First, let me show you what I am talking about...here are two radar images for 8:38 PM on Friday and 6:49 PM on Tuesday. Lots of apparent rain offshore, but very little over land...very strange!
All that rain is not coming from clouds! So if this is not some sort of alien intervention, there must be another explanation! And there is.
Last weekend and early this week the land surface temperatures have been relatively warm, and most importantly the lower atmospheric temperatures have been warm. But the surface temperatures of the eastern Pacific have remained quite cool--roughly 50F. With warm temperatures aloft and cool sea surface temperatures, a low-level inversion (temperature warming with height) formed over the ocean. We don't have a balloon-launched radiosonde over the ocean, but I can show you the simulated conditions from the UW WRF modeling system there. The red line is temperature and you can see a shallow, cool marine layer surmounted by an inversion.
It appears that the radar beam from the Langley Hill radar was not viewing precipitation in the air at all, but rather intersecting the sea surface and reflecting back! The ducting allowed the radar beam to skim the surface for hundreds of kilometers. To see this, look at this radar image I got from my colleagues in the National Weather Service...the radar beam was hitting and returning from coastal terrain way down the Oregon coast.
This problem was only apparent for the lower radar scans (.2 and .5 degrees above horizontal). For the higher scans..1.5, 2.5 and higher...there was nothing out there--consistent with the superrefraction mechanism. Today I was on a conference call with NWS radar experts in Norman, Oklahoma. They told us they had never seen such a profound, sustained superrefraction/ducting event...one for the record books.
The thing is, this is not the end of this issue. When we get warm again, the mysterious ocean rain will be back. The TV weathercaster folks will have to keep this in mind when they show the coastal radar imagery.
The event will be centered south of us, but the event will occur around 6 PM on Sunday. Unfortunately, it looks like most of our region will be clouded over at that time. Sorry. Will update on Sunday AM.
For the eclipse, the map from NASA/Google is awesome. Allows clicking on your exact location to get timing and intensity of the eclipse.
ReplyDeletehttp://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2012May20Agoogle.html
This is fascinating. Thanks, Cliff.
ReplyDeleteAmateur radio enthusiasts are quite familiar with this phenomenon, because the same ducting effect can be used to make VHF radio contacts far beyond the usual line-of-sight range. Hawaii-to-California contacts on the 2 meter (144 MHz) band via ducting are reasonably common certain times of year. It's fascinating how the atmospheric conditions affect radio waves.
ReplyDeletePresumably one must admit that the much-heralded ~0deg elevation angle capability employed for the LGX/Langley Hill (as previously described at http://www.atmos.washington.edu/~cliff/Langleyradar.html) is exacerbating this problem beyond what is routinely experienced at other coastal sites...
ReplyDeleteHappy Mt. St. Helens Day! Of course, it's not REALLY weather, but this is a fascinating report, all the same: Mt. St. Helens Recovering from Blast 32 Years On
ReplyDeleteI had noticed those radar traces and wondered about them, Cliff. I guessed they were a weird sort of ground clutter since there were no real clouds, and I guess I was more or less right. :-)
Although the closest place to see the Annular Solar Eclipse is a band along the OR/CA border, a wider area can see a partial eclipse where the sun will appear as a crescent. With rain/clouds in the forecast for Western Washington and Oregon, can anyone tell me what is the closest place with a good chance (60%+) of visible sun, even if through a little haziness? Parts of Eastern Washington are looking cloudy for Sunday afternoon too, so could I go further East?
ReplyDeleteRegional radar on wunderground.com often shows heavy precip in the middle of the Strait of Georgia on days with little or no precip elsewhere. Same phenomenon perhaps?
ReplyDeleteI don't know where else to share this, but think your readers may like this site that shows wind direction and speed for the entire us in a artful way:
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I enjoy your site - thanks
NRL and NPS in Monterey, CA see this type of ducting behavior--extending over hundreds of km--frequently.
ReplyDeleteThere's actually someone who forecasts tropospheric ducting.
ReplyDeletehttp://www.dxinfocentre.com/tropo_enp.html