Winter 2010/11 Keeps on Giving

The incredible winter of 2010/11 gave so much to Utah skiers and just keeps on giving.

In addition to an estimated 800+ inch snow year at Alta, the runoff from our unbelievable snowpack has helped "restore" the Great Salt Lake and Sevier Lake.

From it's minimum elevation of about 4193.5 feet last November, the Great Salt Lake at Saltair Boat Harbor rose an incredible 5 feet to a maximum elevation of 4198.5 feet in July.

Source: USGS

The view this weekend toward Antelope Island from the Bonneville Shoreline Trail near North Salt Lake showed that Farmington Bay is actually covered with a thin lens of water!

Looking northwest toward Antelope Island and Farmington Bay
from the Bonneville Shoreline Trail

A larger lake does not necessarily mean we'll see more lake-effect this year, since that also depends on the weather that we get, but it won't hurt.

Further to the south, a thin lens of water has also collected in the Sevier Lake Bed.

The Sevier Lake Bed appears to be an important emission source for dust in northern Utah.  For example, check out this satellite image in which dust is identified as pink.

Source: NRL

Many of these dust plumes impact the Wasatch Mountains and contribute to the snirt (snow+dirt) that detracts from our spring skiing experiences.  Maybe this year, the Sevier won't be as active, which may help reduce how much dust loading we see in the snowpack in the spring.

Hurricane Katia Impacts on Sporting Events

Continuing our discussions on the impacts of Hurricane Katia, we discussed about a week ago that it might be a boon for the Association of Surfing Professionals (ASP) Quicksilver Pro surfing competition in Long Beach, New York.

Indeed that turned out to be the case as Katia brought the goods and made for a great competition.  Have a look below and check out the ESPN report.


Following extratropical transition, Katia moved across the North Atlantic and is pounding the British Isles today.

It was so windy that they cancelled the 2nd stage of the Tour of Britain.  After winning stage 1, Mark Cavendish will need to wait another day for another stage victory.

Tour of Britain

Did Katia Go Off?

A few days ago we discussed the anticipated extratropical transition of Hurricane Katia and how the GFS was predicting the central pressure to drop to a remarkable 928 mb over the North Atlantic.

0600 UTC 6 Sep initialized GFS forecast valid 1800 UTC 11 Sep.

We also noted that the GFS was a bit of an outlier amongst all the members of the Global Ensemble Forecast System (GFS), all of which predicted a major cyclone over the North Atlantic, but of varying intensities.

Selected isobars from members of the GEFS ensemble with the GFS wind
speed color filed. 

Well, what happened?  As shown in surface analyses from the Ocean Prediction Center, Katia indeed underwent extratropical transition as it recurved and began to move eastward across the North Atlantic.

Source: NOAA/NWS/OPC

Although the resulting extratropical cyclone broadened in scale, it did not deepen as it continued to move eastward and actually filled somewhat to ~967 mb this morning.  

Source: NOAA/NWS/OPC

We don't have the analysis yet for 1800 UTC, but based on the analysis above for 1200 UTC, the GFS will probably by about 40 mb off on this one!

One could beat up the GFS over such a large error, but let's give this some thought.  It did correctly forecast that Katia would undergo extratropical transition, eventually leading to a powerful cyclone in the North Atlantic.  The timing and position were also quite good, especially when you consider that this was a forecast with a 5.5 day lead time.

Instead, the issue here may not be a problem with the GFS, but the nonlinear, chaotic nature of the atmosphere.  The members of the GEFS ensemble, which start with slightly different atmospheric analyses, showed that there was great uncertainty with regards to the depth of the low center.  In other words, the 5.5 day forecast of cyclone central pressure was very sensitive to the analysis used to initialize the model forecast.

Here's another way to think about it.  Take out a dollar bill and drop it from shoulder height.  Mark where it lands, then do it several times over from the same location.  Even though you release the bill from nearly the same location every time, the bill never lands in the same spot on the floor.  After you've done this many times over, you can probably identify the spot where the bill is most likely to land, but also that there is a fairly wide envelope of possibilities for any given drop.  Why?  The bill's flight is controlled by it's release location and orientation, which are never exactly the same, as well as any motions in the air, which are chaotic and poorly observed (maybe if you add a smoke tracer, you can improve the prediction).

Now, if you want to factor forecast length into this experiment, simply get out a ladder and do it from higher.  The envelope of possibilities will widen.

So, my hypothesis for Katia's extratropical transition is that the overprediction of central pressure by the GFS reflects the lack of predictability in this event instead of an underlying problem with the modeling system.  The GEFS ensemble, which is based on the GFS model, illustrates that there were a wide range of possibilities for the cyclone central pressure given analysis uncertainty and the nonlinear nature of the cyclone evolution.

All of this illustrates the value of looking at an ensemble of model forecasts and not relying on a single model prediction when forecasting the weather.

Storms from the Southeast

I usually keep an eye on the Oquirrh Mountains to the southwest when trying to anticipate the movement of thunderstorms into the Salt Lake Valley during the summer, but that won't work today.  We have large-scale southeasterly flow over northern Utah thanks to a trough centered along the California coast.

As a result, thunderstorms are moving into the Salt Lake Valley from the southeast.

Further evidence that climate is what you expect, weather is what you get.

A Blistering Summer

The National Climatic Data Center has crunched the numbers and reports that this summer (Jun–Aug) produced the 2nd highest average temperature for the contiguous United States in the instrumented period, topped only by the summer of 1936.

Source: NCDC

Why 1936 and the dust-bowl era was so anomalously warm in the contiguous United States would be a good subject for a future post.  Perhaps I'll look into this if the weather and climate ever decide to sleep for a few days!  I emphasize in the contiguous United States because the US temperature record has frequently been misused to suggest it was warmer globally during the dust-bowl era than it is today, and this is simply not the case.

Geographically, average summer temperatures set new records across much of Texas, Oklahoma, and New Mexico and were above or well above average across much of the eastern 2/3 of the United States.  In contrast, average summer temperatures were below or well below average in the Pacific Northwest, Nevada, and northern and central California.

Utah straddled this temperature anomaly dipole, with northern Utah coming out near average for the entire summer.  This was the result, however, of a relatively cool June, average July, and warm August.

The heat in Texas and Oklahoma was simply incredible, blowing all previous statewide summer temperature records in the contiguous US away.

John Nielson-Gammon provides a preliminary analysis of the contribution of global warming to these anomalously warm temperatures on his Climate Abyss blog.  I'm sure this will be the subject of additional analysis in the future.

La Nina May Be Back

The Climate Prediction Center has issued it's latest ENSO diagnostic discussion.  A month ago, it was unclear if we would see a return of La Nina or ENSO neutral conditions during the coming winter.  It now appears that La Nina conditions are returning and are expected to strengthen for the winter.

See the ENSO diagnostic discussion at the link above for a full discussion.  It is interesting that many of the models used to predict ENSO are calling for ENSO-neutral conditions, but the Climate Prediction Center is going for a return of La Nina because that is what is predicted by the NCEP Climate Forecast System, which they feel is a stronger predictive tool, and because of a historical tendency for strong La Nina events to be followed by weaker La Nina events.  The strength of the La Nina, however, remains unclear.

As we have discussed previously, the development of a La Nina doesn't really tell us much about what to expect in the Wasatch Mountains during the coming winter.  Snowfall and temperature in northern Utah simply don't correlate well with La Nina.  This is reflected in the 3-month precipitation outlook for DJF, which shows equal chances for above, near-average, or below average precipitation over the northern Utah.