Tuesday, November 12, 2019

Winter, Interrupted

The end of October arrived with such promise.  Record cold temperatures.  Natural snowfall.  Resort snowmaking.

Alas, things changed quickly and we've been stuck in a dry, warm pattern for over a week.  Since November 3, maximum and minimum temperatures at Alta have been running at or above average.

Source: http://xmacis.rcc-acis.org/
Really, the pattern has been locked in for some time.  The 30-day average 500-mb heights for the period ending Monday November 11 shows anomalous ridging over the Gulf of Alaska and Alaska and anomalous troughing over the Great Lakes region.  This is consistent with the frequent surges of cold air into the high plains and the unusually cold weather we had in October.

In November, it shifted a bit, allowing us to experience more mild weather.  Unfortunately, the spigot has also closed and thus we sit here waiting for snow while the natural snowpack has melted off on south aspects and rotted to facets on the north aspects.  Resorts are still making snow when they can and this morning guns were running at Alta and Snowbasin.

Source: Alta

Source: Snowbasin
Nevertheless, we need natural snow, but the NAEFS forecasts have been like bad reruns the past few days and last night's is no exception.  Little to no precipitation through day 5 with a couple of members from the Canadian Ensemble putting out some precipitation at days 6 and 7.

Thus, a major storm is unlikely and the odds favor little to no precipitation through the coming weekend.  Let us hope that something can slip through the net next week.

Friday, November 8, 2019

Visiting Old Friends and Chasing Cold Air

I've spent the past several days in upstate New York where I visited the atmospheric sciences department at SUNY Albany and attended the Northeast Regional Operational Workshop where I gave a talk on our lake-effect work.

It's great to reacquaint with Anton Seimon (farther right below) who I haven't seen in about 20 years, but who is one of the best meteorological analysts I know.  A cyclone aficionado, he brought some Bombogenesis Double IPA with him.  Given that it was morning and we had work to do, this photo is staged.  No beer was consumed, sadly. 

I also visited the "headquarters" of the New York Mesonet, which has come together in the past few years and includes at least one station in every county.  The Mesonet has had a major impact on weather analysis and forecasting in New York and dear to my heart they have about 20 stations equipped with specialized snow-measurement instrumentation.  These are primarily on Tug Hill and in the Adirondacks, although there are a few in the Catskills and western New York.  At the headquarters, one can see live photos from every station.

I'm staying until Sunday to visit family and reminisce.  It's cold.  I did a short hike in the Adirondacks today and suspect the summit temperature was in the low 20s, with wind.  It looks like Adirondack winter.

With the cold, Gore Mountain has commenced their snowmaking operations. 

Perhaps I should stay?  The models suggest continued dryness over the next few days in Utah. 

Sunday, November 3, 2019

First Scratches

I got out for my first turns of the season Saturday morning.  First scratches might be more accurate since we stuck to skiing Collins gulch where artificial snow has bolstered the cover and snowpack.  Conditions consisted of a mixture of silky man made, trappable crust (from man made covering natural), and chunder.  I heard it was better than a couple of days earlier. 

Many resorts took advantage of last weeks unusually low temperatures to pump out the white stuff, and Alta is no exception.  I suspect they could have opened the main run down Collins gulch this weekend if they wanted to.  It just needed a bit some farming and a good groom.

Photo: Erik Steenburgh
Snowmaking continued while we were ascending in the morning.  However, the guns were all off on our descent, reflecting the warmer daytime temperatures.  Snowmaking conditions over the next week look less optimal and I suspect daytime snowmaking will be challenging until at least next weekend. 

Work has started on the new Mambo half-pipe, sure to thrill freestyle skiers and snowboarders...

Photo: Erik Steenburgh
Turns were best on the man-made silk, although one needed to be attentive as some of the apparent silk was trappable crust. 

Photo: Erik Steenburgh
The next week looks like a good one if you like sun and just want to start building fitness and you don't mind risking a lose filling or two in Collins gulch.  Non-resort options are pretty much DOA on south aspects, although there are reports of some getting out in shark-infested low-tide conditions on high north aspects. 

Friday, November 1, 2019

Thank You

Sometime during the last week, Wasatch Weather Weenies reached 3,000,000 all-time page views.

Readership is far greater than I could have imagined when I started in late 2010.  It grew steadily, however, for several years, peaking in the winter and dropping during the summer.  There's been a small decline the past couple of years, but I'm not worried.  I don't get paid anyway!

Despite the fact that I have no income stream from this blog, I have learned that weather is good for business.  Readership really spikes prior to and during winter storms and other weather events.  Sadly, although we finally did get some October snow this season, the NAEFS ensemble is essentially flatlined for the next week.

Production will once again be high in the central Wasatch facet factory.

Thank you for reading.

Wednesday, October 30, 2019

Hell Has Frozen Over

Here are two things that have never been observed before in Salt Lake City in October.

First is yesterday afternoon's sounding, with a 700-mb (10,000 ft) temperature of -18.5˚C, more than 3˚C colder than the previous record of -15.3˚C.

Source: SPC
If you are wondering, temperatures aloft have already started to increase, so this morning's 700-mb temperature is -15.7˚C.  That's not as cold, but it is the 2nd lowest on record.

Second is the overnight minimum temperature of 14˚F, which is the lowest temperature recorded in the month of October in Salt Lake City with records going back to 1874.

Beyond Salt Lake, it was cold everywhere, but as usual, Peter Sink, a sinkhole in the Bear River Range known for extremely low temperatures, takes the cake.  Looks like a minimum temperature of -43.6˚F based on data available in MesoWest.  

Logan meteorologist Timothy Wright tweeted this morning that the minimum was -45.5˚F and that would be a national October record.  The lower temperature he reports could reflect that he has access to another station or data between the obs times reported to MesoWest.  I'm sure he'll get to the "bottom" of this eventually. 
I would rate this event as one of the most remarkable since I moved here in 1995, up there with the 1999 Salt Lake City Tornado and Thanksgiving 2001 Hundred Inch Storm at Alta.  Extreme cold surges are rare events in northern Utah.  This is why, when one looks at the record daily minimum temperature records for Salt Lake City (light blue line below), there are a small number of truly exceptional minimum temperature records with a spike-like appearance.  Examples include February 9-10, 1933, November 3, 1936, and November 15-16, 1955.  There is another period in December during which cold surges in 1932 and 1972 set extreme minimum records from December 9-16.  

Such cold surges are the meteorological equivalent of drawing a royal flush in five-card draw.  A magic sequence of events must come together to get such extremely low temperatures.  This is especially true given the warming global climate and urban heat island effects.

An alternative perspective on the extreme nature of the event is provided by the analysis below, which is a map of departures of current surface temperatures from the 1979-2000 average for each location (referred to as anomalies).  The coldest anomalies are in western North America, centered over Wyoming.  However, the global average is 0.7˚C warmer than the 1979–2000 average, so global warming is still a thing.  Additionally, patterns that cause cold surgest into the western and central U.S. are often associated with anomalously warm temperatures in Alaska, and you can see that below.  In fact, the high temperature in Anchorage yesterday was 54˚F.

Source: climatereanalyzer.org
If you don't like the cold weather, then you should simply plan on going up to upper Big or Little Cottonwood Canyon tomorrow.  The warming in the mountains over the next 24 hours is going to be remarkable.  At 8am this morning it is -6˚F on the summit of Mt. Baldy (11,000 ft).  By tomorrow it will be close to freezing.  The models are showing more than a 30˚F increase in temperature in the mountains from this morning to tomorrow afternoon.

Tuesday, October 29, 2019

Rapid-Fire Views on the Octobruary Cold Surge

So much to talk about today and so little time.  Hence, I need to do this in rapid-fire mode.

Record Cold Crest-Level Temperatures

Forecast 700-mb temperatures for Salt Lake City at 0000 UTC 30 October (1800 MDT Today) are -17.7˚C by the NAM and -18.1˚C by the GFS.  These are slightly higher than advertised a few days ago, but will still represent records in the upper-air sounding record for the month of October.

Record Cold Surface Temperatures

The NWS forecast of 13˚F for tomorrow (Wednesday) morning would be the lowest temperature ever recorded at the Salt Lake City International Airport in October.  I haven't bothered to see what the records are elsewhere, but the current forecast (image grabbed at 7:30 AM MDT Tuesday 29 October) calls for -11˚F in Randolph and, gasp, 24˚F in St. George. 


Yeah, it's happening today.  Monitor forecasts.  'Nuff said as I don't have time for a proper forecast.

Back-Door Cold Front

In weather and war, bad things come from the east.  If you think it is cold now, the HRRR is advertising the passage of a so-called back-door cold front across the Wasatch Front this afternoon.  A back-door cold front is one that comes from the east rather than the west or northwest.  The HRRR forecast valid 2100 UTC (1400 MDT) this afternoon shows the front with a precipitation band just to the west and south of the Great Salt Lake.  This front is not approaching from the west, but rather it passed through the Wasatch Front from the east. 

Downslope Wind Misery

This afternoon has the very real potential to be the most miserable October afternoon ever along portions of the northern Wasatch Front.  In the wake of the back-door cold front are easterly downslope winds. 

So, we're talking the coldest October airmass ever, with strong winds.  Excuse my sarcasm, but it's going to be really cold, but at least it's going to be windy too!

Crest-Level Whiplash

As remarkable as this cold air is, the rebound to warmer air, at least in the mountains, is also amazing.

The GFS forecast valid 0000 UTC 30 October (1800 MDT Today/Tuesday) calls for 700-mb (crest-level) temperatures of -18˚C over Salt Lake City.  However, the warm air moves in quickly aloft and by 1200 UTC (0600 MDT) Thursday/Halloween, they have climbed all the way to -1˚C. 

Late October Inversion

This is a hypothesis worth checking, but the result of that warming aloft will probably be one of the strongest, deepest inversions on record on Halloween.  The word inversion is often used in Utah to mean pollution, but here I'm referring to the temperature inversion that will develop over northern Utah as that warm air moves in aloft.

Forecast soundings from the NAM show a surface-based inversion at 1200 UTC (0600 MDT) Thursday/Halloween morning with surface temperatures near -9˚C, whereas temperatures at 675 mb are around -3˚C. 

Inversion season "starts" on November 1, but Mother Nature is going to get started early.  Even by late afternoon on Halloween, only a shallow surface-based mixed layer exists, with constant temperatures from 800 to 700 mb near 0˚C.  Technically, this is not an inversion since temperatures do not increase with height, but that's a meteorological nuance.  It's an extremely stable atmosphere with cold air trapped in the Salt Lake Valley. 
Air Pollution?

Probably not an issue for Halloween (Thursday).  I suspect there will be haze around, but air quality should be "good" or at worst low moderate at worst since we will have just flushed the valley with a pristine arctic airmass.  Another brush by system on Friday should ensure that we don't start the inversion season with a major air pollution event.


Beware when the atmosphere is in outlier mode.  That's my go-to phrase this fall. 

Monday, October 28, 2019

How Hell Freezes Over

October is the new January, at least in Salt Lake City where if you think it is cold this morning, just wait.

Really, the past month has been quite cool relative to climatological norms.  The mean temperature at the Salt Lake City International Airport for September 27 through October 27 was 49.8˚F, the lowest mean for that period since 1982 and the 4th lowest on record at the Salt Lake City International Airport (records back to 1928).

Source: http://scacis.rcc-acis.org/
The reason for this cool weather has been a persistent, long-wave, upper-level pattern featuring ridging over the Gulf of Alaska and troughing over the northwest United States.  This has led to northwesterly flow over the western United States, with a series of systems dropping into our area from the northwest or north.

Yesterday, steady light snow fell along the east bench in the wake of the first of two major upper-level troughs that will plunge us into a deep freeze this week.  Snowfall rates were perfect for creating lovely scenes without too much impact on roads or trails.

This morning, we had a minimum temperature of 22˚F at the Salt Lake City International Airport, a new record for the day.  Minimum temperature records have become relatively rare, so this is cause for celebration.  Hooray!

However, this is just the tip of the spear of the cold air as another system pushes in tonight and tomorrow, which will really make it feel like hell has frozen over.

Believe it or not, the circumstances leading to this deep freeze involve typhoon Neoguri, the remnants of which were off the coast of Japan at 0000 UTC 23 October (circled in red).

Neoguri then underwent extratropical transition and greatly perturbed the midlatitude jet stream, building a high amplitude ridge over the eastern Pacific.

The amplification of this ridge (identified at 1200 UTC 27 October by a red line in the image below) led to an amplification and southward "digging" of the downstream trough over the western United States (long brown dashed line below), giving us yesterday's snow.  This process is known as downstream development.

But Neoguri isn't finished yet.  If you look at the image above, there is a second short-wave trough over the Northwest Territories (brown dashed line), and it is coming to Utah tonight and tomorrow.

The analysis below shows the situation at 700 mb (about 10,000 ft above sea level) a day earlier at 1200 UTC 26 October or 0600 MDT Saturday morning.  The cold front associated with the first upper-level trough was just north of Utah.  Cold air associated with the second upper-level trough (circled in red) was north of Alaska.

Now let's put that into motion. The cold front pushes through Utah, and then, the really cold air associated with the 2nd trough moves southward and into the state.

The GFS forecast valid 0000 UTC 30 October (1800 MDT Tuesday) calls for 700-mb temperatures of -19˚C in Salt Lake City.  As noted in an earlier post (A Scary Forecast with Halloween Approaching), temperatures that cold have never been observed in October at the Salt Lake City Airport (upper-air records dating back to the mid 20th century). 

The NWS forecast for the Salt Lake City International Airport thus is calling for a low Tuesday night of 13˚F. 

The record low for the month of October is 16˚F. 

Indeed, this is as close as you can get to hell freezing over. 

And, for God's sake I leave you with this PSA.  TURN OFF YOUR SPRINKLERS. 

Sunday, October 27, 2019

GFS 1, NAM 0

It's a beautiful Octobruary day in the Avenues and on the University of Utah campus where light snow is falling and creating a beautiful scene with the fall colors.  My little corner of northwest campus is especially nice where the University has gardened with drought-resistant plants.  So much nicer than grass!

This morning, I took a look back at the forecasts produced by the models initialized at 0000 UTC 27 October (1800 MDT Saturday).  The contrast between the GFS and the NAM is significant.

Below are 24-hour accumulations (water equivalent) generated through 0000 UTC 27 October (1800 MDT this afternoon).  The GFS (top) has about .1-.25 inches falling over the Salt Lake Valley, with higher amounts in the central Wasatch.  The NAM (bottom) has nothing.   

Downscaling and applying a snow-to-liquid ratio to these forecasts and you get accumulations of 0.5 to 2 inches on the benches and greater than 4 inches over the central Wasatch from the GFS.  Nothing from the NAM (naturally). 

If you are wondering, automated sensors at Alta-Collins suggest 3-4 inches of snow as of 10 am.  Accumulation in my neighborhood is surface dependent, but I'm willing to call it measurable and thus give the GFS a 1-0 win over the NAM. 

So, in this instance, yesterday afternoon's guidance from the GFS was superior.  However, that's a sample size of one.  We'll see how it does in the coming weeks.

Saturday, October 26, 2019

A Scary Forecast with Halloween Approaching

I'm putting in some time at the office today and just took a peek at the models. 

Yup, they are terrifying, with an airmass coming in that is NOTHING like anything we have seen in northern Utah since weather balloons began to be launched in the middle of the 20th century.  If you miss the cold of the old days, Mother Nature is going to be giving you a taste.

The GFS forecast for 0600 UTC 30 Oct (0000 MDT Wednesday) shows 700-mb (10,000 ft) temperatures near -20˚C across much of northern Utah.  You can even find sub -24˚C air near the Uintas. 

These numbers are utterly, totally, and completely ridiculous.  In the sounding archive for northern Utah, there has NEVER been a 700 mb temperature observed below -15.3˚C in October. 

It is not hyperbole to say this is an unprecedented early season cold surge during most of our lifetimes.  According to the NWS Salt Lake City Forecast Discussion, the European ensemble forecast mean 700-mb temperature is -19˚C at 1200 UTC (0600 MDT) Wednesday morning. 

It's going to be a cold halloween.  Yes, it will be important to keep the kiddies warm, but this is also a situation where the homeless will be at serious risk.  Prep your house and car if you haven't already and pick any vegetables you have remaining. 

Finally, monitor official forecasts.  Much is going to depend on the exact track and strength of the synoptic systems responsible for the cold surge, but portions of northern Utah could see some snow (and with such low temperatures, it is going to stick) and it is possible that we could see downslope canyon winds as well.