Separating Fact from Fantasy

Tuesday, January 21, 2014 at 7:18 am


Inversion conditions persist in Utah with dominant high pressure overhead.  A weak system on Thursday will bring a few clouds and breezes with cooler temps in the high elevations.  High pressure returns this weekend.  Pattern change possible around the end of January.


Short term and mid-range details are rather boring.  High pressure will dominate the area with more of the same.  A weak system is riding down the Rockies on Thursday but it has so little moisture with it that I suspect all we’ll see is some clouds and some cooling.  Can’t rule out a stray high elevation snow shower…

High pressure returns for the weekend and through the first part of next week.

Long range:

Unfortunately, the long range (7+ days out) is where all the action is still.  GFS and EC both still in agreement that we’ll have a pattern change at the end of the month.   Right now our first chance for a system is probably the 30th or 31st.  The first system to break through a ridge is almost always torn apart and this is a particularly strong ridge, so my feeling is the first system will be rather weak.  Hopefully it will pave the way however for stronger storms as we head into the first week of February.

Yesterday we had several comments from people who are freaking out about the latest runs of the GFS.   I’m glad that you are looking at the model runs, as it can be a lot of fun (for weather nerds like myself) to track, however, there are a few things you should take into account.  First, the GFS is not a high-performing model relative to the EC.  It struggles mightily beyond 7 days — so while I may take note of what the GFS is doing, I put most of my faith into the Euro.   Second, the precipitation parameter is garbage in the long range.  To begin with, it is one of the lowest resolution models even within 7 days and does a poor job for picking up Wasatch topographic influences.  I get the feeling a lot of people just use the precip param and get concerned when they don’t see a lot of “green” over Utah.  My suggestion is to look at GEFS ensemble heights if you are looking beyond 7 days.  That will give you a better feel for the overall pattern.   Third, don’t get too excited.  Model runs change. That’s what they do.  If you get too happy with one good run, you’ll get depressed with the next run.  It’ll drive you crazy — trust me, I know from experience.  So look at the models, but try to take in the big picture and trends rather that one run of one model… and don’t trust the GFS operational run beyond 7 days….  😉

Ok, with that said, here is what is actually going on.  The pattern looks like it will change.  That does NOT mean we are guaranteed big storms… but it does mean that the door will open for that to potentially occur.  Here is a GFS ensemble average of height anomalies for the upcoming period.  First, here is today:


This is the entire northern hemisphere.  Notice the anomalously high heights over the western US and Canada and the very low heights in the East, which is responsible for another cold outbreak for them.

Now, here is the same image for Feb 1.



Big change!  Heights are actually below average in the West now.

Finally, February 6:


Images courtesy of

The West Coast trough becomes even more pronounced.

Again, we are too far out to forecast big storms quite yet, but it does seem likely that the overall pattern will be changing.  Hopefully that will lead to storminess but there are no guarantees.  At this point, any change is good change in my book.

Keep the snow dances going and wash them cars!


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  • Steve

    Great discussion. What is the difference between the individual runs of the GFS and the ensemble mean? Slightly confusing to non- meterologists.

    • They are very similar… Operational run is higher resolution and puts more weight on specific ensembles, but generally is an average of ensembles made a higher resolution. Ensemble mean is a pure mean of the lower resolution ensembles. Therefore you’re less likely to see phantom storms in the ensemble mean but the operational run is far better in the short term due to its higher resolution. This might sound like a cloudy description because it is. I don’t think I have a full understanding of the exact differences. I like to use the ensemble mean more in the long range because it focuses on the broad picture rather than specific shortwaves.

      A control run is one specific ensemble that weights all factors equally so it usually looks more like the operational but is a lower resolution. Usually a “middle of the road” ensemble… I don’t use control runs too much in the GFS because their operational runs and GEFS ensemble mean runs extend 16 days. The EC deterministic (operational) only goes out 10 days, so I use the control run and ensemble means more frequently in the EC because they extend out 15 days.

      I hope that all made sense…. haha

  • Will it ever snow againt in Tahoe?

    I must be either looking at the wrong stuff or not understanding what I am seeing. When I look at the GFS relative vorticity, it shows what looks like a ridge of high pressure building after the first part of February. It looks like this ridge pushes the storms over California before dumping them into the Midwest (which is similar to the type of pattern we’ve had for the last 6 weeks). The precipitation forecast (which I hope is as worthless as you suggest), shows only a trace of snow for Utah between Jan. 30 and Feb. 6. Why is there such a disconnect between the precipitation forecast (i.e., no significant snow for Tahoe/Utah for the foreseeable future), and the big trough projected on the ensemble mean during the same time period?

    • No, you are right. And you were right yesterday too. Operational GFS sends one weak system through around the 31st then builds a ridge along the coast again. In fact every model does that… The difference is that the GFS ensemble mean, EC, EC control run, and GEM all have this ridging as “shortwave ridging”, meaning that it is just temporary ridging before the next trough moves in during the first week of February. The Operational GFS keeps the ridge in place and keeps the large trough lurking in the east pacific through the end of its run. Right now the GFS is the outlier. My main point is that the GFS operational is one small piece of the pie… and a not very reliable one at that. So don’t get too upset that its struggling to bring the next trough ashore. Latest EC is just in and continues to bring that second trough into the west.

      You can compare like-for-like model heights here:

      • Will it ever snow againt in Tahoe?

        Thank you for the link and the explanation. Keeping my fingers crossed…

  • Steve

    Evan, thanks a bunch. Really feel like i’m learning something here. I was also looking at the GFS operational runs with probably a greater percentage of concern than they warrant. I get what you’re saying. That they are 1 small piece of the whole and you have to weight the precip forecast out past 7 days with a grain of salt. Thanks again.

  • Want to talk fantasies? The latest CFSv2 is a fantasy.. not even going to mention it because it is so inconceivable at this point.

  • jughead

    It looks like there is a very strong low pressure system in the northeast pacific corridor moving due east. Do you think this system may have any luck in breaking down the ridge, at least somewhat?

  • Geoff

    The suspense is killing me. I’m coming to Utah on Feb 7 for two weeks, and hoping for some powder. My friends are at Niseko in Japan right now, where it has been snowing almost every day for the last few weeks. Fingers crossed the Wasatch range gets similar weather by then.

  • chandler

    Well now you have to tell us what the CFSv2 is!

    • Will it ever snow againt in Tahoe?

      I’m a complete novice at reading these charts, but the CFSv2 suggests (to my untrained eye), that LOTS of snow is on the way.

      • Bingo… it shows more and more snow through the third week of February. You know those ads that say you can make $7,000/mo working part time from home…? I trust those more than I trust the CFSv2…still fun to look at.

  • Jake

    How do you look at the CFSv2?

  • Sleepless in ‘stralia

    Getting nervous about the next post…..

  • Spank Tickleman

    I love how your own singular amateur hobby seems to be sparking the same desire in people nationwide and of all different backgrounds to take up amateur meteorology… It’s cool to see people take such interest in something the “common man” wouldn’t give a second thought to… You rock, Evan. Thanks for the devotion to this pursuit…

  • Eric Lewis

    I am willing to rename my first born “CFSv2” if that helps bring it about! But at this point you might as well tell us what it indicates, and what, if any credence we could/should put in it.

    • Yesterday’s CFS showed 200% of normal precip for the area during the month of February. I don’t put any trust in this at all.

  • Eric Lewis

    CFS= Completely Full of Sh** (I hope not!)