Expect "Tough Sledding" Tomorrow

I've been out skiing and lack the time to put together a proper forecast for tomorrow.   Below is the winter storm watch issued early this morning by the National Weather Service.  This is going to be a statewide storm with significant travel impacts.  Plan on a rough commute in the morning, and hope for the best.

The NWS forecast for the mountains looks pretty good as well.  This will probably be the biggest storm of the season so far (although that's a fairly low bar, with water totals somewhere in the 1-2 inch range by 5 PM Tuesday.

Enjoy the storm and be careful out there.

The Paris Agreement

"New agreement is just words.  We're still on a business-as-usual course."

- Jim Hansen

Today representatives of 195 nations approved an agreement that commits every country to reduce greenhouse gas emissions.  The full document, available here, recognizes that climate change "represents and urgent and potentially irreversible threat to human societies" and that "deep reductions in global [greenhouse gas] emissions will be required."  The agreement seeks to hold the global average temperature "to well below 2ºC above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5ºC above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change."  

In case you are wondering we are currently about 0.8ºC above pre-industrial levels [2015 is a full 1ºC above pre-industrial levels, although that's partly due to the intense El Nino], with additional warming already in the pipeline as the climate system has not yet fully adjusted to the rapid increase in greenhouse gas concentrations over the past few decades.  

I've been asked a few times about my views on the Paris Agreement (and before this month, many times about Kyoto before it).  I'm pretty much a political cynic and so my perspectives are similar to Jim Hansen's above.  I am concerned about global warming, which reflects my scientific understanding but also personal values, and thus am glad to see the agreement recognize the pressing need to address greenhouse gas emissions.  My political cynicism is such that I ultimately see agreements like this as something only diplomats could love.  When the rubber hits the road tomorrow, we're still part of a global society in which the long-term greenhouse gas emissions trend is upward.  There's some indication that global greenhouse gas emissions in 2015 will decline slightly from 2014, but we have to reduce global greenhouse gas emissions by about 40% just to get back to 1990 levels.   

Source: Global Carbon Project

At the same time, we need to nearly quadruple our global energy production to bring the developing world up to a reasonable standard of living.  

It has been said that a journey of 1000 miles begins with a single step, and an optimistic view of the Paris Agreement is that it makes the first step on that journey.  However, we shouldn't lose sight of what ultimately needs to be done.  Incremental improvements in efficiency and lifestyle changes such as riding bikes and driving hybrid cars are necessary are good, but they are not sufficient to meet the long term need for carbon neutrality.  As Richard Smalley, the 1996 Nobel Laureate in Chemistry once wrote, we ultimately need "cheap, clean energy in vast amounts."  In other words, innovation is needed to make a quantum leap in how we produce, distribute, and store energy.  

That innovation needs to be priority one today (and unfortunately should have been a priority many years ago).  

A Real Winter Storm May Finally Be Coming

Note: The title of this post has been updated to fix a horrific grammatical gaffe!

Things played out last night pretty much as anticipated for the past few days with a decent round of frontal precipitation, but not much thereafter.  The upper Cottonwoods did the best with 4–7 inches.  I score this EC 1 GFS 0.

The possibility of snow showers at times will persist through the weekend, but accumulations in the mountains will be minimal.  The GFS was advertising a possible snow event for Sunday, but not surprisingly, it has now shifted to the drier EC solution.  It's too soon to say EC 2 GFS 0, but that's looking likely.

I am, however, getting enthused about what I am seeing for Sunday night and Monday, and this is probably the first time this season that I've said anything remotely like that.  The GFS is advertising a strong cold frontal passage Sunday night with a pretty good push of cold, moist, northwesterly flow in its wake.

Unlike previous storms, this one is taking a more northerly track at a lead time of only 60-72 hours, and, more importantly, the EC is actually calling for a similar track and frontal passage.  In difficult times, it's good to have the support of our European allies.

In addition, the downscaled NEAFS members are in fairly good agreement that this will be a more significant event than we've seen of late, and they uniformly generate a bit more than an inch of water (some more) from late Sunday through Monday.

Finally, this will be a colder storm, so for northern Utah, it looks like it will affect all altitudes, including the valley, making it a "real" winter storm.  Snow to the valley floor?  Yes Virginia there is a Santa Claus! (No guarantees yet, however, for a white Christmas).

It's a quick moving system and too early to put numbers on it, and I still worry about the system going south (literally and figuratively), but it's looking fairly likely that we'll have at least some snow at all elevations, with a decent chance that the mountains may do a bit better than they have done in storms the past couple of weeks, especially if we can get something going behind the front.  Keep your fingers crossed.

Satellite vs. Thermometer Temperature Trends

Source: Forbes

Many of you have asked or commented about difference in the temperature trends from satellites or surface-based thermometers, as well as the adjustments that are made to these records.

Marshall Shepherd has an outstanding piece in Forbes today fully summarizing the issues at play.  Marshall is the Director of the Atmospheric Sciences Program at the University of Georgia, host of the Weather Channel show Weather Geeks, and a NASA scientist.  He was also the 2013 President of the American Meteorological Society.  He's an outstanding scientist and an outstanding scientific communicator.

It's clear that Marshall put a great deal of thought went into explaining the strengths and weaknesses of the two approaches.  Note that he emphasizes the importance of looking at the climate system holistically, including the use of oceanic heat content, rather than just surface temperatures.  This is something that we have discussed in previous posts (see Global Warming Hasn't Stopped).  We are seeing unequivocal warming of the climate system.  Arguments that global warming has stopped simply have no basis.

Not Much Change in the Weather or Seasonal Forecasts

There's not much change in the weather forecast from yesterday.  A cold front will move across northern Utah late today and early this evening, ushering in a period of mountain snow.  Snow on the benches may begin as rain and turn to snow, with the transition happening a bit later on the valley floor.  I'm sticking with 4-8 inches for Alta-Collins.  Although mountain snowshowers are possible at times in the wake of the system through Saturday, as things look now, I'm not expecting any major accumulations in that period.  The US models are advertising mountain snow for Sunday associated with a warm-frontal passage, but the EC is a bit less enthusiastic.  Both models are encouraging for the cold-frontal passage on Sunday night.  Keep your expectations low and your hopes high.

In other news, the Climate Prediction Center (CPC) issued their monthly El Nino/Southern Oscillation (ENSO) Diagnostic discussion and not surprisingly, El Nino remains quite strong.  Sea-surface temperature anomalies exceeding 3ºC extend from South America to 160ºW

Strong El Nino conditions are expected to persist through winter, with CPC forecasters expecting it to rank as a top-3 event since 1950.  

We currently sit at 50–60% of average snowpack at upper elevations in the central Wasatch.  The snowpack water equivalent at Snowbird sits at 4.3", compared to an average of about 8.5".  A slow start to the ski season is deeply disturbing, but no cause for panic.  A lack of correlation between El Nino and northern Utah snow is such that we can still end up pretty much anywhere from below to above average by the end of the season in the central Wasatch.  

There is, however, one thing we can guarantee for your backcountry skiing adventures — a persistent weak layer thanks to our current rotten snowpack.  Unfortunately, this weak layer is likely to linger for some time in many areas.  We're all desperate for the steep and deep, but throttling back will be a necessity in many areas as we add weight to this house of cards.  

Looking to the Late Thursday Fropa

Although there is quite a bit of spread amongst the various models concerning precipitation, they are in good agreement that we will see a frontal passage late Thursday.  The image below is the 1200 UTC GFS forecast valid for 5 PM MST tomorrow (Thursday) showing the front entering the Salt Lake Valley at that time.  The timing is a bit earlier in the 1200 UTC NAM and the 0000 UTC EC.

Those of you still walking around in shorts on campus might want to think about wearing pants if you will be heading home late in the afternoon as it will probably be blustery in the post-frontal environment, although it's tough to say of snow levels will immediately drop to bench levels right after the frontal passage or if that will take a couple of hours longer.

I'm seeing some odd precipitation numbers being generated by the various models for the frontal passage.  From 5 PM Thursday to 5 AM Friday, the 12-km NAM calls for .85" of water and about 13" of snow for Alta-Collins.  In contrast, the high-res 4-km NAM calls for only .43" of water and about 6" of snow and the GFS is in with about .42" of of water and about 8" of snow.  It's quite unusual to see the 12-km NAM producing more than the 4-km NAM or even the GFS, which tend to forecast big amounts on a regular basis.  It seems that the model precipitation forecasts are now so out of whack that it's impossible to get a decent calibration going.

Given that frontal precipitation periods tend to feature less orographic enhancement, I'm leaning toward 4-8" for Alta-Collins the Thursday night period ending around 5 am.

As I look at the medium range out to 10 days, I think things look better than they have been the past couple of weeks, and certainly active enough to keep the inversion at bay, but differences between the NAEFS and EC ensemble members are such that I'm not sticking my neck out with any bold forecasts yet. Keep your fingers crossed.