Colorado (and Interior Southwest) forecasts - new edition

Outline for this revised SWcasts webpage (updated on April 21st, 2011; next update by late June, 2011)

This webpage consists of four main parts:

1. Recent summary of the status and outlook for ENSO (El Niño/Southern Oscillation), what this means for Colorado in particular, CPC-based climate forecasts, as well as my latest SWcasts, as presented at the Colorado Water Availability Task Force meeting (14 April 2011);

2. Latest ENSO conditions, CPC climate forecasts, and related links;

3. Executive Summary of this webpage as well as latest SWcasts forecast map;

4. Archive access to previous SWcasts.

The most recent SWcasts are based on observational data through March 2011. They are supported through the Colorado Water Conservation Board which also posts my latest forecast information under Long Term Weather outlook. I will update this website on a seasonal basis. Next update is scheduled for late June 2011. If you have any questions about SWcasts, please contact me at

You are welcome to use any of the material from this website, but proper acknowledgment would be appreciated, especially when referring to figures, forecasts, and assessments unique to this website. PROPER ACKNOWLEDGMENT should state that the used material "was provided by Klaus Wolter at NOAA-ESRL PSD, Boulder, Colorado, from his website at". The forecasts presented here are experimental - users are cautioned that no responsibility for any losses can be assumed by NOAA-ESRL PSD.

Latest presentation at the Colorado Water Availability Task Force meeting

Seasonal Outlook into Summer 2011

This presentation summarizes my latest thinking on the status and outlook for ENSO (El Niño/Southern Oscillation), what this means for Colorado in particular, Climate Prediction Center-based climate forecasts, as well as my latest SWcasts, as presented at the Colorado Water Availability Task Force (WATF) meeting (14 April 2011). I will always post my latest WATF presentation at the above link. Click on the "Archive" button below to find earlier SWcasts, pdfs of earlier WATF presentations (incomplete for now), as well as verification statistics since at least 2004.

Current ENSO conditions, and CPC climate forecasts (links)

Recent sea surface temperature (SST) and wind conditions in the tropical Pacific from Australia to just west of South America. They are discussed in my presentation above. This figure is updated daily at the TAO/TRITON website.

Since this figure reflects conditions over the last five days, the reader may be interested in an ENSO discussion that pays more attention to the longer time scales of this phenomenon. My monthly updated Multivariate ENSO index provides for this by the end of the first week of each month, and features a comparison figure of similar ENSO situations in the Multivariate ENSO Index sense here.

Latest comparison plot of 14 dynamical and 8 statistical model forecasts for east-central Pacific tropical SST anomalies. For those models that are run in ensemble mode (like the ECMWF forecast - note that the one shown here is from the previous month), this graph shows the average outcome. While I normally discuss the so-called 'IRI-plume' in my WATF presentation, I skipped it this time since there was no major change. This figure is taken from the ( IRI ENSO model website) that is updated on the third Thursday of every month, just in time for today's update to this website.

For the first time in several months, the dynamical models are showing more of a tendency towards El Niño by the end of 2011 than the statistical models in this figure. The situation will become much clearer by my June update to this webpage.

Meanwhile, the European coupled model forecast for central Pacific equatorial SST anomalies is still not updated as of April 21st. Their so-called "Nino3.4 SST nomaly plume" (a.k.a. "spaghetti plot") refers to fifty different forecasts that were computed during the last month from slightly perturbed initial conditions, in order to encompass the range of possible outcomes over the next six months. Check out the ( ECMWF seasonal forecast website) for this product that I discuss in my WATF presentation.

For an independent interpretation of the current situation, I recommend reading the latest NOAA ENSO Advisory which represents the official and most recent Climate Prediction Center opinion on this subject. My own monthly updated ENSO discussion is sometimes in agreement with the NOAA ENSO advisories, and sometimes not. The reader is referred to the latter website to get my point of view.

The most recent U.S. government (CPC) precipitation forecast for April through June 2011 (below) is mostly based on their 'consensus tool' that summarizes statistical CPC forecasts as well as their dynamical Coupled Forecast System (CFS), with a net outcome of "EC" (equal chances of below-normal, near-normal, and above-precipitation amounts) for most of Utah and Colorado, while Arizona and New Mexico are mostly xpected to end up dry this season, consistent with lingering La Niña impacts. Both seasonal temperature and precipitation forecasts by CPC are posted on their seasonal outlook website that is updated on the third Thursday of every month, just in time for today's update (they are discussed in my WATF presentation from April 14th). Note that the Climate Prediction Center (CPC) issues seasonal forecasts out to 15 months, not just the next season.

Executive Summary (updated on April 14th, 2011)

1. After reaching levels not seen in 35 years, La Niña has finally turned a corner to weaken more rapidly just in the last month. It will probably take a 'leave of absence' this summer, but odds are still better than 50/50 that it will return later this year.

2. In the Front Range, March ended up dry, windy, and warm, as is typical for La Niña. It stayed wetter than expected in our mountains. April started out in the same fashion, with last night's storm a decisive return to 'near-normal' for the next week or two. I stated last month that April has the best odds of deviating from a general dry spring pattern in Colorado with La Niña. This will curb fire danger in the next two weeks.

3. My forecast for late spring (April-June) shows a tilt towards dryness covering the southern and eastern parts of our state, while near-normal or even wetter-than-normal conditions might linger over northwestern Colorado. The latter forecast is now supported by better skill than in previous months. The first forecast for the summer (July-September) is fraught with uncertainty this far out, but fairly benign (mostly near-normal or even wet), for what it's worth. The expected break in La Niña conditions should help in that respect.

4. Since mid-March, our last WATF meeting, there have been a couple of dust storms in the San Juans, but not at the frequency of the last two years. Given their low snowpack, we may see an accelerated snowmelt in that part of our state next month.

5. Bottomline (unchanged since March): Count your blessings, this La Niña winter has delivered decent amounts of snow in our mountains which will lead to a good runoff season in much of our state. I am much less optimistic for local conditions over the eastern plains, nor do I expect a repeat performance for our mountains next year.

6. Coda: This is the first edition of my renewed 'SWcasts'. For now, funding has been restored to keep them going for at least one more time (into June), with good prospects for the period beyond that. They will probably not stay in this particular format for very long, nor do I anticipate regular monthly updates. I will keep things posted on this website. THANK YOU to the Colorado Water Conservation Board for supporting this effort, and to all of you who wrote letters of support in the past year or so.

The forecast map below shows the calibrated shifts in the tercile probabilities for April through June 2011:

Forecasted shifts in tercile probabilities for April through June 2011. In order to be shown on this map, a forecast tilt in the odds has to reach at least 3% either towards wet, dry, or near-normal. Shifts towards the wettest (driest) tercile are indicated in green (red), with a green plus sign for shifts between +3% and +5%, and a red minus sign for equivalent shifts towards the negative. Tilts towards near-normal are indicated by the letter "N", if at least by 3%. A question mark denotes a forecast with a greater likelihood of being either wetter OR drier than near-normal at the expense of near-normal odds. Positive or negative shifts of over 5% are contoured in 5% increments. If any shift reaches 10%, it is considered significant, even if recent verification skill has been wanting.

Archive access to previous SWcasts

To repeat from the beginning of this webpage: This forecast guidance is experimental, and should be used with caution. NOAA-ESRL PSD cannot assume any responsibility for losses incurred related to them.

To access an archive of earlier public experimental forecasts and verifications, click on the season and lead-time of interest, once you get to the respective directory. Average Heidke Skill scores for each forecast season are listed here. I will update this archive by June 2011 to include all forecasts from Water Year 2000 through 2010.

I am open to suggestions on what should be accessible in this archive. My current plan is to to include as many as pdf's of WATF presentations as are still available, back to 2004 when I started giving powerpoint presentations to that audience. For instance, the six remaining powerpoint presentations in 2004 can be found here. Other WATF talks in 2011 were given in February and March.

Questions about this webpage should be addressed to:
(, (303) 497-6340.