Monday, January 31, 2011

Frontal Fragments

It's not easy to perform a surface frontal analysis tonight.  There are two fairly well defined boundaries, I'll call them frontal fragments, evident in the MesoWest data.  The first is in southwestern Wyoming there there is a wind shift and collocated 10-12F temperature contrast just west of Green River.  This is the likely position of the Arctic front that will push into northern Utah from the east late tonight.

The second is over the Snake River Plain just east of Twin Falls where there is also a wind shift.  The baroclinity here is a bit more broad, with temperatures decreasing from about 30F near the front to the single digits in the upper Snake River Plain.

In contrast, it is very difficult to nail down a wind shift or front in the intervening highlands.  The flow is almost exclusively from the northern half of the compass and finding the leading edge of the cold air is very difficult.  Although Arctic air is leaking into this region, there is no clearly defined airmass boundary.

WRF Canyon Wind Forecast

The latest 1.3 km WRF forecast is in (initialized using the 6-h GFS forecast for 1800 UTC 31 Jan), which includes a forecast projection through tomorrow evening.  It produces a broad region of downslope winds along the northern Wasatch tomorrow afternoon and evening with sustained winds between 30 and 40 knots.

Note that the center of action has shifted southward from the earlier WRF simulation.  The strong winds downstream of the Cottonwoods seem odd.  That is an unusual place for downslope winds.  Perhaps this reflects the lower height of the model topography.  It's also a bit unusual for the downslope flow to be strongest in the afternoon, although this time of year the solar forcing is fairly weak, so that might reduce the diurnal variability.

As previously mentioned, we've never used this model before to examine downslope winds, and it is unclear if reliance on a single high-resolution model might lead to serious "crash and burn," so it will be interesting to see how it verifies.

Back-Door Arctic Front

This morning's (1200 UTC) initialized NAM forecasts the movement of a back-door Arctic front from Wyoming into Utah and across the northern Wasatch Mountains at about 1200 UTC (0500 MST) tomorrow (Tuesday) morning.  I refer to this as a back-door Arctic front because it is approaching from the east.  Below are three perspectives of the NAM-forecast back-door Arctic Front as it moves into the Wasatch Front.

NAM 2-m temperature (color fill every 2C) and 10-m wind
(full and half barb denote 5 and 2.5 m/s, respectively) valid
1200 UTC 1 Feb 2011
Perspective view with potential temperature cross section (white)
More oblique perspective showing potential temperature
"wall" with arctic front merged with mountain wave
induced by the Wasatch Mountains
I suspect tomorrow and possibly Wednesday are going to be a brutally cold area along portions of the east bench from Parley's canyon north.  Not only are we dealing with very cold air, but easterly flow, a strong cross-barrier pressure gradient, and the presence of a stable layer near mountain top level (as indicated by the strong vertical gradient in potential temperature surmounting the arctic airmass) all indicate that there will be enhanced canyon winds that are stronger and more widespread than usual.

We are running an experimental numerical modeling system here based on the Weather Research and Forecasting (WRF) that features much finer (1.3 km) grid spacing than the operational NAM (12 km).  This is the first time we've been able to simulate a potential canyon wind event with it.  The run from last night (0000 UTC initial conditions) produces a modest canyon wind event by 1800 UTC (1100 MST) tomorrow.  At this time, both gap and downslope winds are produced in this simulation along the western slopes of the Salt Lake Valley, although these winds are weaker than those produced downstream of the Raft River range and over the western Great Salt Lake.

Purples and blues along the western slopes of the Wasatch
Mountains indicate canyon winds of 15-25 knots
What we don't know is if this model can reliably simulate the intensity of canyon wind events.  This is also a single simulation (and the snapshot above is of a single time), when one would really like a calibrated ensemble of high resolution simulations to examine the range of possibilities given the potential sensitivity of localized downslope flows to small changes in the environmental conditions.  That is the future - but we don't have those capabilities today.

Attack from the North and East

Enjoy the relatively balmy conditions while they last.  MesoWest observations today are simply fascinating and show cold air approaching northern Utah from both the north and the east.

In extreme northeast Idaho, northeasterly flow is pulling cold air across the continental divide and into the upper Snake River Plain.  At Island Park, temperatures have fallen from a high of 43F yesterday afternoon to a minimum of -5F this morning (although they have since rebounded to 3F).

Meanwhile, cold air is moving westward across Wyoming toward Evanston through the low elevation basin between the Uinta and Wind River Mountains.  Rock Springs has remained solidly at 10F all day today.

Thus, cold air will be approaching Utah from two directions.  There is nowhere to hide!

Sounding of the Day

Glasgow, MT

Here It Comes

The latest surface observations show a balmy 30F here in Salt Lake, but 10F in Rock Springs, -6 in Cody, and a nasty -24F in Great Falls.

MesoWest surface observations at ~1600 UTC (0900 MST) 31 Jan 2011
At Rock Springs, winds shifted from westerly to east-northeasterly between 4 and 5 AM MST.  Temperatures began to fall ahead of this wind shift, but dropped more quickly following it.  Thus, I suspect it represents the leading edge of the arctic air.

Change is most certainly on the way...

Sunday, January 30, 2011

Arctic Blast Update

So much to talk about today and so little time!  An exciting week of weather is forthcoming, and I'm looking forward to it.

As we discussed in the previous post, the models are forecasting a serious blast of cold air to move into Utah this week, with the arctic air arriving Monday night and Tuesday.

The 12Z initialized NAM from this morning (Sunday) drops Salt Lake's 700-mb temperatures down to a brutal -23C by Tuesday afternoon.  There are not many days around here where the 700-mb temperature is that low.

This morning's 0900 UTC initialized SREF is event colder with a forecast ensemble mean 700-mb temperature for KSLC of -25C.

The GFS remains the "warmer" model, with a forecast 700-mb temperature of -22C.  Warm here is clearly a relative term!

The setup for the arctic blast involves interactions between large-scale features in the high latitudes and the mid-latitude Pacific Ocean.  In the high latitudes, a deep low is presently centered near Hudson Bay, with an upper-level ridge centered over interior Alaska.  Note how this yields equatorward flow at upper levels that extends nearly to the pole, opening the "door" for cold air to move southward.

By tomorrow morning, strong warm advection and latent heating ahead of a cyclone over the mid-latitude Pacific Ocean build a high amplitude ridge over the northeast Pacific Ocean.

This Pacific ridge continues to build through Tuesday afternoon, ultimately merging with the aforementioned high-latitude upper-level ridge.  This yields northeasterly upper-level flow that opens the door for cold air to spill southward and westward into the Intermountain West.

Thanks to the Continental Divide, we will be spared the coldest air, but this is still going to be an impressively cold airmass.

Saturday, January 29, 2011

Challenges Forecasting Possible Arctic Blast

The NAM forecast initialized at 1800 UTC 29 Jan (Saturday) has an impressive blast of cold air coming into Utah.  As discussed in October, the 700-mb temperature at Salt Lake City is usually between -20C and 20C, so I use -20C at 700 mb as an indicator of "really cold air."  The 84 hour forecast has sub -20C air covering much of the state of Utah, including about -21C at KSLC.  BRRRR!!!!

On the other hand, the GFS forecast initialized at the same time has a somewhat different solution.  The coldest 700-mb air comes through 12-h earlier, at 1800 UTC 1 Feb, with the 700-mb temperatures at KSLC only falling to -19C.  Cold, but not as far out the tail of the bell curve.

Given the differences between the NAM and the GFS, I thought I would also consult the NCEP Short-Range Ensemble Forecast system (SREF).  As I understand it, the SREF is comprised of 21 forecasts produced by four different modeling systems run with differing initial conditions.  For the SREF initialized at 1500 UTC (the SREF runs at 0300, 0900, 1500, and 2100 UTC), the mean 700-mb temperature forecast valid at the same time as the NAM forecast above was -23C!

So, it appears an arctic blast is likely, but the severity of the cold air remains uncertain.  We'll see if the models begin to converge on a solution over the next day or two.

Wednesday, January 26, 2011

Arctic Report Card

Somewhat related to the previous post, recent changes in the Arctic the past few years are quite remarkable.

NOAA has developed a nice web site called the Arctic Report Card for tracking environmental change in the Arctic.  The YouTube video below provides a nice summary, although the hypothesized linkage between recent sea-ice loss and cold waves over North America and Europe is a subject of ongoing investigation.

Planet B

I've been holed up all week at the American Meteorological Society Annual Meeting in Seattle.  I've attended a couple of interesting talks on climate change and communication, including one by Richard Sommerville in which he conducted an interesting thought experiment that went something like this.

Imagine you are living on a planet that is exactly like Earth, including the rate of fossil fuel consumption that has occurred since the industrial revolution.  What is different on this "Planet B" is that there are no weather observations for examining past and recent climate change, no satellite observations for observing sea level rise, sea-surface temperatures, and ice-sheet changes, and no supercomputers and Earth Systems models for understanding and attributing past climate change.

Planet B...almost the same as Earth
The citizens on such a planet would have no idea that the planet is warming, that the arctic is becoming ice free, that the Greenland ice sheet is shrinking, that sea level is rising, and that the preponderance of evidence suggests that humans activity, especially the burning of fossil fuels, is responsible for most of the warming in recent decades.

Remarkably, more and more people are opting to live on Planet B.  As shown in a recent Gallup poll, the percentage of Americans who believe that global warming is real has dwindled, with only 53% agreeing that global warming has begun or will do so in a few years.  The percentage of Americans who say that global warming will never happen or will not happen in their lifetime has increased to 19% and 16%, respectively, the former more than double the percentage in 1997.

Fascinating results given the observed changes to the climate system over the past decade.

Tuesday, January 25, 2011

More Colleges for Winter Sports Enthusiasts

In the previous post examining the best colleges for winter sports enthusiasts, I opined that "the University of Utah is hands down the best University/College on the planet for winter sports enthusiasts." I also offered up a couple winter-sports worthy colleges/universities that were not included on the US News and World Report list.

I've thought of some additional North American institutions that warrant mention.  They are:

  • University of Vermont.  It's really quite shocking this wasn't on the list as Burlington sits at the best intersection of mountains and snow in the eastern United States.
  • University of British Columbia.  Granted the skiing right in Vancouver isn't great, but you can ski on the edge of town and Whistler/Blackcomb and numerous backcountry adventures are within easy striking distance.  
  • Western Washington University.  Also within striking distance of Whistler/Blackcomb, Mount Baker, and incredible backcountry skiing.
And we shouldn't overlook the rest of the world.  The University of Innsbruck is surrounded by incredible mountains, ski areas, and, like the University of Utah, facilities for other winter sports besides skiing and snowboarding.   In Asia, Hokkaido University in Japan is an obvious choice.

Monday, January 24, 2011

Best Colleges for Winter Sports Enthusiasts

An article in today's Daily Utah Chronicle reports that the U has made the list of Best Colleges for Winter Enthusiasts from U.S. News and World Report magazine.

Let's be real.  The University of Utah is hands down the best University/College on the planet for winter sports enthusiasts.   It isn't even close.  Where else in the world can you get a low-cost, world-class education and ski or snowboard some of the best terrain and snow on Earth just minutes from your dorm room?

The start of this backcountry ski tour is 20 minutes
from the U.  Eat your heart out CU-types.

The other schools on the U.S. News and World Report list:
  • University of Colorado-Boulder.  The article touts the "short driving distance" to Vail and Winter Park.  Apparently the author hasn't spent hours sitting in traffic on I-70 during one of Colorado's rare deep powder days.  How rare are those deep powder days?  Berthoud Pass near Winter Park, one of the snowiest locations near Boulder, averages only 4 days per year with at least 10 inches of snow.  Alta averages 18.  The article also mentions that Eldora Mountain is only 30 minutes from campus.  That's great if you want to run slalom gates on frozen granular all day, but if instead you want to ski deep powder, Alta and Snowbird are only 30 minutes from the University of Utah.  As put so well by a fellow meteorologist, the best place to head for skiing in Boulder is east, to the airport, where you can catch a plane to Utah. 
  • Dartmouth College.  The inspiration for Animal House has a lot going for it, but do powder hounds really want to ski in New Hampshire?
  • Middlebury College.  Another great northeast ski school, with the same issues as Dartmouth - eastern snow. 
  • University of Montana. A solid challenger, but the U gets the nod based on academic strength, more snow, more resorts, and more accessible backcountry.
  • Sierra Nevada College.  Sierra Cement vs. the Greatest Snow on Earth.  Hmmmm....
  • Williams College (Mass.).  Massachusetts?  
  • University of Wyoming.  The article claims that it is only "a 2 hour drive from the best slopes in Colorado."  The author hasn't apparently driven in a Wyoming ground blizzard before.  Google maps puts the time to Steamboat at about 2.5 hours and Winter Park at 3.  Come to the U and you can take the bus from campus and be skiing in under an hour.  
Remarkably, Montana State was left off the list.  With Bridger Bowl and Big Sky nearby, and people like Karl Birkeland on the the faculty, this seems like an obvious A-list school for the ski and snowboard crowd.  The University of Washington (my alma mater) was also overlooked, but has access to great lift-served and backcountry skiing, the latter possible year round.  

Where you go to college depends on many factors, and there are good reasons to attend any of the institutions above.  But based on access, snow climate, and academics, the U is a clear standout.  Don't believe me, just ask swoop.

Sunday, January 23, 2011

NFL Forecast: Cold!

Bears, Packers, Jets, Steelers.  It's hard to imagine a better matchup of black-and-blue-type football teams than that (although the AFL-derived Jets might not be a classic old school team, they have the attitude).

I'm especially pleased to see it is going to be well below freezing for both the NFC and AFC championship games.  Championship football should be cold and a cold anticyclone is in firm control over the eastern United States.

The current (0900 MST) temperature in Chicago (1300 MST kickoff) is an unlucky 13F, with a forecast high of 18F.

Further east, in Pittsburgh, the current temperature is also an unlucky 13F, with a forecast high of 16F.

Kickoff, however, is at 1630 MST, after sunset, so it's going to be colder during the game.  BRRRR.  Fair conditions should prevail at both locations, so a snow bowl scenario is unlikely.  Nevertheless, I'll be happy to watch these games from a warm bar with a cold beer in hand.  

This is of course balmy weather compared to the mother of all cold NFL games: The 1967 NFL championship game played between the Cowboys and the Packers at Lambeau Field, better known as the Ice Bowl.  Considered by many to be the greatest NFL game ever played, Wikipedia lists the game-time temperature as -15F, with a wind chill of -36F.

My forecast, which is strongly influenced by my personal bias, is Packers and Steelers.  At least that's what I'm hoping for.

Saturday, January 22, 2011

Tree Wells and Deep Snow Safety

Something different for your reading pleasure today.  Having formerly skied a lot in the Pacific Northwest, I've had a few encounters with tree wells from hell.  Little did I know there was an entire web site devoted to the topic.

A tree well is an area around the base of a tree where the snow is poorly consolidated.  A fall into one of these wells can be extremely treacherous, especially if you are alone, as it is very difficult to extract yourself without the help of a partner.  A head first fall into a tree well can result in death from suffocation.  This sounds like an urban myth, but it is not.  

Have a look at the Tree Well and Deep Snow Safety web site for more information.

Friday, January 21, 2011

Ski Now, Work Later

What may be the biggest most persistent, high-amplitude, upper-level ridge of the winter is about to build over the western United States.  The good news is that it will be preceded by yet another short-wave trough embedded in northwesterly flow, which should give the Wasatch Mountains another quick hitting storm late tonight and early Saturday.

0600 UTC 21 Jan GFS Forecast Valid 1800 UTC (1100 MST) 22 Jan 2011
That storm will be our last major shot of snow for at least several days, so it is imperative to "ski now, work later."  After that, we'll likely be high and dry as we won't be in a dirty ridge situation like we've had for the past week.  This ridge is very high amplitude.  We will, however, have great weather for long adventure tours and for skiing fast corduroy in the warm sun at the resorts.

0600 UTC 21 Jan GFS Forecast Valid 0600 UTC 27 Jan 2011
Don't forget to wear your sunscreen!

Wednesday, January 19, 2011

Front or Baroclinic Trough?

There are probably as many definitions of front as there are meteorologists and, if there is something that meteorologists love to argue about, it is surface frontal analysis.

Mother nature does not think in terms of fronts.  She thinks in terms of fundamental physical processes.  Those processes frequently produce strong temperature gradients or, what humans, for the sake of convenience, call and frequently analyze as a front.  However, the magnitude of temperature gradient (or temperature contrast) required for the existence of a front remains subject to debate and frequently the position of a front on a surface weather map is ambiguous.  

The classic example is a composite of the fronts and troughs analyzed by the participants of a workshop convened at the National Meteorological Center (NMC, now the National Centers for Environmental Prediction, NCEP) and published in Uccellini et al (1992) and Sanders and Doswell (1995).  Note the lack of agreement with regards to frontal position and, in some cases, the existence of a trough or front.

A frontal zone is traditionally defined as an elongated zone of strong horizontal temperature gradient, with the front analyzed on the warm side of the zone.  Issues arise, however, because strong is a subjective term, limited surface observations frequently preclude accurate analysis of the actual temperature gradient, and diabatic and boundary layer processes can frequently obscure airmass changes associated with frontal passages.  Sanders (1999) proposed that surface fronts be distinguished from nonfrontal baroclinic zones (i.e., baroclinic zones not accompanied by a significant cyclonic wind shift) and baroclinic troughs (i.e., a pressure trough and cyclonic wind shift with an insufficient temperature contrast to be called a front).  At issue is what magnitude of temperature gradient to use to distinguish between a front and a baroclinic trough.  Sanders (1999) chose a minimum temperature gradient of 8C/110 km (which is 8C per degree latitude - hence the odd units), but not matter what value is chosen, we are still dealing with an arbitrary threshold.  

In practice, I like to distinguish between fronts and baroclinic troughs, but don't use an objective temperature gradient threshold to distinguish between the two.  I typically use the term front when there is a clear and abrupt contrast in temperature and the term baroclinic trough when there is a baroclinic zone, but no clear and abrupt leading edge.  This is admittedly subjective, but such are the compromises that need to be made when applying an imperfect conceptual model to a complex atmosphere with limited surface observations.

So lets have a look at what happened early this morning.  If we look at the WBB time series, it is pretty clear that temperatures are several degrees lower this morning than yesterday morning, despite widespread cloud cover, so it appears there has been an airmass change overnight, but was there a frontal passage?

The time series shows the most rapid decrease in temperature occurred at around 1000 UTC (0300 MST).  The temperature fell from about 45F to 35F (about 5C) over a two hour period.  Concurrently, the dewpoint increased from 20F to 34F.  The RUC analysis at 1000 UTC shows broad baroclinity over much of the Intermountain West, but it is somewhat more concentrated along a cyclonic wind shift just upstream of Salt Lake City.  

The RUC surface potential temperature analysis is, however, somewhat convoluted.  The leading edge of strongest potential temperature gradient is over southern Idaho, and the baroclinity is weak over northern Utah. 

Not being a fan of objective surface analyses in our part of the world, I like to take a look at the actual observations from MesoWest.  As shown below, at 1000 UTC, temperatures in the Salt Lake Valley are in the low 40s (44F at KSLC), but the temperature contrast to the north is pretty weak.  If one goes all the north end of the Great Salt Lake, the temperature is still 37F.

Thus, I classify this event as a baroclinic trough.  There is a baroclinic zone and cyclonic wind shift at 700 mb, but the magnitude of the temperature gradient at the surface is weak (the 7F temperature contrast between KSLC and the north end of the Great Salt Lake is <4C/110 km).  Thus, it doesn't meet my definition of a front.  Others may have differing perspectives.  

Hey Surfers!

Great discussion of a monster cyclone over the North Pacific on the Cliff Mass Weather Blog.  Central pressure of 933 mb!  Have a look.

Tuesday, January 18, 2011

Return of the Greatest Snow on Earth?

What Mother Nature giveth, Mother Nature taketh away.  Our run of quality ski conditions and low-moderate avalanche hazard, extending all the way back to early November, ended this weekend.  Ski conditions on the Wasatch Back were said to be like "eastern skiing."  My experience in Little Cottonwood on Sunday was more like something from the Pacific Northwest, but I didn't bother going out on Monday to see if the snow conditions had degraded further.  Evelyn Lees' Salt Lake Avalanche Advisory suggests that the ski conditions are currently something that only a seasoned New Hampshire skier could love:

"Our rain saturated snow-scape is something else…there are smooth, ice rink rain crusts at the upper elevations, with some surprisingly decent turns on lower angle slopes where an inch or so of graupel stuck onto the ice. But, sharpen your edges and glue in your dentures for the sections of wind scoured bare ice sheets and rough frozen crusts at the mid and low elevations – slides for life are a concern on the steep, icy slopes."

The good news is that we have an upper-level trough dropping into Utah late tonight and tomorrow and it should bring with it some of the white stuff.  This should be a colder storm, with 700 mb temperatures falling to below -8C and snow levels dropping to the valley floor.

It appears, however, that it will be a quick hitter, with 6-12 inches likely in the upper Cottonwoods based on the NAM forecast.  Let's hope Mother Nature is a bit more productive than that.  At least this should be a right side up snowfall.  Our automated snow water content algorithm suggests the storm will start at something like 10% water content, but decrease to something near 4%.

Monday, January 17, 2011

Cold Pool Fragments

I may have spoken a little too quickly about the demise of the cold pool.  It appears there still are a few cold-pool fragments persisting around the area.  For example, check out the observations near Lehi, Point of the Mountain, Bluffdale, and Riverton where temperatures range from 39-47F.

Check out the temperature variability at the glider port near point of the mountain, which suggests it sits right near the top of the cold-air pool with the cold air intermittently spilling over the observing site.

Finally, haze and smog within the cold-pool fragment can be seen when looking south from the Avenues.  In particular, check out the visibility obscuration in the saddle of the Traverse Mountains.

Further evidence of the value of MesoWest.

Feeling Like Spring

It is remarkably warm in the Salt Lake Valley today.  As of noon, we've hit the big 50 here at the University of Utah and several locations in the Salt Lake Valley are reporting temperatures in the low 50s.

This morning's sounding showed a strong inversion and surface-based cold pool persisting in the lowest elevations near the Great Salt Lake, but I think we have finally scrubbed out most (but perhaps not all) of the cold pool.  In particular, temperatures at KSLC airport have climbed to 49F (10C), which gets us close to a total mixout, and Hat Island is even 47F.

This is a welcome change from the dreary gloom of the persistent cold pools that have been in place over the past few weeks.  On the other hand, the rain, wind, and warm temperatures have largely trashed the skiing.

Death of an Anemometer

Cup and windmill anemometers are frequently used for remote observations in mountainous regions, including the Wasatch of Utah.

Automated weather station with cup
and vane anemometer on top.
Photo: Walter Siegmund and Wikipedia Commons
Windmill Anemometer.  Courtesy NOAA/NSSL and Wikipedia Commons
Both are vulnerable, however, to heavy riming, which prevents the movement of the cups, windmill, and/or vane.  Such riming occurs frequently in maritime mountain ranges, but is less common in Utah.

The warm storm last night, however, appears to have led to heavy riming and the failure of the wind sensor at Cardiff Peak.  The tell-tale sign of riming is a rapid, unnatural drop in wind speed to zero, and this is what happened at Cardiff Peak between midnight and 1 am MST last night.

Given that the wind direction changes some after 1 AM, it could be that the cups or windmill are not rotating, but the vane is able to move some.  Of course, there's also the possibility that the sensor was blown over, but I suspect this is unlikely.

At issue is if the rime will melt, restoring the instrument to normal operations, or if someone from Little Cottonwood Snow Safety team will need to go up and clean it off.

Sunday, January 16, 2011

Today's Ski "Glopfest"

As advertised a couple of days ago, snow levels have climbed today and as of about 2PM this afternoon sit somewhere near 8500 feet.  The Alta cam photo from this morning summarizes the day nicely.

I'm now ready to "officially" declare that this dirty ridge has reached at least NC-17 status.  I've skied some warm storms at Alta, including some with serious Cascade concrete, but don't recall ever squeezing as much water out of my gloves as I did at the end of the day today.  Dirty indeed!

Skiing at Alta today, I found the "wintery mix" of ice pellets, mist, and drizzle to be quite interesting.  Even above the freezing level, which as of 2 PM sat at about 9500 feet, I was constantly wiping my goggles to see.   The existence of liquid water above the freezing level is not uncommon in warm, shallow clouds like todays, but there were also plenty of ice pellets around and very few snowflakes.  This is speculation, but I suspect that today the the primary mechanism for precipitation growth was turbulence (a.k.a. airmass scrambling) within the orographically lifted stable layer.  This turbulence led to drizzle formation through collision and coalescence and lifted some (but not all) of the drizzle drops high enough to freeze, leading to a mixture of ice pellets, mist, and drizzle in the layer surrounding the freezing level (including above the freezing level).

Of course this is all just an educated guess, and there's a wide range of possibilities given the limited cloud microphysical data available.  If anyone knows of a good study examining similar processes, please let me know.

Saturday, January 15, 2011

Feeling Warm?

Today's maximum temperature of 45F at the University of Utah looks to be the the highest temperature observed on campus since December 18.

As is often the case during winter when snow is present, we have either been in cold post-frontal air or mired in a valley cold pool for quite a while.  It's great to break 40 and see my driveway free of snow!

In contrast, temperatures on Mt. Baldy have peaked above today's maximum of 23F on six calendar days since December 18.  Note that at this high altitude location, the maximum temperature is not always in the afternoon.

This crudely illustrates how decoupled conditions in the valley can be from the free atmosphere.  Further evidence why it would be good to understand the contribution of cold pools to long-term climate trends over Utah.

Friday, January 14, 2011

Dirty Ridge Gets Dirtier: NC-17 or XXX?

As discussed in an earlier post, we're presently under the influence of a "dirty ridge," a long-wave ridge with relatively low amplitude that allows moisture and upper-level troughs to spill over it so that we still see periods of clouds and snow.

For the most part, this is good news as the Wasatch desperately need a freshening up, but I'm thinking about upping the rating for this dirty ridge to NC-17 or even XXX.  Why?  Well, the latest NAM is bringing in periods of precipitation beginning on Sunday, but with 700 mb temperatures rising to near 0C by Sunday evening.

1800 UTC 14 Jan 2011 Initialized NAM Forecast
Valid 1500 UTC 16 Jan 2011 (8 AM MST Sunday)
1800 UTC 14 Jan 2011 Initialized NAM Forecast
Valid 0300 UTC 17 Jan 2011 (8 PM MST Sunday)
So, in the heart of January, the climatologically coldest time of the year in Utah, we are going to see a warm storm, with snow levels Sunday evening near or even above 8000 feet.

Thursday, January 13, 2011

Utah 2010 Temperatures in Review

As discussed in yesterday's post examining global temperatures, the National Climatic Data Center has released its preliminary year-to-date global, national, and statewide climate summary for 2010.

If you thought this was a relatively cool year in Utah, you are right, but only in terms of the recent climate.  The statewide average temperature for Utah in 2010 was 48.9F.  This makes it the second coolest year (after 2009) since 1993, so it certainly seemed cool for recent Utah transplants or native Utahns who are short in the tooth.  Those with a longer memory might have a different perspective as 2010 was still a full degree warmer than the long term average for the 20th century (47.9F).

In fact, Utah has not had a year with an average temperature below the 20th century mean since 1993.  There are ups and downs from year to year, but the dice are loaded for warmer years.

One thing I would like to see done with the Utah temperature records is an analysis of how persistent wintertime cold pools in valleys and basins affect the long-term tend and year-to-year variability.  This could include an analysis of the frequency and intensity of those cold pools.  I suspect one would find differences between in valley/basin locations where these cold pools are common, and mountain locations where these cold pools are infrequent.