Groundhog Day Seasonal Climate Musings

Today is that day when a bunch of old men in western Pennsylvania dress in weird costumes, pull a rodent out of a hole, and claim to forecast the weather for the upcoming spring.  Animal lovers may mildly object to the torturing of the poor groundhog, but meteorologists are horrified!

There will be no discussion of whether or not the groundhog sees his/her shadow and what that means for spring here.  Instead, we'll deal with evidence, knowledge, and predictability.  After that, then we'll guess.

Let's begin with a summary of the winter so far.  As most of you are aware, one of the strongest El Nino's on record was predicted to occur this winter and has materialized.  Outlooks issued in October showed better than climatological odds of below average precipitation during November-to-January in the Pacific Northwest and better than climatological odds of above average precipitation in the southwest.

Source: CPC

As far as mountain snowpack is concerned, the weighted dice have come through to some degree.  Most basins in the southwest are running near or above average (not sampled by SNOTEL is the southern Sierras, but they are at 107% of average) and the interior northwest is below average.  Northern Utah and the Wasatch are near average.

Source: NRCS

If you want to quibble, it would be in the Pacific Northwest, which is at average in most basins, and in the western Great Basin, which sits well above average.  It is worth remembering, however, that the outlooks above are probabilistic and areas in brown and green don't mean that above and below average are guaranteed.  They simply indicate where the dice are loaded.  For  climate projection, I rate the outlooks above as good, at least in terms of capturing the overall pattern, but not outstanding, especially when getting down to the basin scale.

Snowpack in the Wasatch sits about as close to median (the point where half the winters have more water equivalent and half have less) as you can get.

Source: NRCS

Here are a few numbers to back that up in terms of the percent of median on 1 February: Timp Divide 106%, Snowbird 107%, Brighton 107%, Thaynes Canyon 104%, Mill-D North 101%, Lookout Peak 111%, Parrish Creek 86% (an anomaly), Farmington 102%, Ben Lomond 94%.  In case you like average instead, at most sites, we sit at or just below average.  For example, Snowbird is 92% of average and Brighton 102%.

Bottom line: We're pretty much right in the middle of the climatological snowpack distribution. Some have called this an above-average ski season, but I think that perspective is strongly weighted by how crappy the past couple of years (especially last year) have been.  This year, we got off to a slow start and have been dealing with a tricky backcountry snowpack.  On the other hand, we've had a steady progression of storms since mid December, giving us regular refills and I've had a number of good powder days.  Overall, I rate the season as good, but not excellent.  

How about the rest of winter?  Well, the strong El Nino is expected to weaken by late spring or early summer, although there is some uncertainty in exactly when it will wane.  It appears, however, that El Nino conditions will hold through April, even if they might be weaker than the wintertime peak.  Based largely on correlations with past El Nino events and climate model forecasts for the late winter and early spring, the climate prediction center is going for a loading of the dice for above average precipitation in the southwest and below average in the northwest, although the transition zone is shifted a bit northward.  

Source: CPC

So, if you want to be an optimist, hang your hat on that very slight loading of the dice.

There is, however, a serious concern for us in the short term.  The models are calling for a major pattern shift to develop over the next several days, with persistent ridging developing over the western United States.  For example, the GFS has a monster ridge over the west at 150 hours.  

The Euro is similarly ridgy.  No need to panic yet, as much may depend on the position and strength of the ridge, but I'm a bit concerned about the pattern change that is presently being advertised.  Fortunately, we have a storm coming in for Thursday, before the ridge builds in earnest.