Tuesday, December 8, 2015

Important Differences Between the EC and the GFS

In yesterday's post, I asked the question, "should we buy in to the latests forecasts?" Motivating that question was the very optimistic forecasts for snow being produced by the GFS and the NAEFS, as well as the less optimistic forecasts being produced by the ECMWF Integrated Forecast System (a.k.a., the ECMWF, EC, or Euro model and ensemble).

Given the restricted nature of data provided by the ECMWF, I've struggled with how to show these differences, but someone pointed out to me that San Jose State University has a comparison between the EC and the GFS on their web site.  I love it when my job gets easier.

So, here's the basic issue.  Yesterday mornings 1200 UTC GFS (green 500-mb height contours below) produced a much weaker and progressive trough than the EC (red contours) for later this week and weekend.  These result in dramatically different forecasts for precipitation in the central Wasatch, with the former being wetter and more favorable for orographic precipitation enhancement following the anticipated late Thursday/Thursday night frontal passage, and the latter much drier.

Ensembles smooth these differences out a bit, but the GEFS and EC Ensembles generally show similar differences.

Last nights 0Z runs show that the GFS has shifted a bit toward the EC solution, but the trough remains weaker.  Note that the forecast below is for 12-hours earlier than the one above since forecasts are available only every 24 hours.

San Jose State hasn't processed up the 12Z EC yet, but I've looked at it elsewhere and it shows a pretty similar solution to the previous forecasts with precipitation accompanying the front and then not much thereafter.

Bottomline: It looks like we'll get something with the frontal passage, but a major post-frontal snow event, as has been advertised by the GFS, remains somewhat suspect for Friday and Saturday.  I lean toward the EC solution because it has long been the better performing model and the trough evolution it is predicting is consistent with the parade of troughs that have moved through western North America over the past 6 weeks or so.

It will be interesting to see how this all plays out, but I'm betting on a final score that is EC 1 GFS 0, although I would be happy to lose (i.e., big snows Friday and Saturday) or take a tie (i.e., we get some but not a lot of post-frontal snow on Friday and Saturday).

12 comments:

  1. First off. Great blog. Great book. Great comments. Love the site. Thanks for your time and effort!

    This is a bit of a side question. I just moved to the PC area 6 months ago and will be traveling east (mainly I-70/80) often through the year. Does anyone know of a good tool for looking at travel weather? I usually use Wunderground and piece together various forecasts but didn't know if anyone had a better idea.

    Thanks!
    Brad

    ReplyDelete
    Replies
    1. There's got to be something, but it's not something I've looked into before.

      Jim

      Delete
    2. This page might be helpful for road conditions: http://www.fhwa.dot.gov/trafficinfo/index.htm

      Delete
  2. So looking at Alta's historical season snowfall for the last 5 years as of 12/7 this is where we stack up:

    http://www.alta.com/conditions/weather-observations/snowfall-history

    2015-16: 55"
    2014-15: 68"
    2013-14: 101"
    2012-13: 90"
    2011-12: 79"
    2010-11: 142"

    Is it still too early to draw any conclusions and panic, or should we be concerned?

    ReplyDelete
    Replies
    1. Never panic, just pick the right snow god & hope for the best.. today mine is Kun Aymara. Khione did not produce last week so I stopped offering sacrifices to her.

      Long ranges have been fairly correct so far, lighter start, with later season projected to be good. We'll see...

      Delete
  3. One question that I have about the models.... are the GFS and the EC using essentially the exact same set of initialization data? I am wondering if most of the differences are due to initialization differences, or due to the model characteristics (such as resolution, etc).

    ReplyDelete
    Replies
    1. I don't know if the data is the same, but data assimilation today, even if the data and techniques were exactly the same, is still dependent on the quality of the underlying model. Thus, these things are fully intertwined.

      That being said, the last I checked the ECMWF was using four-dimensional variational assimilation that I believe is more advanced than the Gridpoint Statistical Interpolation technique currently used in the GFS, although the latter could eventually be adapted into a four-dimensional variational assimilation.

      I'm speaking well outside my area of expertise, but the bottom line is that the assimilation techniques and the model used by the ECMWF is probably still ahead of the GFS.

      Delete
  4. Really appreciate the great info on this site. I've got a group flying into SLC with plans to ski/stay at Alta this Thursday through mid-afternoon Monday. Are you willing to go out on a limb and provide your best guess for snow totals at Alta for the Thursday/Friday storm? Same question for the Sunday/Monday storm? Do you think there will be enough snow from these two storms to get some of the better expert terrain open/skiable while we are there? Yes, I know, hoping for a miracle! Thanks.

    ReplyDelete
    Replies
    1. Sorry, but I don't do tailored forecasts.

      Delete
  5. Anonymous - I'm no expert on the weather, but I know a thing or two about Alta opening terrain. With 8" for Thursday/Friday and another 8" for Sunday/Monday, I would say Alta will probably not be in a position to open much that isn't already open, especially not before Tuesday or so. Low traverse will be somewhat improved, ballroom might open (if it hasn't already). But we need something substantial to open the high T. It's grim up there.

    ReplyDelete
  6. Hi Jim, thanks for this, I follow the predicted vs. reality fairly closely, and as you say, most of our models have been pretty far off this year. Do you know of a website that has local plume charts or other tools like you do at USU for the ECMWF? The San Jose and ECMWF.int sites don't provide the smaller scale I'd like. I'm not good enough to forecast a pressure trough moving across the whole US at once.

    You are probably right, but as you say, let's hope you are wrong for this weekend! Thanks for all the good work!

    ReplyDelete
    Replies
    1. The ECMWF does not provide their model output freely like the National Weather Service/NCEP. It's quite pricey. You can purchase a subscription to an ECMWF provider (typically graphics) to look at better plots (much better than available from ECMWF.int). Look around and try some out.

      Delete