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Week ahead: Alternating tropical moisture and Canadian cold fronts

Week ahead: Alternating tropical moisture and Canadian cold fronts

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Weather map Wednesday AM

Wednesday's projected weather map shows high pressure wedging down the East Coast with cooler, drier air as Hurricane Sally makes landfall near New Orleans. A cold front will also be sagging south out of Canada, promising to bring a renewal of cooler, drier weather by next weekend, possibly pushing some showers and storms from Sally's remnants ahead of it.

The defining fall atmospheric battle of the tropics vs. tundra will be in full swing this week for Southwest Virginia, with alternating effects of tropical moisture and Canadian cold fronts.

Entering the week we are still dealing with lingering moisture that initially arrived with a diffuse tropical system during the middle of last week, wedged against the mountains by high pressure to the northeast. Some sun will pop out on this Sunday, with a warm, sticky afternoon, but an approaching cold front lifting that moisture will trigger showers and thunderstorms this Sunday evening and into early Monday. Not a soaking rain for everyone, but some locally heavy downpours in the stronger storms.

That front will sweep the moisture out nicely for what looks to be "Chamber of Commerce weather" on Tuesday, with sunny skies, 70s highs, 50s lows (some 40s possible in outlying areas) and low humidity. Wednesday will be similar, with perhaps even a cooler start, but a slightly warmer afternoon. It starts getting warmer and stickier again on Thursday.

The major question hanging over the late week will be what happens to the remnants of Tropical Storm Sally, which may well be Hurricane Sally when it makes a Tuesday landfall somewhere in the general vicinity of New Orleans. The same high pressure system bringing us cooler, drier weather will keep Sally from moving anywhere real fast, which may mean extremely heavy rainfall totals along the Gulf Coast and in the Deep South. But in time, the approach of another strong Canadian cold front from the northwest will kick out Sally's remnants in an easterly or northeasterly direction, and it's then that we may get some rain from it.

The Roanoke area has been very blessed so far with tropical remnants this year, getting lesser-than-expected scrapes from Tropical Storm Bertha in May (a little more potent along/west of I-77), and both Hurricane Isaias (edged east of us) and Laura (mostly lost its punch before arriving) over the past several weeks. Early indications are that Sally will dump most of its moisture south of us, with some showers and storms possible as some of its moisture interacts with cold front by Friday and Saturday, so this may be the fourth minor scrape with a tropical system we've had this year. 

That cold front next weekend looks to be quite potent, renewing cooler, drier weather. Though it's not going to be good at all for Western wildfires, the overall weather pattern over North America generally suggests high pressure aloft over the West and a jet stream trough over the East, which would bring periodic cold fronts with reinforcements of the cooler, drier air to us even as high pressure off the southeast coast and the rampant Atlantic tropical season (no fewer than SEVEN systems, three named, being monitored by the National Hurricane Center as of Sunday morning) occasionally erode it with sticky, showery weather.

Very unlike 2019 with its extended summer heat, and perhaps somewhat off-brand for a troubling 2020, autumn appears to be unfolding more or less on time in our neck of the woods.

Contact Kevin Myatt at kevin.myatt@roanoke.com. Follow him on Twitter @kevinmyattwx.

 

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Since 2003, Kevin Myatt has penned the weekly Weather Journal column, and since 2006, the Weather Journal blog, which becomes particularly busy with snow. Kevin has edited a book on hurricanes and has helped lead Virginia Tech students on storm chases.

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