Wild & Potentially Memorable Pattern Evolving Over North America

Written by on September 17, 2012 in North and South America, United States of America with 0 Comments

GFS Upper heights for Tuesday (NOAA)

If you are into WILD WEATHER then this pattern is the one for you. The jet is buckling majorly over North America and the strong storm that produced 120 mph wind gusts over southern Alaska is acting like a major heat pump, effectively it’s pulling sub-tropical air out of the central Pacific and forcing it all the way up to Alaska and Northwest Canada. This is a big deal because what this is effectively doing is causing disruption over the Arctic, splitting the cold air which has been gradually building with the positive AO, the tanking into negative can be seen from what we’re seeing right now. This heat pump is forcing a piece of the polar vortex to come south and with a major ridge like this, so a major trough is created and where’s that cold air going? Southbound down the spine of Canada and yes even into the Lower 48 too.

All this week you’ll see me writing on here about record heat from California all the way to the Alaska and the Yukon.

How warm?

70s, perhaps 80s for parts of Alaska, Yukon and 90s reach all the way into southern British Columbia and Alberta. Day after day this week the heat is going to be the big story for the entire western flank of the continent.

As a consequence, a major, powerful trough piledrives very cold air into the Northern Tier with low enough heights and thicknesses in which snow showers are possible by as early as tomorrow over Minnesota, Wisconsin and possibly the UP of Michigan. Note the 540 line in the chart below getting as far south as southern Iowa and Wisconsin tomorrow. This shows just how cold the air mass is coming all the way down from the arctic.

This pattern is shaping up to be more and more El Nino-like with an active southern branch and the northern branch dropping out of Canada. This is the perfect setup for phasing and major East Coast storms. We will see an example of this play out over the next 48-72 hours as bucket loads of tropical moisture gets pulled north from the Gulf of Mexico and 70-degree dew points slamming against the front which will all get forced north along the boundary.

Check out the heavy rains this morning in the below radar map. This is associated with the southern branch, notice the northern jet heading south where it should meet this and then it’s fun and games up the Eastern Seaboard tomorrow. Once this branch phases, the low will run up the coast over the next 48 hours, enhancing the rains all the way to New England as well as a severe weather threat in which gusty, possibly isolated damaging winds are possible..

The biggest rains will be focused from Southeast Texas to the Tennessee Valley through the rest of today while tomorrow it’s up the Appalachains to New England. Check out the below chart showing 48 hour rains.

The strong storm system producing strong wind, heavy rains to southern Quebec/New England and the western heat pump is working together in funnelling arctic air south into the Heartland of the US, of course this being in modified fashion but nonetheless, it will likely present the first frost for many over Minnesota, Wisconson, Michigan perhaps reaching as far south as southern Iowa, northern Missouri over the next few mornings. You only have to look at where that infamous 540 height line is going over the next 36 hours to see what’s unfolding here.

I believe lows could hit freezing in Minneapolis and at least to the close in suburbs of Chicago. Northern Minnesota may get near to 20F, perhaps even creeping in the teens in Tower or Embarrass in the Arrowhead in the next couple of mornings. Some spots are likely to see snow showers. All this while deep tropical moisture, heat and humidity surges north up the East Coast. That’s a perfect environment for excessive rains, strong thunderstorms and rainfall rates of 1-2 inches per hour, 2-4 inch 24 hour totals widely. The concern is the Tennessee Valley where an area of 6+ inches is possible over the next 48 hours.

Big time rains can be expected over the next 48 hours up the EC with the focus over the TN Valley (NOAA)


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