A Closer Look at the Western Storm

102609 WatchWarning

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Watches, warnings, and advisories litter the mountain west as two different storms make their way through the area this week.  The first storm is already tracking along the US/Canadian border.  The associated cold front is driving southward through the West bringing much colder air to the region.  A second, more powerful storm is forecast to develop on Tuesday and move through the Four Corners region before exiting into the Plains on Thursday.  Many places will see their first significant snow of the season.  And I do mean significant.  They could be measuring in feet in some spots come Thursday morning.

I thought it would be fun to more closely examine these storms.  To do so, we’ll look through several images after the “read more” link.  I don’t want to slow down the front page too much.

We often look at 850 mb temperatures to get a feel for temperature changes at the surface.  However, 850 mb of pressure is found below the surface across much of the west.  (850 mb is generally found around a mile above sea level.)  So, to better see the cold front advancing through the West, we’ll look at 700 mb temperatures (found around 2 miles above sea level).  There are certainly some peaks that pass 10,000 ft out west, but, for the most part, 700 mb temperatures are found aloft and provide a decent estimation for surface temperatures.  Here are the 700 mb temperatures for this evening (Monday):

102609 700mb Temps12

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You can see the cold air advancing into the Pacific Northwest tonight.  The leading edge of the cold front arcs from northern California through southeastern Oregon to northwestern Montana.  24 hours later (Tuesday night), we can see the cold front has passed through southern California and the cold air has advanced into much of the intermountain West:

102609 700mb Temps36

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At this time, you can see the first cyclone moving just north of the US/Canadian border in the Plains.  Meanwhile, the second storm is beginning to form in the Four Corners region.  During this 24-hour period, the bulk of the precipitation will occur in the northern Rockies:

102609 24hr precip36

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Winter weather warnings and advisories are in place throughout much of this region.  Rain will mix in at lower elevations before changing over to snow, so the snowfall totals will not be extreme in these areas.  Still, higher elevations could see over a foot of snow, especially in the Cascades.

As we move to the next 24-hour period (Tuesday night through Wednesday), the focus for snow transitions southward in the Rockies as the second cyclone begins to form and the cold air continues to advance.

102609 700mb Temps60

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You can see where the cold front has advanced into northern Mexico.  Poor San Diego, CA will see high temperatures only reach the upper 60s while Phoenix will barely nudge into the 60s.  At the same time, higher elevations will see temperatures around freezing and potentially heavy snow.  The winter storm watches in the area mention snowfall in excess of a foot, with some of the Wyoming watches mentioning 25 inches as the upper limit of potential snow.

Beyond Wednesday night, snow will continue out into the High Plains of eastern Wyoming and western Nebraska where over a foot of snow is certainly possible in some areas according to the HPC outlook:

102609 day3 snow

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After moving through the Rockies, the system will exit into the Plains on Thursday where it may undergo rapid cyclogenesis as it moves northward through Minnesota.  Right now, it doesn’t appear the major snow will advance much further east than the High Plains, but there will be some heavy precipitation – with the threat of thunderstorms – as this strong storm moves into Canada.  We’ll wait a day or two before looking into this.

If you live in the West, enjoy the snow, but be safe.  The winds will be very strong in some places and make any transportation very hazardous.  Most every location in the West is under a High Wind Watch or Warning and gusts could easily exceed 50 mph as these systems move through.

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