El_nino_wx_patterns

It took awhile, but it looks like we’ve finally reached that point where we can confidently say that our anticipated El Nino pattern has finally kicked into action.  As a refresher, El Nino is characterized by unusually warm sea surface temperatures in the equatorial Pacific that has an influence on global weather patterns.  The direct impact on us here in the United States is a more southerly position of the subtropical jetstream which is responsible for…as we’ve seen recently…funneling tropical pacific moisture across the southern US.  Two record rainfall events within just the past month in addition to the historic rainfall we had earlier this Spring, then very dry in between, certainly caused some confusion as to whether or not the climate forecasters even knew what they were talking about.  No doubt with the rainy pattern we’ve had this past month, we’re finally starting to feel the effects of our possibly historic El Nino pattern this fall and winter.  But what exactly will that mean for Texas?  Let’s start with the current Winter Outlook and a little further explanation into what those probabilities you see really mean.

Winter Temperature Outlook:

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The temperature and precipitation Outlooks for December through February are provided by the Climate Prediction Center.  A couple of things to keep in mind when looking at the Temperature Outlook graphic (above) and Precipitation Outlook graphic (below) is that these outlooks include historical patterns other than just pure El Nino.  It takes more than just an El Nino or La Nina pattern to determine the general outcome of seasonal temperature and precipitation patterns; however, a very strong El Nino pattern like the one we are expecting to see this winter can certainly play a large role.  Another thing to keep in mind is that these outlooks are tercile based with the “most likely” of three categories represented on each graphic…below normal, near normal and above normal.  For example, the forecast takes into account three basic probabilities…the chance for precip or temps to be above average by a wide enough margin to fall within the wettest or warmest one-third of the historical records, the chance for precip or temps to be below average by a wide enough margin to fall within the driest or coldest one-third of the historical records, or the chance for near-average temps and precipitation.  In the example above, Texas has been given a 45% chance of seeing cooler than normal temperatures during December through February…that also means we have a 33% chance of seeing near normal temps and a 22% chance of seeing warmer than normal temps.  In the graphic below, we see that Texas has a roughly 52% chance of seeing wetter than normal conditions…which will still give us a roughly 33% chance of near normal conditions and a roughly 15% chance we will be drier than normal.  Obviously, the higher the probability one way or another will weigh heavily on the outcome, but it does in no way guarantee our state will see completely colder or wetter conditions throughout the winter months.

Winter Precipitation Outlook:

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Another thing to consider…what does history show us?  We only began tracking El Nino and La Nina weather patterns in the 1950s, and we’ve had fewer El Nino events than we have had La Nina events, but climate forecasters have been able to pick up on the general patterns seen below based on the strength of the El Nino winters we’ve had over the past 65 years.

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It’s pretty easy to pick out that during historically strong El Ninos, above average precipitation is most common along the gulf coast states and California.  Texas stays fairly consistent with above average precipitation…but then there’s the winter of 1987-88 which went the exact opposite direction with less than average precipitation over Texas and many other parts of the US.  That proves that El Nino isn’t the only influence.  During the moderate to weak El Nino years, there’s consistency with seeing above average precip across the western half of the US, but some variable signals with regards to rainfall across Texas.  As far as temperatures go, strong El Nino patterns generally bring Texas colder than average temperatures..but we have had a few in which we were warmer than average.  One thing interesting to note is that winters when we had much colder than average temperatures across not only Texas but a majority of the country, happened during moderate to weak El Nino years.  On top of that, our coldest years were all prior to 1980 which leads climate scientists to surmise that there may be some decadal weather pattern to factor in as well.  That would need many more years of study to verify one way or the other.

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What about Snow?  If it’s supposed to be colder than average, does that mean more snow for Texas?  The answer to that is a big fat “maybe”.  While certain regions of Texas…mainly the panhandle, west central and northern Texas have historically seen more snowfall on average during El Nino years than non-El Nino years, that does not mean a guarantee of more snowfall for everyone…especially for central or southern portions of Texas where snowfall is a rarity anyway.  Another thing to consider, scroll back up and take another look at the Temperature Outlook graphic.  The region where we get the cold arctic air needed for the formation of snow is projected to be warmer than normal on average.  But, that in no way means it will stay like that the entire winter.  We will have a few arctic blasts like we always do, and the fact that we’ll likely have more moisture streaming overhead, because of the more southern position of the subtropical jet, this could lead to greater chance for seeing snow and ice during those arctic blasts.

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Where do we stand right now compared to where we were at the first of November back before the strongest El Nino on record during the winter of 1997-98?  Take a look below and see for yourself.   While the equatorial Pacific waters right now are on average slightly cooler, look at the increased temperatures near the southern California and Baja coast now compared to 1997.  What will this mean?  We’re not entirely sure.  Again, there’s many things besides just an El Nino pattern that will determine the eventual outcome of our temperature and rainfall throughout the coming winter, but this is certainly an encouraging signal for continued wet and cool conditions…just hopefully not all at once like we’ve seen here recently!

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