Friday, October 30, 2015

The Great Salt Lake Is Jacked

The Great Salt Lake may be near its all-time record low elevation and area, but lake-surface temperatures right now are running quite high.  Because the Great Salt Lake is so shallow, lake-surface temperatures often reflect recent temperatures at the Salt Lake City airport and so far this month the average temperature at the airport is a whopping 61.2ºF (16.2ºC).  Consistent with this observation, satellite-derived lake-surface temperatures averaged for the past 2 days are generally above 14ºC, except in shallow areas along the coast, and average 15ºC for the lake as a whole.

It's very difficult to place these lake-surface temperatures in a long-term context.  The satellite record is fairly short, and most of the long-term observations are from Saltair a single location on the south coast.  Nevertheless, if we look at the lake-surface temperatures from Saltair for 1972–1988, we find that 15ºC is near or above the upper margins of the range for November 1 (data is bimonthly).
Source: Steenburgh et al. (2000)
So we can probably safely conclude that the Great Salt Lake is quite warm for this time of year.

Will that mean a big lake-effect storm?  It really depends on whether or not the atmosphere decides to cooperate.

Thursday, October 29, 2015

A Splitting Storm, But Early Next Week Things Get Interesting

The system moving through the western United States today is a very good example of a splitter.  It was a coherent, full-latitude trough over the eastern Pacific, but stretched and split into two distinct short-wave troughs over the western U.S., one that is moving across the far southwest, the other tracking through the Pacific Northwest and Canada.

Although many people feel gypped by splitting storms, the western United States lies climatologically in the exit region of the Pacific jet stream and in an area favoring the stretching and splitting of upper-level systems.  In other words, there's nothing unusual about this happening.

As I was heading home on my after-work bike ride yesterday, I noticed it was getting awfully dark. The end of October is here, we switch to standard time on Saturday night, and November arrives on Sunday.  We've had a good run of fall weather, arguably the best in the instrumented record other than October 2004 when it snowed enough to open the backcountry and resorts by Halloween, but it's time to think about snow once again.  In addition, it also appears that Howie has reset the automated snow-depth sensor at Alta-Collins, which had been reading an "extremely optimistic" 4 inches all summer.  It was reset to zero yesterday, so we're ready for a clean start.

Source: MesoWest
Possibilities vs. probabilities

By now you have heard rumors of a storm in the future, and indeed, the GFS is bringing a healthy and cold upper-level trough across the western United States early next week.  This is the time of year when any possibility of snow gets a mention on the news, but the real question is, what are the probabilities?  Statements like "we may get a major storm next week" are flippantly thrown around without any mention of the probability of that happening.  Let's try and put some numbers on it.

If we take a look at a suite of forecasts for the next 7 days from the North American Ensemble Forecast System (NAEFS), which are lower resolution but downscaled using climatological data, we see a fairly optimistic forecast for Alta–Collins.  Although one of the ensemble members gives us nothing, most are generating from 1.5 to nearly 4 inches of water equivalent through Wednesday afternoon (0000 UTC 5 November).  This particular downscaling technique has a bit of a high bias, so perhaps think in the 1–3.5 inch range.

Most members of the European ensemble are also troughy and wet, although there are a few that are not as wet.

So, if I do a quick qualitative integration of these ensemble forecasts (both the NAEFS and the European) with a bit of a bias correction, I give us something less than a 10% chance of a total skunking at Alta-Collins, with an 80% chance of an inch or more of water equivalent, 40% chance of 2 inches or more, and 10% chance of three inches or more through Wednesday afternoon.   Thus, I think this is a storm worth watching, although sometimes Mother Nature decides to give us something that lies outside the ensemble envelope.  That would be good if she went big, and not so good if she decided to have the storm "go south" (literally and figuratively).

Monday, October 26, 2015

Top 10 Ski Area Microclimates

A microclimate refers to the unique meteorological conditions that occur at a given location or area.  Mountainous regions tend to produce a plethora of microclimates due to the strong influence that complex terrain has on meteorology.  Below are my top-10 U.S. ski-area microclimates, plus some honorable mentions, based on remarkable aspects of the snowfall characteristics compared to the surrounding area or region.

10. Wolf Creek Pass, CO

Colorado is not especially snowy, but Wolf Creek Pass is the exception to the rule.  At an altitude of 10,640 feet, the long-term observing site at Wolf Creek Pass has an average annual snowfall of 435 inches, highest in the state.  In addition, Wolf Creek Pass is well situated to be pounded in warm storms with southwesterly flow, resulting in snow with a higher average water content than found elsewhere in Colorado [10.3% (Judson and Doesken 2000)].

9. Gore Mountain, NY

Not all microclimates are good for skiing.  The problem at Gore is that it is too far east to get much lake effect and a bit to far northwest to receive as much nor'easter snow as the mountains of New England.  C'est la vie.

Source: Northeast Regional Climate Center
8. Mt. Bohemia, MI

Mt. Bohemia might be the most geographically isolated ski area in the contiguous United States.  It's on the Keweenaw Peninsula, about as far north as you can get on the UP of Michigan and nearly surrounded by Lake Superior.

Source: Google Maps
You want lake effect?  Mt. Bohemia is the place.  The resort claims an average snowfall of 273 inches and, although it's difficult to confirm this given a paucity of long-range observing sites in the area, it's clearly the snowiest ski area in the midwest.  And it's bloody cold too.  Deep powder, certain frostbite, what are you waiting for?

7. Jay Peak, VT

In 2008, Trevor Alcott and I wrote a paper for the Bulletin of the American Meteorological Society entitled Secrets of the Greatest Snow on Earth (I ultimately used the article as a springboard for my book of the same title).  When in review, one of the anonymous reviewers took great offense that we did not include Jay Peak in the analysis.  Fair enough.  Jay does especially well in northwesterly flow thanks to the orientation of the mountains of northern Vermont and a lack of substantial upstream terrain.  There are other northern Vermont ski areas benefit from these characteristics, but perhaps not to the extent of Jay Peak.  Plus the Jay Peak powder cult has threatened me enough that I no longer question the power of the Jay Peak cloud.

6. Alyeska, AK

Alyeska rises above the Turnagain Arm just east of Anchorage and has a base elevation of only 250 feet.  Due to the formidable nature of the Chugach Mountains and the maritime nature of the region, it probably has the largest snowfall gradient with altitude of any major resort in the United States, which results from both the increase in precipitation with altitude and the increase in the fraction of precipitation that falls as snow.  Resort statistics suggest a 208" mean snowfall at the base and a 512" mean snowfall at mid mountain (~1400 feet).  That staggering increase is characteristic of coastal Alaska, but where else do you find a major ski area cutting through it?

5. Snow Ridge, NY

In my view, Snow Ridge has the best quality natural snowfall in the northeast United States.  The area reports a very believable average snowfall of 230 inches, most of which is lake effect generated by Lake Ontario.  Even my snow-snobby students enjoyed a powder day there when we were working on the Tug Hill Plateau a couple of years ago.

4. Mammoth Mountain, CA

Mammoth Mountain gets an absolutely sick amount of snow for the eastern Sierra.  If you want to know why, look at the map below.  Note how big and broad the Sierra are to the north of Mammoth, and how big and broad the Sierra are to the south of Mammoth.  Then look at how the San Joaquin River cuts a path right to Mammoth Mountain's doorstep.  As a result, Sierra storms dump less load before hitting Mammoth, and Mammoth gets an unusual amount of snow for it's extreme eastern location.

Source: Google Maps
Meteorologists call the depletion of atmospheric water vapor by precipitation airmass transformation.  An interesting aspect of atmospheric water vapor is a very small fraction of it contains hydrogen isotopes that are relatively heavy (they have one proton and one neutron instead of just a proton).  Water vapor molecules that contain this heavier hydrogen isotope, known as deuterium, tend to condense more readily and rain out as an airmass pushes inland.  As a result, the snowpack in the eastern Sierra tends to be somewhat depleted of deuterium, except at one place.  Mammoth.

The map below is an oldie but a goodie and shows an analysis of deuterium in the Sierra snowpack.  Note the nose of higher values at Mammoth, illustrating that airmasses impinging on Mammoth Mountain have experienced less transformation and water vapor depletion that those that have traverse broader, higher topography to the north and south.

Ratio of deuterium to hydrogen (D/H) in Sierra snow expressed as a per mil
 departure from that found in standard ocean water (Friedman and Smith 1970).
3. Alta/Snowbird, UT

It's a bit self-serving to put Alta/Snowbird at #3 on this list, but I've yet to find an area in the contiguous United States with a better combination of quality and quantity than the upper Cottonwoods, and Little Cottonwood gets the nod here because it is a bit snowier than Big Cottonwood.

Source: Secrets of the Greatest Snow on Earth
All sorts of crazy ideas exist concerning why it snows so much in the upper Cottonwoods, but the most obvious is almost always overlooked.  The terrain around the Cottonwoods forms an island of high terrain that is exposed to flow from nearly every direction.  Alta and Snowbird are well known for snow in northwesterly flow, but they almost always get something even when the flow is from other directions.

Source: Secrets of the Greatest Snow on Earth
This tremendous diversity of storms leads to the large annual snowfall totals and contrasts with other high areas of the Wasatch (e.g., Mt. Timpangos), which lie along linear ridges and have a narrower storm spectrum (e.g., predominantly southwesterly flow).

2. Mt. Baker, WA

Snowiest ski area in the world.  World record 1,140 inches recorded in the 1998/99 season.  Admittedly, Mt. Baker ski area isn't even the snowiest location in the region it sits in due to its low altitude, but an average snowfall of nearly 650 inches puts it at #2 on this list.

1. Snoqualmie Pass, WA

I'm guessing you didn't see it coming, but Snoqualmie Pass has a truly unique and remarkable microclimate.

The problem in the Cascades isn't moisture, it's temperature.  West of Snoqualmie Pass and along much of the western slopes of the Cascades, skiing isn't viable at 3000 feet elevation, the base elevation of the ski areas in Snoqualmie Pass.  If you drive to Snoqualmie Pass from Seattle, the snow line is often above 3000 feet, but turn the corner and enter the pass and you find a huge snowpack.

There's one main reason for this: cold easterly flow.  For much of the winter, the Cascades separate relatively mild marine air to the west from colder continental air to the east.  This cold air frequently pushes into Snoqualmie Pass, resulting in locally lower snow levels than found to the west.

The climate in Snoqualmie Pass is very similar to that in Stampede Pass, which is just to the south and has had an official weather station for many years.  If you look at a wind rose for Stampede Pass in January, you see a predominance of easterly flow.

Source: Steenburgh et al. (1997)
And this has a significant impact on temperature.  If you compare the mean temperature at Stampede Pass to Paradise ranger station on Mt. Rainier, it's actually colder from December to February, despite the lower elevation.  This is because Stampede Pass (and Snoqualmie) are frequently under the influence of cold, easterly flow, whereas Paradise is west of the Cascade crest and cutoff from the cold easterlies.

Source: Steenburgh et al. (1997)
If you could plug the low-elevation corridors that issue from eastern Washington to Stampede and Snoqualmie Pass, the snow climate would change dramatically, a much greater fraction of wintertime precipitation would fall as rain instead of snow, and one of the busiest ski areas in the United States would probably cease to exist or be barely viable.

Although the cold easterly flow is a remarkable refrigerator, it's not going to be able to hold off the inevitable as the planet warms in the coming years.  The snow climate of Snoqualmie Pass is one of the most vulnerable to global warming because of its low elevation and frequent snowfalls at temperatures near (and above) 0ºC.

Honorable Mentions:

Grand Targhee, WY (prolific snowfall on the windward side of the Tetons)
Crystal Mountain, WA (Mt. Rainier cloud and precipitation shadow)
Stevens Pass, WA (cold easterly flow)
Mission Ridge, WA (strongly shadowed)
Mt. Shasta Ski Park, Mt. Bachelor, Mt. Hood ski areas (large volcano influences)
Keystone, CO (strongly shadowed)
Steamboat, CO (large, low-density, seasonal snowfall for Colorado)
Whiteface, NY (really cold, but hey, at least it doesn't snow very much too)
Snowshoe, WV (snowy spot for mid-Atlantic region)

Add your $0.02 by commenting.  I've focussed on ski areas here for brevity, but feel free to think broadly (i.e., backcountry) and globally.

Saturday, October 24, 2015

Powder Envy

There are occasionally times when Utahns do have powder envy and that's often the case in the fall when high-altitude Colorado gets the goods while we are still mountain biking.
Good for them.  Fortunately, we usually get the last laugh.  

Friday, October 23, 2015

The Most Powerful Atlantic and Eastern North Pacific Hurricane on Record

The National Hurricane Center reports this morning that Hurricane Patricia underwent rapid development off the western coast of Mexico last night and is now the most powerful hurricane on record in their area of responsibility, which covers the Atlantic and eastern North Pacific.

Source: NHC
In their 4 AM forecast discussion, they specifically acknowledge the efforts of the Air Force Hurricane Hunters, noting that "without their data, we would never have known just how strong a tropical cyclone it was."  Data collected by the Hurricane Hunter puts Patricia's sustained winds at 175 knots (201 miles per hour), with a central pressure of 880 mb.

The latest forecasts have Patricia making landfall somewhere between Puerto Vallarta and Manzanillo, with hurricane warnings posted for a somewhat wider area.   

Source: NHC
The potential for catastrophe is high.  The NHC public advisory states "Maximum sustained winds remain near 200 mph (325 km/h) with higher gusts.  Patricia is a category 5 hurricane on the Saffir-Simpson Hurricane Wind Scale.  Some fluctuations in intensity are possible today, but Patricia is expected to remain an extremely dangerous category 5 hurricane through landfall.

Thursday, October 22, 2015

The Earth Needs More Cowbell

It's time for our monthly check on global temperatures, which remain at record setting levels.  The National Centers for Environmental Information released the numbers through September and we are running well ahead of previous globally averaged temperatures, as shown in the plot below of January-September temperature anomalies since 1880.

An all-time calendar year record has been anticipated now for several months and at this point is virtually assured.

Wednesday, October 21, 2015

Will This Be a Ski Free October?

Now is the time of year when people ask me repeatedly when it's going to snow.  Actually, I get that almost all season long, but it is times like these, when we are in a snow drought, that people start asking things like "what about next week" or "how does next month look"

The problem with answer questions like these is simple.  The atmosphere is chaotic and weather is unpredictable, at least with current tools, at such long lead times.  This is true despite the fact that Accuweather issues a 45-day forecast.  In some situations, one can predict a shift in the climatological odds of above or below average conditions (an example would be the expectation of a warmer than average winter in the northwest due to El Nino), but if you want to know what the weather is going to be like 10 days from now, good luck in most situations.

Here's a good example.  I confess that when in a snow drought, I often look deep into the extended range hoping for the possibility of a storm.  I did that with yesterday's GFS and here's what I found for 0000 UTC October 30.  A ridge with dry weather over nearly the entire western U.S.  Skiing in Utah?  Fat chance.

Then I did it with today's GFS and here's what I found.  A nice broad trough with precipitation over the western U.S.  Skiing?  Well, we'd not a lot of snow, but this gives us a bit of a chance.

When we see a model shift of that type in the extended range forecast, should we interpret that as a trend?  Probably not.  At such long lead times, one can see large flip flops from one GFS run to the next due entirely to the chaotic nature of the atmosphere.

Here's the proof.  Instead of looking at a single model forecast, let's look at an ensemble.  Below are last night's GEFS forecasts for 0000 UTC 30 October.  These are produced with the exact same model, but slightly different initial conditions.  Over time, the solutions diverge and if we're looking at the forecast many days out, we see dramatically different forecasts.  Some put a ridge over Utah, others a trough, others different flow configurations.

Source: Penn State E-wall
So the weather later this month is pretty unpredictable.  Nobody can reliably predict what is going to happen, so no point getting excited about today's GFS run.  Check in next week when the lead time is shorter.

Tuesday, October 20, 2015

Record Warmth in Salt Lake City

I used to wonder if I would ever run out of material for this blog, but weather and climate are gifts that keep on giving.

Today we'll talk about temperature records of the hottest ever variety.  Let's begin with the past month (i.e., Sep 19 – Oct 19).  Hottest ever?  You betcha.  

Source: NOAA Regional Climate Centers 
How about for October?  Hottest ever?  You betcha, so far.  We still have 12 days until the end of the month, but this is the hottest October 1 – October 19 on record.

Source: NOAA Regional Climate Centers 
How about for the calendar year so far?  Hottest ever?  You betcha.

Source: NOAA Regional Climate Centers
And, while we're at it, when exactly was the last day we had a below average minimum temperature?  Turns out it was a month ago (September 20).
Source: NWS
Yup, the heat is on.  

Monday, October 19, 2015

Does Size Matter for Lake Effect?

It's a question I am asked repeatedly.  Does size matter for the Great Salt Lake effect?

The Great Salt Lake is a terminal lake, meaning that it has no outlet.  The only way for water to escape is by evaporation.  As a result, its size varies during the year, from year to year, and from decade to decade depending on the amount of freshwater inflow.

Landsat satellite images of the Great Salt Lake in August 1985 and September 2010.  Source: USGS Landsat Missions Gallery, "Great Salt Lake 1985–2010," US Department of Interior/USGS.
In the historical record, the Great Salt Lake at its historic high covered 2300 square miles, whereas at its historic low, it covered only 937 square miles.

We are currently near a historic low (see Is the Great Salt Lake Approaching a Record Low Stand?), so should we expect less lake effect this winter?

All else being equal the answer to that question might be yes.  If we could, for example, have an exact repeat of the weather of any given winter, but change the the size of the lake, I suspect we would see an increase in lake effect with increasing lake size.  This increase would probably be small, but it would be there nonetheless.  

However, the most important factor controlling the lake effect in any given winter is the meteorology.  If you get lots of cold troughs you get more frequent lake effect than in a winter dominated by warmer westerly or southwesterly flow storms.   

For example, the top graph below shows the number of lake-effect events per cool season.  There are large variations from year to year with as few as 3 in 2005 and as many as 20 in 2010.  These variations are produced not by changes in lake size, but meteorology.  This is shown in the bottom figure which shows the relationship between the number of events (bars), lake area (solid line with dots), number of trough days (solid line), and the number of days in which the lake-air temperature difference exceeded a minimum threshold for lake effect (dashed).   These are expressed as standardized anomalies.  Without getting into details, a large positive number indicates a greater than normal frequency and a large negative number indicates a smaller than normal frequency.  There is a stronger correlation between the frequency of lake effect and the number of trough days and days that meet the minimum temperature difference threshold than the lake area.  2008 and 2010 both produced a large number of lake effect events despite the fact that the lake was very low.  They were active lake-effect years because the meteorology was favorable for lake effect.  

Source: Alcott et al. (2012)
You'll note that I put frequency in italics above and there is a good reason for this.  Lake-effect events can be pretty short lived and wimpy, or they can be very large.  The graph below shows the amount of snow-water equivalent (SWE) produced during lake-effect periods at Snowbird during the 1998–2009 cool seasons.  Half of those periods produced less than 6 mm of water equivalent, which equates to about 3 inches of snow.  

Source: Yeager et al. (2013)
If we're talking lake-effect periods that really lay it down, we need to look at events that produce more than about 20 mm of SWE, which equates to about 10 inches of snow or more.  These events are pretty rare and average only about one event per year.  They are so rare and episodic that it is impossible to draw any meaningful relationships that we can use to anticipate whether or not we're going to get a big lake-effect event in any given winter.  The largest lake-effect event at Snowbird occurred during the 2001 Hundred Inch Storm when the lake was a bit below average size.

Of course, this analysis is based on historical variations of the lake with an emphasis on the lake effect in any given winter.  If the lake continues to shrink, we could go below a critical threshold where there is a dramatic drop off in lake effect even if the meteorology is favorable.  Further, if the lake remains very low for say a decade or two, that might have a small effect on the total snowfall during that entire period.  It is worth noting, however, that lake-effect periods contribute only about 5% of the total snowfall in the Cottonwoods, so it will be difficult to detect.  The shrinking of the Great Salt Lake is certainly a concern for many reasons, but in the long run, the direct impacts of global warming will have a greater impact on snowfall and snowpack in the Wasatch Range than a shrinking Great Salt Lake.  

Saturday, October 17, 2015

The Never Summer Range May Need To Be Renamed

I've been in Colorado this week attending meetings at the National Center for Atmospheric Research and then taking some college tours with my son.  We had time today to visit Rocky Mountain National Park and do some sightseeing and hiking.

Although I've never spent any time in them, I've always had a thing for the Never Summer Range, which is just west of the park.  The name appeals to meteorologists, and on top of that, the peaks are named after clouds (e.g., Mount Stratus, Mount Nimbus, Mount Cumulus).  As can be seen below, however, the Never Summers may need to be renamed.  They are virtually snow free this fall.

The lack of snow is apparent throughout the Colorado Rockies.  The Andrews Glacier is hanging on, but barely.

Let's hope this winter brings the goods big time so we can have a temporary restoration of some of these dying snow fields.   

Wednesday, October 14, 2015

A Hot Stretch, But Cooler Weather Is Coming

The past month has been quite warm and enjoyable in northern Utah.  If you are wondering where it ranks historically, the answer is quite high.  If we look at the past month (i.e., since September 13), it ranks as the 2nd warmest in the instrumented record.

Source: NOAA Regional Climate Centers
You might recall that in mid September we had a stretch of cooler, rainier weather.  If we chop off that period and look a the stretch from September 20 to October 13 (yesterday), it is the warmest such stretch in the instrumented record.

There are, however, some changes coming.  First, we have a short-wave trough moving in from the southwest on Friday night.  Then we have a another shortwave trough approaching from the west later in the weekend.  Together, these two systems will bring cooler weather and some showers and thunderstorms to northern Utah this weekend.  There probably will be some snow on the high peaks late in the weekend, but unless the one of the outlier ensemble members verify, snow lovers will probably need to wait a bit longer for a major dump.

Monday, October 12, 2015

The Fall Break Forecast

This week is fall break at the University of Utah.  Several years ago, the students voted to have a full week fall break and each year I thank them for doing so as October is a wonderful month in the Intermountain West.

The forecast for fall break week looks pretty good statewide through at least Wednesday.  There is a weak short-wave trough forecast to flirt with the southwest later in the week, as illustrated by the GFS forecast for 1200 UTC (0600 MDT) Friday.  

The timing and strength of this trough remain somewhat uncertain and it's main impact will probably be to increase the threat of showers and thunderstorms, especially in southern Utah.  Check forecasts in a couple of days, especially if you are considering canyoneering in the south later this week or over the weekend.  

If we look out into the extended, some ensemble members are hinting at the possibility of some precipitation  next weekend or early next week.  For instance, if we look at the North American Ensemble Forecast System (NAEFS) plumes for Alta, we see several members calling for precipitation and a bit of high elevation snow on Sunday.  

Of course other ensemble members are drier (you can't see the "no precip" members in those plume diagrams).  Thus, we'll have to see how things look in a few days.

Park City Talk

I'll be giving a talk on my book Secrets of the Greatest Snow on Earth at the Park City Friends of the Library author luncheon on Thursday October 22nd.   The luncheon is at the Park City Marriott, 1895 Sidewinder Drive.  Doors open at 11 am and tickets are available for $36 at the Park City Library.

Sunday, October 11, 2015

Desperate Times for Meteorologists

The weather of late has been great for recreation, but pretty damn boring if you are a meteorologist.

Today's "excitement" involves a trough passage across northern Utah.  It's pretty much cloud free, so we need to dig deep to notice the change.

The NAM forecast for this afternoon shows the trough axis at all levels just past Salt Lake City with westerly or northwesterly flow in its wake.  

The impact on temperatures is quite pronounced as we've been nearly flatlined late last night and for much of the day today.  This is an indication that the transport of cold air into northern Utah, or what meteorologists call cold advection, is nearly perfectly balancing the rise in temperature from solar heating.

Source: MesoWest
Although this is a pretty wimpy trough from a moisture perspective, it is bringing in some dust or smoke.  I was on Grandeur Peak this morning and the visibility at low levels was fairly poor over the northwest Salt Lake Valley and the Great Salt Lake.

That's our weather excitement for the weekend.  Yes, things are boring, but hopefully Mother Nature is storing it up for November.

Friday, October 9, 2015

Spectacular Weather for ESPN Gameday

ESPN's College Gameday is now on campus and setting up shop in President's Circle just outside my office.

The U has really scored on this one.  It's going to be spectacular with mostly sunny skies and temperatures reaching the high 70s today and low 80s tomorrow.  The "natural advantages" of the U should be on full display during the coverage today and tomorrow and conditions will be perfect for the 8 PM kickoff.

Professor Powder has delivered the weather.  Now lets hope the Ute football team can deliver a win.  Go Utes!

Thursday, October 8, 2015

Still on Track for Strong El Nino

The Climate Prediction Center issued its monthly ENSO diagnostic discussion today and not surprisingly continues to go for a 95% chance of El Nino continuing through winter.  As we've seen for some time, sea surface temperature anomalies show a well-developed El Nino signature with a tongue of anomalously warm water extending across the eastern and tropical Pacific.

Source: CPC
The International Research Institute for Climate and Society at Columbia University has a nice simple graphic summarizing the El Nino predictions showing a very high likelihood of El Nino conditions persisting through winter before the likelihood of a decline in strength increases in the spring.

As we've discussed previously, I don't consider the existence of El Nino to have a strong influence on the snowfall odds for this coming ski season in the central Wasatch (see Wasatch Weather Weenies Survival Guide for El Nino).  However, since I'm desperate for material, I thought I'd show another perspective today, albeit one based on a very small sample size.  

In the graph below, I've taken the Nov-Apr snowfall at Alta Guard and have ordered it from high to low, identifying the top 1/3 of years in blue, middle 1/3 in green, and bottom 1/3 in yellow.

Then I've identified the four strongest El Nino winters (1957–58, 1972–73, 1982–83, 1997–98) in red and the next four strongest El Nino winters in purple (1965–66, 1986–87, 1991–1992, 2009–10) based on the December to February El Nino Index.  For those of you who aren't concerned about a small sample size, you'll be glad to know that the four strongest El Ninos fall in the upper half of the distribution (Note that the 1972–73 winter may have been missing November, unless the lack of data for that month in the dataset I grabbed indicates zero).  On the other hand, the next four strongest El Nino winters are in the bottom half of the distribution.

One view of this is that a strong El Nino might be associated with a good snow year.  The other view is that the sample size here is small and that adding more cases yields a distribution that shows little correlation (note that we only have Alta snow data since WWII, so to add even more cases requires using wimpy El Ninos).  CPC has added a few more cases in the plot below by looking at strong El Ninos back to 1915 and the precipitation produced in climate zones.  Their definition of strong is a bit lower than mine and includes a couple of the moderate events that I used above.  In any event, it shows northern Utah to be sitting on the transition zone or having a slight tendency for drier winters.

Source: CPC
So, we have a small sample and imperfect data, but my read continues to be that the dice simply are not loaded very strongly for this coming winter.  However, if it will make you happy, you can cherry pick the Alta bar graph above and assume a big winter is ensured.

Tuesday, October 6, 2015

Eastern Utah Is So Weird!

As noted by David, who commented on the previous post, the valleys and lowlands of eastern Utah are just plain weird climatologically.

If one classifies the precipitation climate over the southwest U.S., there are four major regimes.  The first (row a in the image below), covering most of California, northern Nevada, and the upper elevations of northern Utah and western Colorado, features a pronounced winter maximum.  The second (row b), covering much of Arizona and portions of southern Utah, New Mexico, and southwest Colorado, features a pronounced maximum during the monsoon.  The third (row c), covering the plains of eastern Colorado and New Mexico, is somewhat related and has a maximum in the summer with less precipitation in the winter.  Finally, there is a fourth regime (row d) in the lower elevations of portions of Nevada, Utah, and western Colorado where precipitation peaks in the spring.  This includes the Salt Lake Valley.

Source: Steenburgh et al. (2013)
If you look carefully at those plots, however, you can find a region that is not included and that is the valleys and lowlands of eastern Utah, including places like Vernal and Moab.  The climate there has a maximum occurring in October.

Why October?  I can speculate, but it really deserves some investigation.  As suggested by David, there could be a magic point as the monsoon tails off and we begin to see mid-latitude storm systems coming in that enables more moisture and precipitation to move into this area.  It might also be that this area got pounded by a small number of larger storms during the past few decades, skewing the stats for October (I haven't checked to evaluate the statistical significance of the October maximum).

In any event, eastern Utah has always been a little weird and even Mother Nature likes it that way.

Monday, October 5, 2015

Stuck Between Two Regimes

Precipitation over the western United States over the next week is strongly dominated by two regimes.  The first is associated with the deep upper-level trough moving across the southwest U.S. over the next few days that will result in frequent shower and thunderstorm activity.  The second develops later this week as moist southwesterly flow penetrates into the Pacific Northwest.  

The mean precipitation produced over the next 7 days by the North American Ensemble Forecast System (NAEFS) shows these two regimes quite nicely with the largest accumulations over the Southwest and the Northwest.    
NAEFS mean precipitation 0000 UTC 5 October – 0000 UTC 12 October 2015
Northern Utah is just on the fringe of the more monsoonal regime, but misses out on the precipitation over the Northwest.  Thus, our best chance for precipitation in northern Utah is through tomorrow evening as we are brushed by the upper-level trough.  

Because we're stuck between the two regimes, we won't be seeing skiable snow for at least another week.  The NAEFS forecast plume below is for Alta and shows the precipitation through tomorrow afternoon, after which it's pretty much flatlined (i.e., dry).  It's cold enough that the higher elevations may see a dusting or light coat if there's a strong shower, but that's about it.  

No worries.  Best if it holds off for a bit longer.  

Sunday, October 4, 2015

The Mount Olympus Wilderness

It doesn't matter how long you live in Utah.  You will have days where you are just thankful for the beauty and access of the Wasatch Range.

The Mount Olympus Wilderness is a truly remarkable place.  It's right there.  It starts right on the edge of the east bench and is a remarkably wild and undeveloped place.  The vegetation is thick on north aspects and I saw plenty of deer, grouse, and woodpeckers today.

The Desolation Trail is aptly named.  Plenty of people take it the first couple of miles, but once you climb a couple thousand vertical feet, you'll find few people.

There's still nice color out there, particularly on this side of the range.  I was in Park City last weekend and was shocked at how grey everything was.  Many of the aspens on the Wasatch Back dropped their leaves early this year.  I've heard media reports that a fungus is responsible.  Apparently it's a one-and-done thing and not a long term detriment to tree health.  Let's hope so.

Gobblers Knob showed a bit of fall plumage today.  There's still some aspens that haven't gone over completely yet.  Maybe there will be some color remaining next weekend.

I wonder how many wilderness areas in the United States are so close to a metropolitan area of this size.  We are so fortunate.

The Broads Fork Twin got a nice dusting late yesterday.  It won't be long now.