Monday, December 14, 2015

Twas The Night Before Christmas And All Through The House, The A/C Was Humming.

1:30PM Monday Update... I just reviewed all the long range data for Christmas week and my thoughts have not changed much at all.  However, I want to explain something very important here.  There appears to be a storm system next week and we'll have to deal with it.  These systems have been bringing rounds of heavy rain and that's my worry.  Anytime you have a storm system like this, you wonder about severe weather too.  Specifics this far out are useless as details will change.

Remember, having a storm system moving through means there's a battle in the atmosphere.   Depending on timing, you can get chilly temperatures for a day or two behind the system.  So while the week as a whole will average well above in terms of temperatures, it would not be out of the question to have a day or two of cold weather.  Could that be Christmas Eve or Christmas Day?  Again too early, but I'm looking everywhere for anything. LOL

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Ok, let's hope it doesn't get to that point.  We're talking about a forecast more than a week away, but we have a high degree of confidence temperatures will be well above average in the days leading up to Christmas this year.

While we will get a few days of typical December cold this week, we should go right back to the ridge over the central and eastern United States and a trough over the west.  Ski lovers out there are enjoying this for sure!

In the video I posted Sunday, I talked about the Arctic Oscillation (AO).  In its positive phase, it usually leads to above average temperatures and in its negative, below average temperatures.   The negative supports a suppressed jet stream allowing colder air to move into our region.  There are exceptions to this rule, but the AO is a great tool to use when forecasting 1-2 weeks out.  For example, at times last winter, the AO was strongly positive, but we kept getting pushes of cold air.  This had to do with a ridge building into Alaska dislodging the cold air and sending it south.  However, this does not appear to be the case next week.  

The one thing I have concern over is a storm system both of the main computer models are hinting at.  The Euro and the GFS both show concern around Christmas Eve and maybe Christmas Day for rain.   With mild air in place, you have to wonder about severe weather too.   I'M NOT SAYING THAT IS OUR FORECAST AT THIS TIME.  The only aspect to the forecast we're confident about are mild temperatures.  Specifics this far out are very tough to forecast.

Remember, we're also under the influence of an El Nino.  Let's go back to December 1982.  That was an El Nino winter and we had a swarm of tornadoes on Christmas Eve.   AGAIN, I'M NOT FORECASTING THAT AT THIS TIME, but it's always in the back of my mind.  No El Nino year is exactly alike!  That's another important thing to remember.

This is the 500 mb pattern from the European on December 23rd.  That big red blob over the desert southwest is a very strong storm system.  The trough is out west with the ridge central and east.  If this pulls out of that region, we could have some unsettled weather.

The GFS also shows the trough west and ridge east.... MILD

From Weatherbell.com. This is the AO from  December 5th through Christmas.  Look at the solid blue line.  That's the AO over the past couple of weeks in the positive and we have had mild weather.  Look at the dip below the "0" line this week.  That's the brief cold spell, then it shoots back into the positive.  As a matter of fact, it's almost off the charts positive.  Many times, when we see a rapid rise in the AO, it can lead to significant rain events and mild temperatures.
Also from WeatherBell.com.  These are surface temperature anomalies in degrees C for the period December 21 through the 26th.  It looks like Rudolph's Red Nose splattered all over the central and eastern U.S.  The cold air is bottled up with the trough over Alaska and the western United States while everyone east of the Rockies should be well above average.  

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