, as the front presses farther east and southeast tonight into tomorrow, rain and thunderstorms will redevelop farther downstream. Severe weather is a concern in parts of the Great Lakes and Ohio Valley tomorrow, as this front charges into a tropical air mass with dew points well into the 60s to near 70 degrees.
The front won't stop there. It will continue its march to the Northeast and mid-Atlantic coasts over the weekend, spreading locally heavy rains with some embedded thunder over the Appalachians into the mid-Atlantic and England Saturday and Saturday night. It should all come to an end sometime Sunday as the front moves off the New England and mid-Atlantic coasts and high pressure delivers drier air in from Ontario.
While all of this is taking place, Hurricane Manuel made landfall on the west coast of Mexico early today, west of the town of Culiacan. It will rather quickly fall apart over the next 24 hours as it plows into the mountains, but it will feed moisture northeastward right into the weekend. Here's what that plume looks like on satellite imagery:
As the cold front moves into the southern Plains, it will interact with this moisture feed from the eastern Pacific and the dying remains of Manuel, likely bringing a good soaking to parts of Oklahoma and Texas tonight and tomorrow, with that area of heavy rain and thunderstorms being squeezed southeastward out of Oklahoma and north Texas tomorrow night into Saturday morning.
What is less certain over the weekend is what will become of this moisture. Computer forecasts over the past couple of days had been forming an upper-level low over the lower Mississippi Valley and bring moisture up from the southwestern Gulf of Mexico, but they've since backed off that scenario, making the weekend much less soggy looking across much of the South and Southeast.
The one potential fly in the ointment is the slow development of the area of disturbed weather over the Bay of Campeche. Right now, it doesn't look very healthy, but that can easily change in the next couple of days as it drifts off to the west and northwest and has time to stew and brew over the tepid waters of the southwest Gulf. Right now, though, it looks more as if the high percentage of the moisture associated with that feature gets stuck over the western Gulf through the weekend, with perhaps an increasing impact on the northwest or central Gulf Coast later Sunday into Monday.
The heat and humidity will be erased from much of the East later this week, but warmth will spread from the Plains eastward over the weekend. The tropics could still play an important role in the weather along the Eastern Seaboard this weekend.
A dominant ridge will keep it hot from the Ohio Valley to the East into next week, while the disturbance north of Cuba is slow to develop as it approaches the southeastern Gulf of Mexico.
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.