Fog in the pass

Several of you have asked about the fog in the pass...they thought the mountains should be clear due to their higher elevations...and in fact they have been clear for several days. The cams in Snoqualmie Pass (see attached) do show fog. In fact, the fog has been freezing on trees and other objects. Yet on top of tiger mountain and at Paradise it is sunny...what's up?

The explanation is that eastern Washington is full of low clouds and fog (as it frequently is under high pressure in the winter). They have an inversion overhead. The pressure is higher in eastern Washington than western and this difference is increasing as large scale high pressure is moving eastward. The six hour forecast valid at 10 AM this morning shows the story..cold air in eastern Washington and high pressure there, with a big pressure difference across the Cascades (roughly 10 mb..which is a lot). This difference in pressure is producing strong easterly winds in the Columbia Gorge. It is also pushing the cold air and fog up the eastern slopes of the Cascades and into the passes. You can see this in the visible satellite picture this morning (see picture).

Today, was a good example of a weakness in our current computer models...they failed to produce the low clouds of last night and this morning. We believe that an important reason for this failure is that the models mix the atmosphere too much under stable conditions (like when cold dense air is under warmer, less dense air). The simulation for today at 10 AM is a good example (see below--no clouds over PS).
Today, a good portion of Puget Sound lost the low clouds and we finally saw some sun. One reason is the inversion became so shallow that limited solar radiation could mix it out. Also the strong descending easterlies aloft (forced by the large difference in pressure) might have contributed. WIth solar energy reaching the surface, temps warmed into the mid-forties to 50F. The inversion weakened a bit...but is still there...and will restrengthen tonight as temps cool near the surface. Tomorrow morning I will try tiger mountain..with a thermometer, and see what I find.

PS: Just a reminder...I will be talking about NW snowstorms on Wednesday at 7 PM at Third Place Books in Lake Forest Park.
Will review big historical lowland storms, including the last event, and the rare conditions that produce them.

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Great image

This is an ultra-high resolution image from NASA Aqua satellite....much better quality than the NWS geostationary satellites I have shown you in the past...but only available twice a day (click on the pic to see it better). You can see so clearly the low clouds over Puget Sound and eastern Washington. Look carefully and you can see fingers of low clouds pushing into mountain valleys..and even some contrails over the ocean. Also Tiger Mountain and the Issaquah Alps are apparent sticking out of the murk.

It really has been cold the last few days in the lowlands...with a lack of sun due to the low clouds. Take a look at the temps during the past two weeks (see figure). You can see that the temps the last two days has been hanging around the normal minima.


I am heading up Tiger Mt. Sunday morning..perhaps I will see some of you...want to experience some sun and warmth myself.

PS: I will be at UW Bookstore at 1 PM if anyone wants to talk in person.

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Air Quality Questionnaire

There is a little mystery going on for the air quality folks...why air pollution hasn't increased more with such a strong inversion. Have people reduced their burning of wood without a burn ban? To help answer this question, they have put together a brief web questionnaire, and if you have a few minutes, please give it a try:

http://www.atmos.washington.edu/weatherforecasting/airquality/index.php

and back to our amazing inversion. It has now slowed it ascent...with the base at around 300 m. (see figure). Visibility noticeable increased today and air quality has begun to decline...particularly over the southern Sound from Seattle to Olympia. A few people took to the hills today...and it was amazing. 66F at the top of Tiger Mountain (2500ft) and nearly 70F at Paradise Ranger Station. The ridge will hold in through the weekend, but will slowly progress eastward on Sunday and Monday. The pressure difference across the Cascades has increased (greater pressure to the east), and this is pushing air westward in the Columbia Gorge....Troutdale, east of Portland, has easterly winds gusting to 40 knots now!

A reminder: I will be signing books (no lecture, but happy to answer question) at the UW Bookstore in Seattle at 1 PM on Saturday. On Wednesday( Jan 21) at 7 PM I will talk about Northwest Snowstorms at Third Place Books in Lake Forest Park.

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Even Lower

Here is a wonderful picture from Stephen Van Dyck that was taken at Poo Poo Point (1820 ft) on Tiger Mt. yesterday afternoon a 4 PM. The same view will be available today. Hiking through a sharp inversion is a real treat. If you don't like hiking, drive up to the top of Cougar Mt. Park and bask in the sun.

The inversion is lower and stronger this morning. The first graphic below is the vertical sounding at Quillayute on the coast based on a balloon-carried instrument package (radiosonde). Temps (red) in C and heights in pressure (850 is about 5000 ft, 700 about 10000 ft) Very strong surface-based inversion. The blue dashed is the dewpoint...air is saturated near the surface but VERY dry aloft.


Next, I have the Seattle temperature aloft...the inversion is very strong, with the base now below 400 m (1300 ft).


The surface temperatures at 6 AM are plotted in the next figure. Big variations...from the mid-30s in the coldest locations to 55F up in the mountains. Want to warm up?...go up Keep in mind..if you are driving in fog and the temps are in the mid to lower 30s, be very careful! Black ice on the roadway is a real possibility.

Finally, air quality has held up until now, but a few locations (e.g., Olympia and South Park) have slipped into moderate...look at the latest air quality map from Puget Sound Clean Air Agency I have include.

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This picture was sent to me from Scott (don't know his last name), from Snoqualmie Summit Ski area in the pass. Notice the excellent visibility in the dry air. And you won't believe the latest Seattle profiler imagery...the inversion continues to descent (see image), with a base near 400 m (1300 ft). How low will it go?

Air quality is still fine, but how long can it keep up with such a low inversion. If air quality remains ok there is only one explanation, the people of the region are reducing their burning.

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Lowering Inversion and Low Clouds

As you can see from the satellite image this morning, some areas are in low clouds and fog, while the southeastern sound, the mountains, and the coast were in sun. The lowlands of eastern Washington were also cool and cloudy.



The inversion aloft has been progressively lowering in altitude. The picture below is extraordinary in showing this. What you are seeing are temps and winds above Seattle ( red temp, blue wind) over the past day. The zone of big changes in temperature (lots of red lines close together) is the inversion. Note how it has progressively lowered...right now the base of the inversion is around 600 m. The plots of temperature at particular times (second plot below), shows the inversion changes even more graphically. Within rougly 300 m (1000 ft), the temperature increases nearly 20F (10C)! I bet the top of Tiger Mountain (2500ft) is in sun now (let me know if anyone has been up there this afternoon).

Above the inversion it is really warm and toasty. The observations at Paradise (around 5500ft) showed temps in the mid-50s. This will be true for a number of mountain locations (e.g, Mt. Baker, Crystal). So this is a good time for a mid-elevation hike or ski trip in the mountains.

Air quality has held out...mainly because the inversion has been quite high, allowing the mixing of pollutants in a substantial volume of air (see graphic from Puget Sound Clean Air Agency). With lots of clouds we have not formed a surface-based inversion, and such inversions are associated with the worst air quality situations. However, as the overlying inversion descends, air quality may well decline.

The current long-range forecasts, out 4-5 days, are emphatic that high pressures and resulting inversions will hold out through the period.

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Into the Soup

The inversion is strengthening up now...take a look at the latest observations from the Seattle profiler..which measures temperature above Sand Point (Magnuson Park area of NE Seattle).
Temperature drops off with height to about 1000 meters (roughly 3000 ft) and then increases
rapidly with height--that is the inversion. Above the inversion it becomes not only warmer, but clear and sunny (check the view from Crystal Mt). During this week the inversion should
strengthen and lower, so you can always get out of the murk by moving upward. One of my favorite things to do in this situations is to climb Tiger Mountain. One can bask in the warmth and look down on the clouds below (there is a picture from one of my ascents in my book)

Although there were a few sunbreaks today, I expect low clouds to reform over night. The air near the surface is relatively moist (dewpoints in the mid to upper 30s) and as the air cools down overnight the air will become saturated and fog will form. The problem with fog is that one formed it can become very peristent--solar radiation is reflected off its top (helping to cool) and fog is very good at radiating infrared energy to space (also cools). Sort of like a cloudy refrigerator! So you have a positive feedback that can keep cold, stable air near the surface. Another factor is that the ridging will amplify, producing more subsidence (sinking) aloft that will producing warming aloft and strengthen and lower the inversion. I hate to say it, but this is an ideal situation for us to fog in and stay like that. Our only hope is that there will be enough offshore flow to mix it out a bit during mid afternoons.
Sea Tac often fogs out in this situation...so call before flying out. Sea Tac has a worse fog problem than Boeing Field because Sea Tac is higher (452 ft). During the day the fog often lifts a bit...Boeing can open up enough for landings...but Sea Tac remains in the murk. Portland should be fine because the strong outflow winds from the Gorge.
Air quallity is generally ok now, but it will decline as the inversion strengthens and lowers. More on that tomorrow.

I wanted to mention that I will be giving a talk on Northwest Snowstorms at Third Place Books next wednesday (jan 21) at 7 PM. Will desribe the situations that give us snow here.

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Inversion 101

As high pressure builds overhead this week, the key local feature that will control our weather will be the low-level inversion. So lets do some inversion 101. Inversions occur when temperature increases with height. They are "inversions" because generally temperature decreases with height. Inversions represent very stable configurations in the atmosphere--preventing the vertical movement of air. An example would be cold, dense air with warm, lighter air above.
There are two main ways to produce inversion...and both are encouraged by high pressure overhead. High pressure areas are associated with clear skies aloft. This allows the effective emission of infrared radiation from the surface to space (clouds greatly lessen this emission). Good IR emission allows the surface to cool more than the air above...the result is a surface-based inversion.

High pressure can also producea "subsidence" inversion. In particular, highs are associated with sinking (subsiding) air and this sinking goes to zero at the surface. So strong sinking aloft and weaker sinking near the ground. Sinking causes warming because air is compressed when it sinks and compression causes warming (like in your bicycle pump). So strong sinking aloft produces lots of warming, but that decreases towards the surface. The result: an inversion. Both types of mechanisms can occur at the same time.

So lets see what is going to happen here. Below is the latest vertical sounding at Quillayute on the coast. Temperature is red and dewpoint is blue dashed. The y axis is pressure in mb (850 mb is about 5000 ft). At low levels the air is saturated (temp and dewpoint are the same), but temp decreases with height. A weak inversion is above the moist layer, with very dry air aloft. Now take a look at the computer forecast of the sounding over Seattle in 60 hrs (Thursday AM). A strong, surface-based inversion.


With such a strong inversion and a moist surface, the next issue is fog--and we will certainly get quite a bit of it. The inversion prevents the mixing from above, and the air in the surface layer can cool to saturation..giving fog. And once the fog forms it is very difficult to mix it out...particularly this time of the year when the sun is weak. And a stagnant layer of cool air can facilitate poor air quality. A really good place to get the latest air quality conditions and forecasts for the region is found at the Puget Sound clean air agency web site (http://www.pscleanair.org/)

Reminder: I will be signing books on Saturday at 1 PM at the U Book Store in Seattle and will give a talk on NW Snowstorms at Third Place Books at 7 PM on Wed. January 21st (and signing books there too).

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Update Later

I am going to update in depth later...but at this point the forecast is on track. Big ridge this week with very warm air aloft. The mountains will be in sun...you might see 60F at Paradise before it is over. A low-level inversion will form, as will fog. The question will be whether we will break out during the afternoons. The other big issue is air quality....low-level inversions trap pollutants and by the end of the week the air quality might degrade significantly....

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High Pressure and Air Pollution

The heavy rain is over and today and tomorrow we will transition to a week-long period of high pressure and dry conditions. Sounds like heaven? Well, there is a little detail we have to talk about...

Anyway, right now the pressure over us is already extraordinarily high....about 1040 mb (30.70 inches of mercury). In fact, it really is rare to get rain (as we are right now in some areas) with such high pressure.

All the computers models agree that we are about to transition to an extended period where high pressure will build along the West Coast....take a look at the attached figure for Tuesday at 4 PM--the figure shows the flow at 500 mb...about 18k feet aloft). Like sea level pressure better? The next figure shows that at the same time.

Such high pressure will bring absolutely dry conditions and MUCH warmer temperatures aloft. If this was late spring or summer, we could be looking forward to record-breaking temperatures...and some might cancel that trip to Hawaii. But before you do so, remember this is January in Seattle.
The problem this time of the year is that when high pressure builds over us during midwinter, we often develop low-level inversions and fog. Warming aloft is certain. But the sun is still weak and it can't heat up the ground much and there is good radiational cooling to space during the long nights. Fog can form at night and can become very persistent...and in fact it helps to maintain itself for reasons I won't get into now. So there is a danger we can fog in and stay cool at low levels. Such fog can mess up air travel...so fly out as late as possible in the day if you want some insurance.

Our big hope is that the high pressure will slip sufficiently east to give us offshore and downslope flow...which can mix up the lower atmosphere and destroy the inversion. This is what local meteorologists will be analyzing in great depth this week.

And there is another threat...air pollution. Inversions act to prevent mixing of air in the vertical and pollutants can be increasingly concentrated. My colleagues at the Puget Sound Clean Air Agency are already concerned enough to provide initial warnings. There might be burn bans later in the week...so keep that in mind before you fire up your fireplace or woodburning stove.

So we had snow and ice and then heavy rain and floods. Now we may have fog, murk, and air pollution. But there is one good thing about the latest plague...you will be able to escape it by going up: the conditions will be sunny and warm in the mountains. Last time this situation occurred it was in the 30s and lower 40s in Seattle and 60F at Paradise near Mt. Rainier.

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The Snow Eater

Sometimes strong winds descend our local terrain, such as on the east side of the Cascades. As the air descends, it is compressed and warmed (just like air in your bike pump warms when it is compressed). These warm winds can rapidly melt snow and are often called Chinook winds, with Chinook being a Pacific Northwest Native American word meaning 'snow-eater'. The east wide of the Rockies are also well known for Chinooks.

Quite a Chinook occurred Tuesday evening into Wednesday morning along the Cascades slopes near Wenatchee. On the heights at nearby Mission Ridge ski resort sustained winds of 70-80 mph, with gusts to 121 mph were observed and some home owners with anemometers near Wenatchee reported gusts to near 100 mph. Substantial damage occurred, with power outages to thousands of homes (see picture of tower down).
Take a look at the observations at Wenatchee (see figures). As the Chinook began the temperature climbed from 26 to 45 F in ONE HOUR. And the winds increased from calm to 54 knots (62 mph) over a few hours. Strong winds and warm temperatures rapidly melt (eat) snow. One report I got was that a family went to sleep with 1-1.5 ft of snow on the ground...when they awoke, it was all gone. And many observers in the area that belong to the CoCoRaHs community network reported loses of around a foot overnight. In my book I talk about an even bigger wind storm that hit Wenatchee two years ago...




And did I mention that pineapple express junior is returning? Look at the satellite picture...another nice subtropical stream of moisture...and the computer forecasts show substantial rain...but nothing like what we had last week. Will slow up the dropping of river levels and contribute to soil saturation, which can help promote landslides. Seattle still lucks out with the rainshadow. Good location for the city!

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A Nice Example of a Puget Sound Convergence Zone

A very nice Puget Sound convergence zone occurred yesterday, with a well defined band in the radar (see image).
A classic aspect of the zone you can see is its continuation into the Cascades, where it enhances precipitation in the mountains. Not infrequently, the CZ increases snow for Stevens pass, with less for Snoqualmie. You also notice the enhanced drying to the north and south. I have also included a high-resolution visible satellite image. You can see the convergence band and the clear zones to the north and south. This is a very good thing to keep in mind...if you are in convergence rain and clouds...head north and south and you might have perfect weather for outdoor fun.
Convergences zones occur 12-25 times per year...so if you live in the area...better know about it! A map of the surface observations at 2PM really shows the converging winds of the zone. Winds on the coast are northwesterly...as we often see. If you are observant you may notice another convergence zone over th Strait of Georgia...and that often occurs at the same time as the PSCZ. In fact, look at the satellite picture...you will see the clouds associated with it.

Interesting to look at the observations at the UW as it passed that location around 25 GMT (or 3 PM PST)--the wind direction switched from southerly to easterly, there was a spike in precipitation, and the temperature dropped in the cool, precipitating side (see images).






Finally, I have included a time-height cross section from the Seattle profiler..which show how conditions changed aloft. Time is on the x axis and height in meters on the y axis. Red is temperature and blue are winds. As the convergence zone went through around 23 GMT the
winds abruptly switched from NW to N and temperatures dropped in the clouds and rain. Then the winds turned easterly. I will explain that in another blog.

PS: I am happy to report that FINALLY copies of my weather book from the second printing are becoming widely available. UW bookstore has a big supply--and I will have a book signing there at 1 PM on Saturday, January 17th. Barnes and Noble.com have it and Amazon now has the book in stock. Elliot Bay and Powell books just got copies...and I assume the rest of the local bookstores will be getting theirs soon, if the don't have them already. For links of these, you can go to my web site (click on the book icon).

PSS: There should be a special on the snow and floods on KIRO TV on Sunday...I believe after the football game.

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Precipitation Variations

There were some amazing variations and storm totals in the precipitation...
Take a look at the table below from the National Weather Service.
At the UW we had 1.4 inches for the entire storm (last 48h), and Everett had even less
...1.04 inches.  Sea Tac had 3.42 and Olympia 6.03.  That's a rainshadow.  The most
amazing amounts were in the mountains where some locations had 10-15 inches.

Heavy precipitation was the big reason for the flooding, but the melting of lowland snow
was also important.  This is also true of some other big flood events like the Feb 1996
flood, which was even more damaging than this one.  High mountain snow actually works
against flooding, since the snowpack can absorb some of the water, where it can refreeze.
Interestingly some of the high mountain sites showed very little change in snow water
equivalent...the amount of water in the snow...during this event. But the snow depth can
change dramatically...at Snoqualmie pass the snow depth has gone from 78 to 43 inches in
two days.

Right now have pro frontal conditions with showers in the mountains and a Puget Sound
convergence zone north of Seattle (see radar). Tomorrow will be dry and temperatures
40s.  Some showers over the weekend...and some amazingly dry conditions the middle of
next week.



NORTH...               1H     3H     6H    12H    24H    48H    72H
FRIDAY HARBOR          0.00   0.00   0.00   0.06   0.76   1.35   1.60
ORCAS ISLAND           0.00   0.00   0.00   0.00   0.00   0.00   0.00
OAK HARBOR             0.00   0.00   0.01   0.09   0.55   1.31   1.54
BELLINGHAM             0.02   0.05   0.05   0.28   1.20   2.74   3.20
NUGENTS CORNER         0.00   0.04   0.04   0.41   1.38   3.82   4.01
BURLINGTON             0.00   0.00   0.00   0.00   0.00   0.00   0.00
ARLINGTON              0.14   0.23   0.26   0.31   0.31   0.31   0.31
EVERETT                0.00   0.02   0.04   0.12   0.67   0.80   1.04
GLACIER                0.10   0.20   0.20   0.80   1.60   5.29   5.29
MOUNT BAKER NWAC        MSG   0.10   0.19   0.82   2.81   6.81   6.93
BAKER LAKE             0.00   0.20   0.30   1.00   3.20   7.80   8.20
MARBLEMOUNT            0.10   0.20   0.40   1.40   4.10  10.10  10.50
MARBLEMOUNT CRN         MSG   0.19   0.57   1.97   4.93  12.93  13.82
VERLOT R.S.            0.10   0.20   0.70   2.20   4.80   8.30   9.70
PADILLA BAY FARM        MSG   0.02   0.02   0.11   0.79   1.57   1.99
KAYAK POINT            0.06   0.13   0.37   0.43   0.67   1.56   1.88
SMOKEY POINT           0.11   0.13   0.31   0.52   1.02   1.93   2.55
SUNNYSIDE              0.07   0.10   0.59   0.70   1.30   1.85   2.33
SILVER LAKE WD          MSG   0.06   0.11   0.30   1.25   1.32   1.78

CENTRAL....            1H     3H     6H    12H    24H    48H    72H
SEATTLE-TACOMA APT     0.00   0.00   0.00   0.16   1.87   3.42   3.55
BREMERTON              0.00   0.00   0.00   0.00   0.00   0.00   0.00
GRAY AFF               0.00   0.02   0.03   0.28   1.92   4.58   4.88
STAMPEDE PASS           MSG    MSG    MSG    MSG    MSG    MSG    MSG
DARRINGTON             0.10   0.20   0.40   1.30   2.70   2.70   2.70
SKYKOMISH LARC         0.00   0.20   0.30   1.60   3.40   7.50   8.80
SOUTH FORK TOLT         MSG   0.01   0.05   1.00   1.10   1.06   0.92
CHESTER MORSE LAKE WX   MSG    MSG   0.03   0.85   2.78   6.14   7.13
FIRE TRAINING ACADEMY  0.01   0.01   0.01   0.93   2.69   6.86   7.68
SF SNOQUALMIE- GARCIA  0.00   0.01   0.08   1.34   3.57  10.62  11.63
HOWARD HANSON RES       MSG   0.03   0.18   1.83   4.04  15.57  16.56
RAVENSDALE              MSG   0.00   0.03   0.55   2.08   4.14   4.50
ROCK CREEK BRDG SR516  0.00   0.00    MSG   0.39    MSG   4.05    MSG
ORILLA                  MSG    MSG   0.00   0.13   1.61   2.73   2.80
GREENWATER              MSG   0.03   0.06   0.75   2.02   6.82   7.55
BUCK CREEK CAMP         MSG    MSG    MSG   0.04   0.14   1.48   1.48
SOUTH PRAIRIE           MSG   0.00   0.02   0.32   1.66   4.08   4.37
ORILLA                  MSG    MSG   0.00   0.13   1.61   2.73   2.80
BUCKLEY                 MSG    MSG    MSG    MSG    MSG    MSG    MSG
ELECTRON               0.00   0.00   0.00   0.00   0.00   0.00   0.00
SNOQUALMIE FALLS        MSG    MSG   0.00   0.60   2.60   4.90   4.90
SNOQUALMIE PASS        0.00   0.10   0.50   1.20   3.90   9.20  14.70
RENTON                 0.00   0.00   0.00   0.17   1.54   2.47   2.60
BOEING FIELD           0.00   0.00   0.00   0.18   1.35   1.92   2.03
ENUMCLAW               0.00   0.00   0.00   0.04   0.08   0.31   0.51
GIG HARBOR             0.00   0.00   0.00   0.25   2.18   4.94   5.20
MCCHORD AFB            0.00   0.03   0.03   0.27   1.95   4.60   4.87

SOUTH....              1H     3H     6H    12H    24H    48H    72H
OLYMPIA                0.00   0.00   0.00   0.32   2.65   6.03   6.38
TOLEDO                  MSG    MSG    MSG    MSG    MSG    MSG    MSG
KELSO                  0.01   0.01   0.01   0.07   0.07   0.07   0.07
VANCOUVER              0.00   0.03   0.06   0.42   0.68   0.72   0.83
RAINIER NP LONGMIRE    0.00   0.00   0.20   1.30   2.70   6.00   6.00
RAINIER PARADISE NWAC   MSG   0.04   0.23   0.93   2.81   7.52   8.27
CHINOOK PASS NWAC       MSG   0.10   0.21   0.43   1.51   3.27   3.84
CRYSTAL MOUNTAIN NWAC   MSG    MSG    MSG    MSG    MSG    MSG    MSG
OHANAPECOSH RAWS        MSG    MSG    MSG    MSG    MSG    MSG    MSG
HAGER CREEK RAWS        MSG    MSG    MSG    MSG    MSG    MSG    MSG
NATIONAL               0.54   1.24   3.01   10.57  12.56  13.94
14.25
PACKWOOD               0.02   0.09   0.33   1.36   3.09   6.95   9.32
TILTON R NR CINEBAR    0.01   0.12   0.21   0.95   2.62   8.57   9.96
SF CHEHALIS- WILDWOOD   MSG   0.02   0.02   0.49   2.50   4.32   4.54
SF NEWAUKUM- ONALASKA  0.00   0.00   0.02   0.50   1.54   4.87   5.15
NF NEWAUKUM - FOREST   0.00   0.00   0.00   0.00   0.00   0.00   0.00
CINEBAR                0.00   0.20   0.20   1.00   2.70   6.90   6.90
FRANCIS                0.00   0.00   0.10   0.80   3.50   3.60   3.60
CENTRALIA              0.00   0.00   0.00   0.60   2.00   3.90   3.90
WINTERS MOUNTAIN       0.04   0.04   0.04   0.04   0.04   0.04   0.04
BOISFORT PEAK           MSG    MSG    MSG   0.71   1.85   1.46   1.61

OLYMPIC PENINSULA....  1H     3H     6H    12H    24H    48H    72H
QUILLAYUTE APT         0.00   0.09   0.09   0.31   1.96   4.72   5.67
SHELTON APT            0.00   0.00   0.00   0.21   2.72   7.15   7.61
HOQUIAM                0.03   0.03   0.05   0.32   2.15   4.61   5.08
PORT ANGELES           0.00   0.00   0.00   0.19   1.01   1.90   1.97
HOH RANGER STATION      MSG    MSG    MSG    MSG   0.00   8.80   8.80
CUSHMAN DAM            0.10   0.10   0.10   0.50   2.70   5.70   6.00
STAIRCASE OLYMPIC NP   0.00   0.01   0.03   0.22   1.90   4.65   5.84
BLACK KNOB             0.07   0.08   0.15   0.68   3.26   8.09   9.73
HURRICANE RIDGE NWAC    MSG   0.00   0.03   0.24   0.89   1.65   1.73
HUMPTULIPS RAWS        0.03   0.06   0.11   0.42   3.16   9.04   9.77
TOMS CREEK RAWS        0.09   0.16   0.23   0.68   2.76   8.79   9.81
QUILCENE RAWS           MSG    MSG    MSG    MSG    MSG    MSG    MSG
QUINAULT CLIMATE       0.11   0.15   0.25   0.80   5.55  15.64
162.32
ELK MEADOWS             MSG    MSG    MSG    MSG    MSG    MSG    MSG
WYNOOCHEE LAKE         0.07    MSG    MSG    MSG   0.12    MSG    MSG

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Just a little change in angle makes all the difference

A look at the current radar shows a major change from this morning...the rain shadow protection of Seattle is gone and now the rain shadow is NE of the Olympics. Moderate to heavy rain is now spread over the entire region from the Olympics to the Cascades. Why the change? The flow direction on the coast has shifted slightly from nearly westerly to southwesterly. You can see this by looking at the observations in the vertical (called a "sounding") at Quillayute on the coast (see figures). These observations are taken by balloon-launched weather observations (radiosondes) twice a day (4 am and 4 PM).

The first sounding is for 4 AM and you can see the winds (blue pennants) are nearly westerly at low levels...the second one is 4 PM this afternoon....a turn to the SW. The Y axis is pressure...850 (millibars) is about 5000 ft and 700 is about 10000 ft. The red line is temp and the blue dashed is dew point. The x axis of the plot is temperature in C.


The storm total precipitation from the local radar is shown below...pretty amazing..with some values over 15 inches! Note..this is uncalibrated and the radar could be high...but this is a major event and some rivers are hitting record amounts.

Interestingly the computer simulations were indicating record streamflows yesterday...these are from combining atmospheric and hydrological models...that is why the National Weather Service was hitting it so hard. I could hardly believe what they were saying...now I do.

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rain shadow moves north

As the computer models have been suggesting for a while, the rain shadow is slipping northward, bringing moderate rain into Seattle. The reason--the large scale flow approaching the Olympics has shifted from westerly to southwesterly...which results in the rain shadow moving northward.

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