Going to Snow Around Puget Sound Very Soon!

It is 1 PM and snow is heading towards Puget Sound during the next few hours.

Weather radar  (at 1:05 PM) shows a modest front, with associated precipitation, approaching  the coast (see image).

You can also see the front in the latest visible satellite imagery:

The air is PLENTY cold to snow.  The latest observations at SEA-TAC airport show the temperature is -10C at 850 hPa (about 5000 ft) and below freezing pretty much down to the surface (see temperatures and winds below in a time-height cross section)

And the air is quite dry.  That is important because precipitation falling into the cold air will evaporate (sublimate) and cool.

The only issue is how much.    There we have a problem for snow lovers in Seattle.  The winds are westerly/northwesterly approaching our region and this will result in a rainshadow (or in this case snowshadow) in the lee of the Olympics over central Puget Sound.

Our snow will be light....not much more than about a half-inch around Seattle, with more north and south.  Here is a forecast of the 24-h total precipitation (ending 4 AM Saturday).  You can see that pesky rain shadow.  There will be plenty of snow in the mountains, and several inches over parts of NW Washington.  The Kitsap will get several inches.

Anyway, a least the Seattle commute will not be too bad with the small amounts expected...but be careful in any case.

Postfrontal Orographic Effects

I've had a busy morning with no time to write, which is a shame given the weather. 

I can share one quick observation from the storm today.  The radar is showing some orographic effects in the post-frontal northwester flow from 1738–2032 UTC (1038 AM – 132 PM MST).  Note, for example, the persistent echoes on the western (windward) sides of the Oquirrh and Wasatch Mountains, which contrasts with the shadowing seen over the southwest Salt Lake Valley. 

Clearly better skiing above the Kennecott Smelter than at the open pit mine. 

When the Ridge Is in Its Happy Place

Over the past week and in forecasts for the next 10 days the overall pattern remains in some ways similar to what we have seen all winter.  The flow is very high amplitude, with strong upper-level ridges and troughs.  This can be seen in the dynamic tropopause analysis below, which is essentially a map of jet stream level winds with areas of locally low tropopause pressure (warm colors) indicating ridges and areas of locally high tropopause pressure (cool colors) indicating troughs. 

What has changed, however, is that the mean ridge position has shifted upstream to what I'll call its "happy place" over the central Pacific Ocean.  As a result, we will see several amplifying upper-level troughs digging into the western U.S. over the next 10 days.  This is a much colder pattern than we have seen all winter.

It is also a more "active" pattern.  Forecasts for the next 7 days show a series of weak but frequent storm systems moving through.  Total accumulated water equivalent produced by our downscaled NAEFS product for Alta ranges from 1 to 3 inches of water.  The former would be a bit below average, the latter almost double. 

Thus, beginning with last week, this looks to be the best stretch of winter weather we have had all season.  Anything close to average beats the previous 3 months. 

The Steenburgh Effect is in full force. 

The Olympic Mountain Snow Shadow and Prospects for Snow this Week

Some light snow is falling over Seattle now, as a weak upper level disturbance moves though.  Perhaps a half-inch on the ground in North Seattle.

But in general, Seattle has been left out of the bounty, even though we are cold enough to snow.  More snow north, south, east and west of us.  But why are we being short changed?

There IS a reason.

Let's start by showing the distribution of snow depth tonight at 10 PM from the NOAA National Snow Analysis.   On the left, is last night and on the right, 10 days ago.

Quite a bit more over the west lowlands, particular south of Olympia, and east of the Cascade crest.  Very light amounts over Seattle and south King County.

A year ago? More snow than this year over the Oregon Cascades, less over the western lowlands and slightly more over the WA Cascades.

So why has snow been generally light or absent over central Puget Sound?

A major reason:  winds in the lower atmosphere have been too persistently out of the Northwest, leaving Seattle in the rain shadow of the Olympics.  To illustrate, here is the National Weather Service precipitation analysis for the last week....lots of precipitation in the mountains, but major rain shadowing over Puget Sound. And with cold air over us, that means snow shadowing as well.

Another issue is that the atmosphere is relatively dry west of an upper level ridge--and that is the pattern we have had for days (see map).

Only when a strong trough works its way around the ridge and drives southward can we get real snow in Seattle in such a situation.

Getting back to the current snow situation....snow should end during the next few hours as the upper trough moves by.  Thursday should be dry.

But we have another chance of snow on Friday, as two weak disturbances make their way south from SE Alaska to our region on Friday/Friday evening, and another on Sunday (see upper level maps for these times).

There is a good chance for light snow over the lowlands on Friday...and much more in the mountains.   Here is the European Center  high-resolution 24-h snow total forecast between 10 AM Friday and 10 AM Saturday. Over a foot in the mountains and about an inch in the lowlands.

In their ensemble (many model runs), the Seattle accumulated snow forecast starting 4 AM this (Wed) morning shows the light snow today (good prediction of about a a half inch), but more (about an inch) on Friday.  I should note that there is some uncertainty in the exact amounts, but some snow looks likely.

So at this point, no big snowstorm in view (at least through Saturday), but enough to think about getting that hot chocolate and enjoying the flakes.

Winter Storms from Salt Lake City to PyeongChang

Lake-effect snows added a bit of frosting to the President's weekend winter storm last night.  Alta is reporting a 22" storm total, but only 3" overnight.   In the end, I think the storm did a little better than anticipated through yesterday morning and a little worse than anticipated yesterday and last night.  Such is the post-frontal crap shoot. There are reports of more than 20 inches (through yesterday afternoon) in Sandy and Cottonwood Heights, so this was an event in which storm totals did not increase significantly with elevation up the canyon.  

Temperatures this morning are bone chilling in the mountains.  The latest from MesoWest shows predominantly teens in the Salt Lake Valley, which isn't all that bad, but above about 8500 feet, most stations are at or below zero, with a -12ºF at 11,000 feet.  

Source: MesoWest
Ski touring on days like these requires constant movement.  I recall doing a huge day several years ago in conditions like this.  The skiing was outstanding, but I was cold the entire day, despite being heavily layered.  There were no breaks.  Did I mention that the skiing was outstanding?  

Turning out attention westward, the schedule for some weather-sensitive events is being shuffled due to the weather forecast.  The fly in the ointment is a surface trough moving across the Yellow Sea and the Korean Peninsula from 0600-1500 UTC 22 Feb (1500-2100 KST Thursday).  

This trough then intensifies into a cyclone over the East Sea (Sea of Japan) and, along with a secondary trough to the west, drives strong winds across the Korean Peninsula on Friday, as illustrated by the forecast valid 0300 UTC 23 February (0900 KST Friday).  

As currently scheduled, the Women's Downhill is 1100 KST Wednesday (7 PM MST Tonight).  This is well in advance of the trough and the main concern will be the omnipresent gusty winds and perhaps some flat light from cloudiness.  I think they will get it in.  Later Wednesday are the Team Cross Country Sprints, which they should also get in.  The DVR will get a workout tonight for that as the finals aren't until 1900 KST (0300 AM MST Tonight).   

Thursday at 10 AM KST is the Men's Slalom Run 1, 1130 AM is the Women's Alpine Combined Downhill, 1330 is the Men's Slalom Run 2, and 1500 is the Women's Alpine Combined Slalom.   This covers a period from 0100-0600 UTC 22 February and as can be seen in the plots above, those events are scheduled to occur before any precipitation arrives, but also as pre-trough southerly flow is increasing.  Official forecasts for the top of the downhill show 5 m/s (10 knot) winds through 1200 KST, then increasing.  It's going to be close.  

Assuming it does go off, tomorrow night (MST) should be a great viewing for ski fans.  Helping in that quest, there's no figure skating scheduled.  Hooray!

Record Cold and the Northwest Stays in the Freezer for a While

The air over us now is unusually cold for this time of the year, in fact, record breaking cold in some ways.  For example, let's start with the temperature around 5000 ft (850 hPa pressure) at the radiosonde station at Quillayute, on the Washington Coast (see below).   In this plot, the blue line shows the daily record low 850 hPa temperatures.  Today's temperature (-12.5C, shown by a circle) was not only a record for the date, but the lowest for the surrounding dates as well.  Really unusually cold.

The surface air temperatures last night (see below) were held up by the windy conditions (which mix down warmer air above the surface) and some clouds, but still temps dropped into the mid 20s F in much of western Washington and single digits in the mountains  Some valley locations dropped below 0F.  Teens dominated in eastern WA.

Tonight is going to be much colder, with colder air aloft, clear skies, and less wind. The temperatures predicted for tomorrow morning suggest mid-20s in the west and single digits east of the Cascades, with some valleys in eastern WA dropping below -8F.

The latest forecast model output predicts another four days of the really cold stuff.  Here is the NWS GEFS ensemble forecast for Seattle.   Several more days of lows in the mid-20s ahead.

The large scale atmospheric pattern is really locked into a super La-Nina configuration with high pressure offshore and cool northerly flow over the NW.   To show you this, here are the upper level (500 hPa) weather maps for Wednesday and next Tuesday. Quite similar really.

There are occasional disturbances moving southward in to the flow east of the upper level ridge of high pressure that will bring some occasional precipitation, and in some places, snow.

To illustrate, here is the total snow fall forecast for the next 72 h.  Most of the snow is heading for Oregon and SW Washington.  None over Seattle or the WA Cascades.

The next 72 hour is quite different, with massive snows in the WA and Oregon Cascades. Skiers will be pleased.

Keep warm....

Boomer Sooner?

I've spent more of my life in Oklahoma than anywhere else.  I like the weather here, given my passion for severe thunderstorms.  I like the physical geography of the state, with its large contrasts from east to west.  I was rather satisfied with the education I received here at the University of Oklahoma (OU) and had some great mentors who were OU faculty and staff.  However, recent postings on social media have raised a point of concern with regard to the University's "mascot" - the Sooners.  The school's fight song is "Boomer Sooner", composed by Fred Waring (!). 

 Many people are unaware of the origin of the term Sooners - it's tied to the Oklahoma Land Rush of 1889.  The "Boomers" were settlers who tried to grab parcels of land blatantly in the so-called "unassigned lands" (that was home to Native Americans) before the official starting date of 22 April 1989.  The US Army removed as many of them as they could.  The "Sooners" were people who sneaked into the unassigned lands early but kept a low profile, hoping to make a legal claim after the official starting date.  Both Boomers and Sooners were, effectively, cheaters seeking to grab the land of the Native Americans before they were allowed to do so.  These are not exactly the sort of folks that one would choose as a role model and certainly should be somewhat embarrassing to the University.  But I have my doubts many associated with OU ever give it any thought.

We already have seen a growing chorus of discontent by indigenous people with using Native American-associated terms for sporting team and Universities.  Recently, the 'mascot' of the University of North Dakota was changed from "The Fighting Sioux" to "The Fighting Hawks" in response to many protests by the Sioux tribe.  The controversy there was long and bitter.  There also has been concern about the Kansas City Chiefs, the Florida State Seminoles, the Washington Redskins (!), the Cleveland Indians, the Chicago Blackhawks, and many others.  Not surprisingly, there's been considerable pushback from those who rationalize such uses of these nicknames and logos.  I'm not about to enter the morass of that debate, but I do generally believe that our use of such cultural icons for our own purposes is disrespectful to Native Americans and their cultures.  Obviously, there are those who disagree.

Here at OU, the mascot is even worse than the preceding examples, because it honors those who participated in the plundering of Native American lands by white settlers.  The Boomers and Sooners grabbed their parcels of land by illegal means.  The Native Americans were the ultimate losers, sadly.  The whole of the lower 48 states represents the home of Native Americans who were here long before any white European settlers arrived to claim all those lands (except for reservations of generally worthless land assigned to those Native Americans who were not killed).  The indigenous people of the Americas were subjected to various forms of genocide and destruction of the original environment on which they depended.

Our treatment of indigenous people is shameful and it continues right up to this very day!  Anyone with a conscience should be deeply ashamed of this aspect of our national history.  As usual, the rationale for this history has been based on viewing them as primitive savages who were not even qualified as human beings with unalienable rights.  I have little expectation that OU will be changing their mascot any time soon.  White privilege is alive and thriving here in Oklahoma, and that isn't likely to change in the foreseeable future.  But I don't have to like that situation, and I don't have to support robbing Native Americans of their cultural heritage.

Eruption of Mount Sinabung volcano

Himawari-8 RGB images [click to play animation]

Himawari-8 RGB images [click to play animation]

An explosive eruption of Mount Sinabung began at 0153 UTC on 19 February 2018. Himawari-8 False-color Red-Green-Blue (RGB) images from the NOAA/CIMSS Volcanic Cloud Monitoring site (above) showed the primary plume of high-altitude ash moving northwestward, with ash at lower altitudes spreading out to the south and southeast of the volcano.

Mutli-spectral retrievals of Ash Cloud Height (below) indicated that the explosive eruption injected volcanic ash to altitudes generally within the 12-18 km range, possibly reaching heights of 18-20 km. Advisories issued by the Darwin VAAC listed the ash height at 45,000 feet (13.7 km).

Himawari-8 Ash Height product [click to play animation]

Himawari-8 Ash Height product [click to play animation]

Ash Loading values (below) were also very high within the high-altitude portion of the plume.

Himawari-8 Ash Loading product [click to play animation]

Himawari-8 Ash Loading product [click to play animation]

The Ash Effective Radius product (below) indicated that very large particles were present in the portion of the plume immediately downwind of the eruption site.

Himawari-8 Ash Effective Radius product [click to play animation]

Himawari-8 Ash Effective Radius product [click to play animation]

In a comparison of Himawari-8 “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.4 µm) images (below), note the very pronounced warm thermal anomaly or “hot spot” (large cluster of red pixels) on the 0150 UTC image — Himawari-8 was actually scanning that location at 01:54:31 UTC, just after the 0153 UTC eruption. Prior to the main eruption (beginning at 0120 UTC), a very narrow volcanic cloud — likely composed primarily of condensed steam — was seen streaming rapidly southward from the volcano summit.


Himawari-8 “Red” Visible (0.64 µm, left), Shortwave Infrared (3.9 µm, center) and “Clean” Infrared Window (10.4 µm, right) images [click to play Animated GIF | MP4 also available]

The coldest Himawari-8 cloud-top infrared brightness temperature was -73 ºC at 0300 UTC, which roughly corresponded to an altitude of 15 km on nearby WIMM (Medan) rawinsonde data at 00 UTC (below).

Medan, Indonesia rawinsonde data at 00 UTC on 19 February [click to enlarge]

Medan, Indonesia rawinsonde data at 00 UTC on 19 February [click to enlarge]

A Terra MODIS True-color RGB image viewed using RealEarth is shown below. The actual time of the Terra satellite overpass was 0410 UTC.

Terra MODIS True-color RGB image [click to enlarge]

Terra MODIS True-color RGB image [click to enlarge]

An animation of Himawari-8 True-color RGB images can be seen here.

Everybody Gets Some, Plus Tonight’s Lake-Effect Intricacies

Finally, a great storm.  All elevations, all locations.  Some cherry picked storm totals so far based on reports to the NWS (time of measurement in parentheses):

Smithfield, Cache Valley (4 PM Sun): 12"
Ogden (5 PM Sun): 2"
West Valley City (6 AM Mon): 5.2"
Salt Lake Airport (5 AM Mon): 3.6"
Cedar Hills, Utah County (5 AM Mon): 9"
Powder Mountain (5 AM Mon): 12"
Brighton Crest (5 AM Mon): 16"
Alta-Collins (3 AM Mon): 14"
Spruces (4 AM Mon): 10"

Through 8 AM, Alta Collins is up to 18", blowing my 7-14" expected through 9 AM out of the water. 

With the KMTX radar up-and-down overnight (and currently down), getting a good handle on the action is more difficult than usual.  One thing that caught my attention is described in the tweet below, issued last night.  From 8-10, Alta-Collins recorded 6" of snow (3"/hr mean rate) and I saw some tweets of impressive accumulations near Alpine as well.  During this period, a very pronounced band extended across northern Utah County and far northwest Wasatch County, and stronger radar reflectivities also lingered over the upper Cottonwoods. 

One option when KMTX is down is to examine data from the Terminal Doppler Weather Radar (TDWR) operated near the east shore of the Great Salt Lake west of Farmington.  The primary purpose of this radar is to detect hazardous weather and wind shear over the airport.  It is blocked significantly by the surrounding topography, and provide little to know information about what is happening over the Wasatch and the broader region.  You can see, however, returns related to snow showers over portions of the Salt Lake Valley. 

Periods of snow look to continue today and tonight in the mountains and also in the valley.  The latest NAM forecast shows us transitioning into deeper northwesterly flow during the day today, with the flow transitioning to westerly overnight.

The situation for tonight is really interesting.  The latest forecasts show a pocket of remarkably cold air moving over northern Utah, with the latest NAM forcasting -22ºC over the Great Salt Lake at 1200 UTC.

In fact, the absolute minimum is an astounding -22.9ºC at 1500 UTC (8 AM).  That is a remarkably low 700-mb temperature.  It would not be a record for February (-25.9ºC is the all-time low), but we don't see too many days around here with temperatures that cold.

The Great Salt Lake is actually not that warm compared to climatology, but still, the average lake-surface temperature is almost 4ºC. 

As a result, the HRRR is fairly excited about a possible lake-effect event tonight.

Our statistical forecast system, based on the 6Z NAM, shows elevated lake-effect probabilities ovrenight tonight, peaking at 90% at 2 AM.   Note how the affected area shifts from the Cottonwoods to the northern Wasatch with the flow shift overnight. 

There are, however, three important issues to keep in mind.  The first is that wind directions beneath these upper-level troughs are tricky to forecast, so one can't count on that forecast precisely. 

The second is that we tend to fixate on lake effect, when we need to keep in mind that we could see post-frontal snow showers generated by other processes.

Finally, the third is the cold.  This is a remarkably cold airmass.  Temperatures at crest level are going to be so cold that instead of favoring dendrites, they will favor higher density crystals.  I've seen situations where this has put a damper on snow amounts in the past.  There aren't a lot of days at Alta that are this cold, but if you look at the snow-to-liquid ratios when the 650-hPa temperature is below -20ºC, there is a tendency for lower values. 

I'm thinking another 3-6" in the upper Cottonwoods through 6 PM this afternoon.  After that, I'm happy to sit in my ivory tower and watch this one play out.  Hopefully the radar will come up.