Monday, October 31, 2016

After the Deluge

A varnish of snow at higher elevations in the Wasatch this morning
Last night proved to be quite productive in terms of wind and valley rain with car-wash-like conditions for a while.  At the University of Utah, a sharp front passed just after midnight, resulting in a rapid temperature drop of more than 15ºF, a shift in wind direction to NNW, and wind gusts reaching over 55 mph.  Strong winds with gusts in excess of 30 mph continued for about 2 hours during which about 0.34" fell (data below courtesy MesoWest).

Reports to the National Weather Service show some locations received event greater precipitation amounts including 0.71" at one site in the Salt Lake City area (5102 ft).

It was a relatively warm event in the mountains, but at least a dusting of the white stuff extends down to about 8000 feet based on web cam imagery.  The Alta-Collins snowstake sits at about 2".  Woot woot!

Is this the start of a trend?  I don't think so.  Another weak system is on tap for tomorrow and tomorrow evening, but I see nothing in the 7-10 day guidance to get excited about.  November begins tomorrow.  These are the times that try skiers' souls.

Sunday, October 30, 2016

Lessons in Orographic Effects from Big Beacon

Big Beacon is the nickname given to the 7143 foot peak immediately east of Research Park and the University of Utah with a small tower on top of it.  Officially on USGS maps it is known as Mt. Wire, but Big Beacon is easier to remember.

I've hiked it many times, usually in bad weather.  The peak is fairly exposed to southwesterly flow and it can be quite breezy, as it was today.  It has, however, a nice view of the central Wasatch and I like to visualize the flow and its impacts on cloud development from the summit.

Today we were on the summit at about 1430 MDT when the crest-level flow was out of the south-southwest, as illustrated by the vector wind time series from Mt. Baldy above Alta.

Source: MesoWest
From Big Beacon, one looks south-southeastward toward the high terrain of the central Wasatch.  The view is not perfectly perpendicular to the flow, but close enough for meteorology.  One could see very well the influence of that high terrain on the low-level cloud pattern with shallow orographic cumulus over the central Wasatch (and a few showers) and a decline in coverage over lower terrain further downstream to the east.  I've highlighted this transition in the photo below.

Click to enlarge
The beauty of the central Wasatch, and one of the reasons why the snowfall is so great there climatologically, is that it is an island of high terrain that is exposed to the flow from multiple directions.  Clearly today that island of high terrain is influencing cloud development.  Although not leading to much precipitation today, one can imagine that such effects would contribute to precipitation enhancement during winter storms.  As Yogi Berra said, "you can observe a lot by watchin'".

Friday, October 28, 2016

Juicy Air for Late October, But Will We Get Much Rain?

A major slug of tropical and subtropical moisture reached California late yesterday in advance of a land-falling upper-level trough and began to push inland overnight.  As of 1200 UTC (6 AM MDT) this morning. a narrow band of heavy precipitation was pushing through the Central Valley with a broader band of precipitation extending inland from northern California to southwest Idaho.  Some scattered showers were found over northern Utah, although only a few drops were reaching the ground.

Precipitable water, a measure of the depth of water you would have if you condensed all of the water vapor out of the atmosphere, is very high with this event, reaching 40 mm along the southern California coast.  Although losses to precipitation and other factors favor a decline in precipitable water as airmasses move inland, we're still looking at relatively juicy air over northern Utah by late October standards.  Precipitable water in this morning's sounding at the Salt Lake Airport was 0.76" (19 mm) and the 0600 UTC NAM calls for values that high to remain over the northern portion of the state as a filament of high precipitable water air pushes up the lower Colorado River Basin through this afternoon.

The highest observed in the sounding record for Salt Lake City after mid October is .91 inches (23.1 mm).
Source: Storm Prediction Center
Looking through the NAM data, there are two peaks in precipitable water today and this evening, one at 22.8 mm, the other at 20 mm, so we're unusually high for this time of year.

Of course, if you want rain, you need to convert that moisture to precipitation.  To our north, that will happen today as the large-scale forcing favors ascent there and the band will spread inland across southern Idaho.

The challenge we have in the Salt Lake Valley is that although the total water vapor in the atmosphere is very high, that reflects moisture at mid and upper levels rather than near the surface.  As can be seen in this morning's sounding, dewpoint depressions are more than about 10ºC below 700 mb.

Source: NCAR/RAL
As a result, the sky is overcast and grey, but it's hard to anything other than a few drops to the valley floor.

As the upper-level trough swings in, however, we should start to see more showers get going.  Still most members of the NCAR ensemble call for .05 to .15 inches at varying times during the afternoon and evening.  Those are relatively modest amounts.  However, there is one member that goes for 0.3 inches, so there is a slight chance that someone will do better than that.

I'm scheduled to have my roof partially replaced today, so the odds are good for that .3 inches to fall in the avenues just after they strip off the old roof and just before they put on the new moisture barrier...

Wednesday, October 26, 2016

More World Records "Fall"

World Record?  I don't think so.  Credit: CBS
All observations are bad; some are useful.  This paraphrasing of George Box's famous quote, "all models are wrong; some are useful" is something I preach to students in my weather analysis and forecasting classes.  Given the spatial complexity of the atmosphere, meteorologists are data starved and we tend to worship any observations we can get our hands on.  However, observations, even those collected by and through "official" channels do have errors and uncertainties, and these are critical to consider in operational or research applications.

This is especially true when it comes to extreme events.  By their very nature, extreme events are rare and highly unusual.  Observations of extreme events, especially in isolation, require careful analysis and vetting.  As Carl Sagan used to say, "extraordinary claims require extraordinary evidence."

There are a number of world or national weather records that I have long considered dubious.  One is the 134ºF world air temperature record held by Death Valley, California and set on July 10, 1913.  My view, however, has always been anecdotal.  It just seemed too far out there.  Now there is evidence and analysis suggesting that the record is indeed erroneous.

The case is made in a recent blog post by weather historian Chostopher Burt on the Wunderblog based on his work with William Reed.  They provide a credible and solid argument showing how the record high is unlikely and likely reflects observer error, which could be accidental or willful.

Burt does a lot of great work of this type.  He also has a book, Extreme Weather: A Guide and Record Book that Wasatch Weather Weenies will enjoy.  

Perhaps he can tackle some additional questionable records, especially those related to snow.  The most dubious are the records from Tamarack, California, such as the US monthly snowfall record (390 inches, January 1911) and seasonal snow depth records (454 inches, March 1911).  The 24-hour snowfall record from Silver Lake, Colorado also sits on somewhat shaky ground (discussed in our post Looking Back at the World 24-Hour Snowfall Record), although there's probably not enough evidence for a decertification.  Plus, my friends in Colorado would lose their minds as they need something to boast about in the mountain snowfall department. 

Tuesday, October 25, 2016

Yesterday's "SnowEater" Conditions

Yesterday was a net loss for what little snowpack that we had at pretty much all but the highest elevations.  We didn't have a lot of snow on the ground yesterday morning, but a couple of inches was lingering on shady north aspects, and most of that snow is gone today.

Yesterday.  Source:
Today.  Source:
Here's another perspective looking up Collins Gulch.  Yesterday there was a white strip in High Rustler and environs, and spotty snow down almost all the way to the base (unfortunately I didn't grab an image).  Today, gone.

Today.  Source:
During fall and winter, it's very hard to melt snow on north aspects when skies are clear, even when the temperature is well above the melting point (0ºC).  On these aspects, there is simply not enough energy from the sun to melt snow when the sun angle is low, and the energy transferred from the relatively warm atmosphere to the snowpack is insufficient to drive significant snowmelt.

Yesterday, however, we had a boost in energy input to the snowpack from two additional sources.  One was the rain, which when it hits the snowpack cools to 0ºC, releasing energy for the melting of snow.  The other was the cloud cover, which provides long-wave radiation for snowmelt, a process sometimes referred to as "greenhousing" and which also results in cloudy nights not being as cool as clear nights.  Thanks to those two energy sources, poof, what little snow we had is now gone except in the highest elevations.

During winter, when the sun angle is low, the worst-case scenario for snowmelt is not a warm, sunny day, but a warm foggy day with rain.  A couple of hours of snowmelt is about all you get on a warm, sunny day during winter, but fog and rain work 24/7.  In the eastern United States, warm, foggy, rainy days just destroy the snowpack, creating "snoweater" conditions.  Here in Utah, such effects are sometimes seen in the lower elevations.  For example, in December and January, snow will linger in shady areas in the Salt Lake Valley under clear skies even if it is well above the melting point, but if you get a day with rain and low clouds, it can melt away.

Monday, October 24, 2016

Perspectives on the Snow Season So Far

Yeah, it's only October, but it's worth a quick look at the snow season so far.

Outside of Utah, aggressive resorts are getting on it, mainly with the help of artificial snow.  Arapahoe Basin, CO opened last weekend.  Killington, VT opens this week.  Mt. Rose, NV planned to open October 31 based on early-season natural returns, although looking at their web cams, I wonder if that is now a pipe dream.  You want natural snow?  Grand Targhee remains the big winner in the interior west so far, as we mentioned previously, and some high-altitude areas of the North Cascades might offer up some skiing as well.  The Northwest Avalanche Center observing site at Washington Pass has a 21 inch base this morning.  If you really want to feel jealous, even Vermont got some this weekend.
Here in Utah, we remain on hold.  I did some stomping around upper Albion Basin yesterday and snow remains limited to a couple of inches in shady upper-elevation aspects.

Portions of the Catharines area almost looked skiable.  Ah, wishful thinking.

The snow distribution pictured above is typical of a dry, continental climate.  When the humidity is low, it's hard to melt snow without the help of the sun and that's why it lingers for so long on shady aspects.  On those shady aspects this time of year, snow losses are due largely to sublimation, or ice transitioning to vapor, rather than melt.

Things are changing, however, today, but depending on elevation, not necessarily for the better.  We've had a surge of moisture from the sub-tropics into Utah, or what I'll call the last gasp of the 2016 monsoon.  The analysis below shows a tongue of high precipitable water air extending northward across southern California and southern Nevada and into Utah.

Temperatures at 700 mb are fairly high and around +4ºC.

A look at surface observations shows Alta-Collins (~9700 ft) is sitting at about 38ºF and Mt. Baldy (11,000 ft) at 30ºF as of 8 am.  Thus, we have a snow level sitting around 10,000 feet, which is roughly consistent with what I'm seeing on the Alta web cams.  Note the thin layer of sticky snow on the dormant snow gun near Germania Pass, which is near the bottom of the melting layer.

Although there may be some fluctuations in snow level today, snow will be confined primarily to the highest peaks.  Below 9500 feet or so, we might see a net loss of snow today as the combination of higher humidity and cloud cover is more favorable for melt on those north-facing aspects.

No need to panic, however, as it's only October.  Nevertheless, the natives are starting to get restless...

Saturday, October 22, 2016

Inversion Season Is upon Us

A quick look at yesterday afternoon's sounding shows that inversion season is indeed upon us.  The afternoon boundary in which surface heating drives turbulence and mixing, extended to only 850 mb, just a couple hundred meters or so above the valley floor.  This mixed layer was capped by a series of stable layers and inversions, effectively putting a cap or lid on the valley atmosphere.  In other words, what you emit is what you breath.  

Source: SPC
Welcome to late October.  We are now moving into the time of year during which surface heating is often not enough to mix out the valley atmosphere.  In other words, its inversion season.  However, don't blame the inversion for our air pollution problems.  In fact, meteorologists like myself hate it when people say "the pollution is bad because of the inversion."  Nope.  The pollution is bad because of emissions.  We have met the enemy and it is us.  

A shallow layer of pollution could be spied in all directions while on my bike ride this morning.  

And, in case you were wondering, PM2.5 concentrations at Hawthorne Elementary have been running in what I'll call the "Low Moderate" category at around 20 ug/m3.  

Source: DAQ
With southwesterly flow on tap for the next couple of days, this should be a brief-lived, moderate episode without major concerns.  It is, however, a stress test for the coming winter.  

Friday, October 21, 2016

One Last Monsoon Surge?

As future Senator Blutarski said in Animal House, nothing is over until we decide it is.

Or, in the case of the seasons, nothing is over until Mother Nature decides it is, and she still hasn't decided to call it over on the 2016 monsoon season.

Model forecasts are showing another monsoon surge into Utah late on Sunday, with the potential for some scattered showers and thunderstorms through Monday night.

Right now, it appears we'll squeak the UAE (Utah Education Association) weekend in with good weather, although there's a chance something will sneak into southern Utah late on Sunday.  After that, we'll see how things look in a couple of days.

Thursday, October 20, 2016

September Temperatures: Pleasantly Near-Average Locally, Hot Globally

With the climate data now in and processed, I thought we would take a quick look back at the month of September locally and globally.

For the State of Utah, the mean temperature for September was about as close as you can get to the 20th century average.  
Source: NCEI
Given that September is typically a "Goldilocks Month" in the Salt Lake Valley (not too hot, not too cold, but just right), the month overall rated as quite pleasant in my book, requiring neither air conditioning or heating of the home and most of the days.  

While the whims of the jet stream looked favorably on us, globally September was still beastly warm, rating as the 2nd hottest in the instrumented record.  

Source: NCEI
That's a fairly significant change as the last month that did not set a record for the hottest all time based on analyses by the National Centers for Environmental Information was April 2015.  That's quite a stretch of record setting warmth, although there are a few months in there where 2016 and 2015 are probably statistically indistinguishable (i.e., so close that they are essentially tied).  Even September 2016 and 2015 might fall into that category.

For the year to date, 2016 easily remains the hottest on record, 0.99ºC warmer than the 20th century average.  

Source: NCEI
Developing La Nina conditions in the tropical Pacific will knock the global temperatures down just a touch in the coming months, so the "race" between 2015 and 2016 will probably get a bit tighter between now and the end of December, but it's a virtual lock that 2016 will be the warmest calendar year on record.  

Wednesday, October 19, 2016

You Could Be Skiing This Weekend

Yes, you could be skiing this weekend, but not in the Wasatch Range.

A quick look at the snowpack snow water equivalent (SWE) at western U.S. SNOTELs shows the highest values are nearby at the 9200 foot Grand Targhee site.  Take a quick gander, and you'll see a yellow dot near the Wyoming–Idaho border at that site.

Source: NRCS
Observations show a snowpack SWE of 8.1 inches.  Pretty healthy for October and the equivalent to the climatological median in late November.

Source: NRCS
Web cams show a wintery scene.

Source: Grand Targhee
If you go, add your report to the comments.

Note: To my knowledge, the ski area will not be open.  I don't know their policy for access this time of year.  You will need to earn your turns, possibly outside the resort boundary.

Monday, October 17, 2016

A Blustery Fall Front

It was great to be woken up last night by wind, rain, and even a bolt of lightning as a frontal precipitation system pushed through northern Utah.

This is fall, as it should be — blustery, chilly, and wet, with blowing leaves and a dusting of snow in the mountains.

Although it appears change is upon us, don't wax your skis yet.  Accumulations have so far been minimal in this storm and the remaining snow showers this morning won't add up to much.  A colder storm will bring some mountain snow showers Tuesday and Tuesday night, but nothing to get excited about.  However, the trails should be tacky and the riding good as we approach the weekend, so keep the cardio up until the snow really flies.

Sunday, October 16, 2016

Tushar Heights, Overnight Fropa

I've lived in Utah for over 20 years, yet still find new places to visit.  My son and I spent the past three days in southern Utah enjoying Fall Break and on a whim elected to return home over State Route 153, which climbs over the Tushar Mountains from Junction to Beaver.  The drive is spectacular (closed in winter and partially dirt) with great views.

Along the way, we elected to bag Delano Peak, which at 12,169 feet (you can find other heights online, but I'll use this since this is what it said on the sign on top) makes the Tushars the third highest range in Utah (behind the Uinta and La Sal Mountains).  

The route begins along the Piute ATV trail, which I had no problem accessing via my minivan from SR-153.  There's no trailhead sign, but you start just before Poison Creek (there is a trail marked on USGS topo maps).  The route is fairly straightforward.  You just climb until you can't go any higher.

About sixteen or seventeen hundred vertical feet later,  you reach the top.  The Tushars reminded me a great deal of Colorado.  It would be fun to hike around the high meadows in summer as the terrain around Delano Peak is relatively modest and good for off trail exploration.  Although the slopes of Delano are quite wind exposed,  some impressive terrain surrounds the area and might make for some exciting skiing in the winter or spring.  Tushar Mountain Tours operates two yurts in the area.

One can also look down at the Eagle Point Ski Resort.  It's a small resort, and looks way down there from the summit, but actually tops out at more than 10,000 feet.  Perspective is everything.

Meanwhile back in northern Utah, we had a frontal passage last night with showers over the Salt Lake Valley this morning.  Wind gusts in the prefrontal southerly flow reached about 45 mph, making for a loud night at my place.

A rainy day is perfect for me today as I need to get caught up around the house and get to the office for a bit.

Wednesday, October 12, 2016

Getting Real along the Pacific Coast

For the Pacific Coast of the northwest U.S. and southwest Canada, the doldrums of summer are officially over.  Two major cyclones are expected to bring strong winds to the area, along with a litany of other impacts, although the precise locations of the most intense winds with each cyclone remains unclear.

The first windstorm is associated with a midlatitude cyclone expected to develop off the coast of Oregon and Washington tomorrow and track northeastward toward Vancouver Island or the Olympic Peninsula.  The 0600 UTC NAM placed the ~970 mb low center very near the tip of the Olympic Peninsula at 0900 UTC Friday, a near optimal location for strong winds over western Washington.

The GFS solution was not quite as deep and has the low center making landfall along the central coast of Vancouver Island.  In terms of the severity and location of the strongest winds, much will depend on the precise track of the system.

As if that's not enough, a second cyclone follows over the weekend.  Forecasts at present push it further north, limiting wind severity over the Pacific Northwest, but it is a storm worth watching and its history is quite fascinating.

Just a couple of days ago on 10 October 2016, a decaying Typhoon Songda was minding its own business over the western Pacific Ocean just east of Japan (identified by red box below).  That's a good place for Typhoons, well off the coast and away from densely populated southeast Asia and Japan.

However, as is prone to happen in the fall, Songda meandered slowly northward and, as shown in the loop below, is forecast to be swept up by the midlatitude westerlies.  As it sweeps around the Aleutian low, it is expected to undergo extratropical transition, redevelopment as a extratropical cyclone, before crashing into the Pacific Coast.  

Storms of this type can produce powerful windstorms along the Pacific coast.  For example, the infamous 1962 Columbus Day Storm, was produced by the extratropical transition of Typhoon Freda. 

I've always wanted to be on the west coast of Vancouver Island or the Olympic Peninsula for a storm series like this.  It is fall break, but I have plans for southern Utah, so I think I'll stick with those.

For more on these storms, see the Cliff Mass Blog.

Tuesday, October 11, 2016

Updates to Our NAEFS Ensemble Forecast Products

For those of you who use our downscaled North American Ensemble Forecast System (NAEFS) products on, they have recently been updated.  We have a new algorithm for doing the downscaling that we believe reduces bias, especially the tendency for overforecasting. We now believe, as Donald Trump would say, that this product is so tremendous, absolutely tremendous, that you are going to love it.

Monday, October 10, 2016

Biases in Weather Forecasting

When it comes to biases, meteorologists have to deal with at least three.

The first is bias in our modeling systems.  All modeling systems have shortcomings and tendencies.  Some of these are systematic, in that they appear frequently (but not necessarily consistently).  For example, many lower resolution ensemble modeling systems underpredict the frequency of significant precipitation events over the western United States.

Let's take a look at the Global Ensemble Forecast System as an example.  The GEFS is based on a relatively low resolution model and it struggles to predict major precipitation events at mountain locations in the western U.S.  The plot below shows the frequency of occurrence of observed events at SNOTEL stations compared to that produced by the GEFS control and GEFS mean.  The key line is the black dotted one, which is the ratio frequency of observed events compared to that predicted by the GEFS control (known as frequency bias, scale at the right).  Ideally, this dotted black line would be near 1, which would mean the model produces as many events as observed.  In the Pacific Ranges (i.e., the Cascades, Sierra Nevada, and coastal ranges) the GEFS doesn't do too badly for smaller vents, but it clearly underpredicts the frequency of events larger than 25.4 mm (1.0 inches).  In the western U.S. interior, the situation is even worse.

Source: Lewis et al. (2016, in prep.)
It is possible to adjust the GEFS forecasts to correct for these biases.  One approach that the National Weather Service uses is known as statistical downscaling.  The basic idea here is to use gridded, high-resolution analyses of climatological precipitation to add detail to the GEFS forecasts.  If one does this (I'm going to sweep the details of how this is done under the rug, one can significantly improve the biases.

Source: Lewis et al. (2016, in prep)
That looks fantastic.  A near-perfect model right?  Wrong.  There are also random errors.  Perhaps with these adjustments the GEFS gets the number of events of a given size right, but unfortunately there will be times it forecasts an event and it doesn't happen or it doesn't forecast an event and it does happen.

The second is human forecaster bias.  Some meteorologists are prone to overforecast precipitation, whereas others tend to underforecast.  Bias can sometimes change depending on event size as it is possible for one's biases to be different for large events than garden-variety events.  Meteorologists, like all scientists, need to guard against these biases.  One of the advantages of consensus forecasts produced by a team of meteorologists is that human biases often cancel, leading to a more objective forecast.  On the other hand, teams are not immune from bias either.

The third is public bias, which complex and multifaceted.  In part, it is affected by prior forecasts.  People become desensitized by false alarms.  Weather "surprises" erode public confidence.  People are also affected by their experiences (or lack thereof).  For example, some people that have gone through hurricanes unscathed assume they can survive the next one.  Unfortunately, hurricane damage is highly localized and variable, so one's experience in one hurricane may not be transferrable to another.  Biases also creep through our communities, TV, and social media.

Hurricane Matthew provides thousands of case studies of all of these biases and how they affect the forecast process and the societal response.

Friday, October 7, 2016

A Narrow Escape for Winds, but Not Surge

We are now up to 4001 days without a major hurricane landfall in the United States.

The center of Hurricane Matthew has yet to cross the coast of Florida and remained far enough offshore that most (maybe all) of the southern and central coastline escaped hurricane force winds.  The loop above shows tardar imagery from 1045–1840 UTC this morning and shows how the eyewall just grazed Cape Canaveral, which likely saw the strongest winds along the central coast.  I have seen reports of gusts on Cape Canaveral of just over 100 mph, but am not sure what the sustained winds were and if these measurements were taken at standard instrument height.

The strong winds of a hurricane tend to be very tightly wrapped the low center with the eyewall.  If the storm shifted just a bit west, the winds would have been far worse.  The track was about as close as you can get without producing hurricane force winds at the coast.

Although Matthew has weakened a bit, it is still a very dangerous major hurricane with maximum sustained winds near 115 mph .  The eye bobbled a bit closer to the shore near Daytona Beach and it could flirt with the coast again.  In addition, storm surge is a graver concern along portions of the coast to the north than it was to the south.  The National Hurricane Center warns of the danger of life-threatening inundation along the coast all the way to Cape Fear, North Carolina during the next 36 hours.

Enjoy a comparatively tranquil weekend here in the Intermountain West.

Thursday, October 6, 2016

Matthew Is a Beast

KAMX (Miami) radar loop from 1328–1644 UTC October 6
It has been 4000 days since a category 3 or higher hurricane has made landfall in the United States, but that could change tonight or tomorrow, as Hurricane Matthew tracks of the Florida-Atlantic coast.  Technically, landfall requires the center of the storm to move across the coast and it is possible that the center of Matthew will remain offshore.  My read of the latest model guidance suggests, however, that landfall is more likely than not to happen.  Regardless of whether or not Matthew makes an official landfall, this is an extremely dangerous storm.  As noted by the National Hurricane Center this morning, "Matthew is likely to produce devastating impacts from storm surge, extreme winds, and heavy rains in the central and northwestern Bahamas today and along portions of the east coast of Florida tonight."  More info below.

Source: National Hurricane Center
The last official update from the National Hurricane Center was issued at 11 AM EDT (9 AM MDT) and reported that Matthew is a category 4 storm with sustain winds near 140 mph with higher gusts.  The radar loop above suggests Matthew likely remains category 4 with an extremely tight and well-developed eyewall.  Official forecasts note that some additional strengthening is possible, but the storm is expected to remain at category 4 as it approaches the Florida coast.  The central pressure is 940 mb.

There are better people than me to follow concerning tropical cyclones.  Keep an eye on Jeff Master's Wunderblog, for example.

Here are a few links from our MesoWest team to monitor surface observations from the storm.

Current observations:

Stations reporting tropical storm force sustained winds or gusts:,GG39

Stations reporting hurricane force winds or gusts:,GG74