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Climate Prediction Center Issues La Niña Watch

Good morning bloggers,

ENSO Alert System Status: La Niña Watch
Synopsis: There is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18.

Over the last month, equatorial sea surface temperatures (SSTs) were near-to-below average across the central and eastern Pacific Ocean (Fig. 1). ENSO-neutral conditions were apparent in the weekly fluctuation of Niño-3.4 SST index values between -0.1°C and -0.6°C (Fig. 2). While temperature anomalies were variable at the surface, they became increasingly negative in the sub-surface ocean (Fig. 3), due to the shoaling of the thermocline across the east-central and eastern Pacific (Fig. 4). Though remaining mostly north of the equator, convection was suppressed over the western and central Pacific Ocean and slightly enhanced near Indonesia (Fig. 5). The low-level trade winds were stronger than average over a small region of the far western tropical Pacific Ocean, and upper-level winds were anomalously easterly over a small area of the east-central Pacific. Overall, the ocean and atmosphere system remains consistent with ENSO-neutral.

A majority of the models in the IRI/CPC suite of Niño-3.4 predictions favor ENSO-neutral through the Northern Hemisphere 2017-18 winter (Fig. 6). However, the most recent predictions from the NCEP Climate Forecast System (CFSv2) and the North American Multi-Model Ensemble (NMME) indicate the formation of La Niña as soon as the Northern Hemisphere fall 2017 (Fig. 7). Forecasters favor these predictions in part because of the recent cooling of surface and sub-surface temperature anomalies, and also because of the higher degree of forecast skill at this time of year. In summary, there is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18 (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

What does this mean?  I personally do not like it when we see a developing La Niña. Why? For Kansas City it increases our chance of a dry winter. And, it increases our chance of below average snowfall.  I do not like those two things as a weather enthusiast.  I love wet winters, stormy winters, and snowy winters.  We will have much more analysis, but the topic discussed in the paper we are submitting for peer review is the ending of the western drought last winter.  Last winter there was a weak La Niña as well. And, the forecasts from the Climate Prediction Center and so many other sources was for a continuation of the major western drought. What happened? The drought got obliterated despite La Niña conditions. And, many of you know the reason: The Cycling Pattern Hypothesis! The pattern set up in such a way that storm systems got directed through California.  Something bigger is going on, so this gives us some hope for this winter.  According to my hypothesis, a unique pattern will set up.

Now, in my ENSO and snow analysis and I will share much more of this with you when we issue our winter forecast in late November, weak La Niña episodes, moderate La Niña episodes, and strong La Niña episodes have very different snow averages in KC.  KC averages 14.6″ of snow in weak La Niña years, and last year we had close to 5″ of snow total for the entire season.  In moderate La Nina’s however, KC averages around 25″ of snow.  Take a look at one La Niña forecast, the one being weighted heavily in the CPC alert:

Screen Shot 2017-09-21 at 8.14.28 AM

This La Niña developmen, if it comes close to verifying, would fall into a potentially moderate La Niña winter.  As I just said, the snowfall amounts in those years have a much higher average that strong or weak La Niña’s.  As shown in last years weather pattern La Niña is still just an influence. Something much bigger is going on and Weather2020 has been getting better and better at forecasting the weather for locations around the United States in the past decade.  Take a look at this forecast map:

1

Now, this is the 384 hour forecast map and it will likely be wrong, but one thing stands out on it and it is something we monitor for in every early fall season: A negative Arctic Oscillation (AO) and a negative North Atlantic Oscillation (NAO).  That arrow is pointing to a closed off upper high north of Alaska, and there is a big ridge in the Atlantic that extends up to Greenland. In the past three winters with very low snowfalls in KC there has been very little blocking up at high latitudes. I am not saying it is going to happen, but we often identify day 1 of the pattern as around happening near October 7th. It would almost have to be essential to have major blocking for KC to end up having an exciting winter ahead. It is something to monitor and it is something we have discussed in each winter forecast and it will be a big topic again in a couple of months.

Hurricane Maria:

SAT_CAR_VIS

Major Hurricane Maria, a CAT 3 storm, is just north of Hispaniola. It is just north of the Dominican Republic and still spinning heavy rain and thunderstorms over Puerto Rico that pretty much got destroyed yesterday.  It is going to be a tough year or two ahead for the people of this U.S. Territory.  The good news on Maria is that it appears that it will curve north into the open waters of the Atlantic.

115317_5day_cone_no_line_and_wind

The Bahamas are the next target so a harder turn would be nice. Have a great day everyone and thank you for reading and participation in this Action Weather Blog experience featuring Weather2020 and the Cycling Pattern Hypothesis. Let us know if you have any questions and go to www.Weather2020.com and join in the conversation over there.

Gary

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