Monday, 11:59 A.M.
The weather pattern is beginning to accelerate across the Northern Hemisphere, as the normal expansion of the circumpolar vortex continues here in mid-October. This week will show a marked change, particularly in the East, where a storm off the East Coast has had an influence on the weather for several days by generating plenty of clouds and episodes of rain. There have been some day-to-day changes, of course, as the excessive rains Thursday into Friday become much lighter and more limited in scope. Up to this point, though, no front has been able to climb over the Appalachians and reach the East Coast.
The latest attempt at a frontal passage is this morning, with a front basically falling apart as it slides across upstate New York into New England. There will be no impact on the weather across much of New England and the mid-Atlantic states.
Still another front is moving out of the eastern Rockies and onto the Plains, associated with a storm developing over the central Plains. The 12z Oct. 14 NAM forecast for this evening:
As the front swings out of the Rockies and into the central and southern Plains, it will encounter a lot of moisture, and that will lead to a much larger area of rain and thunderstorms from Texas to Nebraska. To the north and west of the track of the storm, a cold rain will fall with some snow in the high ground of Colorado to southern Montana, and even the Black Hills of South Dakota:
This storm will really begin the process of accelerating the pattern the rest of the week into the weekend, and beyond. By Thursday morning, the storm will have weakened some, but will also have moved into southern Quebec. The front attached to the storm will be moving into New England and to the East Coast, as best depicted by the NAM 700 mb moisture at 72 hours:
This will finally erase the mild air that has been in the East, though the air mass behind this front is hardly cold. Instead it will simply be drier, which means a lower overnight low. That will certainly be the case west of the Appalachians Wednesday night, and east of the mountains Thursday night.
If you look at the bottom of that same image, you'll note high relative humidity values - that's tied to what is now Tropical Storm Octave in the eastern Pacific. While it is weakening, and will continue to do so prior to landfall, its moisture will move over Mexico into central Texas tomorrow and tomorrow night into Wednesday, and will be the seed for a wave of low pressure that will scoot for the East Coast Thursday night.
Behind THAT feature, another cold front will come out of the northern Plains and into the Midwest, sweeping to the East Coast this weekend. It is behind this front that a more widespread chill enters the pattern for the weekend into early next week.
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