Saturday, January 23, 2010
Record Low Pressure
As readers of this blog can attest, I enjoy talking about record-breaking weather...and during the past several days records have been broken in spades with one of the most unusual West Coast weather situations in years.
I have talked about our torrid month here in the NW, with April temperatures in January. But even more amazing have been the extraordinary low pressures over the western U.S. and particularly the U.S. SW. Here is a sample from the National Weather Service:
...THE LOWEST PRESSURE EVER RECORDED AT PHOENIX SKY HARBOR OCCURRED AT 644 PM MST THURSDAY EVENING WITH A READING OF 29.20 INCHES OF MERCURY. THIS BREAKS THE PREVIOUS RECORD BY A FULL TENTH OF AN INCH.
Other ALL TIME RECORD low pressures:
LINDBERGH FIELD IN SAN DIEGO WITH 29.15 INCHES OF MERCURY AT 1222 PM PST...
LOS ANGELES INTERNATIONAL AIRPORT WITH 29.07 INCHES OF MERCURY AT 121 PM PST...
LAS VEGAS MCCARRAN AIRPORT WITH 29.03 INCHES OF MERCURY AT 514 PM PST.
YUMA WAS 29.12 INCHES OF MERCURY AT 259 PM MST
.Medford, San Francisco,and many others, also had record low sea level pressures.
I mean...this is really historic stuff. Perhaps your grandchildren will ask you about it someday....(maybe not).
The origin of these record low barometric readings? An extensive, very deep low over the western U.S. Below I have a sea level pressure map for Thursday afternoon...you can see this massive low. And also I have an upper level chart for the same...a massive trough over the West Coast with a strong jetstream (where the lines are close together) headed straight into the southwest.
The impact of this jet was profound: record precipitation into southern CA, Nevada, and Arizona. Heavy snow in Flagstaff and northern AZ.
Although we did not set pressure records in Washington in terms of the minimum, we did have very low pressure for an amazing length of time. Check out the plot of pressure at Sea Tac. I cannot remember an event in which our pressure stayed so low for so long (days below 990 mb).
I sometimes get calls from people suffering from arthritis, wanting to know about low pressure and big pressure falls--which they feel worsens their condition. I wonder if anyone noticed anything?
Finally, today will have a few showers and plenty of clouds....and a more serious system comes in tomorrow afternoon (Sunday). But absolutely nothing major happening. No threat of flooding in the Cascades as far as the models can predict. I think those worried about the Green River and Howard Hansen Dam can relax and go on vacation soon. After Jan 1 El Nino years rarely have major flooding and in any case, floods are very rare on west side rivers after Feb 20th...and our computer models show nothing significant for the next week. Plus, the dam water level is way low and there is room for a fairly major storm.
Posted by Cliff Mass at 8:48 AM