Friday, May 29, 2015

Still In Long Term Drought

The Salt Lake City International Airport has had 4.19 inches of precipitation so far in May, good for the 6th wettest in Salt Lake since 1874.  Most of the state is well above average for precipitation.

If you are wondering if the drought is over, it isn't.  The U.S. Drought Monitor released this week shows long-term abnormally dry conditions in the northeastern portion of the state to extreme drought in the west desert.

This might seem surprising given how wet it has been, but long-term drought is a 6 month to multiyear phenomenon and considers indicators that include groundwater levels and reservoir storage.  Although it's been really wet the past month, we have considerable ground to make up in these and other areas affected by long-term precipitation deficits.

Thursday, May 28, 2015

The Advantages of Altitude

Amongst the more interesting aspects of this past winter and spring is the contrast in snowpack evolution between the mid and upper elevations.  It's a great example of why, in a warming climate, high-elevation ski terrain and resorts are likely to have an increasing "competitive advantage" with regards to natural snowpack compared to low-elevation ski terrain and resorts.   

We begin at the Mill-D North SNOTEL at 8967 ft in Big Cottonwood Canyon.  Here the snowpack crested well below median, but it also melted out from mid-March to late April.  With the wet weather this month, there have been a couple of events that have laid down some snow, but there's been no recovery in the snowpack at all.  

If we go a little higher to the 9640 ft SNOTEL at Snowbird, we see that the melt out began later (this is a result of not only altitude but also aspect as the Mill D SNOTEL has more sun exposure) and that over the past month the snowpack has been able to survive with minimal net loss.  

There are no higher SNOTELs in the central Wasatch, so we now jump eastward to the Uinta Mountains.  At the 9992 ft Trial Lake SNOTEL just off the Mirror Lake Highway, the melt begins in late April, but it abruptly stops in early May, after which there is a net gain in snowpack of about 2.5 inches.  

Finally, if we go even higher to the 10,966 ft Lakefork Basin SNOTEL, we find minimal loss of snowpack in late April and a complete recovery in May with an increase in snowpack snow water equivalent (SWE) of about 4 inches.  The current snowpack SWE of 13.8 inches is just a shade lower than the peak of 14.2 inches in mid April.  

The bottom line here is that the snowpack at warmer, lower elevations is more sensitive to an increase in temperature than at colder, higher elevations.  It's a double whammy at lower elevation.  When it warms, your not only dealing with an earlier, faster snowmelt, but also a much greater fraction of cool-season precipitation falling as rain instead of snow.  

We had an especially warm, dry winter this year and in contrast to what you may hear on the news, it is not yet the new normal.  Good snow years will return, but over the coming decades as global warming amplifies, the competitive advantages of high elevation terrain will increase as the lower elevations take a greater proportional hit to snowfall and snowpack.  If you think the pressure is on in the central Wasatch now, wait a few more decades.   

Wednesday, May 27, 2015

Short-Range Prediction with the HRRR

The newest model in modeling suite at the National Centers for Environmental Prediction is the High Resolution Rapid Refresh or HRRR (pronounced Hur, although you get bonus points if you can let the r drag on for a while).

With 3-km grid spacing and radar data assimilation, the HRRR is the first operational US modeling system capable of near-storm-scale prediction.

Here's an example from today.  At 1445 UTC (0845 MDT) an area of precipitation was located over northwest Utah and was moving eastward.

Here's the HRRR forecast from 1300 UTC (0700 MDT) through 1800 UTC (1200 MDT).  For the first part of the loop, I've overlaid the HRRR reflectivity on top of the observed.  After that, you see the HRRR forecast reflectivity, which calls for showers to be located over the Salt Lake Valley at 1700 UTC (1100 MDT).  That's about the time I walk across campus for a swim.  I'll keep an eye on the radar and adjust my plans if necessary.

Radar data assimilation is challenging over the mountain west due to poor radar coverage and constraints posed by topography.  Nevertheless, I have been using the HRRR the past few months in my forecasting class and for planning personal activities and have found it to be quite helpful.  It is perhaps best at the timing of arrival and departure of well-resolved and strongly forced fronts and precipitation systems.  It does less well with precipitation intensity.  For instance, I'm not sure one can count on the precipitation system to decay and for the northern Wasatch Front to be rain free as advertised above by the HRRR.  I'd probably go with showers moving into that area later this morning based on the recent radar loop.

I was hoping to use the HRRR more extensively this past winter for short-range snowfall forecasting in the mountains, but Mother Nature wasn't very cooperative.  We'll have to check it out next winter when hopefully we see more snow.

Tuesday, May 26, 2015

We Need More Rain

I know you're thinking that I'm nuts, but as a meteorologist, I hate falling just shy of key thresholds and records.

So far this month, the National Weather Service has recorded 3.88 inches of precipitation.  That's only good for the 8th wettest May on record if we use the Salt Lake City International Airport record for the past several decades and other nearby observing sites to go back to the late 1800s.

Source: NOAA Regional Climate Centers
It is, however, the 4th wettest since the mid 20th century, behind 1993 (3.99"), 1997 (4.76"), and 2011 (5.14").  The wettest year if you go way back is 1908 (5.76").

I think the key psyche points are 4" just because it's a nice round number and 4.27" as that would get us into the top 5 all time.  Given the hit and miss nature of these storms, I make no specific predictions, but climbing up the list is certainly possible and if we can get a big dump right at the airport, perhaps we'll do even better.

Sunday, May 24, 2015

Great Colorado Ski Conditions

I have a reputation for giving Coloradoans a hard time about their lack of snow, but it is well worth a trip to the Centennial State when they are having a spring like this one.

Most of Colorado did not have a great ski season if you measure it by the peak snowpack.  However, the spring has been outstanding for two reasons.  First, it has stayed cold and snowy.  Second, a lot of that snow has been of the sticky, high density variety and it has coated just about everything and the cover is exceptional above 11,000 feet.

Here's an example from the Grizzly Peak snotel at 11,100 ft in Arapaho Basin.  The highest snowpack snow water equivalent of the water year is right now.  It's about at the median peak for this site, but that typically happens in early April rather than late May, putting them way above average for so late in the year.

Source: NRCS
For the Memorial Day holiday, my son and I decided to check out this snowpack for ourselves.  We spent the day yesterday at A-basin experiencing a mixture of sun and snow, as well as a one-hour lightning shutdown about mid morning.  Once that was over, conditions were great for late May with some fine cream on crust conditions.

Today we spent touring near Independence Pass and had another great day, bagging our first 13er on skis.

 Low angle, but we're not used to climbing at 12,000+ feet.  Missing those Wasatch Ohs.
By Colorado standards, the snowpack is bomber, with mainly new snow instabilities to deal with.
A little shameless U of U promotion in the Sawatch 
Happy summiters.
The kid getting some creamy goodness.
We even ran into a fan of Secrets of the Greatest Snow on Earth, who somehow recognized me from the back cover photo.  Great to hear Coloradans are reading it.

I guess this year provides a great example of why you should never give up on the ski season.  I've had more fun skiing in April and May than I did during much of the winter.

Thursday, May 21, 2015

The Memorial Day Weekend Forecast

In the Harold Ramis directed movie Groundhog Day, a weatherman played by Bill Murray relives the same day over and over and over again.  

I've thought of that movie a lot the past week or two and it suspect you will to as we move forward through Memorial Day weekend.

The bottom line is that the unsettled weather will likely persist over the state through the weekend.  Just watch the NAM forecast below which runs through Sunday afternoon and you get a good idea of what we're looking at.  

Yup, showers and thunderstorms with some variations in the timing, coverage and intensity of precipitation from day to day.  That's the pessimistic view.  The optimistic view is that there will be  some breaks where you can get in outdoor activities and there are no unusually cold airmasses making an appearance.  Nevertheless, keep the shower and thunderstorm threat in mind during your outdoor recreating.  Move indoors or into a closed vehicle if you can hear thunder, etc.

If you are thinking of skiing, this is a pattern of primarily hit-and-miss upper-elevation snow showers that are impossible to time.  Really for good freshies this time of year you want something to keep it snowing fairly hard for an extended period as happened last weekend, but right now I don't see anything to organize the precipitation in that manner.  Nevertheless,  this is an extended forecast and I can't rule it out if we get a bit better large-scale forcing than advertised in the latest model runs. I expect snow levels to be fairly high this weekend, perhaps in the 8500-9500 foot range, except during periods with stronger precipitation when they might lower temporarily.  Daytime maximum temperatures will probably reach near or above freezing even at 11,000 feet.  What can I say, it's late May.  Get on it if it starts snowing hard for an extended period, otherwise be thankful the snirt is still buried.

Wednesday, May 20, 2015

An Evolving El Nino

For a good part of this past Northern Hemisphere winter, above average sea-surface temperatures (SST) persisted near the dateline (180º) in the equatorial Pacific.  For example, the image below shows the weekly SST anomaly (anomaly means departure from a 30-year climatology) for the last week of February with the positive SST anomalies centered on the dateline in the equatorial Pacific.
Source: ESRL/PSD
Since then, positive SST anomalies consistent with weak to moderate El Nino conditions have strengthened and developed across the eastern Pacific and now extend to the coast of South America.

Here's another perspective based on a loop of the SST anomalies since late February, showing very nicely the development of the weak to moderate El Nino.  
Source: CPC
Concurrently, enhanced convection and cloud cover developed over most of the central and eastern tropical Pacific, especially just to the north of the equator along the Intertropical Convergence Zone (ITCZ).  This is reflected in negative outgoing long-wave radiation (OLR) anomalies over the past month.  More cloud cover (especially upper-level clouds) means less outgoing long wave radiation at the top of the atmosphere.

Source: CPC
And, along with this convection, we've seen anomalous upper-level anticyclones to the north and south of the equator, the former associated with the active subtropical jet we've seen across the southwest the past couple of weeks.  

Source: CPC
The latest diagnostic discussion from the Climate Prediction Center calls for a 90% chance of El Nino to continue through the Northern Hemisphere summer and a greater than 80% chance it will last through 2015, but also notes that there is considerable uncertainty regarding the strength of the event.  As we have discussed in the past (e.g., Outlook for the 2013–2014 Ski Season), the potential existence of El Nino does not strongly load the dice one way or the other for snowfall in the Wasatch Range next ski season.  Nevertheless, it would probably mean a different large-scale flow pattern than the one we had last season, which would provide much needed new material for this blog!

Tuesday, May 19, 2015

It's Been Pouring Cats and Dogs!

I haven't read it yet, but given the weather we have had the past two weeks, I think we should all run out and pick up Cynthia Barnett's new book Rain.  

Over the past 14 days, precipitation is well above average statewide, with large portions of the state running more than 300% above average.  
In the Salt Lake Valley, Alta is the climatologically wettest regular observing site and has picked up 7.65 inches of precipitation so far this month (not including overnight and possibly part of the day yesterday).  A good chunk of that total fell over the weekend when the upper elevations got 16 inches of high density snow.  

Source: NOAA Regional Climate Centers
The Salt Lake City International Airport is the climatologically driest location and has still recorded 3.38" of precipitation (through midnight MST last night), nearly three times average.   

How does that stack up relative to past Mays?  Records are pretty spotty at Alta, but May 1981, 1983, and 1986 produced more than 9 inches of precipitation.  

At Salt Lake City, the 3.38" we had through May 18th would be good for the 16th wettest (time series below based on observations from the Salt Lake City area prior to the establishment of the Salt Lake city International Airport).  Two Mays have had more than 5 inches of precipitation, 2011 (5.14") and 1908 (5.76").  We have some time to catch up though as those are totals for the entire month.  

Surely you remember May 2011?  If not, let me refresh your memory as I always like looking back on the winter of 2010/11.

Memorial Day Weekend, May 30, 2011
It's wind scoured here, but at 8 am that morning Alta-Collins had recorded 10" new with a 193" settled snow depth
BDOME: Best Day of May Ever
There may be some variations in precipitation coverage and intensity from day to day, but the weather looks unsettled for the next 7 days.  We will probably be climbing up the rankings for May rainfall.  A minus with regards to skiing this weekend is that it appears it will be a bit warmer than last weekend and I'm not seeing a precipitation system as organized as what we got Saturday night.  Nevertheless, one can always hope as we see how things come together.  

Monday, May 18, 2015

Sunday, May 17, 2015

Huge Spring Dump, Avalanches Likely

After depriving us of quality powder for most of the winter, Mother Nature turned on the spigot big time last night.  Automated observations from the Alta-Collins observing station (9662 ft) show the total snow depth increasing from around 64 inches yesterday (multi-hour average) to 80 inches as of 7 am this morning.  I'm calling it a 16 inch storm total, although it looks like 14 inches of that fell after 6 PM yesterday.  Total water during this period was a whopping 2.41 inches.  

Radar images from last night show the remarkably juicy northwesterly flow and how Alta was fortuitously located in the narrowing band as the night dragged on.  

Source: NCAR/RAL
Source: NCAR/RAL
I've looked at some radar loops and there may have been some lake augmentation at times, but the large-scale precipitation band was an important component of this storm (note how it extends well upstream of the lake in the images above).  

The Utah Avalanche Center is closed for the season, but they did issue a tweet overnight highlighting that avalanches are likely, including terrain within closed ski areas, which is de facto backcountry right now.  

As much as I was hoping to get out this morning and followup on yesterday's creamy turns, I'm electing to stay home.  Today is the epitome of too much of a good thing

Saturday, May 16, 2015

Creamy Goodness

More snow at Alta this afternoon.

Sorry kid, you have to earn your turns today.

The reward for hard work was more creamy goodness.

Want some?  Get up early tomorrow as the snow won't last long.  Be careful as the snowpack could be cranky especially if it keeps snowing and if it warms tomorrow.  Further, the snow is high density and any wet sloughs or slabs will pack a much bigger wallop than we Utahn's are used to.

May Freshies Forecast Lookin' Good!

Things are coming together for several inches of fresh today and tonight in the upper-elevations of the Wasatch for those of you who still feel the need to feed the habit (count me in).

As of 7:45 this morning, all was relatively quiet over the Salt Lake Valley and the Wasatch Mountains to the east.  Given the southwesterly pre-frontal flow, an orographic cloud hung over Lone Peak and the downstream central Wasatch Mountains.

However, a glance to the west shows the Oquirrhs shrouded in cloud cover and light snow.  A harbinger of things to come?

Indeed, the regional radar looks optimistic with returns to our west that will slowly spread over the area and into the central Wasatch this morning. 

Source: NCAR/RAL
The NAM calls for valley rain and high elevation snow this afternoon.  Below is the accumulated snow-water equivalent from 3PM to 6 PM MDT.  No yard work today!

And the grid point output for Alta shows about 0.75" of SWE and a bit over 6 inches of snow from late this morning through midnight tonight.  

Thus, things look good for creamy May freshies in the upper elevations late today and first thing tomorrow morning.  It won't be the Greatest Snow on Earth, but who cares.  It's May.  

Friday, May 15, 2015

Best Chances for Good Skiing

It may be deja vu all over again this weekend.  Alta-Collins has had 0.4" of water equivalent in the past 24 hours and will likely see some snow in fits and spurts today as well.  Then we have the potential for snow this weekend.

My approach when it comes to spring storms is to get out during or just following periods of significant snowfall.  If you wait too long, everything gets warm and manky, which not only results in poorer skiing, but also the potential for wet avalanches.

We spoke in the previous post (This NAM Forecast Is a Work of Art) about the dramatic comma-shaped character of the cloud and precipitation pattern for Saturday, as well as the pronounced dry slot.  Today's 1200 UTC NAM shows a similar pattern for 1500 UTC (0900 MDT) Saturday, with much of the area around Salt Lake City in the cyclonically wrapped dry slot, but precipitation just to our south.

Eventually the band of precipitation moves moves into northern Utah, but not until later in the day.

As such, my strategy for tomorrow may be one of patience.  If I get up and it's snowing and it looks like it will continue, I'll probably jump on it.  A bird in hand is worth two in the bush.  If it's not doing anything, I'll probably wait until late Saturday or early Sunday and hope the band comes through (the GFS is less optimistic about that band, but it's also been producing colossally terrible precipitation forecasts since it was upgraded this winter).    Given the convective nature of precipitation processes this time of year and the warm conditions, one needs to weigh the odds, but ultimately flexible.

One thing is for sure, this is likely to be another warm storm.  700 mb temperatures will be between -3 and 0ºC through noon Sunday (then they go even higher...all the more reason to get out early), which means wet snow and best accumulations above 9000 feet.  Total accumulations will probably be limited, in part by the high density.  The NAM is calling for about 0.6 inches of water at Alta-Collins from today at 6 AM through Sunday 6 AM, which translates to 5 inches of snow.  Something in the 4-8 inch range for that period is probably a best guess above 9000 feet.  Less below.

Thursday, May 14, 2015

This NAM Forecast Is a Work of Art

We rarely see such a beautiful comma cloud and precipitation pattern over the Intermountain West as forecast by the NAM for 0900 UTC (0300 MDT) Saturday.  Simply spectacular!

0600 UTC 14 May 2015 NAM forecast of 500-mb wind (vectors), temperature (red contours every 1ºC)
3-h accumulated precipitation, and outgoing long-wave radiation valid 0900 UTC 16 May 2015
Patterns like this are associated with well developed upper-level troughs, but often such troughs have cloud and precipitation patterns that are broken up by the topography of the west. That's not the case in the NAM forecast above.

The beautiful comma cloud and hook-shaped precipitation pattern is associated with two major airstreams.  The first is sometimes called the TROWAL (TRough Of Warm air ALoft) airstream.  The TROWAL airstream is associated with warm advection and ascends along a tongue of warm air that wraps round the back side of the upper level low, forming the comma.  

The second airstream descends on the back side of the upper-level trough, wraps around the forward side of the upper-level trough, and forms the dry slot.  At upper-levels, this airstream is typically dry because it has descended from the upper-troposphere.  The interlacing of these two three-dimensional airstreams leads to the beautiful comma cloud.

The term dry slot can give the false impression that this is an area of benign weather.  Au contraire in some situations.  Although the dry slot may be cloud free and feature low relative humidity air at upper-levels, at low levels, the air beneath the dryslot can vapor laden.  The airmass beneath the dry slot often features large Convective Available Potential Energy (CAPE), which is jacked up further by solar heating during the day if the dry slot is cloud free.  Being ahead of the upper-level trough, the forward portion of the dry slot is also an area of rising motion.  As a result, convection frequently breaks out within or at the leading edge of the dry slot.  The vertical wind shear in the dry slot region is also sometimes favorable for the development of severe convection.  Even the low-resolution NAM is generating some dry-slot convection in the forecast above.  

Wednesday, May 13, 2015

Get High If You Want to Ski

Although Utah is home to the Greatest Snow on Earth during winter (except for perhaps this year), once spring rolls around, I'm more inclined to think about skiing elsewhere.  There are big lines and beautiful views to be had around the west, but this year, you might have to work a bit harder than usual to find some that are adequately snow covered.

Below is the basin-wide percent of average snowpack analysis for the western U.S. from the NRCS.  These numbers are simply heinous for most of the west.  Only portions of Colorado and SE Wyoming are near average (the high numbers in SE Utah are either spurious or the result of what we call the "statistics of small numbers" — there's very little snow there).

In the Sierra and Cascades, the snowpack is non-existent or <10% of average in most basins.  One plus is that with no low-elevation snow, access to higher elevation tours is much easier than it typically is in May.  For example, the road to the South Climb Trailhead on Mt. Adams is melted out.  The climber's report suggests you'll find snow starting at 6100 feet.

Averages can be deceiving.  Let's instead look at the actual water equivalent of the snowpack.  No matter where you are, given the warmth of this past winter, if you want to find snow, you need to get high.  Specifically, you need to look to the upper elevations of the North Cascades, Montana, Wyoming, and Colorado.  The Cascade Volcanoes will probably work too, although those aren't sampled by SNOTEL.

Source: NRCS
The highest SWE in the west is at Easy Pass (5270 feet) in the North Cascades, which currently sits at 45 inches. Moving east, Noisy Basin (6040 ft) and Flattop Mountain (6300 ft) near or in Glacier National Park sit at 33.7 and 31.1 inches, respectively.  Moving south Grand Targhee on the west slope of the Tetons (9260 ft) is at 31.7 inches and the MedBow Snotel in the Medicine Bow Range sits at 32.4 inches.

In Colorado, the snowpack SWEs are not as high as found in other areas, but they have a healthy snowpack near or above average at upper elevations along the Continental Divide from Independence Pass to Niwot Ridge.  The plot below shows only only SNOTELs above 10,000 ft, with green signifying 90-110% of average, light blue 110-125% of average, medium blue 125-150% of average, and dark blue 150-175% of average.

Source: CBRFC
The Grizzly Peak Snotel at Arapohoe Basin didn't quite crest at average, but the cool and intermittently snowy weather in the recent past puts it a bit above average at present.

So, all is not lost.  There's not a lot of snow to be had in Utah.  Upper elevations of the Cottonwoods are about your best bet.  Road tripping and getting high will get you turns elsewhere.  In some instances, access may actually be easier than it typically is this time of year.