North Georgia Weather Blog

Meteorological Winter Begins December 1

11/29/2014

We're coming up on meteorological winter (December 1) and it's time to start to get serious about some winter weather.

Looking back at all of the parameters that we looked at back in October such as Siberian snow cover, El Nino patterns and strength, location of warm SST's off of the western US coast, and some local statistics showing correlations between monthly temps and our winter outlook, all pointed toward well below normal cold and above normal precipitation for the December through February season.

November and December are transition months for winter weather here in Georgia, and winter usually doesn't get into high gear for us until late December into early January. Moving into December, we start the month with average highs of 57/36 degrees, but by the end of the month, those drop to 50/31. The chaotic atmosphere is making it very difficult for the computer models to pick up on changes much more than 5 days out right now. Because of that, the weather weenies that hug every model run looking for chances of snow, get all out of sorts and are ready to call off winter before it even starts. :-)

So to address those that are ready to jump off a cliff, I'd like to repost this discussion by meteorologist John Homenuk from New York City (his weather blog here), that will help to understand some things that are brewing in the background and setting the stage for the winter that everyone has been expecting.

To the quickly accumulating amount of people panicking about the pattern evolution over the next few weeks, I have three words:

Stay the course.

The pattern and evolution of global circulations remains generally on track with forecasts from earlier this month, especially our winter forecast which was released back at the beginning of November. The progression of Wave 1/2 stratospheric warming events and their position remains on schedule (despite a generally failed and hyped first wave), and the response in both the Pacific and Atlantic remains excellent.

Beginning two weeks or so ago, a large Pacific ridge soared northward into Alaska and British Columbia as a result of an extra-tropical cyclone. But the extra-tropical cyclone wasn't the entire story...the pattern was amplified as it stood anyway. And so the ridge moving northward simply dislodged arctic cold to the south (go check your thermometers this morning). The AO and especially EPO took a nose dive, as did our mid level height and temperature departures.

Monthly SSTA's show a continued "textbook" +PDO pattern and Atlantic pre-NAO loading pattern setup. Those of you panicking about the NAO not going and staying negative over the past few days will have to take a step back from your computers --- because it probably won't do so for a few more weeks. The SSTA pattern we observed in October has a very correlation to -NAO winters, but almost all of them didn't develop fully until mid December.

Further aiding in our progression is the stratosphere. A much hyped Wave 1 event occurred but was not strong enough to disrupt or split the vortex. The Euro shows this vortex holding strong for the greater part of the next seven days. But then, as if directly on cue, a huge development occurs. The Euro is now splitting the PV at multiple levels...most notably 70mb and 10mb...as a result of stratospheric warming in Eurasia/Siberia.

This is a huge development as it means that heat flux from the above normal snow there has done its job. The stratosphere is responding.

While I can't speak for the exact timing and accuracy of individual models, recent medium range forecasts play right into the forecast from several weeks ago. Much above normal snow cover over Siberia and the heat flux results in a step-down progression of a stratospheric warming event, eventually leading to a disrupted PV and changing pattern by Mid December. Historically, these events have led to a -AO and -NAO response in 2-4 weeks lead time.

Although these stratospheric events are unpredictable, here's what I anticipate over the next several weeks:

A moderating but changeable pattern compared to the current one will take over through the 1st week of December. Pacific energy and waves will continue to crash into the West Coast, but the slower response from the Atlantic side will make it difficult to achieve any winter weather prospects in our area. Still, the anomalous cold will remain impressive in shots behind storm systems. The pattern changes wont' become extremely noticeable until the middle of December, when the response to a changing and disrupted PV will be felt.

With the MJO favorability increasing in-time with the effects from the changing stratosphere and increased high latitude blocking, early signals are for heightened potential of winter weather events in the Northeast US from December 15th onward, with indications suggestive of the active period continuing through at least January 1st.

While variance can be stressed and understood, it must be known that this isn't a forecast for significant snow -- it is impossible to tell the details of individualized events at this range. But the potential for snow -- and an active period of potential -- certainly seems to be heightened during this period as it stands right now.

Stratosphere

I have quite a few pages of stratospheric information at DaculaWeather.com.

http://www.daculaweather.com/4_strat_temp_time_series.php

Teleconnections

The Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) help to determine the amount of blocking that may or may not appear. The SCE and SAI indexes that have to do with the Eurasian Snow Cover were strongly pointing toward a negative AO which would imply cold air intrusions into the US. If we get a negative NAO, that in conjunction with a -AO would lock in the cold air for an extended time.

But what has happened is that there have been contradictions between the models... within the same model. The 500 MB patterns don't match the teleconnection forecast from the same model. The 500 MB patterns imply warmer weather while the teleconnection patterns point toward cooler than normal temperatures.

So the model battles begin. It's always a battle between the models, but rarely is it a battle within the models. It's going to be fun to watch all the twist and turns as the models struggle to come to grip with the change over to the winter pattern. According to all the signs, we're still heading toward a winter to remember.

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Highest November Snow Cover in 11 Years

11/17/2014

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I was flipping through the records for November snow cover in the US this morning and discovered that this November is FAR ahead of the last 11 years of record keeping, with the next closest year (2005) at 20%. We are currently sitting at 50.4% on November 17th, and that's pretty astounding for November. It's important to keep in mind that this snow cover drastically effects the arctic temperatures as they move south toward Georgia, in that the temperatures don't moderate (or warm up) nearly as much as they otherwise would do, therefore this snow cover can have huge implications down the road as we get closer to the actual Winter season.

November 17, 2014 Area Covered By Snow: 50.4% Area Covered Last Month: 0.2%

November 17, 2012 Area Covered By Snow: 13.7% Area Covered Last Month: 0.5%

November 17, 2010 Area Covered By Snow: 14.9% Area Covered Last Month: 0.0%

November 17, 2008 Area Covered By Snow: 7.3% Area Covered Last Month: 3.5%

November 17, 2006 Area Covered By Snow: 10.0% Area Covered Last Month: 5.1%

November 17, 2004 Area Covered By Snow: 4.1% Area Covered Last Month: 1.3%

November 17, 2013 Area Covered By Snow: 12.5% Area Covered Last Month: 4.9%

November 17, 2011 Area Covered By Snow: 13.5% Area Covered Last Month: 0.8%

November 17, 2009 Area Covered By Snow: 14.2% Area Covered Last Month: 9.1%

November 17, 2007 Area Covered By Snow: 5.6% Area Covered Last Month: 0.7%

November 17, 2005 Area Covered By Snow: 20.0% Area Covered Last Month: 0.5%

November 17, 2003 Area Covered By Snow: 13.6% Area Covered Last Month: 1.1%

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January Temperatures in November

11/12/2014

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Hope you enjoyed fall, because after tonight, it's only going to be a nice warm memory. As I've been discussing on my North Georgia Weather Facebook page, all the signs have come together and pointing toward a cold and potentially snowy December through February. It just so happens, we're starting early! Also, keep in mind that our "normal" highs and lows right now are 61/40 degrees.

Arctic air is slowly oozing south and will enter the metro area later this evening. The front will be slow to move through Atlanta as a small lee side low develops over South Carolina and slows the progression. Of course, the mountains are another obstacle and another reason that this low forms. But the cold air will finally win and by Friday we'll really start to feel the effects.

Here's what the Atlanta NWS has to say right now:

THE NEXT BIG CHANGE BEGINS SATURDAY NIGHT AS AN OVERRUNNING FLOW DEVELOPS WITH LOW CHANCE PRECIP POTENTIAL STARTING LATE. CURRENT RUNS OF THE EUROPEAN AND GFS ARE NOW SLOWER AND TEMPERATURES WILL BE CRITICAL FOR SOME AREAS OF N GA. THINK LOW TEMPERATURES IN THE LOWER 30S WILL OCCUR EARLY BEFORE PRECIP CHANCES KICK IN AND THIS WILL NEED TO BE MONITORED FOR THE POSSIBLY OF A RAIN/FREEZING RAIN/SNOW
MIX. THINK THE COLDEST PORTION OF THE AIRMASS WILL BE MODIFYING WITH LIGHT RAIN CHANCES PREDOMINATING. RAIN CHANCES LOOK TO MAXIMIZE ON SUNDAY/SUNDAY NIGHT WITH HIGHEST POPS OVER N AND PORTIONS OF CENTRAL THEN SHIFTING TO THE EAST AND SOUTHEAST CWA. TEMPERATURES COULD BE CRITICAL BRIEFLY EARLY SUNDAY BUT STILL THINK RAIN WILL PREDOMINATE.

GFS AND EUROPEAN STRUGGLING HANDLING A SURFACE WAVE AND TIMING OF A COLD FRONT ON MONDAY AND THIS COULD DELAY THE ENDING OF PRECIP CHANCES. TIMING OF THE COLD AIR COULD ALSO LEAD TO A MIX OR CHANGE OVER TO SNOW SHOWERS ACROSS FAR N GA BEFORE ENDING. TEMPERATURES WILL AGAIN BE CRITICAL ACROSS N GA EARLY MONDAY.

PRECIP CHANCES LOOK TO HAVE ENDED MONDAY NIGHT AND TUESDAY WITH A REINFORCING OF A COLD AIRMASS ACROSS THE AREA.

STAYED TUNED TO CHANGES TO THIS FORECAST FOR THE WEEKEND AND MONDAY.

These temperatures are going to hang around for a while as a -AO as well as a -NAO continue to build.

Here's a look a temperatures for the next 7 days, at 7 AM (left side) and 4 PM (right)