Sunday, March 31, 2013

A Very Different March

With a spectacular finish, March 2013 represents a huge change  from some of the cool early springs of the past few years.   Let's compare at Seattle-Tacoma Airport!

March 2012 was dismal.  As shown in this plot of temperature (the average highs and lows are shown by the red and blue lines), no day got above 60F and only five days got to or above the normal high in 2012.  Many days cooled to below the normal low.
In contrast, March 2013 had several days above 60F and 19 days got to or above the normal high (note scale on left is different). 
Precipitation?   March 2012 had nearly 7 inches of rain, roughly 3 inches above normal
March 2013?  Drier than normal (by about an inch) and nearly no rain during the last third of of the month.
The National Weather Service Climate Prediction Center is going for much warmer than normal for the next 6-10 days (see below) and the latest model runs suggest dry conditions for the next four days.  The reason:  major ridging over the western U.S.
Enjoy.


Today (Sunday) should get near 70F over the western lowlands, with clear skies over the entire region (except for some low clouds offshore).  Eastern Washington--mid 70s.





Thursday, March 28, 2013

COSMIC: Filling the Weather Satellite Gap

The media has been full of headlines and stories about a looming gap in weather satellite coverage (see NY Times story here) and the U.S. General Accounting Office (GAO) has identified the weather satellite gap as a high-risk threat to the nation (GAO info here).   The U.S. weather satellite network has been an essential driver of improvement in numerical weather prediction during the past several decades, but mismanagement of the nation's weather satellite program by NOAA (documented by a number of independent groups such as this) has cost the nation billions and threatens  a serious gap in weather satellite coverage.  The biggest problem have delays and cost overruns for the polar-orbiter satellite program, with the costs of replacing the current satellites in the many billions of dollars (weather satellites are not cheap).

The COSMIC Satellite 

But there have been some great successes in weather satellite acquisition, and none have had more positive impact at a lower cost than the COSMIC constellation of satellites that use the bending of GPS signals to get temperature and humidity soundings (soundings describe how these variables vary with height).   But an enhancement of this extraordinary satellite system, called COSMIC-2,  is now being threatened by NOAA's inability to secure a small congressional appropriation to support their role in an international partnership and the aggressive congressional lobbying of some private-sector groups who would like to get into the satellite business.And as noted below,  an enhanced COSMIC system could go a long way towards filling the looming satellite gap.

So how do GPS weather satellites work?  Relatively inexpensive satellites in low earth orbit (LEO) receive the signal from GPS satellites placed in orbit for navigation.  The bending and delay of the signal by the earth's atmosphere allows one to determine the vertical variation (soundings) of temperature and moisture with height in a very accurate way (see graphic).  This is like having many


weather balloons (radiosondes) over the entire planet...very useful information.  And the receiving satellite can be quite inexpensive, since all they have to do is receive the GPS signal.

A group of these GPS-receiver weather satellites have already been placed in orbit by a joint Taiwan-U.S. initiative called COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate).  This has been a bargain for the U.S. taxpayer since Taiwan has provided hundreds of millions of dollars for this project and many of these micro-satellites can be launched at the same time.  The University Corporation for Atmospheric Research, including Drs. Bill Kuo and Richard Anthes, have played an important role in the organization, management, and development of this satellite system.  In 2006 the first six satellites (COSMIC-1) were launched and they were an extraordinary success.   Thousands of atmospheric soundings worldwide are being taken per day---here is a sample of those taken during a 3-h period (see graphic).


The impact of the COSMIC satellite for improving weather prediction has been huge with major operational centers such as the European Center and the U.S. Environmental Modeling Center (EMC) finding that even the limited initial system was the one of the most valuable sources of information for improving forecasts (see graphic showing the GPS satellite data was fifth in importance for the European Center).  Really stunning.  Can you imagine the impact of have 100 instead of 6 COSMIC satellites?

With the original constellation aging, Taiwan and its U.S. partners (including the U.S. Air Force) have planned COSMIC-2, with far superior GPS receivers and increased coverage.  Improvements in antenna design and signal tracking algorithm will provide better quality data. Ans  in addition to tracking GPS, COSMIC-2 will also track GLONASS (the Russian system) and GALILEO (European system) navigation systems, which will considerably increase the number of soundings per COSMIC-2 satellite.  COSMIC-2 will provide a factor of 5 more soundings than COSMIC, with even better quality.

In summary, the new COSMIC  system will be a great deal for the U.S. taxpayer with Taiwan providing large amount of funding.  A proven, cost-effective, satellite program with profoundly positive impacts on weather prediction skill.   NOAA requested a small amount of COSMIC-2 funding in the FY11 and FY12 budgets but these requests were turned down by Congress, delaying the program and threatening the partnership.   These are startlingly bad decisions.  However, there is hope that NOAA will secure a share of COSMIC-2 with funding from the Superstorm Sandy supplemental appropriation, recently passed by Congress.  This is appropriate because COSMIC has been shown to improve hurricane predictions

Lack of congressional action on COSMIC may in part be traced to lobbying by a group of private sector firms that believe there is money to be made in stopping COSMIC and then hitting the government for funding of their own satellites.   A prime example is a company called PlanetIQ, whose CEO testified to Congress recently about their company taking over the GPS satellite business.   I learned first hand about this company when one of their representatives contacted me, offering to set up a call with their CEO.  He wanted me to blog about them and how THEY were the solution.  But the information he provided me was full of untruths.  For example, the PlanetIQ rep told me that COSMIC

"misses most of North America, all of Europe and Russia. It also doesn’t cover most of the South-Pacific, a major contributor to global weather activity. "  This is totally false, COSMIC and COSMIC-2 have global coverage as illustrated by the map above.

"The experimental COSMIC prototype constellation is dying, the government of Taiwan has not a penny budgeted for its replacement,"  Not true.   COSMIC-2 is well along and Taiwan is investing tens of millions of dollars.

"COSMIC is not the answer, nor is a U.S. government program to subsidize programs of other nations in the new austere federal budget environment realistic. "  This is really bizarre.  We are getting a great deal with Taiwan covering a large part of the cost of COSMIC.  What could be better in an "austere federal budget environment" than having someone else help pay the bills?

Recently, the CEO of PlanetIQ, Anne Miglarese, provided testimony to Congress where she stated:

"But the satellites that currently collect this data are degrading while planned replacements have been delayed, are insufficient to meet the stated needs of users around the world, and will cover only a small sliver of the United States."

Much of this is simply untrue...for example COSMIC will cover ALL of the U.S. and not a "sliver." and COSMIC-2 will very much serve the needs of users from around the world.
  

The Cosmic-2 coverage is far denser than Cosmic-1 over the entire planet.


It appears that either the folks at PlanetIQ are either being disingenuous or their SatelliteIQ is far less than their PlanetIQ.  According to her testimony in Congress, CEO Miglarese wants NOAA to reject COSMIC and sign a contract with her firm committing NOAA to purchase their services.  Reject a proven system that is heavily supported by another country to commit to a firm that has no proven track record in financing and launching such a satellite constellation.  As Texans would say a group that is "all hat and no cattle."

I believe that the private sector should be taking an increased role in the numerical weather forecasting enterprise, but rejecting probably the most effective and cost effective weather satellite effort to date, one whose costs are shared with another nation, is incomprehensible.  But to make COSMIC-2 a success. NOAA needs to make a commitment to participate and to provide the needed partial support.   NOAA and DOC leadership needs to act and act soon, particularly since COSMIC-2 could greatly mitigate the upcoming weather satellite gap caused by their previous errors and mismanagement.


Tuesday, March 26, 2013

Can a weather satellite read your license plate?

A question that I am often asked is:  what are the finest details observable from weather satellites?

Let me show you some examples.   Most of the weather satellite imagery you see on TV and the web is from the geostationary weather satellites, located over the equator at an altitude of 36,000 km.  In that orbit they remain over the same portion of the earth as the earth rotates during the day.  There are five of these satellites, two owned by the U.S.


The highest resolution imagery from those satellites are in the visible part of the spectrum (roughly .4 to .7 microns...millions of a meter), the wavelength your eyes are most sensitive.  The pixel size over the equator is roughly 1 km and that resolution degrades a bit as the satellite observes to the north and south.    Here is an example of a high-resolution visible image from one of these satellites (GOES-W, position at 135W) on March 23rd at 1 PM PDT.


And to illustrate what it can see better, let me show you a blow up over Puget Sound.

If you look carefully, Lake Washington and Lake Samamish are visible, as are the major river valleys in the Cascades.   No worries about license-plate reading!

But there is another class of satellite, called polar orbiters, that is positioned much closer to the surface (only about 800 km above) in orbits that allow them to see constantly changing swaths (often about 1000-2000 km wide) of the earth below.  I often show imagery from the MODIS polar orbiting satellites on this blog and they have pixel size of 250 meters.  Let me show you a sample of this for nearly the same time as the geostationary satellite image shown above, again for visible wavelengths.

You see the difference?   Much sharper.  And you can see the individual puffy cumulus clouds that were forming over land that day (as the land heated up the atmosphere destabilized, producing convection).  Look how well defined Seattle's harbor....Elliot Bay.. is!  You can even see the sand spit at Sequim.  One can learn a lot from such images.


Now there are other, non-meteorological, satellites that have much finer resolution.  For example, LANDSAT imagery has resolution of 15-30 meters.   Here is a sample:


And I assume that the CIA has satellite imagery capable of doing much better....

Want to look at the weather satellite imagery yourself?   A few good websites:

National Weather Service Western U.S. Products:  http://www.wrh.noaa.gov/satellite/?wfo=sew

NWS Aviation Weather Center Server:  http://aviationweather.gov/adds/satellite/

NCAR RAP Satellite Server: http://weather.rap.ucar.edu/satellite/



Saturday, March 23, 2013

Why don't we get rain and wind at the same time?

An interesting aspect of Northwest storms is that generally we don't get heavy rain and strong winds at the same time.    This week's early spring storm was a good example:  first came the rain and THEN came the wind.  Why don't they occur at the same time?  It has to do with the nature of the structure of Pacific storms.

Let's start with a plot of wind, precipitation, and other weather parameters over a 72-hr period this week at the University of Washington.  The top panel shows the winds and the fifth panel presents precipitation.  Time is in Greenwich Mean Time (GMT or UTC).  Lots of rain from 0000 to 1500 UTC on the 20th, but the big winds waited until 1800 UTC on the 20th.  Classic.  Remember the Chanukah Eve Storm in 2006?  Pouring rain during the day, but the big winds came during the evening and early morning hours after nearly all the rain was over.  I could give you a hundred examples of this behavior.

So why the separation? Consider the storm on the 20th.  Here is the surface weather map for 1200 UTC on the 20th during the rainy period.   The low center and the big pressure differences (gradient) was still offshore, but moist, warm southwesterly flow was coming into the area and the storm's front was approaching the coast.   Wet, but not particularly windy.

Here is the radar for that time.  Lots of rain....yellow is very heavy stuff.


Now, fast forward to 2100 UTC (2 PM)--here is the map.  Lots of pressure gradient and strong winds as the low moves past us to the north.  But the front is inland and the flow has switchws to the west and northwest....much cooler and drier are moving in.  Yes, we can get a few showers, but not much more.

Here is the radar at this time---pretty wimpy precipitation--except for the convergence zone over the northern Sound.  Major rain shadowing fro Seattle to Olympia.


A schematic of an oceanic cyclone and attendant fronts summarizes the situation. Shading shows the main clouds.  The big precipitation is generally with the fronts, which lead the low center.  The big winds are south and west of the low.


 Yes, there are some situations where we can get driving rain and wind, but generally and with most of our windstorms, there is a substantial separation between heavy rain and wind.

Thursday, March 21, 2013

How Low Can It Snow?

Spring is here...and often we get some of our coldest air aloft during the early part of this season.

Behind yesterday's strong front, we are getting some very cold air moving in aloft, with temperatures at roughly 5000 ft (850 hPa) dropping to -6 or -8C. Those temperatures are much colder than usual and cold enough, in the presence of heavy precipitation, to bring snow levels down to near sea level...and certainly to the tops of higher hills (500-1000 ft).    The cold air aloft, coupled with the warming of the surface (yes the sun IS getting stronger), produces a lot of convective clouds and showers (convection...associated with cumulus and cumulonimbus clouds... is forced by large changes in temperature with height).  Such convection produces intermittent heavy precipitation and is being enhanced by convergence zones in the lee of the Olympics and upslope on our local terrain.

Why do heavy showers cause the snow level to descend?  Melting of snow falling into warmer air is the big reason.  Evaporative cooling can be important as well if the air below is not saturated (100% relative humidity).

The latest visible satellite and radar imagery really shows the instability clouds and showers.



A proof, here is a picture earlier today of a light dusting  of snow at Clearview, northeast of Seattle near Mill Creek, provided by Lori McConnell.

Take a look at the predicted temperatures for 8 AM on Friday at roughly 3000 ft (925 hPa) from the UW WRF model--the blue is cold air air!


And here is the 24-h snowfall predicted by our flagship, super-high resolution WRF model...1.3 km horizontal grid spacing for the period ending 5 AM on Friday.   Some snow getting real low---nothing heavy of course....   so Jim Forman of KING-TV can keep his parka in the closet.   More of a change over NW Washington and over central Puget Sound where the convergence zone will be active.

And there will be lots of snow in the Cascades... some locations (particularly those feeling the enhancement of the convergence zone) could get a foot or more.

View from Peter Benda's House in Bellevue on Thursday
View from Peter Benda's house in Bellevueon Thursday

Wednesday, March 20, 2013

Strong Spring Storm

A vigorous low pressure system and attendant front is now moving through the Northwest.
A 3-h forecast for 8 AM this morning shows a moderately deep low (985 hPa) crossing northern Vancouver Island and the surface occluded front now over western Washington (solid lines are isobars, colors are low-level temperatures, wind barbs as well--if you have good eyes).  Strong pressure differences exist west and south of the low and some of that will be moving into the region later this morning and during the afternoon.   So expect a major uptick in winds. Very strong pressure gradients and powerful winds west and south of low centers is very typical for oceanic cyclones...lots of names of this--bent-back trough, poisonous tail, and others.

Take a look at the 8:30 AM visible satellite image.....stunning picture showing the front over western Washington and the cold unstable air behind it. (click on it to get an enlarged view)


 Here is the forecast for this afternoon at 1  PM---you can see how the low has moved inland and large pressure gradients extend over western Washington and the coast.  Big pressure gradient cause strong winds.

 Of particular note, as the low moves past us, a very large pressure difference will be set up at low levels over the Strait, while aloft the winds will be aligned along the axis.  As a result, expect a strong surge of westerly winds down the Strait, with gusts reaching 40-60 mph.  Here is the sustained wind forecast for 2 PM this afternoon.  The green winds are sustained at 35 kts.


 The other major story with this system is snow---lots of it in the mountains.  For the first time this winter Mt Baker has reached 200 inches of snow depth with 203 inches reported at 6 AM PDT after 11 inches of new snow fell since late yesterday afternoon.  Normal snow depth for March 15 is 165 inches at Mt Baker.   And lots of new snow at Mt. Rainier....here is a view from Paradise this morning.


And congratulations...we are now officially into spring, which stated 4:02 AM this morning!



Monday, March 18, 2013

Ode to Northwest Rain Shadows

(Coming Attraction:  Windy on the coast, the Strait and NW Washington on Wednesday, as a moderately strong low crosses northern Vancouver is)

 ...........................

We think about our lives here in the Northwest being shaped by the rain, but one could argue that our lives are even more influenced by the rain shadows, those locations downstream of major mountain barriers that are considerably drier than much of the region.  Most Northwest folks live in rain shadows---locations with less annual precipitation than the bulk of the eastern and central U.S.

Precipitation enhancement occurs on the upstream (windward) sides of mountain barriers as terrain forces air to rise.  On the other hand, precipitation is suppressed as air descends the downstream (lee) sides of terrain.  Often the drying (the rain shadow) extends quite a distance from the barrier, with the driest conditions often stretching 50-150 miles away.   The immediate lee of the barrier still can have quite a bit of precipitation, since precipitation generated on the windward side can blow over for 5-10 miles (or even more under strong winds).

One is always struck by the annual precipitation map of the region (see below), which shows some of the greatest precipitation gradients in the U.S.   Yes, we have very heavy precipitation (over 160 inches a year) over the SW side of the Olympics, yet in the rain shadow to the NE of the barrier they only get 15-20 inches a year.  Why is the annual average heavy rainfall and rain shadow oriented that way?  Because the winds approaching the region below 8000 ft during the winter are generally from the SW when precipitation is occurring.  Although Sequim, San Juan Island, and northern
Whidbey are in the middle of the rain shadow, the Puget Sound lowlands also get a piece of the rain shadow action because we also in the lee of the Olympics and coastal mountains to some degree.  The farther north one goes over the Puget Sound lowland, the drier.  Olympia and adjacent areas are wetter because they have a fairly clear shot to the oceans...thus less rain shadowing.

So what would Seattle be like if the Olympics and coastal mountain were removed?  You don't want to know!  Seriously, I would expect it be similar to say Grayland, a station on the central WA coast. (see table below).  A place with 73 inches of rain a year, summer highs around 67F, and nearly no snow.   Grayland indeed.


We should be thankful for the Olympics!  But the most profound rain shadow is to the east of the Cascade crest, with large areas getting less than ten inches a year.   This is very special rain shadow....one with an abundant water source from the Columbia River, which drains off the terrain of British Columbia and northern Washington.  The combination of the two provides ideal conditions for some of the best grape and orchard areas in the world, as well as other valuable crops like hay and hops.  Head a bit farther east, where precipitation starts to edge up a bit, and the rain shadow provides a superb zone for dry-land wheat.

Can rain shadows move?  You bet.  If the flow approaching the mountains shifts direction, the rain shadow will follow....thus when air is from the west, the Kitsap Peninsula and Seattle can be dry while those usually smug folks around Sequim and Port Townsend are getting a good soaking.  As noted in my blog last week...such a shifted rain shadow occurred last week.   Here is a nice radar image of this event (late Tuesday).


Looking farther afield, rain shadows maintain their importance, with Portland and the Willamette Valley profoundly drier than the Oregon coast.  I could write volumes about local rain shadows....and some have (see below).  And I hear that werewolves don't like rain shadows.

Rain shadows define our lives here in the Northwest.   We should never forget that.









Saturday, March 16, 2013

Climate Tribes


"Deniers" versus "Warmists"
"Skeptics" versus "Alarmists"

They are mirror images of each other in many ways.

Both have close communication among an "in-group" of similarly minded individuals with denigration of the character and intelligence of the "other side."  Each has its heroes and incarnations of evil among its opponents. Both see themselves as guarding the sanctity of science and protecting the interests of mankind.  In a bizarre sort of way, they need each other.

The climate "debate" is about a technical subject-- whether mankind's addition of greenhouse gases to the atmosphere is causing and will cause global warming-- and it has become a tribal conflict; a development that one can argue is not helpful for either the science or mankind's efforts to deal with a potential threat.

The battle among these groups is particularly intense in the blogosphere:

Watts Up With That, Climate Audit, Climate Science, Climate Depot, Roy Spencer's Blog, among others, on the "skeptic" side.

Real Climate, Climate Central, Climate Progress, and SkepticalScence represent only a few of the "warmist" blogs/webpages.

The media, crippled by a reduction in science reporters and unwilling or unable  to carefully analyze a technical subject, headlines the most ominous warnings and predictions, which are often based on press releases or material lacking proper peer review.

And perhaps most of disturbing of all, this scientific issue has become a political football, with Republicans and Democrats increasingly divided on this and other environmental issues.   Recently I went to a talk by Harvard Professor Theda Skopol in which she showed a figure on the environmental voting records of the two parties (see below) and it was stunning.  Before roughly 1992, both parties had a middle of the road stance, with Democrats being modestly more likely to support environmental spending.  But during the last few years, the differences have become profound (roughly 90% for Democrats, 10% Republicans).  Talk about polarization.
As noted above, in a strange sort of way the extreme sides of the climate debate feed off of each other.   Here is an example of how this works.

Many believe that global warming is going to be very real and a threat to mankind (and about that they are certainly correct). The evidence of human-induced global warming is subtle right now because natural variability is large and obfuscates the relatively weak global warming signal AT THIS TIME.   However, actions must be taken now to stop large warming later in the century.   The problem is that few folks are willing to make substantial sacrifices NOW to use radically less fossil fuels (including climate scientists, by the way, who probably fly more than anyone else).

So what do some "alarmist" folks do?   In the hope of getting society to do the right thins, they hype current big storms, droughts, and other weather events, claiming that such events are either signs of or "consistent with" human-caused global warming.   The media, always hungry for apocalyptic headlines and unwilling to fact check the claims, highlights these scary, but generally unfounded, claims.


Now these unsupported claims (e.g., Hurricane Sandy is a sign of global warming) are fairly easy to disprove and the skeptic sites (e.g., Climate Audit, Watts Up) have a field day tearing them apart.  Surely, if the alarmist claims of warming-induced extremes are obviously false, the whole global warming business is unfounded!

On the other hand, the "skeptic" side is fixated on the lack of warming during the past decade, wrongly believing that the warming due to greenhouse gases must be linear and continuous.  The "pro" global warming side can easily show that natural variability will inevitably produce such plateaus in temperature, particularly today when the global warming signal is relatively weak, and use this obvious fact to criticize the skeptics.

The "pro" side accuses skeptics of being on the payroll of oil and coal companies.  The skeptics suggest that global warming researchers are swayed by the allure of big research grants for "right-thinking" studies.

The blogs of each side are followed and commented upon by similar thinking communities, folks that feel camaraderie with each other and enjoy making fun of their confused opponents. God help you if you express a dissenting opinion.   I tried that on skepticalscience.com and it was suggested that I was either a liar or ignorant.  Name calling has become a frequent characteristic of some of these sites.  To some degree, having thoughtful folks on both sides of an argument can be good thing, and I do think that blogs such as Climate Audit, Real Climate, and Watts Up often make valuable contributions to the discussion.  But the debate too often gets ad hominem and extreme, even on these sites.

The transition of an essentially scientific and technical issue to one being divided on political/social lines surely reflects the increasing polarization of our society, as reflected in our hapless Congress.   One could argue that with  the climate issue, no one has contributed to this division more than Al Gore.   The 2000 election divided the nation in many ways, and when a Democrat partisan took up the issue (along with his movie), politicization was perhaps inevitable.


I believe that one of the most problematic effects of this tribalism has been its influence on the scientific community.   Nearly all members of the atmospheric science community recognize the potential for substantial warming of the globe due to anthropogenic (human-caused) emissions of greenhouse gases (and other impacts such as deforestation).  But it is more than that..there is an orthodoxy and accepted view.   Talk about serious impacts, one gets knowing nods. But dare to say that some claims are overblown, and a cool wind blows.

I learned this first-hand about ten years ago when some local scientists and politicians were making claims of huge reductions in NW snowpack due to mankind's emissions, and the deputy WA state climatologist was fired for bringing the claims into question. I supported him and was pulled aside by some other UW faculty, who warned me that I was providing aid to the "deniers."  A bunch of us wrote a paper on the subject and sent it to Journal of Climate.  I have never had such a difficult and poorly handled review process--the sub-editor was obviously trying to kill it.  Finally, after a huge effort and the intercession of the editor (who was local) it was published.

And the pressure of the skeptics have made some scientists defensive, circling the scientific wagons, so to speak.  The Climategate emails show the unfortunate result.

The politicization of climate change also has had a major impact on government resource allocation, with bountiful funding going into climate change research, while other areas, such as weather prediction are poor cousins.  How else can one explain that climate research gets more than one hundred times the computer resources provided to weather prediction, with the latter having huge benefits for people TODAY?  NOAA administrators have continuously pushed the climate agenda, while downplaying weather prediction.  This needs to change.

How we get out of this polarized situation?   I am not sure.  But it sure is a problem.




Wednesday, March 13, 2013

Poseidon's Shadow

Today has been one of amazing contrasts.   A river of moisture (a.k.a. the finger of Poseidon) has been approaching the Olympics and North Cascades, producing very heavy precipitation, while in the rainshadow of the Olympics it is has been nearly dry.    We are talking about a hundred-fold variation in rainfall over a few dozen miles.  The multi-radar image at 9:14 PM Tuesday shows the contrast vividly.


 Let me further illustrate by starting with the storm-total rainfall at of 9 PM Tuesday from the coastal (Langley Hill) and the Camano Island radar.  First, consider the Camano Island radar (remember it does a poor job over the Olympics).  You will notice the central and northern Cascades are getting hammered with peak values of roughly 5 inches.  In contrast, nearly nothing fell from Seattle across the Kitsap, with heavier values towards the north Olympics and Strait (5 inches plus).


The Langley Hill radar (see below) shows at least 5 inches on the western side of the Olympics and a substantial decline over the ocean.  


We can also look at the rainfall measured at the ground.  Here are the values for the 24-h period ending 9 PM Tuesday.  In central Puget Sound many locations had only  .01-.04 inches--barely enough to wet the concrete.  And yes, those dessicated folks in Sequim had only .01 inches.  In contrast, lots of locations on the western and southwestern side of the Olympics and in the north Cascades had 3-4 inches.   Extraordinarily short distances (say from Bothel, just north of Seattle, to the nearby foothills (roughly 20 miles to the east) brought a change from a few hundredths to well over three inches.  Amazing.  This is why one has to love Northwest weather...the contrasts are extreme.


Just as amazing is that our numerical models had a pretty good handle on the situation.  Here is the 24-h precipitation prediction starting 4 PM yesterday (a close match-up in time for the plot above).  Not perfect, but it realistically predicted the rainshadow and heavier precipitation in the Olympics, mountains of Vancouver Island, and the central/north Cascades.


Based on this forecast, I biked to work on Tuesday.  Piece of cake.