Wednesday, March 9, 2011

A Progressive Pattern

Spring is here and a very progressive large-scale pattern is setting up for the next week.  This means, like a two-faced politician, the weather will be flip-flopping with each trough passage.

Dynamic tropopause (DT) analyses are extremely useful for examining the upper-level large-scale flow.  Unlike conventional pressure-level analyses (e.g., 500 or 250 mb), the dynamic tropopause cuts through or near the core of both the polar and the sub-tropical jet.  The DT analysis shows not only these two jets, but also upper-level troughs and ridges, which are indicated by the wind analysis as well as locally low and high DT pressure, respectively (cool and warm colors on the image below).  Thus, a DT analysis packs a lot into a single plot and is generally more useful than a single pressure-level analysis.  Further, for advanced users, the dynamic tropopause is defined based on potential vorticity, so it has a number of advantages for diagnosing large-scale flow behavior, although we won't bother pulling out the heavy duty math for this post.

The GFS Dynamic Tropopause loop below shows a series of major troughs passing through the northwestern United States and clipping Utah over the next seven days.  If the forecast verifies, we'll see four trough passages in the next 8 days.

What this means is a very changeable weather pattern with quick hitting snowstorms for the mountains.  Bottom Line: Keep the sunblock, hardshell, and puffy jacket nearby.

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