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WARNING: Cold Air Ahead for Georgia

Is a massive cool down coming?

 

If you're like me, it's not winter until it gets COLD. Last winter was one of those, mild with no real shots of cold weather. If you don't like winter or cold weather, close your eyes for a moment and savor those memories from last year... then back to reality as we look ahead. Winter is FAR from over and as far as we're concerned, it begins in about two weeks or so.

I wish I could come up with dramatic ways to say we're going to get cold, but since we're 2-3 weeks away, I have a little time to pick the best words. But it's going to get cold, plain and simple. The arctic air that's been bottled up in Alaska and Canada is about to take a trip south and make some dramatic changes to our weather here. Here's why.


In my last few blog posts, I've talk about several weather indices as well as changes that are occurring in the upper levels of the atmosphere. I'll try to piece all of that together so it make some sense.


Sudden Stratospheric Warming (SSW)
The first thing I'll discuss is the Sudden Stratospheric Warming or SSW. I talked about this in my last post and alluded to the fact that this was going to occur and would be a Major SSW, and this IS occurring right now. There is still a lot of research being done on SSW's and the study of how the upper levels of the atmosphere play an important part in what happens to our weather at the surface. But what we do know is that these type of events have direct correlations with blocking patterns and temperatures. In this case, it appears the SSW will be to be the kicker to get the cold air to start moving our direction. 


As of this morning, the 10hPA temperatures have risen more than 40ºC (from ~-80C) and the zonal winds have decreased from ~80 m/sec to almost zero with a reversal expected to take place. Click this link to view the temps and winds in the stratosphere. If you click through the 10hPA images, you'll see a total split of the stratospheric polar vortex by 72 hours. This also occurs at the 30hPA level even sooner. 


These changes are important and imply that this is a Major SSW and we haven't had one of those in several years. Here's an Abstract from a paper on SSW's
"The dynamics of the stratosphere sudden warming phenomenon is discussed in terms of the interaction of vertically propagating planetary waves with zonal winds. If global-scale disturbances are generated in the troposphere, they propagate upward into the stratosphere, where the waves act to decelerate the polar night jet through the induction of a meridional circulation. Thus, the distortion and the break-down of the polar vortex occur. If the disturbance is intense and persists, the westerly jet may eventually disappear and an easterly wind may replace it. Then “critical layer interaction” takes place. Further intensification of the easterly wind and rapid warming of the polar air are expected to occur as well as weakening of the disturbance. The model is verified by numerical integrations of the adiabatic-geostrophic potential vorticity equation. Computed results possess features similar to those observed in sudden warming phenomena."

One important thing to note... since the stratosphere has warmed almost 100 degrees, there is a corresponding drop in temperatures at lower levels and this has important implications for temperatures at the surface. I wanted to share this link, it shows through time-lapse animations, the process of SSW and how the polar vortex breaks down. Very cool. 


Blocking Patterns
The next piece is are the blocking patterns that need to be in place in order to get the cold air here. Specifically, we're looking at three patterns, the Arctic Oscillation (AO), the North American Oscillation (NAO) and the Eastern Pacific Oscillation (EPO). For us, it's a matter of having the right combination of blocking to squeeze the cold air south instead of allowing it to slide east and north.


The models have been hinting about a negative NAO and EPO for a few weeks now. One of the issues we've had so far this winter has been the active upper air pattern that has brought air that originated over the Pacific Ocean. While that was good for rainfall, it prevented any real cold air to penetrate south. That pattern had to do with a EPO+ or positive EPO. That's all getting ready to change with the EPO forecasted to go negative shortly. A EPO- brings a nice blocking ridge of high pressure over the Pacific, effectively blocking that warm moist air from moving this way, and providing a barrier that keeps the cold air channeled within the continental US. 


In order to channel cold air our way, the AO and NAO need to be in a negative state, and both models are forecasting some very negative states toward the end of the month. Blocking created by NAO- will force the winter storm tracks as well as cold, south instead of the zonal (east-west) flow that we've had for most of this winter. 


So what does all of this mean? 
There is a lag between what happens in the stratosphere and what we see on the ground,,, roughly two weeks or so. The blocking that will accompany the effects of the SSW is also about that far off. So we're looking at about 2 weeks or so before we experience any of these changes. We will have a period of mild weather between now and then, and then the vodka cold arrives (it's been -60ºF in Russia this winter). At this point it's anyone's guess as to how cold, but meteorologist have been saying the coldest air in more than two years will be coming. Right now expect the last week or so of January, and possibly the whole month of February, to be well below normal for temperatures... and possibly above normal for winter precipitation. 


Hold on to your hats! This is going to be fun!


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Kristi Reed January 15, 2013 at 01:19 AM
I expect the next post to be a far more positive report. In the words of the late Zig Ziglar, "Positive thinking won't let you do anything, but it will help you do everything better than negative thinking will." Remember that Steve. Positive = warm
North Georgia Weather January 15, 2013 at 11:33 AM
Last few post here about the coming cold. I'll have a new blog post tonight. Right now the latest HPC discussion matches what I was thinking about the date of the cold weather. THE ARCTIC FRONT RESPONSIBLE FOR BRINGING IN MUCH COLDER TEMPERATURES SHOULD BE WORKING THROUGH THE EASTERN CONUS THROUGH THE MEDIUM RANGE... A RESULT OF ENERGY ROTATING UNDER/TROUGH THE VORTEX... BUT THE 18Z GFS WAS MORE AGGRESSIVE WITH ITS COLD PUSH THAN THE ECMWF SO A COMPROMISE SOLUTION... TEMPERED BY THE 12Z/14 ECMWF ENSEMBLE MEAN... SERVED BEST. WITH A NW FLOW OUT OF CANADA THE CONTINENTAL DIVIDE SHOULD GENERALLY BE THE BARRIER TO THE WEST FOR THE COLDEST AIR THOUGH THE ECMWF HAS TRENDED WEST WITH ITS SHORTWAVE ENERGY DIVING SOUTHEASTWARD OUT OF CANADA OVER THE WEEKEND WHILE THE GFS FOCUSES ON A SOUTHWARD PUSH. AGAIN THE ENSEMBLE MEANS /BOTH THE ECMWF AND GEFS/ LIE IN BETWEEN. CAPITALIZED ON THE DECENT AGREEMENT BETWEEN THE GFS/ECMWF WITH THE ECMWF ENSEMBLE MEAN FOR THE FORECAST. SENSIBLE WEATHER... THE TEMPERATURE TREND EAST OF THE DIVIDE WILL BE DOWN NEARLY EVERYWHERE... WITH FLORIDA AND SOUTH TEXAS THE LAST HOLDOUTS AS THE ARCTIC FRONT PUSHES SOUTH AND EAST INTO EARLY NEXT WEEK. MOST LOCATIONS NORTH OF 30N SHOULD DIP BELOW FREEZING BY TUE/D7 WHILE SUBZERO TEMPERATURES SHOULD BE CONFINED TO THE DAKOTAS/MINNESOTA/WISCONSIN/MONTANA... AS WELL AS NORTHERN MAINE. THE WEST SHOULD BE NEAR TO ABOVE NORMAL EXCEPT IN THE MOUNTAIN LOCATIONS TRAPPED UNDER AN INVERSION.
North Georgia Weather January 15, 2013 at 11:34 AM
Keep in mind that the coldest air is probably 2-3 weeks away, so what we'll see this month is not the worst of it.
North Georgia Weather January 15, 2013 at 12:32 PM
OK... one more. This system that's beginning to develop in Texas is beginning to stir some interest, including us here in north Georgia. Something that bears watching..... "Just a heads up for you folks. Conditions are deteriorating quickly across N Central and E Texas this morning. Once again the models have under estimated the short wave progressing E across Northern Mexico and there are some indications that a negative tilted 5H low will develop that was not modeled. Just something to keep an eye on today. College Station in Northern SE Texas is reporting freezing rain at this hour as well."
North Georgia Weather January 15, 2013 at 06:29 PM
1227 PM EST TUE JAN 15 2013 ...WINTER WEATHER POSSIBLE ACROSS NORTH GEORGIA ON THURSDAY... A STRONG LOW PRESSURE SYSTEM WILL MOVE ACROSS THE STATE ON THURSDAY. AHEAD OF THE SYSTEM... A DEEP SOUTHERLY FLOW WILL SPREAD AMPLE GULF MOISTURE NORTHWARD... RESULTING IN WIDESPREAD RAIN ACROSS NORTH AND CENTRAL GEORGIA. AS THE ASSOCIATED COLD FRONT PUSHES INTO THE CAROLINAS THURSDAY AFTERNOON... A DEEP COLD AIR MASS WILL BEGIN TO SPREAD INTO THE AREA FROM WEST TO EAST THURSDAY AFTERNOON AND EVENING. AS A RESULT... THERE IS A POTENTIAL FOR RAIN TO CHANGE OVER TO SNOW ACROSS PARTS OF NORTH GEORGIA IF SUFFICIENT WRAP AROUND MOISTURE CAN SPREAD BACK INTO THE COLD AIR MASS BEHIND THE DEPARTING COLD FRONT. DESPITE WARM GROUNDS FROM RECENT UNSEASONABLE WARM TEMPERATURES... THERE IS THE POTENTIAL THAT STRONG UPPER FORCING COULD ENHANCE SNOWFALL RATES ENOUGH TO ALLOW FOR SOME LIGHT SNOW ACCUMULATIONS ACROSS PARTS OF NORTH GEORGIA BY MID TO LATE THURSDAY AFTERNOON OR EARLY EVENING... BUT THIS WOULD BE MAINLY OVER ELEVATED AND GRASSY SURFACES. ALTHOUGH LIGHT SNOW COULD BE SEEN AS FAR SOUTH AS A LA GRANGE TO ATHENS LINE... IT APPEARS THE GREATER CHANCES FOR SNOW ACCUMULATION WOULD BE GENERALLY NORTH OF THE I-20 CORRIDOR WEST OF ATLANTA... AND THE I-85 CORRIDOR EAST OF ATLANTA.

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