The Bear Lake Boating Tragedy

On Monday night, strong winds and waves on Bear Lake capsized a small boat killing one adult and three children.  It sounds like a terrible tragedy and my thoughts and prayers go out to the friends, family, and all involved.

Bear Lake straddles the Idaho/Utah border and is roughly 30 km long and 10 km wide.  The accident apparently happened in the Idaho portion of the lake.  

Although details are still fuzzy, the Salt Lake Tribune reports that winds gusted to 76 mph, with waves reaching 10 feet in height.  Seven people were on board when the boat capsized, all with life jackets on.  The water temperature, however, was only 53º.  It is likely that the victims died from exposure or downing before they could reach the lake shore.  

I've taken a quick look at the weather contributing to this tragedy and it provides a cautionary tale about just how quickly disaster can strike on Utah waters (and elsewhere) seemingly from nowhere. 

The strongest wind gust I could find near Bear Lake from observations collected by MesoWest was  48 mph at the Bear Lake County Airport, just north of the lake.  The meteograms below show that at 1655 MDT (~5 PM), the temperature was 79ºF with sustained winds of 14 mph.  Then things changed dramatically for the worse.  At 1755 MDT (~6 PM), the temperature was 60.3ºF with sustained winds of 35 mph and gusts to 48 mph.  The tempest continued for another hour and and by 1855 MDT (~7 PM) winds were still gusting to 46 mph and the temperature had dropped to 54ºF.  

In addition, satellite and radar imagery shows that Bear Lake was on the edge of most of the thunderstorm activity (the lake is just west of the UT-ID-WY triple point), which was associated with a weak cold front that was moving through the area.

Source: NCAR/RAL

Source: NCAR/RAL

Although there were some weak radar returns in the vicinity of Bear Lake, the strength and duration of the strong winds strongly suggests that a mesoscale outflow boundary (a.k.a. gust front) produced by precipitation and thunderstorms to the north and west likely propagated through the area.  

Indeed, numerous sites in the area reported strong winds during this period, including the Grace RAWS station just northeast of Bear Lake, which hit 65 mph.  There probably were some clouds and showers in the vicinity of Bear Lake ahead of the gust front, but the change in wind, temperature, and waves experienced by the boaters would have been abrupt and severe.  Further, the persistence of strong winds and waves combined with a further drop in temperature following the gust front passage greatly increased the likelihood of drowning or hypothermia before the boaters could reach shore.   I suspect the boaters were hit by something that they never saw coming, or had little time to respond to, and were cast into a nightmare situation.  

This sort of weather situations is, however, not all that uncommon in Utah, highlighting the need for boaters to remain vigilant for rapidly changing conditions when storms are around.  It's especially important to recognize that the strong winds and rapid temperature changes associated with outflow boundaries can sometimes propagate well away from the generating storms, in some cases into areas experiencing clear skies.  

The Snow Is Going Fast

Although we had a stay of execution for most of May, the snow is going fast now that the heat is on.  Snow melt at the Snowbird SNOTEL went into overdrive in late May with the snowpack water equivalent dropping from 9.5 inches on May 27th to 0.3" yesterday, a mean melt rate of about 1.5" a day.  0.3" rounds to 0, so I'm officially calling an end the snow-cover season at this site.

Source: CBRFC.  

The snow depth at Alta Collins has similarly been plummeting and is now down to 52 inches.

Source:  MesoWest

The Alta Lodge web cam shows patch cover at the base of Alta.  If you want a top-to-bottom run, you'd better get on it ASAP.

Source: Alta Lodge

The end is near.  Much work will be needed to earn turns after this week.

Happy 20th Anniversary KMTX!

Weather prediction over northern Utah reached a major milestone this week with the 20th anniversary of the KMTX WSR-88D radar on Promontory Point (right image in the @NEXRADROC tweet below).

Celebrating 20 years for KMSX @NWSMissoula and KMTX @NWSSaltLakeCity #wsr88d pic.twitter.com/WhDlSBS8YX

— NEXRAD ROC (@NEXRADROC) June 1, 2015

WSR-88D stands for Weather Surveillance Radar, 1988, Doppler, a name only the National Organization for the Advancement of Acronyms [(a.k.a., National Oceanic and Atmospheric Administration (NOAA)] could love.  The non-technical name is NEXRAD, for NEXt-generation RADar.

The development, installation, and subsequent operation of the 160-radar NEXRAD network is a great success story, paying dividends to the American taxpayer many times over.  Mike Smith, author of the book Warnings: The True Story of How Science Tamed the Weather, calls the NEXRAD network "one of the best investments the federal government has ever made when viewed on a cost/benefit basis."

The NEXRAD network replaced the pre-existing network of WSR-57 and WSR-74 radars, adding increased resolution and the ability to measure Doppler velocity, the magnitude of the flow towards or away from the radar, which is critical for warnings related to severe convective storms and tornadoes.  The NWS recently added polarimetric capabilities to the NEXRAD network, which allows each radar to send and receive horizontal and vertical radar waves and better discriminate between rain, hail, snow, and other precipitation types.

Although beneficial across the country, the NEXRAD network was a revolutionary advance across most of the western United States and northern Utah, which were completely uncovered by the WSR-57 and WSR-74 radars.

Source: National Academies Press (1995). http://www.nap.edu/catalog/9056/assessment-of-nexrad-coverage-and-associated-weather-services.

In fact, prior to the installation of the KMTX radar, forecasters at the Salt Lake City National Weather Service Office relied on hand-drawn analyses from a FAA radar — hardly a recipe for success during rapidly evolving severe and hazardous weather events.

Today, thanks to KMTX, you can view radar loops in real-time on your smart phone while skiing in the Wasatch.  That's what I call progress!  Chances are you are using radar apps developed by private sector companies, which have leveraged the NEXRAD network to tap into all sorts of emerging markets in weather sensitive areas.  None of this was possible when I started graduate school.  Kudos to all in the weather enterprise who have contributed to these advances.

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.

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.   

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.