A Very Dry Week When It Should Be Wet

The weather gods are being extra kind to us this year, providing a usually dry period during the climatologically wettest time of the year.

To illustrate, here is the climatological probability of receiving a hundredth of an inch or more in Seattle over the year.  The climatological probability of rain each day is over 60% from November 7 through mid-December.  This is typically the wettest time of the year!


The forecast for this week?    Absolutely dry with plenty of sun.   Take a look at the forecast precipitation total through Saturday at 4 PM.  No rain over the Northwest and California.

The reason for these dry conditions?   The big West Coast ridge is back, as shown by an upper-level map (500 hPa, about 18,000 ft) on Tuesday around 4 PM.   The solid lines are heights, but you can think of them as the pressure at around 18,000 ft. 


To get a better view of the upper-level situation, the following map is at the same level, with the shading showing the anomalies from climatology (normal).  Red colord indicate above-normal 500-hPa heights and blue/green are the opposite.  

You can see our ridge has "bookend" troughs of low pressures/heights.   This is a very stable pattern, called an omega block.  We will be dry, but the eastern half of the U.S. will be cold and wet.




It does appear that this pattern is destined to breakdown next Sunday, with the 72hr precipitation totals ending on Wednesday the 23rd being quite soggy (see forecast below).

My advice...enjoy the pleasant weather this week, with highs in the lowlands around 50F.   It won't last.





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