California's Fourth Climate Change Assessment

California's Fourth Climate Change Assessment was released yesterday and contains some sobering findings for the future of snow and skiing in the Sierra Nevada.  The assessment can be accessed at www.climateassessment.ca.gov, with the regional report for the Sierra Nevada available at http://www.climateassessment.ca.gov/regions/docs/20180827-SierraNevada.pdf.

California is perhaps one of the more climate-vulnerable regions of the contiguous U.S. and is already feeling the effects of global warming.  On the other hand, it has incredible expertise to draw from, with the regional report from the Sierra Nevada seeing contributions from manny oustanding scientists, led by Mike Dettinger of the USGS.

Some key points from report on the Sierra Nevada:

• Climate change is already underway

• Recent/ongoing trends foreshadow changes to come

• By the end of the 21st century, temperatures are projected to warm 6-9˚F

• Future precipitation is expected to be within ±15% of current totals, but extremes (deluge and drought) will increase

• Snowpacks will "very likely be eradicated below about 6,000 feet elevation and will be reduced by more than 60% across nearly all the range."  

Using ten different climate models, they specifically examine projections of historical and future climate, the latter under two scenarios, RCP4.5 in which greenhouse gas emissions peak around 2040 and then decline, and RCP8.5 in which greenhouse gas emissions rise throughout the 21st century.  Below are projections of temperature and precipitation for four regions within the Sierra Nevada. 

Source: Dettinger et al. (2018)

Under RCP8.5, locations at or below 6000 feet in the Sierra Nevada experience at least an 80% reduction in April snow-water equivalent.  The smallest declines occur in the southern Sierra due to it's higher altitude and colder climate.  Soil moisture declines at all locations. 

Source: Dettinger et al. (2018)

The graph below presents the probability that the April snow water equivalent will fall in the historical lowest 10% of seasons.  Translation: this is the likelihood of a truly shitty snow season.  In 2000, this comes near 10% as one would expect.  In the Northern Sierra under RCP8.5%, the odds increase to 90% by the end of the century.  In other words, nine out of every ten years would be truly shitty.  The odds of a truly shitty season are lower, but still higher than current, in the northern Sierra Nevada under RCP4.5 in which greenhouse gas emissions peak in 2040 and then decline.  Increases in the odds of truly shitty seasons are much smaller in the southern Sierra Nevada which thanks to altitude sees less vulnerability of the April snowpack.  It's a bit unfortunate that they don't present data for later months when declines in the southern Sierra may be more dramatic. 

Source: Dettinger et al. (2018)

Overall, these results are consistent with the expectations that snow at lower, warmer elevations is more vulnerable to warming.  It also highlights that fact that although we are already committed to some future climate change, reductions in greenhouse gas emissions can still reduce the magnitude of that warming and its associated impacts. 

Winter Is Coming!

Summer is bad and getting worse.  This year was no exception, with the summer so far (1 June - 26 August) rating as the 6th warmest such period on record at the Salt Lake City International Airport with an average temperature of 78.9˚F.

Source: NOAA Regional Climate Centers

Throw in a lack of precipitation (0.74" thusfar, 15th driest since 1874) and persistent smoke, and we can all be grateful that the end of August is nigh and that signs are apparent of a change in season. 

We begin in the Alps, where severe-weather.eu reports up to 35 cm of snow this morning.  That's right, 35 cm!  That's nearly 14 inches for the metrically challenged.  Doesn't everything sound deeper in metric? 

The video below is from the Rifugio Bioche Hut in Alta Badia (2079 meters) in northern Italy.   Looks like 25 cm by their ruler.  Guessing the sun chairs won't see much traffic today. 

Meanwhile in the states, a cold upper-level trough is pushing across the Pacific Northwest, with 700-mb temperatures below the coveted 0ºC mark across much of western Montana, northern Idaho, and eastern Washington.  That means those radar echoes in the image below are producing upper-elevation snow.  

Below is the view at Logan Pass, Glacier National Park this morning.  

Source: NPS

Hopefully the precipitation and cool weather will help with the wildfires, which have resulted in a number of evacuation orders and warnings in the park.  

Northern Utah will see cooler air from the system as well.  The NWS forecast calls for a high of 76˚F both today and tomorrow at the Salt Lake City International Airport.  76!  Scream it from the highest mountaintops!

The last day we saw a sub-80 high here was June 30th.  If we are really lucky, and the HRRR-SMOKE is reasonable guidance, the flow will shift enough that we may even see this smoke abate.  Note in the forecasts below how the flow shifts to northernly and eventually the smoke shifts southward and we get into cleaner air later today and this evening.  

Source: NOAA

Source: NOAA

Source: NOAA

Should this all come to fruition, enjoy the airmass and every breath you take.  

Can We Just Give the Smoke a Rest?

Yesterday evening was simply gorgeous, with clear skies and clean air.  I went to bed hoping to awake again to clean air, but alas, it wasn't to be, although I discovered that for once this summer, the mountains offered an escape. 

I opted for a quick early ascent of Snowbird so I could return to the valley and get some work done.  Although the valley is smoky, Snowbird was clean as a whistle, at least when I summited around 10 AM. 

In contrast, smoke fills the valley.  If you look carefully at the photo below, taken around 10:35 or so, you can see that the smoke is a bit shallow and doesn't appear to mountaintop level. 

What appears to have happened overnight is that there was a weak shift in the wind, with some surface stations exhibiting northwesterly flow that could transport smoke southward into the valley from the north.  Hat Island, for example, saw a shift to northerly flow (wind direction blue dots below) just before midnight, which persisted until about 9 AM this morning. 

The distribution of fires and the large-scale flow pattern right now is one in which the snow lies to our north and northwest, whereas the clean air is to the south and east.  A few hours of northerly flow was enough to bring the smoke at low levels into the area. 

Last night's HRRR-Smoke forecast handled this situation really well.  Below is the forecast valid at 1800 UTC (1200 MDT) today.  Looking for clean air?  Head southeast. 

If you are wondering, that forecast (the last available since this is an experimental product and only run when computer time is available) keeps us in the smoke through tonight. 

It's much nicer in Utah county.  Below is the web cam from BYU.  If you are looking for clear skies, you could head down there. 

Ha ha.  Just kidding!

Intricacies of Hawaiian Climate and Lane Rainfall

Some impressive rainfall totals have been produced by Lane on the Big Island of Hawaii over the past 2-3 days and it's worth doing a quick comparison and contrast with the climatological rainfall as this is relevant for understanding flooding.

Owing to the quasi-persistent northeasterly trade winds, the eastern slopes of the Big Island, especially those to the west and northwest of Hilo, are very wet, with a maximum of over 8000 mm (300 inches). 

Source: Department of Geography, University of Hawaii at Mãnoa

Note, however, that that maximum is not on the high-altitude slopes of Mauna Kea and Mauna Loa, but instead on the lower slopes.  In fact, the maximum lies at altitudes between 2000 and 4000 feet above sea level.  This is a bit surprising for those of us in the western U.S. who typically expect precipitation to increase with elevation, but it is a consequence of several factors including the persistent trade-wind inversion, which frequently limits the vertical extent of precipitation-producing clouds, and also the microphysical processes that generate rain in the region.  

One can almost infer this rainfall maximum and the general distribution of precipitation from Google Earth imagery of the Big Island.  Note in particular the green, densely vegetated areas on the eastern slopes of Mauna Kea and Mauna Loa, at moderate elevations on the southeast and western slopes of Mauna Loa, and along the northeast shore.  These correspond vary well to areas with more than 750 mm (30 inches) of rain in the analysis above.  

Now let's take a look at some precipitation totals for the 2-day period ending at 1900 UTC (9 AM HST) Friday 24 August.  For simplicity, I will focus on two locations, the Hilo International Airport at 36 ft above sea level and the Hakalau Remote Automated Weather Station at 6549 ft on the eastern slope of Mauna Kea.  During the past two days, Hilo has received 20.04 inches of rain, and Hakalau 33.34", as indicated below.

How unusual is such a 2-day total?  We can estimate that at the National Weather Services' Precipitation Frequency Data Server.  At Hilo, 20 inches of rain in 2 days has a recurrance interval of about 20-25 years or, perhaps better put, has a likelihood of happening in any given year of 1 in 20 or 25.  Unusual, but not hugely so. 

Source: https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_hi.html

Hakalau, however, is a different story.  Because of it's relatively high elevation, it actually sits a bit above the heavy rainfall area of the Big Island and 33 inches of rain in 2 days at that elevation is a much rarer beast.  That amount of rain at that location has a recurrence interval of more than 200 years or, perhaps better put, has the likelihood of happening in any given year of less than 1 in 200.  

Source: https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_hi.html

Intensity, duration, and coverage all matter for runoff.  Lane is a big rainfall producer, but it is not only producing big numbers, but it is doing it at elevations and in the upper reaches of drainage basins that don't typically see such big numbers.  I hypothesize that this may be exacerbating the intense runoff and flooding on some parts of the Big Island.  

What the Hail?

Strong and severe thunderstorms made for an exciting day and evening yesterday.

I was most impressed with the reports (and photos) of hail in Farmington, Kaysville, Layton.  Photos on twitter were impressive.

Hail size verified! 2” hail in Kaysville. Protect your cars with these severe thunderstorms! #utwx @KUTV2News pic.twitter.com/hfbzKXK3D7

— Chase Thomason (@ChaseThomason) August 22, 2018

Hail of that size can be damaging, and left some dents in cars in the area.

Aftermath of hailstorm on freeway in Davis Co., my car is riddled in dent marks. How does this even get fixed!? #utwx #weather pic.twitter.com/1BkaJJkllv

— Jen Hicks (@Jebbowie) August 22, 2018

Severe hail with a diameter of 0.75 inches or greater is relatively rare in our part of the U.S. and most common in the high plains. 

Source: Cintineo et al. (2012)

Nationwide on an annual basis, hail does more than $1 billion in damages to crops and property, including cars.  In Colorado, damages amount to about $3 billion/decade. 

The cell that may have produced the largest hail is plotted below and is located just to the south of Hill Field (HIF).  Note that radar reflectivities for that cell are higher than seen for many other cells and include a number of pixels higher than 60 dBZ. 

Algorithms that identify precipitation type using the great variety of information collected by National Weather Service radars indicated large hail was likely. 

Update on Lane

The latest (1415 UTC) Goes-15 IR imagery shows the center of Hurricane Lane to the SSE of the Island of Hawaii. 

Source: NRL

The 2 AM HST public advisory from the Central Pacific Hurricane Center reported that Lane remained a major hurricane at category 4 with 130 mph maximum sustained winds.  There is a tendency to focus on winds and hurricane categories, but the reality is that it is water, through storm surge and flooding, that is responsible for most deaths associated with hurricanes and tropical storms.  Although Lane is expected to weaken as it it moves northward, wind, rainfall, surf, and storm surge threats remain high for the Hawaiian Islands. 

The Hurricane Lane Local Watch/Warning Statement from the National Weather Service is available here.  If you, friends, or family are in the islands, monitor official statements from the National Weather Service and local emergency officials. 

Powerful Lane Approaches Hawaii

The Hawaiian Islands are blessed in many ways and from a meteorological perspective, they are fortunate to sit in the central Pacific where the frequency of tropical cyclones (e.g., hurricanes, typhoons) is relatively low compared to that found in the eastern and western Pacific. 

Historical tropical cyclone tracks (Source: https://coast.noaa.gov/hurricanes/)

One reason for this is that the sea surface temperatures in the central Pacific are climatologically lower than those found at similar latitudes in the tropical eastern and western Pacific Ocean.  Hawaii also benefits from a protrusion of cooler sea surface temperatures to its east and south which, combined with climatological atmospheric circulations, often steers tropical cyclones to the south.  

Source: Climate Prediction Center

There are, however, exceptions.  The images below illustrate the tropical storms and hurricanes passing within 200 (top) and 75 miles (bottom) of the Hawaiian Islands since 1950.  Hurricane landfalls in which the low center crosses the coast of an island while at hurricane force are rare and since 1950 consist of Dot (1959) and Iniki (1992), both of which passed over Kauai, Dot as a category 1 hurricane and Iniki as a category 4.  Other tropical cyclones storms have weakened to below hurricane force or passed near the islands.  Note that impacts extend from the low center, so landfall is not necessary for a tropical storm or cyclone to bring hazardous and high impact weather to the island.  

Source: Central Pacific Hurricane Center

As I write this at approximately 8 AM MDT Wednesday 22 Aug, Hurricane Lane is a very powerful storm approximately 300 miles south of the Island of Hawaii, with a very well formed high and compact, symmetrical cloud shield.  

Source: NOAA/NESDIS

The 2 AM HST advisory issued by the Central Pacific Hurricane Center reports that Lane is a category 5 hurricane with maximum sustained winds near 160 mph, with higher gusts.  Aircraft penetration into Lane show the remarkable drop of estimated sea level pressure as the Air Force Hurricane Hunter traversed the hurricane (red line, upper left), with an estimated minimum sea-level pressure just below 935 mb, which is the atmospheric pressure one typically finds at about 650 m (2100 feet) above sea level.  So, moving into the center of Lane at a constant altitude results in a drop in pressure similar to that if you were to climb from sea level to 2100 feet. 

Source: Levi Cowan - tropicaltidbits.com

Remotely sensed wind speeds are presented at upper right and shows the rapid increase in speed as the aircraft approaches the eyewall, the relative calm of the eye, and then a second max as it exited the eye and traversed the eyewall again.  At present, Lane is a very compact system with hurricane-force winds extending 40 miles from the center.  

Lane will likely remain a hurricane, possibly a major one (i.e., category 3 or greater) as it approaches the Hawaiian Islands. The cone below, issued at 11 PM HST Tuesday, illustrates the region that will likely contain the probable path of the storm, illustrating the possibility of a track very near one or more of the Hawaiian Islands, or somewhat further offshore.  A track traversing one or more of the islands remains possible (note that the tropical cyclone track is within this cone about 2/3 of the time, so there is a low probability possibility that Lane's track is outside it), although landfall is not needed for major impacts to be felt by the islands as a track just off the west coast of Hawaii, for example, would likely result in the strong winds and heavy precipitation accompanying and surrounding the eyewall moving over the island.  Hurricane warnings currently cover the Island of Hawaii, with watches for Maui, Lanai, Molokai, Kahoolawe, and Oahu.  

Source: Central Pacific Hurricane Center

The latest advisories and information are available at the Central Pacific Hurricane Center web site from the National Weather Service.  Hurricane impacts include not only wind, but also surf, surge, and rainfall and related flooding that can occur even if there is not a direct landfall.  The National Weather Service and emergency management agencies are your best sources of information prior to and during this and other storms.