A Winter Soaker
January 28, 1998
By Mark Hoover
There's a strong Pacific storm moving into the northwest US and British
Columbia tomorrow, a classic El Niño winter soaker that's going to add
another couple of inches of rain to the swollen total so far this year, and
there's no end in sight.
This one accelerated faster than expected yesterday as it moved from its
birthplace south of western Alaska - one more example of just how difficult it
can be to predict the details of a storm, especially in an El Niño year.
The fast-moving storm caused a general scramble among the California-based
scientists planning to fly out to measure it, as well as those who race to
position mobile Doppler radars to probe the storm's windspeeds from shore (more
on these DOWs, or Doppler On Wheels, tomorrow). Even as I post this dispatch,
a P-3 turboprop and its research crew is taking off and heading out to meet the
storm: alas, without me—a casualty of the general rush. Fortunately, the next
storm—and the next stormflight opportunity—is already assembling itself.
Storms along the west and east coasts of North America. Composite satellite image of total precipitable water vapor
(the amount of liquid water, in millimeters, if all the atmospheric water vapor in the column is
condensed) Browns is the driest, red is the most moist, and clouds are represented in gray.
Larger version of image.
In fact, the storms have been as regular as a metronome this winter. The
persistent low pressure center south of Alaska has been kicking out a new one
every three to five days. Meteorologists call this storm-making process
cyclogenesis. What they mean is that cold polar air interacts with relatively
warm updrafts from the ocean, spinning up cyclone after cyclone. The northern
jetstream, which has been pushed farther north than usual this year by El
Niño, then conducts these north Pacific storms with regularity to their
landfall, the Pacific northwest.
There are two jetstreams involved in our weather in the middle latitudes, the
northern and the southern. The southern jet is also displaced north, and has
been bringing a lot more warm air, heavily charged with tropical moisture, into
the US this winter. Normally this air would stay south of the continental US.
The wet warm air has been clashing with colder Canadian air, and setting up
eastern storms. The very large storm off the Atlantic coast right now shows
what can happen when all that El Niño moisture starts condensing out
into a storm center. On this morning's real-time GOES satellite image, you can
see these two storms clearly. You are looking at El Niño's handiwork.
East and west, the US is being squeezed by the teleconnected effects of a large
pool of warm water off the coast of Peru. Look for the pattern again this
winter. You will see it often.
Check back tomorrow for an update on the next Pacific storm as it enters "the
chute," and the next opportunity for StormFlight.
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Satellite image: NOAA/CIMSS/University of Wisconsin-Madison.