The Radar Shows Heavy Rain Offshore Without Clouds: How Can That Be?

The radar imagery from the National Weather Service Langley Hill radar close to Hoquiam confirmed heavy showers over the coastal waters final night time.   To illustrate, right here is the radar imagery over the Northwest for 1:14 AM this morning.   The reds point out heavy precipitation!  Was it pouring offshore?

A take a look at the infrared satellite tv for pc picture on the similar time reveals no climate disturbances on the market (see under).  Just some clouds to the north (related to system that may convey us rain on Saturday).

A excessive decision seen satellite tv for pc picture taken simply earlier than sundown on Thursday confirms the dearth of climate offshore.   But notice the low stratus and fog proper alongside the coast….that might be necessary later!

So is the costly Langley Hill radar damaged?     Is rain falling out of clear skies?   Is there a proof for this thriller?
There is a solution:   tremendous bending of the Langley Hill radar beam by an unusually robust and low inversion, the place temperature will increase with top.
Let us check out the vertical sounding of temperature, dew level, and winds with top from the balloon-borne radiosonde launched at Forks, on the Washington coast, round 5 AM this morning.  
Note how temperature (the right-hand line) will increase with top within the decrease ambiance.  That represents an inversion.  The left line is dew level temperature; when dew level and temperature are the identical, the air is saturated, which was true close to the floor.
Yesterday afternoon, cool, however shallow, marine air moved into the coast, whereas heat air remained aloft.  The end result was a reasonably robust inversion within the decrease ambiance.  The seen satellite tv for pc picture exhibiting the low clouds on the coast had been a touch of what was happening.
So why will we care about inversions?   Because they will bend the radar beams (that are within the microwave portion of the electromagnetic spectrum–around 10 cm in wavelength).    
A powerful inversion can bend the radar beam all the way down to the earth’s floor in what is called superrefraction (see picture).  The earth’s floor (on this case the ocean) is a fairly respectable reflector of the radar sign and quantity propagates again to the radar, giving a false sign of heavy precipitation.  That is why the radar confirmed the arc of supposedly heavy rain offshore.   Totally bogus.

Now within the typical ambiance, with denser air at low ranges and fewer dense air above, there’s usually some bending of the radar beam, which is an efficient factor as a result of it offers the radar higher vary (see under)

There was merely an excessive amount of of factor final night time!  And don’t fret, actual rain will get to Washington this weekend, with our weekend climate curse persevering with.