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Stormy Weather Possible for Christmas

Is winter weather in our not so distant future?

This is my favorite time of year for weather forecasting. Winter weather forecast in the southeast are always tricky since it's not always easy to get cold air and moisture to come together at just the right time to produce winter precipitation here. But we're going to let you know well in advance what the meteorologist are seeing on the horizon, and make sure you have the latest weather information available so you can better prepare for your holiday travels and events. 

We've been watching as the models have struggled to make sense of the chaotic changing winter atmosphere. There have been signs for some time that have pointed toward a pattern change toward the end of the month, and more and more people are getting on board with that thought. I've included four different quotes below, all suggesting that we will see some major changes in our weather right around or shortly after Christmas, and the signs are getting a little more focused on a major system developing and potentially bringing cold and winter precipitation to parts of the southeast. We're still a long way off and the whole system could change or even disappear. But it is beginning to become apparent that the models are latching on to something big for next week. The bold are my highlights.

This from a meteorologist in Texas:

"The overnight guidance and ensembles continue to advertise a major winter storm event potential cross the Southern Rockies/Southern Plains during the busy Christmas Holiday travel period. The Euro is a bit faster by 12-24 hours ejecting a powerful trough across Texas/Oklahoma, while the GFS suggests a meandering closed core 5H low tracking a southern track across Central/SE Texas into Louisiana/Arkansas. Normally we see the GFS suggesting a more progressive pattern while the European guidance is slower. The Operation and ensembles paint a very interesting Winter Storm across a region that does not normally see this type of potential setup. Very cold air with wintry weather may extend as far S as Houston/Lake Charles with possible blizzard condition from N Cental TX/Oklahoma (Dallas/OKC) on E. Very cold sub freezing temps may reach as far S as the S Central Texas and on E along the Gulf Coast depending on the final storm track. The blocking regime does suggest abit more southerly track across the CONUS during the upcoming busy travel period. This feature may also offer a severe episode as well as it ejects from the Southern Rockies on Christmas Day."

And this from the Birmingham National Weather Service office this morning (Tuesday 18th):

"AS IF ALL OF THIS ISN'T ENOUGH...CHRISTMAS WEEK IS SHAPING UP TO BE VERY INTERESTING AS WELL.  ANOTHER EXTREMELY DYNAMIC SYSTEM IS IN OUR LONG RANGE GUIDANCE.  WHILE I'M NOT EXTREMELY IMPRESSED WITH THE LOOKS OF SEVERE WEATHER ATTM...A GOOD AMOUNT OF RAIN COULD BE IN THE CARDS FOR CENTRAL ALABAMA CHRISTMAS DAY.  IT'S THE BACKSIDE OF THIS SYSTEM THAT WILL LIKELY GET MOST PEOPLE IN A TIZZY AS THICKNESS VALUES COUPLED WITH SOME LEFT OVER MOISTURE COULD SPELL SOME OF THE UNMENTIONABLE BY THE END OF NEXT WEEK.  KEEP IN MIND...THIS IS WELL OFF TOWARDS THE END OF OUR MODELS...SO THIS COULD VERY WELL NOT BE THE CASE COME THE MOMENT OF TRUTH...BUT WITH BOTH OF OUR LONG RANGE MODELS SHOWING THE IDEA OF THIS SYSTEM FOR THE LAST FEW DAYS...I HAVE GONE ABOVE GUIDANCE FOR POPS IN DAY 8."

In addition, my buddy Robert Gamble at WXSouth.com had this to say:

"For now I say batten down the hatches and prepare for a rough stormy ride starting right after Christmas and likely beyond.  It looks to turn generally colder for awhile following this storm.  I’ll also say I won’t be surprised to see the models begin shifting soutward more if the 50/50 vortex shows some staying power. The models never account enough for that, but the big question we don’t know is how strong a vortex that will be.  This looks like a major precip event as well for the entire southeast except maybe central and southern Florida.  Wrap around snowfall could likely occur in the Tenn Valley as far south as Alabama on the storms backside, with front end snow to ice on the eastern side of the Apps."

And finally, the Hydrometeorological Predication Center this morning:

"THE BULK OF GUIDANCE FROM MOST MODELS AND ENSEMBLES OFFER A REASONABLY SIMILAR LARGER SCALE PATTERN EVOLUTION FOR THE NEXT WEEK. THIS FLOW IS HIGHLIGHTED ALOFT THIS WEEKEND BY AN AMPLIFIED TROUGH JUST OFF/ALONG THE WEST COAST...AN AMPLIFIED RIDGE OVER THE W-CENTRAL US...AND ANOTHER AMPLIFIED TROUGH/CLOSED LOW CENTEREDOVER THE NORTHEAST. THE LEAD SYSTEM AND ASSOCIATED DEEP SURFACE LOW/SYSTEM AND ASSOCIATED SENSIBLE WINTER WEATHER FOCUS SHOULD PROVE SLOW TO EXIT INTO THE CANADIAN MARITIMES WORKING INTO BLOCKED FLOW. THIS WILL LEAVE PLENTY OF ROOM FOR COOLING BACK ACROSS THE ERN AND CENTRAL US DOWN THROUGH THE SRN TIER STATES WELL IN ITS WAKE...INCLUDING PROTRACTED LAKE EFFECT SNOW POTENTIAL. UPSTREAM...ERN PACIFIC TROUGH ENERGIES AND ASSOCIATED UNSETTLED WEATHER/COOLING/PCPN ARE EXPECTED TO WORK INLAND ACROSS THE WRN US BY SUN/MON BEFORE EMERGING INTO THE CENTRAL US NEXT TUE WHERE SRN PLAINS CYCLOGENESIS/GULF INFLOW/DEVELOPING PCPN COULD OCCUR TUCKED UNDERNEATH A MID-HIGHER LATITUDE DOME OF COLDER HIGH PRESSURE."


Time to think about waxing the runners... :-)

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R++ One of the Famous Dacula Crew December 23, 2012 at 08:42 PM
I was way half expecting to find a photo of a snowball sitting next to a guy with a pitchfork and horns in his corporate office …
North Georgia Weather December 23, 2012 at 11:08 PM
Birmingham AFD... THERE ARE MANY ELEMENTS THAT CAN INFLUENCE THE SEVERITY OF A WEATHER EVENT...BUT FROM A SYNOPTIC STANDPOINT THIS SYSTEM IS ABOUT AS CLASSIC AS IT GETS. ALL MODES AND TYPES OF SEVERE WEATHER ARE POSSIBLE...BUT TORNADOES AND DAMAGING STRAIGHT LINE WINDS ARE EXPECTED TO BE THE MAIN THREATS. THE THREAT COULD BEGIN DURING THE EARLY AFTERNOON ACROSS THE SOUTHWESTERN PART OF THE AREA WELL IN ADVANCE OF THE SURFACE LOW AS THE WARM FRONT LIFTS NORTHWARD AND INSTABILITY INCREASES. IN THIS AREA...THE BROAD NATURE OF THE DIFFLUENT UPPER JET WELL IN ADVANCE OF THE UPSTREAM JET MAX SUPPORTS THE IDEA OF SUPERCELL DEVELOPMENT. THE THREAT FOR SUPERCELLS MAY THEN BECOME MORE WIDESPREAD DURING THE EVENING HOURS AS THE NOSE OF UPPER JET STREAK CONTINUES TO APPROACH. THE PROSPECT OF SUPERCELL DEVELOPMENT IS ALSO SUPPORTED BY THE LOW AMPLITUDE NATURE OF THE MID LEVEL SHORTWAVE AS OPPOSED TO A SHARPER TROUGH AXIS WHICH WOULD SUGGEST MORE OF A LINEAR MODE OF CONVECTION. A TRANSITION TO BROKEN LINE OF SUPERCELLS AND BOWING SEGMENTS IS EXPECTED TOWARD 06Z EAST OF INTERSTATE 65 AS THE FORCING BECOMES MORE LINEAR IN ASSOCIATION WITH THE COLD FRONT.
North Georgia Weather December 23, 2012 at 11:19 PM
And from the Atlanta NWS forecast discussion REAL PROBLEM BEGINS TUES/TUES NIGHT AS MUCH STRONGER JET STREAK DROPS INTO THE SRN PLAINS AND BOTTOMS OUT OVER THE LOWER MS VALLEY. FAVORABLE DIFFLUENT PATTERN ALOFT AND STRONG WAA WILL ALLOW SHRA WITH A FEW EMBEDDED TSRA TO SPREAD NORTH IN THE AFTERNOON. AS FRONT APPROACHES TUES NIGHT...SHOULD SEE AXIS OF SBCAPE APPROACH 500 J/KG WITH VERY STRONG LOW LEVEL VERTICAL WIND SHEAR. 0-1KM BULK SHEAR VALUES OF 40-50KT NEAR THE STRONGEST WE'VE SEEN THIS COOL SEASON. SURFACE LOW STILL DROPPING TO AROUND 995MB AS IT PASSES TO OUR NORTH. 12Z MODELS NOW SLOWER WITH THE TIMING OF THE FRONT... PARTICULARLY THE NAM. 18Z NAM JUST NOW COMING IN AND MAY BE EVEN SLOWER. ANYWAY FRONT SHOULD PUSH INTO THE STATE AROUND 09Z AND NOT EXIT THE SOUTHEAST CWA 16-18Z. WILL HAVE TO ADJUST OUR GRAPHICS AND HWO. IF ANY BOW ECHO OR LINEAR SEGMENTS CAN ORIENT THEMSELVES PERPENDICULAR TO THE MEAN FLOW...COULD EASILY SEE MESOVORTICES WITH WIND DAMAGE OR ISOLATED TORNADOES. TOO SOON TO PIN THIS DOWN BUT WILL CONTINUE TO PROVIDE OUR BEST INTERPRETATION. STAY TUNED. SNELSON
North Georgia Weather December 24, 2012 at 11:06 AM
Severe discussion from the Atlanta NWS this morning, my comments in (): ...SEVERE WEATHER LIKELY CHRISTMAS NIGHT... EXTENDED PERIOD INITIALIZES QUITE ACTIVE FOR CHRISTMAS NIGHT WITH THE INCREASING LIKELIHOOD OF SEVERE WX ACROSS THE AREA. A MODERATE RISK OF SEVERE STORMS HAS NOW BEEN POSTED BY SPC (http://www.daculaweather.com/4_spc_day2_outlook.php) WITH SLIGHT RISK ENCOMPASSING MOST OF WEST GEORGIA FOR DAY 2. MODELS IN EXCELLENT AGREEMENT IN SHOWING A DEVELOPING 995 LOW OVER THE TENNESSEE VALLEY PROGRESSING NNE...LEAVING THE LOCAL AREA IN THE WARM SECTOR BY 06Z WED WITH DEWPOINTS LIKELY IN THE UPPER 50S TO LOWER 60S (lots of energy to work with). ALTHOUGH RESULTANT CAPE VALUES WILL NOT BE AS HIGH AS LOCATIONS TO THE WEST...EXPECT DYNAMICS OF SYSTEM ALONE INCLUDING IMPRESSIVE DIFFLUENT PATTERN ALOFT (the diffluent winds aloft will cause lift) TO COMPENSATE LACK OF CONVECTIVE FORCING. SHEAR WILL NOT BE AN ISSUE (lots of it... especially at the lower levels. Shear causes rotation) WITH THIS SYSTEM WITH A 60 KT 850MB JET TRAVERSING THE AREA AND 0-1KM HELICITY OF 400 M2/S2 TO 600 M2/S2. IN FACT ANY TORNADOES ABLE TO FORM WILL BE CAPABLE OF ACHIEVING F2 STATUS OR PERHAPS GREATER AND EXHIBIT LONG LIFE CYCLES GIVEN STP OVER 2 INDICATED BY MOST MODELS. TOOK A LOOK AT THE CIPS ANALOG SITE FOR THIS EVENT AND SEEMS MOST SIMILAR EVENTS DID PRODUCE SEVERE WEATHER OVER THE AREA INCLUDING TORNADOES WITH THE EMPHASIS ON THE SOUTHERN CWA.
North Georgia Weather December 24, 2012 at 11:30 AM
One thing I find interesting is that the low that will cause the severe weather tomorrow, hasn't even formed yet. The piece of energy is still over the Pacific NW. This will be one of those systems that forms through cyclogenesis. A lee-side trough or low is caused by the stretching of a column of air as it descends on the lee-ward side of highly elevated terrain such as the Rocky Mountains. This stretching causes a spin-up of vorticity and a resulting upper level divergence. Lee-side cyclones can intensify over time as they move with the upper level flow and can initiate cyclogenesis. A downslope flow will be most intense if the wind flow is perpendicular to the mountain range and the winds have a high velocity. Here are two maps that show the potential track of the low pressure systems. http://www.daculaweather.com/4_hpc_sig_lows.php

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