Wednesday, November 22, 2017

Giving Thanks for the NCAR Ensemble

For nearly three years, the National Center for Atmospheric Research (NCAR) has produced a daily, 10-member, cloud permitting ensemble at 3-km grid spacing known as the "NCAR Ensemble". 

For those of us in the western U.S., the NCAR Ensemble forecasts, available from web sites hosted by NCAR and the University of Utah, attempted to do something that no current operational forecast system could three years ago — capture the extreme spatial contrasts and quantify the inherent uncertainty of precipitation over the western United States. 

Last night's forecast, for example, shows the major deluge expected to affect the Pacific Northwest through Thanksgiving.  At 3-km grid spacing, the NCAR ensemble accounts for many regional and local topographic influences and, with 10-members, one can derive statistics related to the range of possible forecast outcomes and the likelihood of precipitation above certain thresholds (our standard 1" and 2" thresholds work well for the Wasatch, but not the Cascades!). 
Plume diagrams allow one to examine precipitation at various locations, including Mt. Baker Ski Area below.  Such a pity that nearly all of that water will fall in the form of rain.

These products are popular with readers of this blog, friends in the snow-safety community, and operational forecasters.

Recently, NCAR announced that the NCAR Ensemble will sunset at the end of the calendar year.  More information is below. 


Although I'm sad to see it go, I believe this move makes sense.  NCAR is a research lab, not an operational center.  They need to be unshackled from routine forecasting and free to explore creative ideas and pursue modeling breakthroughs.  The NCAR Ensemble did this for three years.  It has allowed us to learn a great deal about cloud-permitting ensembles.  For example, we have a paper examining the performance of the NCAR Ensemble that may be the subject of a future post.   

Given that tomorrow is Thanksgiving, it seems fitting to toast the NCAR Ensemble team that includes Kate Fossell, Glen Romine, Craig Schwartz, and Ryan Sobash.  Thanks so much! We look forward to a few more weeks of NCAR Ensemble forecasts, and hope that Mother Nature shifts this damn pattern so that we can actually use them for powder hunting in Utah!

Tuesday, November 21, 2017

Mini Snow Eater Conditions

It's not quite like an east-coast snow-eater event when temperature are near 50, fog, and rain, but for Utah, this is as close as it gets.

Current (7-8 AM) temperatures in the central Wasatch are 37 at Spruces, 39 at the base of Park City, 38 at the base of Alta, and 33 at Alta-Collins, and 31 at Germania Pass.  That puts the freezing level at about 10,000 feet. 

In addition, dense, mid-level overcast is draped over the mountains, with some west snow at upper elevations, rain at mid elevations, and the transition zone in between.  The Alta webcam below summarizes the dreary conditions quite well. 


For the most part, snow on north facing aspects will survive just fine this time of year under clear, dry conditions, even when temperatures are above 32ºF.  Without direct sunlight, you simply don't have enough energy to melt snow.

However, if you can add humidity and cloud cover to the mix, things change.  You lose the cooling effect of snow sublimation and gain the energy input of infrared radiation from the clouds. 

The eastern U.S. gets these conditions in spades at times, with fog and rain doing it's number on snow frequently during the cool season. 

We don't really get such a snow-eating extreme in Utah.  Today is about as close as it gets.  Above 9000 feet, everything will be fine.  Below 8000 feet, we're going to see snow losses.  In between there may be a net loss, but it probably not a huge one. 

Fall continues it's grip on the Wasatch, with no desire to let go and let winter take control....

Monday, November 20, 2017

Precipitation Overprediction Problems with the NAM Conus Nest

High resolution forecast models are not necessarily better forecast models and precipitation forecasts produced by the NAM Conus Nest (hereafter the NAM-3km) are a prime example of this. 

The NAM-3km covers the continental US at a grid spacing of 3 km, four times the resolution of the 12-km NAM in which it is nested.  With such high resolution, you would think the NAM-3km would be especially useful for precipitation forecasting over the complex terrain of the western US, but it isn't, because it has a major overprediction problem.

Tom Gowan, a graduate student in my research group, recently led a study examining the performance of several forecast models at mountain locations across the western U.S. during last winter.  I have been holding off on publicly sharing these results broadly since the paper describing this work is still in review, but the results are too pertinent to forecast needs right now not to share at this juncture.  In the case of the NAM-3km, we used pre-operational test runs from last winter that were kindly provided by NCEP.

The plot below shows the ratio of mean-daily precipitation produced by the NAM-3km to that observed at SNOTEL stations.  Overprediction is evident at the majority of sites, with on average the NAM-3km producing 1.3 times as much precipitation as observed.
Source: Gowan et al., in review.
A major reason for this is that the NAM-3km produces far more major precipitation events than observed, especially over the interior western US.  In the plot below, the frequency bias is the ratio of the number of forecast events to the number of observed events in each event size bin.  The NAM-3km has by far the largest overprediction problem.  Note that the NCAR ensemble also produces too many large events, although the magnitude of the problem is not as acute.  

Source: Gowan et al. in review.
I bring up these issues today because the NAM-3km is going batsh-t crazy for the storm later today and tonight.  For Alta-Collins, the 12-km NAM is producing .08" of precipitation through 10 AM tomorrow.  In contrast, the 3-km NAM is producing 2.04"! 

The loop below shows steady, drippy precipitation over the Wasatch and nearby ranges during the overnight period. 


Now, it is always dangerous to say a model is wrong before the forecast verifies, but I'm going to say it anyway.  This forecast is wrong.  There's little evidence to support such huge precipitation totals.  Even in the NCAR ensemble, 7 of the 10 members produce less than 0.2" of precipitation, and the wettest goes for about .57".  

This issue plagued the NAM Conus Nest when it was run at 4-km grid spacing and it appears to carry over to the higher resolution upgrade. 

The bottom line is this.  If you want great deep powder skiing, consider using the NAM-3km for your holodeck experience.  However, if you live in the real world, avoid using the NAM-3km precipitation forecasts unless you want to be severely disappointed on a regular basis.  

Sunday, November 19, 2017

Three Thoughts on This Sunday

1. Yes Virginia, there is skiing

I debated for a while whether or not to ski this weekend.  I'm not a fan of low snowpack, bony conditions and often stick to skiing the main run along Alta's Collins lift under such conditions.  With Alta closed to uphill, we opted to take a couple of laps at Brighton in the Great Western area since rumors were that they were asking tourers to avoid other parts of the mountain.  I pulled out my oldest sticks for the day, a pair of Karhu Jak BCs that are probably 10-12 years old.


However, I was pleasantly surprised to survive both runs without harming a single rock.  I was also glad to rediscover that the Jak BC really was a great ski, even if you didn't see them much in Utah. 

We stuck to grassy runs that were heavily traveled.  The touring and skimo crowd cut up the area pretty good. 


Some sections of untracked could be found in some areas and we went home satisfied, without injury, which is the main goal of any first day.  

2. The snowpack isn't really all that meager

It's worth remembering that it is only November 19.  Thanksgiving is pretty early this year.  Our snowpack seems pretty meager, but really it isn't.  The Snowbird SNOTEL is measuring 3.1 inches of snow water equivalent (SWE).  Median is 4.1 inches.  An inch of water equivalent is basically one modest storm.  So, we're one storm below median.  Yes, it hurts to look at the snowpack in the Tetons and Sawtooths (or should I say Sawteeth?), but we're not really doing all that bad.........yet.

3. The next week may suck

The model forecasts for Thanksgiving week don't look so great for Wasatch skiers.  The NAM forecast for 5 PM MST tomorrow (monday) shows a classic "dirty ridge" scenario with moisture spilling over a low-amplitude ridge and into Utah.  700-mb temperatures are a balmy 0ºC.  This is a recipe for riming and perhaps some wet, rimed snow at times in the mountains.  It probably won't add up to much for the snowpack and we'll probably see a net loss at elevations below 7000 feet (not that there's much there currently).


Eventually, a high amplitude ridge builds over for Thanksgiving Day.  Beautiful weather across Utah for driving over the river and through the woods to grandmother's house.  Good valley mountain biking.  Good canyoneering. 


However, 700-mb temperatures are a whopping +6ºC, which would be a record for the last week of November (although we have observed 700-mb temperatures of +8ºC in mid December).   Brighton was making snow today where they could, with the low-angle sun and dry conditions allowing for it in shady spots.  The resorts will probably need to continue to selectively pick spots and times over the next few days for making snow.  

Saturday, November 18, 2017

The Beauty of Antelope Island

Antelope Island has been very good to me the past two days.  On Friday, we had a great IOP basing near the Fielding Garr Ranch.  U grad student Trey Alvey took the shot below at the end of the IOP.  Talk about a great vantage point for orographic precipitation research.


Driving around the island in the rain yesterday morning reminded me that I needed to return, so we took a quick trip there this morning to survey the views and the bison.  The photo below is from Buffalo Point.  Hard to believe this is a short drive from metropolitan Utah.  There was an interesting cumulus streamer reminiscent of a banner cloud forming on the lee side of Farnsworth Peak (Oquirrh Mountains). 


One has to wonder what it was like for the pioneers to gaze upon this body of water after traveling for weeks across the plains and mountains. 


A highlight of the day was watching this beast lumbering through the grass.


Medium range forecasts suggest a below average snow week ahead with above average temperatures.  Not good for storm chasing or skiing.  Perhaps I'll return to Antelope Island with my bike over the holiday weekend. 

Friday, November 17, 2017

Update on Storm Chasing Efforts during IOP2

I like to joke that "storm chasing" Utah style involves sitting in one place and scanning storms repeatedly, which is exactly what we've been doing today for OREO IOP2.

After our overnight team returned to Salt Lake late last night, today's day team deployed to Antelope Island near the Fielding Garr Ranch.


Antelope Island is a great place to operate the DOW as there are unblocked vistas of much of the northern Wasatch and even the Salt Lake Valley.  It's a bit farther from the Cottonwoods than we like, but we can do a great deal looking at other parts of the Wasatch.

Much of the day we scanned a relatively broad frontal band.  Pretty boring by our standards, but it might still yield some interesting data.  However, during the afternoon, the flow shifted to WNW and the atmosphere destabilized, yielding some shallow convective showers. 


These showers produced a bit of graupel in downtown Salt Lake City and the Avenues (and perhapse elsewhere).


One thing we can do with the DOW is take vertical scans through storms.  The orange and yellow stuff at the bottom of the vertical scans below are ground clutter produced by mountains, but the purples are some of the convective showers, which you can see are shearing off downstream with height. 


Given a relatively pessimistic storm chasing forecast after Monday night, we'll probably work this shallow stuff to the last gasp.

Storm Chasing Update

Forget lectures and death by powerpoint.  This is what I call teaching.
Too busy to write much this morning.  We had a great night in Huntsville last night getting some very interesting data.  We are now redeploying the Doppler on Wheels to Antelope Island where we hope to get some data on today's precipitation. 

We got some great coverage last night from KUTV.  Check it out at http://kutv.com/news/local/doppler-on-wheels-helps-u-of-u-scientists-improve-weather-forecasting.

Thursday, November 16, 2017

DOW7 Deployed in Huntsville for IOP1

DOW7 is now deployed in Huntsville for OREO IOP1.

The weather is perfect right now.  Radar has shown a quasi-stationary precipitation cell immediately downstream over the Wasatch crest and over our area.  For a while, it was noticeably clearer west of the Wasatch from our vantage point.

This is just the sort of thing that we're looking for and trying to better understand. Very few studies have examined lee-side precipitation processes.

OREO IOP1 Is ON!

It's great to finally have some weather again in northern Utah.  I was woken last night by strong southerly winds, and they appear to have transported in a pretty good plume of dust this morning. 

We have a team leaving the University of Utah today at noon to begin operations for the Outreach and Radar Education in Orography (OREO) Intensive Observing Period 1 (IOP1).  Every meteorological field program needs a good acronym (hence OREO) and we usually name each observing period as an "IOP."  IOP0 is typically used for a practice IOP, which we did about 10 days ago on Antelope Island.  Since then we've been waiting on weather.

We plan to operate this evening and tonight from a site just east of Huntsville to examine the spillover of precipitation across the northern Wasatch and into the Ogden Valley.   Already, there's some interesting things happening there.  Radar imagery very clearly shows echoes developing not on the windward side of the Wasatch, but downstream.  Much of this is just sprinkles or virga, but it is a hint that perhaps there is some sort of lee wave present at the moment. 


The HRRR forecast for 1Z (6 PM MST) is optimistic, with band of precipitaiton extending across central Nevada to the northern Wasatch.  The location and movement of that area of precipitation will partly dictate the success or failure of our mission tonight.  We're hoping it is in the right place at the right time. 


Tomorrow, we may be working on post-frontal snowshowers in northwesterly flow.  We have a couple of sites selected to operate out of, but will make final decisions in the morning with updated forecasts in hand.

Keep your fingers crossed!

Wednesday, November 15, 2017

Core Dump on Our Pending Storm

The Doppler on Wheels (DOW) has been in town now for two weeks, and we've yet to have a significant storm during that period.  At Alta, the best we've done is 4 inches on November 4th, which isn't much of a storm.  We've kept ourselves busy with various educational and outreach activities, but are in desperate need of a storm.

Fortunately, it looks like Mother Nature will give us something tomorrow afternoon through Friday.  It's been an interesting storm to follow in the forecast models for a number of reasons.

1. It's taking forever to get here.

The GFS forecast initialized at 0000 UTC 12 November (5 PM MST Saturday) showed the upper-level trough making landfall onto the Pacific Northwest coast at 1800 UTC 16 November (11 AM MST Thursday), with precipitation across the Wasatch Mountains, Uintas, and even western Colorado.  Under this scenario, we'd want to be out storm chasing early tomorrow (Thursday).


During the past three days, however, the GFS has really slowed the progression of the trough.  The forecast from 0000 UTC 15 November (5 PM MST Tuesday) has the trough much farther west and well off the coast at 1800 UTC 16 November (11 AM MST Thursday).  Precipitation is just sneaking into the northern Wasatch and Bear River Range area, and there's no precipitation over Colorado.  Instead, we'll be able to sleep in tomorrow!


2. The Sierra Nevada really take a bite out of storms

Through flow blocking and water vapor depletion in mountain-induced rain and snowfall, the Sierra Nevada have a dramatic impact for the worse on moisture transport into the Great Basin.  This can be seen in the GFS forecast pannels immediately above.  Note in particular the how the column-integrated relative humidity in the lower left panel decreases abruptly across the southern "High" Sierra, with moisture only able to sneak in across the lower northern Sierra north of Lake Tahoe.  This effect is also apparent in theNAM forecast for the same time and, in this case, it is a contributor to the delay of precipitation spreading into northern Utah.  Without the High Sierra, moisture would penetrate more easily into the Great Basin and the Wasatch would light up even earlier.  Pity.


The time-height section from the NAM shows a classic "cloud-storm" environment tomorrow over the Salt Lake Valley.  Cloud storm is a phrase we jokingly call events with high clouds and virga, but little precipitation reaching the valley floor.  There's copious moisture at mid levels, but dry environment down low.  Deep moisture doesn't penetrate into the Salt Lake Valley until Friday night.  More evidence of further delays in the storm really getting going over the Salt Lake Valley.


Add all this up — the delay in the arrival of the trough, the drying influence of the High Sierra, and the dry low levels over northern Utah — and you have a recipe for restless natives anxious for the arrival of a storm that has been promised for Thursday.

3. Many storm chasing options

We of course have a mobile radar, so we can put it wherever we want and don't have to necessarily wait in the Salt Lake Valley for weather.  That being said, it takes time to move the DOW around and configure a reasonable scanning strategy to do real science.   We have a number of possible targets through Friday afternoon, including the spillover of precipitation across the northern Wasatch Mountains and into the Ogden Valley, multi-ridge interactions between the Stansbury and Oquirrh Mountains or Oquirrh and Wasatch Mountains, a cold frontal passage presently forecast for Friday morning, and post-frontal convection in northwesterly flow in the wake of the cold front.  It's going to be a busy time!  We'll have an interesting planning session this afternoon and then will need to keep a close eye on things in the field to maximize our opportunities.

4. Mountain snow possibilities

The situation this week has been pretty grim for skiers.  Not only has it been dry, but it has also been warm.  I don't follow the snowmaking activities at the resorts, but I suspect they were limited at best.  That situation will continue today and even tomorrow looks to be pretty warm.  In addition, the early phases of the storm when it does arrive look quite warm.  For example, the NAM forecast for 1200 UTC (5 AM MST) Friday morning has 700-mb temperatures of around -2ºC.  That equates to a snow level around 7000 feet or so.


Thus, while the upper elevations of Snowbasin are likely to get a pasting, the base may see rain for at least a portion of the storm.  PCMR may also see rain at the base during the early stages.

However, the snow level will be lowering during the period, especially on Friday.  Friday has some potential to be productive in the Cottonwoods due to cold, unstable, northwesterly flow.  Overall, the NAM-12km is generating about an inch of water and 9 inches of snow at Alta Collins through late Friday.  The numbers, however, vary widely across models and ensemble members.  At this point, I'd lean toward 6-12 inches at upper elevations in Little Cottonwood, with the potential for more if the post-frontal environment is highly productive.  Water totals in the northern Wasatch should be higher.

Snowmakers had better be ready to release the torrents Friday, Friday night, and Saturday morning.  After that, ridging returns and more marginal snowmaking conditions return for a couple of days.

Addendum at 10:15 AM 15 November

The SREF plume diagram below was unavailable when I wrote this post, but I've added it here and it shows remarkable spread for the event at Alta Collins.  Talk about forecaster heartburn!  Hope for the high members to verify.


Monday, November 13, 2017

Überströmungs Cyclogenesis!

A classic example of Alpine lee cyclogenesis of the "Überströmungs-type" is bringing heavy snowfall to portions of the Alps and southern Europe.

Alpine lee cyclogenesis is the birth of a cyclone in the lee (downstream side) of the Alps.  Überströmungs-type Alpine lee cyclones form in northwesterly large-scale flow as cold air is blocked and flows cyclonically to the west of the Alps, while the upper-level trough continues to move downstream, inciting cyclone development in the western Mediterranean region.  Terrain impacts are especially pronounced in cyclones that form in this fashion.

The satellite and sea level pressure loop below shows the situation from 1200 UTC 11 November through 1200 UTC 13 November.  The system begins as a surface trough that plunges southeastward across the British Isles, France, and Germany.  The cold air plunges southward through the low elevation region between the Alps and Pyrenees (note faint rope cloud in the loop), and strong cyclogenesis occurs over northern Italy.


@severe-weather.EU is the feed to monitor this morning as they are tweeting out some wonderful images from across the region.  Here are a few.

 Enjoy the look at the fresh snow.  Let's hope we can join the party later this week.

Sunday, November 12, 2017

Curb Your Enthusiasm

We've reached the time of year where every wiggle in the jet stream becomes enticing. 

Call it what you want.  The November doldrums.  Purgatory.  There's not enough snow to ski in the central Wasatch and we need more.

I'm already getting inquiries about the storm later this coming work work week.  My advice?  Curb your enthusiasm.

That advice is not because I think the storm will be a bust, but because we are still a few days out and the ensembles are showing a wide range of possible outcomes, from relatively light accumulations to up to 14 inches at Alta-Collins.  Typically, ensembles are underdispersive, meaning that range probably underestimates the full range of possible outcomes.  In other words, we don't really know much yet except that a trough will be coming through and we'll probably see some snow. 

What I do know is that today will be a lovely mid November Sunday.  Enjoy it. 

Friday, November 10, 2017

Veterans Day Reflections

Tomorrow (Saturday) is Veterans Day, but many will observe it today.  Two days instead of one seems appropriate. 

Given the emphasis of this blog on weather, we take a few moments today to reflect on the sacrifice made by Air Force Captain Nathan Nylander. 

Captain Nathan Nylander.  Source: http://www.airadvisormemorial.org/home/Nylander.html
Captain Nylander was a distinguished graduate of the Air Force Weather Observer and Weather Forecaster courses.  He was the 56th Operational Support Squadron Forecaster of the Year in 1999 and 2000.  In 2006, he graduated #1 in his class at Officer Training School.  He was a leader in meteorological services in the Air Force and a friend to Air Force officers who have come to the University of Utah to pursue graduate degrees in atmospheric sciences.

Captain Nylander was killed in Afhanistan on April 27, 2011, when an Afghan colonel opened fire at the Afghan Air Force Headquarters at Kabul International Airport.  During the attack, Captain Nylander evacuated the conference room he and others occupied, returned fire, and, began treating the wounded.  When the attacker began to fire again, Captain Nylander returned fire again, but was ultimately killed.

Captain Nylander received the Silver Star, the third highest honor for combat valor, on September 24, 2011.

On this Veterans Day, take a few moments to learn more about Captain Nylander in this article from the Air Force Air Combat Command web site and this Air Advisor Memorial

Photos from Campus Dow Exhibit

Thursday provided perfect weather for showing off the DOW on the University of Utah campus.  Thanks for coming!









Wednesday, November 8, 2017

Campus DOW Exhibit

We will be exhibiting the Doppler on Wheels on the sidewalk east of the William Browning Building on Thursday, Nov 9, from 11–3.  That's tomorrow as I write this on Wednesday afternoon.  Stop by and have a look.

Here's a preview, although we will have the video monitors loaded with radar animations of data collected from the landfall of Hurricane Harvey, tornadoes in Kansas and Wyoming, and lake-effect storms on Lake Ontario.

November Doldrums

One of the great things about the central Wasatch is that they get snow from a great variety of patterns.  Unfortunately, the pattern we'll be in for the next week (and maybe longer) isn't one of them. 

For the next week, the northwest US will be active, but we're just to the south of the strong flow and moisture for much of the period.  Thus, we may get some brush by clouds and snow showers, but that's about it. The GFS forecast below shows the action in the northwest, but not a hint of precipitation over all but the far north of Utah. 


Is there hope in the ensembles?  Not really.  Most members generate an inch or less of snow for Alta-Collins.  A few go for more than that.  If a trough zipping through the jet can strengthen some, maybe that wetter member can verify, but I'm not optimistic. 

The November doldrums are here.  A good period perhaps to go to southern Utah for late fall adventuring, or the Tetons, where the snowpack looks pretty good for November.  Twelve inches of snowpack water equivalent at the Grand Targhee SNOTEL is more than double the median for this time of year. 

Tuesday, November 7, 2017

Under the Hood of Numerical Weather Prediction Models


Numerical Weather Prediction models, or computer models for short, form the backbone of modern weather forecasting.  They assimilate a diverse mix of observations collected all around the globe by satellites, weather stations, aircraft, radars, and other instruments, form a coherent analysis of the atmosphere, and integrate forward to produce a forecast. 

How the hell do they do it?  We'll focus here on two aspects of computer modeling, discretization and parameterization

Discretization

Today's computer models begin with a set of partial differential equations, known as the primitive equations, that describe fluid motion and are based on conservation of mass, conservation of momentum, conservation of energy and the ideal gas law. The primitive equations can be used to describe the flow and behavior of fluids in a variety of contexts, including ocean circulations.

Unfortunately, computers can't solve these types of equations directly.  The primitive equations must be converted into algebraic equations to be solved on a computer.  There are a variety of steps and techniques for doing this, which is known as discretization. 

Discretization requires approximations and compromises.  One aspect of the discretization process that most weather hobbyists are aware of is resolution.  For grid cell models, this is commonly expressed as a distance.  For example, the NAM has a horizontal grid spacing of about 12-km.  Often, these grid cells are conceptualized as rectangles, but other shapes can be used.  For example, the Model for Prediction Across Scales (MPAS), being developed by the National Center for Atmospheric Research uses hexagons, with the occasional pentagon or septagon, to cover the sphere. 

Source: https://mpas-dev.github.io/
Not all models are based on this grid cell concept.  For example, the GFS is a spectral model which, instead of using grid cells, represents the atmosphere as a combination of waves with differing wavelengths.  

The National Weather Service is currently developing a new modeling system that will replace the GFS, known as the FV3.  It is based on a third approach, known as finite volume (the "FV" in FV3).  More info at https://www.gfdl.noaa.gov/fv3/.

Parameterization

The primitive equations describe fluid motion, but a computer model also needs what meteorologists call "physics" — for example, radiation, clouds, precipitation, and interactions with the land surface.  This is really where the rubber hits the road, as in general we can't simulate these things directly.  For example, we can't simulate the evolution of every cloud drop in a cloud.  There's simply too many of them.  As a result, we need to take shortcuts and make simplifications, known as parameterizations. 

In the case of the cloud, since we can't simulate every cloud drop, we might instead simulate how much total cloud water is in each grid box, and then specify how that water is spread across small, medium, and large droplets.  Similar shortcuts are made in how we deal with other physical processes. 

In some cases, we have a good understanding of the physical processes and the parameterizations, while a shortcut, are quite accurate.  In others, understanding is weaker (in some cases much weaker), and we are using educated guesses and tuning to get something that looks reasonable. 

All Models Are Wrong, But Some Are Useful

That famous George Box quote is a good one to keep in mind when using numerical weather prediction models.  Really, modern day numerical weather prediction is a remarkable scientific achievement, and the forecasts are getting better every day.   There's every reason to expect them to improve in the future, as knowledge and techniques advance, provided we continue to invest in our global and regional observing systems.  A perfect model will give you a lousy forecast if it doesn't start with a good analysis of the atmosphere, as well as land, sea, ice, and lake conditions.  But that's a subject for another post.  

Monday, November 6, 2017

Dancing with the DOW

We had a great weekend with DOW7.  On Saturday, we spent the day at the Natural History Museum of Utah giving DOW tours and doing some fun weather related activities.





Sunday we did a shake-down deployment to Antelope Island, with some scans into the northern Wasatch. 



Today we're doing some work with classes on campus.  It's a good day for it. with some light precipitation around. 

Friday, November 3, 2017

No Skiing This Weekend

Between now and late Monday, we are in this sort of bits and pieces pattern, one in which there is strong southwesterly to westerly flow at crest level, but the main moisture plume is to our north.  The Tetons are in the cross hairs and we're on the fringe. 

As a result, we will see some periods of snow and snow showers at upper elevations through Monday afternoon.  These snow and snow showers will add up some, with the average water equivalent produced at Alta-Collins by our downscaled SREF product reaching just over 1.5 inches by Monday afternoon (07/00Z). 

Most members are between about 0.5 and 2.0 inches of water, which would probably be anywhere from 5 to 20 inches of snow at these temperatures.  There's an outside chance that we'd do better if the orographics kick in or the plume drifts a bit further south than currently predicted, but my view is that there won't be any skiing this weekend. 

It's worth taking a look at the broader regional picture.  Note in particular that the highest water equivalents forecast by our downscaled SREF product through Friday afternoon are found in the mountains of eastern Idaho and western Montana, including the Tetons and Wind Rivers. 

The plume diagram for Rendezvous Bowl at Jackson Hole Mountain Resort is tightly clustered, with a range of accumulations of about 1.5 to 3 inches from midnight last night through the forecast period.  Much of this precipitation falls by late tomorrow afternoon.   
A break is likely after Monday.  There are hints of the potential for more action later next week, but it's too far out to waste energy on at this time.