Western US weather
Our Cool Jet Leads to Severe Weather Farther East
4/25/2011, 2:57:11 AM
All week long, the West has been under a suppressed jet stream that has kept temperatures cooler than normal, but only brought light, spotty precipitation as weak disturbances moved through. But as these disturbances move off the Rockies into the Plains, they are the catalysts to produce severe weather.
Here is the 500 mb pattern for this evening, which is pretty representative as to what has been occurring all week long:
You can see a split in the flow with one branch of the westerlies turning north up into northwestern Canada, and the other branch forced to go through California and the central Great Basin.
This southern branch of the westerlies has caused all the ingredients to come together for an outbreak of severe weather over the east-central and south-central Plains on east. As the disturbances come off the Rockies, they bring a westerly flow of dry, cool air that collides with warm, moist air farther east. In addition, the stronger-than-normal winds aloft from the west help create quite a bit of wind shear as they meet a good southerly flow of low-level air. These are all ingredients for severe weather, including destructive tornadoes, large hail and damaging winds.
More severe weather is likely this weekend out in portions of the Plains. Here are the outlooks from the Storm Prediction Center.
It does look like the storm track in the West will do two things next week. One is that it will go farther north, and two, disturbances moving inland will be stronger. This will lead to more precipitation in the Pacific Northwest, but warmer weather in the Southwest. However, this could eventually lead to a nasty severe weather outbreak in the Tuesday-Wednesday time period, first in the southern Plains Tuesday, then to the Ohio Valley, Tennessee Valley, and parts of the central Gulf States for Wednesday.
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