Homeward Commute Weather: No Problem.

 I will do an update at 9:30 PM for tomorrow's commute....cliff

I am totally unimpressed with the precipitation coming in later this afternoon.

First, it will be cold enough for snow later this afternoon and early this evening.  Forget the talk of freezing rain.  The roads are cold.   The atmosphere is too cold.  No icing threat in the early to late evening.

What about precipitation?  There is hardly any in the western interior.  Here is the latest radar image (1213 PM) A few snow showers on the coast.  There has been some on and off light snow at Quillayute and Hoquiam.   Virtually nothing getting past the Olympics...these are very shallow showers.

The NOAA Rapid Refresh and HRRR models have pretty much nothing over us through commute time.  Here is the accumulated snowfall through 4 AM from the Rapid Refresh.  Nothing over Puget Sound.

The latest NWS NAM model has a few light snow showers coming in.  The accumulated precipitation from the latest (10 AM) run of NAM has nothing over Puget Sound if you look closely (bad graphics unfortunately).

Satellite imagery:  completely unimpressive.  A weak band to the north of us.  No organized circulation approaching us over the Pacific.

Bottom line:  homeward commute is no problem.  At worst you might see a few snow flurries.  With cold roads and no freezing rain, there won't be an ice problem.   Watch the radar (here is a good place) if you want to follow the situation in real time.

Several models have the precipitation picking up a bit over night...but still light.  Seattle and central Puget Sound and Kitsap will be heavily rain shadowed (snow shadowed).   Some light snow from northern King County into Snohomish County and south of Tacoma is possible but light is the operative word...less than an inch.   North Seattle might get a dusting.  This is not a serious snow event if you believe the current models.  There is a bit of hyping going around...but no names here.

 Along the coast where there has been some occasional snow showers.

Are you in venture capital/private equity and have an office in the Bay Area, or knows someone who does?
If so, I have a question for you. Please send me an email (cmass at uw.edu) ....thanks, cliff

Snow and Freezing Rain Tomorrow?

 6:30 AM Update

The coastal radar shows a weak area of snow showers moving over Hoquiam and the SW WA coast and moving inland over SW WA (see echo).  Very light stuff.   NOTHING ELSE OUT THERE. So some light snow showers over SW WA is all that we will see this morning.  Update for the evening commute and overnight at noon.  Could be snow showers this evening.

The forecast for Monday is a very difficult one.  

We will have air that is quite cold enough to support snow tomorrow morning.  A very weak weather disturbance will approach during the mid afternoon and will bring some light precipitation to the area.  As the disturbance moves through temperatures will begin to warm as increased onshore flow occurs.  By Tuesday morning commute time it will probably be warm enough for rain over Seattle, with snow holding a bit longer over NW WA.

So for those of your worried about driving to work tomorrow, the morning commute will be fine.  No problems at all.  Enjoy.

South Seattle should be substantially rain shadowed (or snow shadowed in this case). So if snow falls, it probably will be heavier in the north part of the city--but still not more than an inch.  Could easily be much less.  As the temperatures warm up aloft, we might see a few hours of freezing rain.

To illustrate, here is the 24 hr precipitation and snowfall ending 4 AM on Tuesday AM. The mountains will get snow ...guaranteed and NEEDED.  NW Washington including Everett to Bellingham to the San Juans will get perhaps an inch. Between the rain shadowing in NW flow and warming, Seattle to the Kitsap will not get much...perhaps 1/4-1/2 inch at most.  Or virtually nothing.

 Not a big event...but any snow in our area can cause problems.  And we could get a few hours of freezing rain.  God knows what the TV stations will make of it!   We will have a much better handle on this tomorrow..I will do a NOWCAST around noon. 

Temperatures are already warming quickly aloft.  Take a look at the wind and temperature above Seattle Tacoma Airport. At around 5000 ft (850 hPa on chart)  the temperatures have warmed from -12 to -6C (that is a warming of around 11F). 

Watch the radar tomorrow...you will see in real time what is happening.  Precipitation amounts will be everything.  No precipitation...no worries.  If you see it coming in when you need to be driving or biking...you might get an early start.  No big blizzard, but roads can get slick with a little snow.  Sea-Tac Airport is 4 F warmer than the same time yesterday--that is true for many local stations.   Changes are beginning....

Finally, for those in my ATMS 101 class taking their final exam tomorrow at 8:30 AM....there are no snow excuses.  Be there!

Which has Worse Air? A Hazy Airport Smoking Lounge or a Major Chinese City?

Sometimes you learn a fact that is just stunning.   The poor air quality of Chinese cities is well known, but here is an amazing piece of informaton.  The amount of small particulates in the air in major Chinese cities last week was WORSE and sometimes MUCH WORSE than smoking lounges in airports.

You know those smoking lounges.  Laden with smoke--you start coughing if you enter one. Hazy.

Recently, the U.S. Center for Disease Control (CDC) did a study of the particulate levels in major airport smoking lounges.  They reported the amount of small particles of less than 2.5 microns (millionth of a meter) in size.  These kinds of particles are particularly dangerous because they are small enough to move deep into the lungs.  The result is lessened lung function, asthma, and even death for vulnerable groups exposed long enough.  Nasty stuff.

The study found that the average airport  lounge had a particulate level of 188.7 micrograms per cubic meter. The average small particle level in the four smoking-permitted bars and restaurants was 276.9 micrograms per cubic meter.   Contrast that to the average level in smoke-free airports: 8 micrograms per cubic meter.   Or our air right now in the Northwest, say Queen Anne Hill in Seattle (graphic below).   You can see that this month that the small particle levels there ranged by from around 2 to 14 micrograms per cubic meter.  EPA regulations say that U.S. cities are out of attainment for air quality if the small particulate level is above 12 micrograms per cubic meter averaged over a year.

Now prepare to be shocked.  Here is a snapshot of the small particulate levels at some Chinese cities yesterday.  Many were over 300 micrograms per cubic meter at that time....WORST than the smoking lounges or the smoky bars.  And it is worse than that.  Earlier this week Shanghai got over 600 micrograms per cubic meter.

Think about that...more than twice as polluted as a horrible airport smoking lounge.  No wonder Ambassadar Locke wants to get his family out of there.  Can't blame him.

To get some intuition about the problem, here are pictures of Shanghai during a clean period and this week.  You can guess which one is which.

There are many reasons to try to reduce the use of fossil fuels, but certainly the air quality implications of burning oil and coal are some of them.  China can do a great deal to clean up their atmosphere (including burning cleaner fuels and insisting on more pollution controls).  But they need energy to support their growing economy and improvement of the living standards of their people, and non-carbon energy sources (e.g., hydro, nuclear, wind, solar) will have to take on a larger role.  This air pollution is taking a horrible toll on the health of the Chinese people.

Thanks to Professor Joel Thornton for noting to me the smoker's lounge vs. China air pollution equivalence.

Snow Hits Southwest Washington and Oregon and a Reverse Convergence Zone

As predicted by the models for several days, a low moved southward along the Northwest coast, bringing light snow to the coast and SW Washington and much heavier amounts to the western interior of Oregon.   A light dusting spread last night into the Kitsap Peninsula from Olympia southward. 

Here is the visible satellite around noon on Friday.  You can see the swirl of clouds associated with the low off of northern Oregon.

The amount of snow that has fallen across the region has varied substantially as of 12:30 PM.  Four inches were on the ground in Salem, Oregon at that time (6 inches at 4 PM) and I have an unofficial report of 9 inches near Corvallis, Oregon.   Take a look what Oregon State in Covallis looked like today:

 Here are a few cam shots on I5 near Eugene--this does not look like pleasant travel.

 The Washington Coast got around 1/2 inch as did some locations around SW Washington.

As the low moved south of Washington, easterly flow has increased over Washington State--thus air is approaching the Olympics through depth from an unusual direction...from the east.  A plot of the winds over Seattle shows this change clearly (time increases to the left, the y axis is pressure, red lines are temperature).  The atmosphere is cooling and the winds are easterly to 700 hPa (roughly 10,000 ft)

With easterly winds approaching the Olympics we are getting an interesting phenomenon...a convergence zone on the WESTERN side of the mountains, with an accompanying band of clouds and even some precipitation.  Many are familiar with the Puget Sound convergence zone, in which westerly winds approach the Olympics, move around the Olympics at low levels, and converge over Puget Sound producing a band of clouds and precipitation (see graphic).

Now reverse the winds and you get a convergence zone to the west of the Olympics.  

Let me prove it to you.  Here is a MODIS visible satellite picture at 12:10 PM Friday.  You see the band of clouds extending southwestward from the Olympics?...that's it.  There are also clouds north of the Olympics, produced by the NE flow coming out of the Fraser River gap and passing over Bellingham and the San Juans  before being forced to rise by the Olympics.  Perhaps some snow over south Port Angeles!

 We can get an even better view of the offshore convergence zone by viewing an image from the Langley Hill radar in Hoquiam (see below).  An amazing image...you can see a narrow plume of precipitation in the coastal convergence zone.

Today, our models are good enough to forecast such features. Here is an 8 hour forecast of clouds by the UW WRF (1.3 km resolution).   Both the coastal convergence zone and the upslope clouds south of Port Angeles is in there.  We have come a long way.

A model forecast of the winds  at 1 PM show the converging winds west of the Cascades.

The coldest temperatures are coming the next two nights...here is the forecast temperature at 7AM Saturday AM.  16-20F over many locations on the eastside of Puget Sound.  Single digits and negative temps in eastern WA.  Wind chills in the mountains will be brutal...below -20F will not be uncommon.  Be prepared if you go up there.

Question
Are you in venture capital/private equity and have an office in the Bay Area, or knows someone who does?
If so, I have a question for you. Please send me an email (cmass at uw.edu) ....thanks, cliff

Cold Facts and Coastal/Oregon Snow

We are now experiencing our coldest weather since January, with temperatures falling below zero in "favored" spots of eastern Washington and Oregon.  Snow is coming to the Northwest during the next two days, but unfortunately will miss most of Washington.

But first, this morning there was an unusual sight:  a line of clouds down the center of Puget Sound (see picture from the UW web cam facing the Olympics).  The cause?  The cold air!

Last night we had a land breeze on both sides of the Sound.  A land breeze occurs when the land is colder than the water, generally by at least 5-10F.   Last night that happened:  the water temperature is roughly 50F while the land temperatures dropped into the 20s.  Air from the cold land moves towards the water.   The land breezes on both sides of the Sound converged over the central Sound and rose, producing a line of clouds. You can see a hint of this from the winds taken over Puget Sound this morning by the Washington State ferry traveling between Edmonds and Kingston around 8:30 AM (see below)

The next map shows you the low temperatures across the region last night.  Some of the coldest temperatures were at Pullman (-3F) and in the nearby Blue Mountains.  Why was it so much colder at Pullman than say Moses Lake?   The answer is found in a satellite image taken this morning:  Pullman had snow on the ground (see picture below).

Snow covered NW Oregon and SE Washington.  Snow is associated with cold temperatures:  it reflects the sun during the day and is a very effective emitter in the infrared.   And it can insulate the lower atmosphere from warm ground.

Now let's talk forecast.  An upper level trough is moving southward around the high, causing upward motion, clouds, and precipitation (see map at 10 PM Thursday at 500 hPa).  Associated with the

upper trough is a low center at and near the surface (see surface map).  

 The frustrating thing for snow lovers is that the low is passing too far offshore to bring snow to most of Washington, perhaps light snow on the WA coast and moderate snow over central and southern Oregon as the low swings eastward south of us.  If the low was one hundred miles to the east and Seattle would be white.  Here is the projected 48h snowfall ending Saturday at 4 AM.  Oregon is nearly COMPLETELY covered with snow, with the  exception of Portland and Columbia Gorge.  Northern CA gets snow.   Just not fair.

 Then you expect dry and cold conditions through the weekend.   One notable weather feature:  very strong winds are expected on Friday and Saturday downstream of the Fraser River Gap--we are talking Bellingham, San Juans, and the neighborhood.  Here are the gusts at 4 PM Friday.  50 kts over the Strait of Georgia from the NE and strong easterlies over the Pacific and Strait.

And expect windy conditions along the western slopes of the Cascades, particular in Enumclaw, Black Diamond, the Issaquah Highlands, and North Bend.

Announcement

Are you in venture capital/private equity and have an office in the Bay Area, or knows someone who does?
If so, I have a question for you. Please send me an email (cmass at uw.edu) ....thanks, cliff

Nowcast: No Snow Problems for Evening Commute or Seahawks Game

I have gotten a number of emails from folks worrying about snow during the commute and after the Seahawk's game in Seattle tonight.

There will be no problems during the commute tonight and I don't think driving home from the game will be much of an issue.  But don't be surprised if some snow flurries/dusting occurs around 9-10 PM or so.

Right now (4:45 PM), the SnowWatch web site shows that air temps around 40 and the road temps are in the mid-40s (see graphic)

Cold air has just started to push out of the Fraser Gap into Bellingham, where snow began at 4:42 PM.  It is very light and will take 4-5 hrs to reach Seattle.  The latest radar shows two major local bands of precipitation over the lowlands: a convergence zone band over Snohomish County and northern King County and a band south of Bellingham associated with the Fraser River outflow.  The latter band will move south in time.  It may rev up when it interacts with the convergence zone band, which should weaken in time.    Anyway, there should be a line of weak convective showers leading the northerlies that pushes southward into Puget Sound during the middle evening.

According to the Snowwatch temperature information, the freezing level was at around 2000 ft at 4 PM.   The snow level is about 1000 ft below that.  The air is cooling, so the snow level will probably get to around 500 ft by 10 PM.   So near sea level I would expect the precipitation to start as rain as the band comes through.  Over time, melting and evaporation could help bring some flakes to near sea level, but road surfaces will be warm.   And the snow will move through quickly.

Bottom line:  no real threat at sea level even if the worst scenario occurs.  So enjoy shopping or going to the Seahawks game...the weather won't stop you....


PS:  There are more chances of snow in our future!


Announcement

Are you in venture capital/private equity and have an office in the Bay Area, or knows someone who does?
If so, I have a question for you. Please send me an email (cmass at uw.edu) ....thanks, cliff

Sunday Update: Amazing Rain Shadow and Snow Outlook

If you have lost your sun glasses, as many Northwesteners do during the winter, you better find them.  Bright sunshine and cold, crisp conditions are only 1-2 days away.  Cold air will be streaming over our region tomorrow, with only a few pesky snow showers in portions of western Washington.  I don't think there will be major problems with the Seahawks game on Monday night, unless the models are very wrong.

The big weather story today  is heavy rain and wind...but many of you are experiencing neither!  How is that possible?

Here is the precipitation over the past 24h (ending 11 AM Sunday) at a collection of NW stations.  Some folks to the east of the Olympics and Vancouver Island have gotten only a few hundredths of an inch, while the western slopes of the Cascades have received 2-3 inches (and will get more).

 Take a look at blow up of the 24 h totals.   ONE HUNDREDTH of an inch on Kitsap, while a few inches fell on the western Cascade foothills.

 Why this profound rain shadow in central Puget Sound?  The reason is that we have a strong trough embedded in northwesterly flow and the flow at crest level is westerly....producing a rain shadow to the lee (east) of the Olympics.

Here is the flow at 850 hPa (around 5000 ft and a good level to see what is approaching the mountains at crest level) at 8 AM.  VERY strong winds from the west to northwest (the winds are proportional to the gradient of heights shown by the solid lines.  The heights are like pressures on a surface chart.  Winds are parallel to the lines).  The air over us this morning is quite warm (denoted by red/orange colors in that chart)

 Warm enough that rain is falling in the passes (as shown below)...heavy rain at that.

 With a large north-south pressure difference and strong winds aloft, some locations, particularly in the south Sound and the Strait, have been buffeted by winds gusting about 40 mph (see graphic)

 Anyway, no issues for travel across the Cascades other than water ponding on the roadways and poor visibility.

      As I mentioned before, the cold air is coming on Monday.   The models are NOT producing major snowfall in the lowlands, but some of you will see some light white stuff.   As the cold air pushes out of the Fraser River gap on Monday AM, there could be some light snow at its leading edge over NW Washington (see map of 3-h snow ending 10 AM).

 As the cold air pushes south and west, some of it will be forced to rise by the Olympics, perhaps producing some light snow over Port Angeles and southern Sequim (see map for 3-h snow ending 1 PM)

During the next few hours Monday afternoon the cold air pushes south through Puget Sound.  The various models I have looked at are not producing much (see map below)...perhaps a few snow flurries.  If our models are wrong, this is when any snow would fall...Monday afternoon.

 Why are we not getting a big snowstorm in the lowland?  The set up is not correct.  The upper trough...and the upward motion associated with it...is sliding to the east too quickly, so there won't be good upward motion when the cold air pushes in.  Furthermore, the position of the trough is not good for setting up a strong convergence zone over Puget Sound when the cold air approaches.  The subtleties are important in snow forecasting in our area...everything needs to be just right to overcome the ocean's warmth.

The total predicted snowfall for the next 48-h is shown below.  The mountains should do some business on Monday, but the lowlands are mainly snow free.  Disappointing to kids.

Anyway, get those sunglasses and protect your hoses, pipes, plants, and animals from unaccustomed cold.

Announcement

Are you in venture capital/private equity and have an office in the Bay Area, or knows someone who does?
If so, I have a question for you. Please send me an email (cmass at uw.edu) ....thanks, cliff