Far East Connections

We've already discussed how the initial source of moisture for the pending storm cycle is being extracted from the tropics and subtropics near Hawaii.  Subsequently important is a second filament of moisture originating in the Far East near the Philippines.

Both of these can be seen in the global precipitable water (color contours every 5 mm), 925-mb wind (vectors), and dynamic tropopause pressure (color fill) analysis below.  The filament originating near Hawaii is streaming northeastward in the eastern Pacific, whereas the filament originating in the Far East is streaming eastward across the western Pacific.  

I think of how far we have come meteorologically compared to the pre satellite era when the ability to identify and trace these moisture filaments was essentially non existent.  Today, more than 99% of the data ingested into operational numerical weather prediction models comes from satellites.

Cascade Concrete Is Coming

After weeks of waiting, snow is coming.  Surely you won't be picky?  I hope not, because the first storm looks to be loaded with Cascade Concrete.

The 1200 UTC GFS from this morning calls for precipitation to move into northern Utah during the day tomorrow (Wednesday).  The forecast valid 5 PM MST tomorrow shows a classic scenario for a heavy, high water content snowfall: Wet, windy, and warm.

Snow density in the Wasatch Mountains is most strongly related to the crest-level temperature and wind speed and the formula for Cascade Concrete in Utah is pretty simple: Warm Temperatures + High Winds = High Water Content Snow.

One of our student's here, Trevor Alcott, has developed an algorithm for predicting snow water content from the GFS and other computer models.  Based on the GFS, his algorithm calls for a snow water content at Alta of between 13 and 17% from noon tomorrow through 6 PM Thursday with the snow level reaching as high as 8600 feet at 3 PM Thursday.

Personally, I see this as a good thing.  Lay down some high density stuff that sticks to everything.  Let's just hope that snow level doesn't creep up too high.  

Mr. Blutarski Moves In

Rarefied air has moved in and the Mr. Blutarski isotherm (i.e., 0.0ºF air) is hovering somewhere near 10,500 feet, as indicated by observations at the top of the Collins chair at Alta.

Meanwhile, Andrew McLean reports pandemonium in Park City over this mornings "angry inch." 

Locked and Loaded!

After weeks of boring weather, I can barely contain my excitement about what is coming later this week and beyond.  Everything is lining up for a major storm cycle.  It will bring much needed base-building snowfall to the Wasatch, but also hazardous backcountry avalanche conditions.

To understand the setup for this event, one has to look to the Hawaiian Islands where two streams of tropical moisture are being injected into the mid latitudes.  In particular, there is a subtropical ridge centered just to the east of Hawaii that is pumping moisture directly from the tropics over the islands that is confluent with a potent river of subtropical moisture associated with a trough to the northwest of the Islands (click to enlarge).

1600 UTC 16 Jan 2012 precipitable water (contours every 5 mm) and
925 mb wind vectors (click to enlarge).

This is the initial source of moisture for the storm cycle, which will begin to rage late on Wednesday as this moisture streams into and across the western United States.  Apologies that the loop below is a bit dark, but it should be sufficient to get your attention.

1200 UTC 16 Jan 2012 precipitable water (contours every 5 mm) and
925 mb wind vectors forecast loop valid through 0000 UTC 21 Jan

Things look very active through the weekend, after which things continue to look great, as illustrated in the CPC 6-10 day outlook, which was issued yesterday but, based on what I'm seeing, I don't think will change much today.

Source: NOAA/NWS/CPC

Bottom Line: The atmosphere is locked and loaded.  Buckle up for a wild ride.

Small Storm, Lousy Roads

This morning's storm rates a 1 on a meteorological scale of 1 to 10, but, at least near downtown Salt Lake City, it had a disproportionate impact on the morning commute for those who need to work today.

In particular, although accumulations remain (as of about 8:30 am) less than an inch or two, the roads are slick as snot.  This is because of both meteorological and societal reasons.  From a meteorological standpoint, a key reason is the lag between the frontal passage and the snowband.  This can be inferred from the meteogram from the University of Utah (WBB), which shows a temperature fall into the mid 20s  following frontal passage at around 3 am, with precipitation beginning at around 7 am (inferred from the increase in relative humidity).

Source: MesoWest

The lag between the surface front and snowband can also be seen in the satellite loop below, which includes an overlay of 700-mb temperature contours.  There is a cloud band with relatively cold cloud top temperatures accompanying the leading edge of the cold air, but the main band producer is a cloud  band that lags farther behind in the colder air and has somewhat warmer cloud top temperatures.  This is a good example of why you can't count on precipitation accompanying the surface based cold front.  Sometimes, especially in Utah, the precipitation band lags behind.  It is also a good example of why cloud top temperatures are often not a great indicator of precipitation rates in the wintertime, especially over Utah.

On radar, this is not a strong snowband, and precip rates based on my highly scientific glimpses out the window appear to be near or slightly less than an inch an hour.

So, this is not a big storm, but the commute this morning was difficult.  From a meteorological perspective, the passage of the cold front ahead of the snowband enabled the roads to cool so that snow stuck immediately.  From a societal perspective, the response of road crews, at least in the neighborhoods I travelled through this morning, was somewhat delayed, especially given that this was a well anticipated storm.  Perhaps this was related to the MLK holiday.  On the plus side, the MLK holiday meant that traffic was light.

This is a good example, however, of how even a small amount of snow, when delivered under the right conditions, can make travel difficult.  On the other hand, if you are a late riser, you probably won't experience the full brunt of the white knuckle driving that some encountered this morning.

Bleak Present, Brighter Future

Regime change is coming, but Mother Nature is going to make it as rough as possible.  We went up to Alta today to run laps with my father who is visiting and to bid adieu to the rotting snowpack before it gets buried this coming week.  It doesn't get much bleaker than this in mid January.

First, the view of the south facing aspects above Little Cottonwood.  Brown.  On the plus side, there's no facets where it's brown, which could be advantageous for touring once we have a snowpack.  Of course, one will need to be extremely careful when skiing on these slopes not to venture into those areas where pockets of faceted snow presently persist.

Second is something I thought I would never see at Alta.  There is no snowmaking off the Supreme Chair and keeping it running is taking a "supreme" effort.  After the strong winds of yesterday and today, it's incredibly grim up there.  They were actually filling buckets with snow at the bottom of the chair and unloading them at the top, presumably to maintain the cover in the unloading area.

Shovels and buckets at the bottom of the Supreme

Unloading at the top

Finally, to add insult to injury, after skiing the loose and frozen granular, it's always wonderful to descend into a wind-blown dust event.

Looking southwest toward the Oquirrh Mountains from the Avenues

Fortunately, our long nightmare is almost over.  As discussed in yesterday's post, a cold front will push through late tonight and tomorrow and give us some snow.  Then, after day or two of cold dry weather, the floodgates open.  Things are starting to setup in the western Pacific today where a pronounced plume of subtropical moisture is getting setup near the dateline.

Source: SSEC/CIMSS

Wednesday afternoon through Friday look wet, warm, and windy.  It's going to be a mess (backcountry avalanche conditions are likely to be extreme), but the pattern will give us the sort of base building snow that we desperately need.  And, it looks active (and cooler) through at least next weekend.  Keep thinking snow!