The Changing Weather Pattern

Good morning bloggers,

We hope everyone is having a great Tuesday. The time change is so awesome for those of us fascinated by weather.  Why? For the simple reason that the weather data, the computer model data, still comes out at 00z, 6z, 12z, and 18z every day. Zulu (Greenwich Mean Time) does not change, so when the time changes to fall back 12z is now 6 AM instead of 7 AM and the data comes in an hour earlier. This is huge for me as Chief Meteorologist at KSHB-TV. The NAM model now will come in beginning around 8 AM and 8 PM, and the GFS model rolls in beginning around 9:30 AM and PM. This allows us enough time to make a quick analysis when a storm system is approaching, or for any day really. I would rather not ever change this time again. We should petition to keep it as it is now instead of doing the spring forward thing to what is somehow called daylight savings time. What do you think?

Wow! Look at the first evidence in on  this years cycling pattern. This is for the 30 days ending November 5th:

Precip Anamalies Ending November 5

It was extremely dry over California. Last year the forecast from the Climate Prediction Center came out for the winter season to be dry in California due to a weak developing La Niña.  What happened? The exact opposite happened; one of the wettest winter seasons ever recorded out there and many of the reservoirs filled up, but it also lead to a lot of dry vegetation this summer leading to the bad fire season.  The previous winter one of the strongest El Niño’s ever recorded was in progress. The Climate Prediction Center forecasted a very wet year in California two winters ago.  What happened? The exact opposite; one of the driest years ever with the drought worsening.  And, now we have this year with a La Niña possibly developing. It isn’t confirmed yet, however.  The index is below La Niña at the moment, but it is forecast to  become a moderate La Niña winter season.  More on this in the next few weeks. Why were these past two years forecasts from the Climate Prediction Center so far off baae? They are not including the biggest piece of the forecast puzzle.  The LRC.  One of the indexes we use internally is this Eastern Pacific Blocking Indexes:

The Eastern Pacific Blocking Index (EPBI):

EPBI November 6 2017 Final

Figure 1:  This is the EPBI from October 7th through October 31st. The black line shows the neutral line. When this index is well above zero, then storm systems will most likely be blocked and deflected north of California.  If the index is below zero, then this would indicate a much more likely period for storm systems to blast California and the western states.

In Figure 1 above one can see the past two Octobers and this October lined up. When this index goes positive, then storm systems will likely be blocked from hitting California. A very positive index implies high heights aloft near the west coast. This is the 500 mb index for Seattle, WA.  The yellow line shows the strong El Niño year and it was mostly positive in October.  The white line shows last winter, showing the unblocked west coast. And, this year is somewhere in the middle, the red line. But, even though this index has been in the middle with unblocked times and blocked times in the past month, it has been extremely dry to start this season.

Screen Shot 2017-11-06 at 11.29.02 PM

The temperatures over the past 30 days show a very warm beginning to this season, with the exception of the Pacific northwest states. Kansas City has been closer to average in the past 30 days. The eastern United States has been quite warm to start the season.

Now, let’s not underestimate a current trend on the Arctic Oscillation:

Screen Shot 2017-11-07 at 8.15.52 AM

When the AO goes deep into the negative, there is a very good chance of the blocking up of the flow over North America which would likely lead to Arctic Blasts.  As you can see above, the latest AO, and the NAO looks similar, forecasts show a big dip by around the 20th of November. Some of the models show this, and some of the models do not show this.  Let’s see what actually happens, but as discussed yesterday, the pattern may be cycling in the 45 to 48 day range, give or take a day or two.  If the early October part of the pattern does return, I can see this dip happening.  It didn’t happen early in October, but there was room for the blocking to develop. In other words some ridging near Greenland was close to happening in this first cycle, but it broke down before fully developing. Maybe in this next cycle it will form? I am not sure yet, quite obviously.  Let’s see what today’s models show us.

Right now, it has turned colder. Temperatures are below average. The weather pattern is still evolving and setting up. We will look ahead in the next few blogs!

Thank you for spending a few minutes of your day reading the Action Weather Blog featuring Weather2020 and the LRC. Go over to Weather2020.com and click on the blog there and joint in the conversation.


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