The Heavy Rains of Poseidon

The Weather Channel is now naming major storms, most recently referred to two major East Coast events as Nemo and Saturn.  Since the WC seems adverse to naming West Coast storms, those of us facing the Pacific must take the matter into our own hands.   No one will name our storms if we don't.

So today, this blog will begin leveling the playing field by announcing that Atmospheric River Poseidon will soon hit our coast, bringing torrential rains and possibly flooding to some rivers drainages.

Be advised. Poseidon is approaching!

Poseidon arrives on Tuesday.  The WRF model prediction of the total water vapor in an atmospheric column for 1 PM that day shows the watery "finger" of Poseidon stretching from near Hawaii to the Northwest.  Yes, some folks have called this a "Pineapple Express", but we are beyond that now.

Poseidon's humid, warm finger will be touching us for days!  Let's look at the forecast precipitation for several 24-h periods.  The first, ending 4 PM on Tuesday (see graphic), shows the intensification of the precipitation as it is forced to rise by the local terrain, with the main impacts being in southern B.C. and NW Washington. 2-5 inches will pummel the windward side of Vancouver Island.

But Poseidon is not finished with us!  The next 24-h (ending 4 PM on Wednesday) enhances the terrible wrath, as his briny, wet finger strengthens and drifts down across Washington (see graphic). The western side of the Olympics will be particularly hard hit, as will the central Cascades.

And the final 24-h period I will show you (ending at 4 PM on Thursday), shows Poseidon's watery revenge moving a bit northward.

To get the whole wet picture, here is the 72hr precipitation total ending 4 PM on Thursday.  5-10 inches over the Olympics, north Cascades, and mountains of southern B.C.   Enough to bring some rivers to near bankfull.  (The National Weather Service has a hydrological outlook that notes the potential threat).  The interesting thing is that from Portland southward it will be dry...and quite warm. This time the Willamette will be favored by the trident-clad one.

But Poseidon's influence will go beyond rivers and streams, it will bring a current of very warm air at low levels, causing the freezing and snow levels to rise above the Cascade crests....here is the 850 hPa (around 5000ft) temperature and wind map for Wednesday night...warm air and strong southwesterly winds will extend over the region.  Great sadness will spread across the skiing community. 

For the middle of March, this will be a notable event, worthy of a proper name.  Too far away for the Weather Channel's attention or even a visit by Jim Cantore.  But we will honor it, in our fashion.

The Birds are Back!

For many people, the arrival of spring is signaled by daffodils pushing out of the ground, blossoms erupting on cherry trees,  and increasingly ragged lawns.

But for meteorologists, another sign often comes to mind:  the return of birds on our weather radars as our winged friends migrate northward into and across our region.

As I have described before, weather radars are quite capable of seeing targets other than precipitation.  Stationary targets (like hills and mountains) are removed by clutter and terrain suppression algorithms.  Birds are actually quite good targets since they are so much bigger than raindrops or snowflakes;  the amount of radiation scattered by a target goes with the fifth power of its diameter, so a bird that is say 2 inches across (roughly 59 mm) scatters radar far more effectively than a raindrop (typically a few mm across).

Let's go back to Thursday evening at 6:47.   Not long after sunset, there was very little visible in the Langley Hill coastal radar (you will notice a little bit of return from the ocean surface off of Hoquiam).

 But as the skies darkened, the radar blossomed with echoes...echoes that stayed over land...these are the birds.  They like to fly at night, a time with less predators and a period during which they can use celestial navigation.

 Here are the Doppler velocities from the radar at the same time.  Remember, radar shows you the velocity of the "target" towards or away from the radar.  Green indicates approaching, yellow little velocity towards or away, red indicates moving away.   With green to the south and red to the north, this implies our feathered targets are moving north!  Consistent with the bird theory.

Now let me show you something really neat.   NOAA has a special vertically pointing radar on the coast at Westport that gives the strength of the radar return and the Doppler velocity for the volume above the radar (see below).  The plot shows the signal to noise radar, with red being the most signal.  You will also see the Doppler velocities, plotted in the normal meteorological style (barb pointing in the direction the target is going).  You notice the "signal" gets large around 03 UTC (7 PM) 8 March (calendar day 7 March here) and then dies around 14 UTC (6 AM).  The birds like to fly at night, with most around 2000-7000 ft.  The Doppler winds show southerlies and southeasterlies, consistent with northward migration.

With dry weather the next few days, the birds should be pretty obvious in the radar imagery.