Wednesday, November 30, 2011

Highest Pressure in Decades Over The Northwest?

Do you feel the pressure?  Is it like the weight of the world is on your shoulders?  There may be a reason:  right now we are experiencing some of the highest atmospheric pressures in years and probably decades.

Take a look at the National Weather Service sea level pressure analysis at 7 PM (below).


A very strong high pressure area is centered over the Northwest and southwest Canada, with pressures greater than 1040 hPa over much of the region and a 1046 hPa center over southern BC.  1046 hPa is equivalent to 30.89 inches of mercury.  Folks, this is REALLY high sea level pressure.  At Sea-Tac the 9 pm pressure was 1042.6 hPa--and it is still going up!  There has been a huge pressure rise over the past 24h--roughly 20 hPa. The highest SLP I see at 9 PM is 1045.2 hPa at Lytton BC (elev 751 ft).

From experience I know these pressures are very unusual, but lets check the UW pressure archives.  Here are the hourly pressures at Sea-Tac airport since 1996.  Looks to me like the pressure last hour (9PM Wednesday is the final plotted red dot) was the highest during the entire record shown here (I confirmed by looking at the numbers).  So the highest pressure in 15 years!  That is impressive.

And the pressure is still going up!  The Portland International Airport has recorded a maximum barometric pressure reading of 30.76" (4:53am observation) which is tied for the second highest reading since records began at the airport in 1940 (thanks to Steve Pierce for this information). The bottom line is that we are experiencing truly unusual pressure right now...I wonder what this does to people with arthritis and sensitive joints.

 This push of high pressure over the Northwest is creating huge pressure gradients over the southwest U.S.  Here is the latest model prediction for tomorrow morning.  High pressure over us and a big pressure differences over Colorado, Utah, Nevada, California, and the offshore waters.


Very strong winds will be the result of these big pressure gradients, including gusts hitting 50-80 mph in places.   In fact, it has already started.  Take a look at the latest wind reports of greater than 45 mph over the western U.S.---quite a few of them.


And here are some recent reports from the National Weather Service office near Los Angeles.  Gusts as high as 69 mph so far.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OXNARD CA
802 PM PST WED NOV 30 2011

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..

0557 PM NON-TSTM WND GST 1 NW SANTA CLARITA 34.42N 118.53W
11/30/2011 M67 MPH LOS ANGELES CA MESONET

67 MPH GUST AT SAUGUS RAWS LOCATED 1450 FT

0555 PM NON-TSTM WND GST 5 N SAN FERNANDO 34.36N 118.42W
11/30/2011 M64 MPH LOS ANGELES CA MESONET

64 MPH HOUR GUST AT CAMP NINE RAWS LOCATED AT 4000 FT

0753 PM NON-TSTM WND GST 8 ESE CASTAIC LAKE 34.60N 118.58W
11/30/2011 M69 MPH LOS ANGELES CA MESONET

69 MPH GUST AT WARM SPRINGS RAWS LOCATED AT 4930 FT


High pressure will bring us dry conditions and some sun...but air quality may decline.

Monday, November 28, 2011

Climatologically, The Worst of Winter is Over!

Yes, you read that right.

The last week or two of November is climatologically the worst period of the year by many measures.   For example, consider the average precipitation per day at Sea-Tac Airport (below).  It peaks in last November and most of December is a drier.


Or how about extreme daily precipitation at the same location?


Big peaks in November and a radical reduction in extreme precipitation in December. 

Just like clockwork there is going to be a major break in the coming up this week, but first we have to get through one more storm. A low center and accompanying clouds and precipitation is moving towards us from the northwest and should bring precipitation to the region late tomorrow and Wednesday AM.  You can see it off our coast in this satellite image:


This system should be unremarkable. After that a very strong ridge will build northward into the eastern Pacific and will remain in place for at least a week.  You heard me...a week.

Like Wednesday morning

Thursday morning


 Friday morning
Saturday morning


You get the idea.  And we will have lots of sun...and some fog in the AM.  The biggest threat to your life and safety will be ice on the roadways.  Will we have another big storm...of course we will. And a good chance of some lowland snow.  But ON AVERAGE things typically improve as we move out of late November into December.

The National Weather Service has this regime going into next week...here is their latest 6-10 day precipitation forecast:  below normal in the West.


 This looks like a good time for local meteorologists to go on vacation.  Or to rake some leaves.

PS:  I know "official" winter starts on December 22 and ends in March.   The point is that calendar winter is really quite different than meteorological winter in many parts of the country...and we are a good example of that.    Around here the end of February could really be considered the end of winter....sun is much stronger, far less weather systems, chance of flooding goes to near zero, etc.  And the grass starts growing again on the west side of the Cascades.  When I have to mow my lawn, winter is over..period.

Saturday, November 26, 2011

Why is Northwest Washington So Windy?

It seems like it occurs during nearly every storm.  Before a front or low center hits our region, one area gets winds first--and they are often very strong and from the southeast .  We are talking gusts about 50 mph and higher in the stronger events.  And then after the storm moves by, they get hit by powerful winds from west.

What is this benighted region, one in which Seattle TV stations often stage their camera crews for dramatic wind shots?

The answer:  Northwest Washington...the region extending north and west of Everett, over northern Whidbey Island, to the San Juans and down to the NE tip of the Olympic Peninsula.

Why is this region so windblown?  And why only certain directions? Why can the winds be blowing at gale force there, while Seattle is practically calm?  I will try to explain in this blog.  We have had a number of major NW Washington wind events this month and another will hit tomorrow (Sunday, 11/27).

Northwest Wind Land
I got my first personal taste of the NW Washington winds in the 80s while I spent the night at Rosario Resort  on Orcas Island.  The winds came up quickly that night and they were roaring!  Just heaven.

A mild event is going on right now (Saturday, 9 PM).   Here are the winds:

Calm in Seattle and Port Angeles.  Very light winds at Sequim and Victoria. 30 knot sustained winds at Smith Island and northern Whidbey Island. Gust over 40 mph.  These radical differences in weather over short distances are why we love Northwest weather!

Sunday morning things will really be blowing: here is the lasted WRF model forecast of sustained winds at 4 AM.  Sustained winds of 40 kts (46 mph)...with higher gusts, of course.


 So why the strong winds?  One reason is the extensive amount of water in the area and winds blow much stronger over water because it is aerodynamically smooth.  But there is something else....the OLYMPICS!.   The mountains distort the local pressure field, with pressure being increased on the windward side and decreasing on the leeward side.  The winds in these situations are almost always from the south...thus there is high pressure on the southern flanks of the Olympics (rising air causing cooling and cool air is more dense and thus results in higher pressure) and lower pressure (leeside trough) on the northern side where air sinks and warms by compression.  Here is a graphic of the situation at the same time as the previous figure...the lines are isobars (lines of constant pressure) and the wind barbs are shown too.   See the distortion of the isobars by the Olympics?  Nice lee low by Port Angeles and Sequim.  Do you see how the distortion caused the isobars to bunch up from roughly Everett to Whidbey Island?  Such a large change in pressure is called a large pressure gradient.  That causes the winds to accelerate greatly as the air moves from higher to lower pressure....and is the essential cause of the strong winds observed tonight and on Sunday....and many other times!


You need good southerly flow approaching the Olympics to get this effect...and such southerlies often precede a strong front or accompany an approaching low that is headed to the north of us.  In fact, when a low goes north there is a background south to north pressure difference that can really add to the strength of the southerlies forced by the Olympic effect noted above.  Here is a larger scale view of the pressure situation tomorrow at 4 AM... a strong front IS approaching.


Just to show how windy Smith Island (just west of Whidbey Is) can get, take a look at he recent max gusts there.  Lots of 35-40 kt gusts the last day and nearly 60 kts on the 24th.


But wait until tomorrow morning! You can check the winds yourself at this site:

http://www.ndbc.noaa.gov/maps/NW_Straits_Sound.shtml

Friday, November 25, 2011

Weather Gifts

Today is Black Friday when many people are thinking about getting that perfect gift for friends, loved ones, and even for yourself!

Why hit the malls for a sweater or electronic luxury when you can get a weather-related present? 
A weather gift is great for that budding young meteorologist or to determine the weather at one's home or business.  To connect in an intimate way with the environment around you. I have gotten a lot of questions over the years about the best weather stations or weather instruments--and I will answer some of them here.  You don't have to spend a lot of money on weather gear to get a good start, and remember many of the founding fathers of our country (Washington, Jefferson, and Franklin) were weather enthusiasts and took their own observations for years!  To quote Benjamin Franklin:   

Some are weatherwise; some are otherwise.

My own career in meteorology began with a Lionel weather station my parents gave me as a nine-year old.

Books and Calendars


     It is always good to read up on the subject.  Now, of course I am biased and recommend my own book:  The Weather of the Pacific Northwest, available in local bookstores and online (Amazon, Barnes and Noble, etc).  This book was written for layman and has lots of color pictures and graphics and is reasonably priced ($20-30).

 You want a general introduction to weather?   A good book, although  pricy, is the textbook I used in Atmospheric Sciences 101:  Essentials of Meteorology by Donald  Ahrens. The new books are an absolute rip-off (like $140!) but you can get used books for $20-30. (Some day I will blog about the corrupt textbook publishing industry).  Get an old edition...essentially the same.
AMS Weather Books also has an accessible introduction to weather and only costs around $25.00:  The Ultimate Guide to America's Weather.
A weather calendar is also a nice gift, particularly one directed towards your area, with information about daily climatology and records.  Well, the Washington Weather Calendar is available for only $14 and has local weather records and average conditions for each day...plus, $1 of each calendar helps support the UW Student Chapter of the American Meteorological Society.

Cloud Charts

   Want to learn the clouds and get a nice poster at the same time?  Get a large cloud chart! Perhaps the best was created by UW's Art Rangno and is available at many outlets and online for only about $7.00! 


Inexpensive Weather Instruments


  Want to start observing the weather but your budget is limited?   Rain gauges are both fun,  useful, and relatively inexpensive.  You can pick up garden rain gauges for $10-15 at garden stores or Lowes/Home Depot, or you get a truly high-quality gauge for around $30.  A good one is used in the Cocorah national rain gauge network and can be order online at http://www.ambientweather.com/strgloteprra.html (see below)



Remote temperature sensors are also reasonably prices ($20-30) and can be purchased at local stores (Bartell, Fred Meyer) or online.
These units are relatively accurate and give you high and low temperatures.

Complete Weather Stations

For real enthusiasts who have more available funds, a complete weather station might be what you want.  Such units measure temperature, humidity, pressure, precipitation, and wind speed and direction--and for more money you can get even capabilities (e.g., solar radiation).   The quality of these units range from modest to professional quality and prices extend from just over one hundred dollars to a thousand dollars and more.  Many allow you to interface your weather statoin to a computer for display and archival, as well as putting your data on the web in real time.

Based on our experience at the UW interacting with many networks and installations, probably the best deal (quality and price combined) is for the Davis Vantage Pro systems. The Vantage Pro 2 costs about $500:
Cheaper unit, but not as good, are available online, Costco, and other outlets. A good list of them is available at: http://www.weathershack.com/home-weather-stations.html

Few activities are as enjoyable as understanding and observing the weather, and these gifts give you a good start at it.


Tuesday, November 22, 2011

An Extraordinary Storm

This is turning out to be a major winter storm, with serious rainfall, flooding, and winds.  And it is not over yet...some of the biggest action is yet to come.  This event is also spotlighting a lot of new technology:  coastal radars, super-hi resolution modeling, and others.

A lot of the rain is still yet to come, but consider the rainfall of the last 48h as shown in our RainWatch site:


Over five inches near the Hood Canal area and 2-3 inches extending eastward to the Cascades where precipitation picks up again.   You can add at least another inch or two to this before the event is over.  However, the real precipitation hot spot is to the south over the southern Cascades and northern Oregon coastal mountains.  Here is the latest storm precipitation total from the Portland radar (not as well calibrated as the above image) at 8:23 PM Tuesday (roughly past 48h):


Some values in the southern Cascades reaching 8 inches according to the radar.  Several raingauges there have reported 5-6 inches over the past 24 hr.

The National Weather Service is now predicting flooding on several rivers, some with moderate flooding, as seen by this figure from their website:

A particular threat is for the Chehalis River, where moderate flooding is predicted--although there is lots of rivers flooding over southwest WA and NE Oregon.  Even the Snoqualmie is getting to bankfull.  The Skokomish always floods...but that is another story.

A few of you have commented that this seems too cool for a pineapple express event and you are right.  This is not a classic pineapple express event in which warm, moist air feeds up from deep in the tropics and subtropics.  Temperatures are far more moderate and a look at the cloud shows that moisture is streaming from the southwest but not down to the vicinity of Hawaii (see picture).  In fact, some of the moisture can be traced back far, far to the west--perhaps we should call it the Sushi Express.


But the other story here is wind and we have had some amazing winds...including 97 mph at Mt. Hebo in the Oregon coastal mountains, 70 mph at Bellingham, 70-85 mph on the Cascade crests, and 60-70 mph gusts all along the Washington and Oregon coasts.  But the big action is about to happen over the Oregon coast, where the WRF high-resolution model is going for sustained 50 kt winds tonight, with higher gusts (see graphic).  If you are on the Oregon coast, you better get some batteries.
Forecast winds at 1 AM Wednesday
 The new coastal radar has been a real boon to local meteorologists during this event...telling us what is coming and how long the rain will continue.  Here is a great shot showing a front (narrow line with red embedded) approach the coast last night...a front that represented the temporary end of rain this morning:

 The models have really been good--getting the timing and major features correct.

And did I mention the over a foot of snow in the mountain passes today and more over the North Cascades.  With high to extreme avalanche danger as all this wet heavy snow falls on the light snow with embedded weak layers.  This is really a good time to be a local weather lover...more action than one can keep track of.

Monday, November 21, 2011

Major Storm: Heavy Rain, Flooding and Very Strong Winds Along the Coast

A VERY serious storm is going to hit the Northwest during the next two days--one that will cause flooding and coastal wind damage.  And the urban areas are doing to experience a deluge.

Here is the forecast precipitation over the next 48h over the region and over western Washington.The Olympics, the north Cascades, and the mountains of southwest Washington and NW Oregon are going to get hammered with 5-10 inches of rain (reds).   Even Seattle will get nearly 4-5 inches if this forecast verifies.

Folks, this will be a major event.


There is a serious threat of flooding on a number of rivers.  The Skokomish is a given.  It looks like there will be flooding of the Chehalis...and that means those near the river should prepare.  The NWS River Forecast Center is going for a major flood at points along the Chehalis....here is an example:

And there are others that I won't list now.

The other threat of this event is wind--HUGE winds along the Washington and Oregon coasts (worst along the Oregon coast).  Take a look at this forecast of sustained winds for 1 AM on Wednesday morning.  Sustained winds of 50 kts with gusts heading to 70-80.


The Washington coast will get the strong winds earlier...tonight...see below:
Regarding snow, the models are putting a few feet over the north Cascade...and far less to the south where the freezing level will be relatively high.  An interesting aspect of this case is that it is NOT a pineapple express event with a moisture plume extending from just north of Hawaii.

Anyway, I believe a major storm event is about to unfold...and it will be fascinating to use the new Langley Hill radar.

Sunday, November 20, 2011

Northwest Flood Myths and A Major Flood Threat

As we gird ourselves for a period of heavy precipitation and probable flooding on some local rivers, it is probably a good time to talk about some "myths" regarding Northwest flooding events.  Some of these I have discussed previously in this blog, but recently I read a very nice summary of these misconceptions prepared for the USGS by Joseph Jones.  Here are a few:


MYTH:  A "100-year" flood only happens every 100 years on average.
FACT:  a "100-year" flood happens about every 4.5 years on rivers draining into Puget Sound

How many times have you heard on the news about some locale in the region having a "100-year" flood?   A few I bet.  When there is more than one over a relatively short period (5-10 years)  some people suggest something is wrong with the way meteorologists/hydrologists decide such things.  Others suggest that this is PROOF that global warming causing more extreme precipitation (I have a collection of such statements by activist groups and NGOs s that I will spare you right now).  How many 100-year floods have we had lately? January 2009 for the central WA Cascades, December 2007 over southwest Washington and Northwest Oregon, October 2003 over Northwest WA, February 2006 for northern Oregon and southwest WA.  And there are more.

Believe it or not, having frequent "100-year" floods over the region is just what one would expect.  Let me explain. When we use the term "100-year flood" we mean a 100-year recurrence interval...a flood we would expect to be observed once in 100 years at some location.  Or to put it another way, a flood with a 1% chance of being exceeded at a point in a given year.

Now the first thing to consider is that if there is a 1% chance of something happening in a year, it is possible for two events happening two years in a row.  Just like getting two heads in a row when an unbiased coin is flipped.   But there is something else that is more important in this case.   The term 100-year flood is talking about the chances of getting a flood at some location.  As the distance between points increase, the flooding at the points becomes less and less correlated.  You can get a flood at one location and not another.  Think of it this way....it is like flipping coins at more than one location and so the chances of getting two heads in a row are increased.   Thus, if one considers a  region, the chances of getting a 100-year flood somewhere in the region is greatly enhanced over a single point.   A careful evaluation of the probabilities (e.g., Troutman and Karlinger 2003, Water Resources Research) reveals that for the rivers draining into Puget Sound one would expect a 100-year storm every 4.5 years!   If you widened your viewpoint to the all of western Oregon and Washington, the chances would even be better.

So if we have an 100-year flood every year or so around the region..that is exactly what one would expect and you don't need climate change to get it.

MYTH:  Rain-on-snow events, where warm rain falls on and melts a lot of snow, is a major cause of severe flooding.  In other words, melting snow is a critical component of major floods.

FACT:  Rainfall intensity and duration are the keys elements for all major local floods.  Melting snow might contribute in a minor way, but is not required.

If one analyzes the major floods in western Washington, all have been associated with extreme precipitation that could explain the vast majority of the flooding (reference:  hydrological expert Professor Dennis Lettenmaier of the UW, chief US Army Corps of Engineer meteorologist in Seattle--Harry Schick).  Several major floods early in the season occurred when there was little if any snow to melt--just as October 20, 2003.

This Week's Situation

There is a very serious heavy rain and flooding event setting up this week.  Originally it looked like the Olympics would be be in the center of the plume of moisture, but the latest model runs suggest the heaviest precipitation could be over southwest WA, northwest Oregon, and the southern WA Cascades.  Even the Puget Sound region will get a lot of rain and it would be worse for Portland.  Here is the 48-h total precipitation ending 4 PM Wednesday.  The reds are 5-10 inches--and most of this occurs over 24h (see second graphic for 24-h precipitation ending 4 AM on Wednesday). 



 Here is a blow-up 48h rainfall over Washington--Portland is going to get hit hard if this is true with some isolated areas of over 10 inches of precipitation.  It is going to fascinating (and scary) to watch this unfold with the new coastal Doppler radar.  This is the kind of situation it was installed to help with.




My Lost Dog Situation
       Leah, our black and white female cockapoo, is still on the loose in Mountlake Terrace...we have had some sightings and one person even gave her a hamburger before she bolted.  Our biggest problem is that the City of Mountlake Terrace is removing our signs, even ones on private property.  Last sighting was near the Moose Casino off of SW 220th.  If you live in that area, please let us know if you see her.

Friday, November 18, 2011

Snow Update

It is is looking increasingly unlikely there will be any significant snow over the lowlands tonight north and west of Olympia.  Just a few scattered snow showers, particularly over higher hills and in a dying convergence zone near Everett and extending east.  The latest model runs show far less precipitation and a much more amorphous low center (see graphic below).  Less cold air moving in...in fact, the freezing level has gone up to

Forecast 4 AM sea level pressure and temperatures

2000 ft, which implies a roughly 1000 ft snow-level.  Our wonderful new Langley Hill radar show some strong showers coming to the coast right now...but very little significant precipitation behind it (see below):

8:20 PM radar
The ensemble forecasting system and probcast concur on predicting dry conditions for the Sound and northwards, but some light snow showers to the southeast of the Sound. Perhaps some light snow over the NE slopes of the Olympics and eastern Vancouver Is.  Here is the predicted 24-h snowfall ending 4  PM Saturday.  There could be some light snow in the Centralia/Chehalis area and over SW Washington.   Of course, with it being  cold enough for snow tomorrow morning...so we will need to be attentive for the forecast going wrong...



Mixed clouds and sun tomorrow after the late morning, but quite cool (lower 40s should be it). Heavy rain still on tap for Tuesday.  This is a serious threat for those living near the Olympic Mountains...and will be the first major event observable with the new Langley Hill radar.

Thursday, November 17, 2011

Lowland Snow?

 Snow Update on KPLU (88.5 in the Puget Sound area) at 9 AM Friday--Available on the Their Website

Yes, there has been lots of talk about lowland snow--enough to give local mayors insomnia.  And some local TV stations are claiming that they have reports of snow on a few local hills.  I bet Jim Forman of KING TV is getting his famous parka dry cleaned or something.

Right now the air over is cold, but really too warm for significant lowland snow.  Here is the latest temperatures aloft from the UW SnowWatch system, which makes use of aircraft observations (ACARS) coming into Seattle. The blue dots are temperatures from the profiler system at Sand Point, which are not as dependable.  The freezing level is around 1800 ft, which generally means the snow level is 800 ft, 1000 ft lower.  Snow melts out in that 1000 ft. A really heavy shower could drive the snow level a bit lower.
Some showers are moving through right now, bringing rain to the lowlands and more snow to the mountains.  Lots of snow.   (see radar below).  It is a bit colder in the NW part of the


state and there has even been some NE flow coming into Bellingham where they have had a bit of freezing rain reported. Seattle and the north Sound have been rainshadowed for the last few hours...so nothing fun there and the worst of the showers are moving to the south.  The Langley Hill radar shows things quieting down offshore.

Tomorrow will be cool and dull, with a few chilly showers and not much more over the lowlands.  Decent for the Occupy Seattle protestors and for the helicopters that are following them aloft.   The fun waits until later Friday when a low center moves towards the SW corner of the state (see graphic at 7 PM Friday).  Now normally I would be getting REAL excited when such a situation, which has a lot in common with major snow events in western WA, but there are problems for lowland snow lovers.  The temperatures are still marginal at this point and the air to the north is not super cold.  There is some leakage of colder air through Bellingham at this point though.  The big problem is a lack of precipitation, with the upper level support (producing strong upward motion and precipitation) being weak.

 Here is the three hour precipitation for the three hours ending at 7 PM Friday.  Pretty sad.

 There is simply too little "juice" for this system. Here is the 24h snow predictions for the period ending 4 PM on Saturday. Some folks will get snow:  the southern Cascades and the southern part of eastern Washington will get a nice white blanket and the northeasterly flow coming out of the Fraser valley will move southwestward and slam into the Olympics giving some snow to the foothills and the southern suburbs of Sequim and Port Angeles.  And some odd snow showers here and there. 

But now the warning and why we need to stay alert.  As the low goes by the temps will cool enough for snow over most of the lowlands.  If the precipitation is heavier than forecast there could be considerably more snow over sections western WA.

And another warning...the models have been consistently suggesting a strong pineapple express with very heavy rain in the mountains Tuesday/Wed. of next week.  This will really mess up the snow at many of ski areas (the lower ones).

PS:  Apologies to engaged retirees.  In my previous analysis of the School Board race I speculated why the early voters supported the incumbents and suggested that non-engaged retirees might have been to partly to blame.  There are certainly many highly engaged retirees who supported change in the District.  Sorry.