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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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North Georgia Weather December 21, 2012 at 11:30 PM
I love what a meteorologist just said... "I am liking what I am seeing between euro and GFS....winter is coming. wow. winter....hard to believe."
North Georgia Weather December 22, 2012 at 01:27 AM
Excerpt from the 7:05 pm AFD tonight from the Atlanta NWS: AREA FORECAST DISCUSSION...UPDATED FOR AVIATION NATIONAL WEATHER SERVICE PEACHTREE CITY GA 705 PM EST FRI DEC 21 2012 ALSO LOOKS TO STILL HAVE A POTENTIAL FOR SNOW MIXING INTO NORTH GA WEDNESDAY NIGHT FROM WRAP-AROUND MOISTURE ON BACK SIDE OF SYSTEM. HAVE LOWERED TEMPS A BIT WEDNESDAY AND WEDNESDAY NIGHT AS BLEND OF LATEST GUIDANCE AND INFLUENCE OF AFOREMENTIONED COLD FRONT. REST OF FORECAST LOOKS TO BE ON TRACK.
North Georgia Weather December 22, 2012 at 02:28 AM
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PEACHTREE CITY GA 815 PM EST FRI DEC 21 2012 .UPDATE... COLD AIR ADVECTION WITH A BREEZY NORTHWEST WIND WILL PREVAIL TONIGHT THROUGH SATURDAY. NO CHANGES NEEDED TO THE PREVIOUS FORECAST PACKAGE AS CLEAR SKIES WILL CONTINUE WITH THE MIN TEMPS ON TRACK. STILL EXPECTING THE COLDEST NIGHT SO FAR THIS WINTER SEASON WITH TEMPERATURES IN THE 20S. LOWEST TEMPS RECORDED SO FAR AT OUR FOUR CLIMATE STATONS ARE... ATL 30 ON NOV 25 AHN 27 ON NOV 25 CSG 30 ON NOV 25 MCN 25 ON NOV 26
North Georgia Weather December 22, 2012 at 12:38 PM
After looking at the 2 meter temp's, I can now say that this 0Z GFS, as modeled, would appear to be a devastating ice storm for much of the CAD (cold air damming) areas possibly as far south as the ATL/AHN areas on 1/1. The 2 meter temp maps actually show 32 or colder after the precip, ~1.75" worth, has already fallen as far south as ~Gainseville. The details aren't important now, but they do show the potential of what could occur. Everyone please note. The models will be going back and forth with solutions this far out. They will swing one way, and the next model run swing a different direction. But what you can start to get a feel for is the cold and the moisture. The details will only be known a few days in advance, if even then. Forecasting winter weather is MUCH more difficult than any other season of the year, as the timing of the cold and moisture have to be pretty close to perfect in order to get it right. So if you start hearing differing solutions right now, that is completely normal and expected. Every time a new model run comes out, weather weenies and meteorologist are all over them, frame by frame. In case you didn't know, the Euro and GFS have 4 model runs a day, at 00Z, 06Z, 12Z, and 18Z. Right now there is a 5 hour difference between our time and Z time, or Greenwich Mean Time. So 00Z = 7pm 06Z = 1pm 12Z = 7am 18Z = 1pm
North Georgia Weather December 22, 2012 at 12:41 PM
I even have a page that allows you to check on the NCEP model run processing. If you look at this page, you see that there are a LOT of models (and calculations) that basically run 24/7. http://www.daculaweather.com/4_model_run_status.php
North Georgia Weather December 22, 2012 at 12:59 PM
WARNING... weather geek speak to follow... Here's part one of the forecast a meteorologist made on December 13th. As you can see, he was spot on with this last storm and the current cold. My clarifications in () "With the MJO (http://www.daculaweather.com/4_mjo_phase_forecast.php) going into phase 1 and the 5-7 day lag for MJO induced waves to traverse the eastern US it would set us up for a wave to arrive in the east between Dec. 18-20 which is progged on the 180hr GFS and Euro moving across the upper Midwest or Great Lakes (this is what we just had). The same wave also ushers in relatively "colder" air (what we currently have) and plays nicely into the idea I spoke of the other day in my post about the pocket of relatively "colder" air arriving during the Dec. 21-23 time frame based off of GWO analogs for the eastern US. Using that same concept for the GWO I expect another batch of colder air Dec. 27-30. And following the spike in the 10 and 30 mb temps (stratospheric temps http://www.daculaweather.com/4_stratosphere_temp.php) that peaked back on Dec. 6 seems we should see a good shot of colder air Dec 30-Jan 3." ... continued.
North Georgia Weather December 22, 2012 at 01:01 PM
... continued. "I don't know if this wave was directly attributable to the MJO since some raise valid arguments that this wasn't a true MJO signal in the phase 1 region but we have our wave moving through the Great Lakes as discussed on Dec. 13 and temps for example in Detroit will be dropping from the upper 40's Thursday-Dec. 20 down to highs in the low 30's for Dec. 22. GFS and Euro both hinting at another wave moving through the Great Lakes Dec. 27-28 which would allow colder air to settle into the region for Dec. 28 by current models. Models indicate another pocket of cold air arriving to reinforce the prior batch with a short wave Jan 2-3 across the Eastern US which falls into the Dec. 30-Jan 3 date I laid out previously. The Euro and GFS both give credence to this time frame with a shortwave modeled off the coast of CA for 0z Dec. 30 giving it 4-5 days for it make it out into the Plains to the Great Lakes/East Coast. Although the GFS has been wavering in the magnitude of the cold air for this time frame, which I was expecting to be some of the coldest of the season guessing along the lines of -15C to -20C 850mb over southern Michigan and eastward. So the GFS is still not modeling that type of air mass as of right now I will leave that TBD as we get closer." ... continued.
North Georgia Weather December 22, 2012 at 01:03 PM
... continued. "With the newest GWO numbers today the latest analogs indicate a 15-20F warm up in surface temps Jan 3-Jan 6 compared to prior days highs across Midwest or NE (the Dec. 31-Jan 3 cold episode) and analogs suggest a stair stepped 15-20F temperature fall behind the warm up 1-2 days after that, meaning another spell of colder air Jan 5-8. I extended my outlook through Jan 8 on Dec. 14. I still feel comfortable with those dates and with the newest GWO analogs and latest 10 and 30 mb temp forecast it appears the time frame between Jan 8-10 will see a warm up over the east with a short wave moving through the east Jan 10-11 with cooler air dropping in behind it for Jan 10-13 across the mid-west/Great Lakes and then pockets of cooler air arriving Jan 15-19 time frame for the east followed by a second reinforcement of cooler air Jan 20-24. My GWO analogs only take me out to Jan 9 so there may be another short wave or two to add to the 2 already expected for the Jan 9-24 time frame. I will update as the newest GWO numbers come out over the next week and half."
North Georgia Weather December 22, 2012 at 01:08 PM
EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 106 AM EST SAT DEC 22 2012 VALID 12Z TUE DEC 25 2012 - 12Z SAT DEC 29 2012 ...CHANCES INCREASING FOR A MAJOR WINTER STORM FROM THE LOWER MIDWEST TO THE EAST COAST... THE 12Z/21 AND 00Z/22 GLOBAL NUMERICAL MODELS ARE CONVERGING ON A SOLUTION THAT THREATENS THE NATION FROM THE CENTRAL MISSISSIPPI VALLEY TO THE MID ATLANTIC REGION AND NORTHEAST WITH WIDESPREAD SNOW AND ICE DAYS 4 AND 5. A LOW IS EXPECTED TO TRACK ACROSS THE GULF STATES AND SOUTHERN APPALACHIANS EARLY IN THE PERIOD, THEN REFORM ALONG THE MID ATLANTIC COAST AND DEEPEN RAPIDLY EARLY DAY 5. HOW CLOSE TO THE ATLANTIC COAST THE SNOW AND ICE GET WILL DEPEND ON THE TRACK OF THE LOW AND THE SUPPLY OF DEEP COLD AIR TO THE NORTH AND WEST. THE REMAINDER OF THE PLAINS AND UPPER MIDWEST WILL BE DOMINATED BY COLD, DRY AIR THIS PERIOD. THE WEST WILL REMAIN UNSETTLED AS ENERGY POURS INTO THE REGION ON THE OTHER SIDE OF THE BLOCKING RIDGE AXIS ASTRIDE THE CONTINENTAL DIVIDE.
North Georgia Weather December 22, 2012 at 02:21 PM
From my buddy Larry with my comments in (). His first comments are the Christmas system, The "one to follow" is the New Year's system, which I also believe will be our first significant winter precipitation event. "With the 0Z CMC having gone a good bit NW, which would easily be enough to take the snow away from the bulk of N GA, with no CAD related wintry precipitation, with no model now giving sigificant wintry precip. to the bulk of N GA, and with run after run if both the GFS and Euro doing the same, I'm reducing the chance from 5% to 3% for that area and from 10% to 5% for far north GA (non-mtn areas) for significant wintry precip. The one to follow for these areas is the one near 1/1. Right now, I'm giving that storm a 25% chance of producing significant wintry precip. for the bulk of N GA ATL-AHN north."
Charles Welch December 22, 2012 at 10:41 PM
GFS is prolly my least favorite model, but it's always the model that "hypes" all the storms up. Then later the Euro comes out and says, "that GFS he's such a joker." LOL, anyways I'd rather skip any CAD stuff cause you can't have any fun w/sleet or ice. It's gotta be snow and just snow preferably, and hopefully there's something and not another rainstorm. At least a little bit of severe weather if we do get warm.
North Georgia Weather December 22, 2012 at 10:43 PM
Starting to look like possibly some severe weather on Christmas.
R++ One of the Famous Dacula Crew December 23, 2012 at 04:01 AM
I have to admit NGW, you made that call correctly ... It's the only channel that I can tune in that more often that not, that isn't actually COVERING the weather anymore. Thanks for keeping us informed around here but be forewarned, if you start covering extreme planes we'll be outta here!
R++ One of the Famous Dacula Crew December 23, 2012 at 04:08 AM
Have to admit though the evergreens that are lit up in the evening hours look dressed up and seem to be dancing the hula out there... And during these winds coming across Lake Lanier, I swore I heard Helen Hunt screaming "We have Debris!! We have Debris!!" half expected a flying cow but had to settle for trash cans aplenty...
North Georgia Weather December 23, 2012 at 11:04 AM
BOTH GFS/ECMWF/NAM/SREF INDICATE THE COLD FRONT ASSOCIATED WITH THE CHRISTMAS EVE SYSTEM WILL NOT PUSH AS FAR INTO THE STATE AS PREVIOUS RUNS HAVE INDICATED. THIS IS A SIGNIFICANT CHANGE. THIS MEANS THE WARM GULF AIR WILL SPREAD INTO MOST OF NORTH GEORGIA CHRISTMAS AFTERNOON. AS THE COLD FRONT MOVES INTO THE STATE CHRISTMAS NIGHT...THE INSTABILITY AND SHEAR WILL INCREASE RAPIDLY ACROSS THE ENTIRE CWA BRINGING THE THREAT OF SEVERE WEATHER TO THE ENTIRE CWA CHRISTMAS NIGHT INTO EARLY WEDNESDAY MORNING. WRAP AROUND MOISTURE WILL OCCUR DURING THE DAY WEDNESDAY BUT SHOULD BE OUT OF THE CWA BY WEDNESDAY NIGHT REDUCING THE RISK OF SNOW SHOWERS TO A FEW FLURRIES WEDNESDAY NIGHT ACROSS THE MOUNTAINS.
North Georgia Weather December 23, 2012 at 11:42 AM
It's now looking like a severe weather Christmas for us in Georgia. There will be a chance of thunderstorms and tornadoes during the day on Tuesday and into Tuesday night. A strong cold front will push into our area and the SPC has this to say. FORECAST SOUNDINGS AT MIDDAY TUESDAY IN THE LOWER MS VALLEY DEVELOP AN IMPRESSIVE SHEAR ENVIRONMENT AS THE MID-LEVEL JET APPROACHES THE REGION FROM THE WEST. NAM FORECAST SOUNDINGS VALID TUESDAY AT 21Z JUST SOUTHWEST OF JACKSON MS SHOW MLCAPE VALUES AROUND 1500 J/KG WITH ABOUT 60 KT OF DEEP LAYER SHEAR. THIS COMBINED WITH 0-3 KM STORM RELATIVE HELICITIES AROUND 400 M2/S2 COULD BE FAVORABLE FOR SUPERCELLS AND TORNADOES. IF MANY CELLS CAN REMAIN DISCRETE... THEN CONDITIONS COULD ALSO BE FAVORABLE FOR STRONG TORNADOES AS THE LOW-LEVEL JET MOVES EWD ACROSS THE CNTRL GULF COAST STATES FROM TUESDAY MORNING INTO THE AFTERNOON. AT THIS POINT...THE POTENTIAL FOR WIDESPREAD WIND DAMAGE APPEARS JUST AS VIABLE. THE MAGNITUDE OF THESE THREATS MAY DEPEND UPON THE DOMINANT STORM MODE. IF THE FAVORED MODE ENDS UP BEING LINEAR...THEN WIND DAMAGE COULD BE THE GREATER THREAT.
North Georgia Weather December 23, 2012 at 11:47 AM
Mt Washington currently has steady hurricane force winds with gust to almost 120 mph http://www.daculaweather.com/4_mt_washington.php
North Georgia Weather December 23, 2012 at 12:11 PM
Everyone is becoming very concerned about the Christmas storm. The severe weather parameters are already not good and could be getting worse. Very warm moist air will be in place from the first system that passes through on Sunday/Monday, and couple that with deep level shear, and you end up with rotation in some of these storms and bring the chance for tornadoes and straight line winds. Shear is the change in wind direction as you go up in height. If you have strong winds that are changing direction as they rise, then you have potential for tornadic development. The threat for us will even carry through Wednesday morning. The Storm Prediction Center has us in a Slight Risk area for severe weather, but it is possible for that to be changed as this system evolves. Stay tuned... I'll be providing updates as soon as they are available, and way before you'll hear it from your favorite TV weatherman! :-)
Kristi Reed (Editor) December 23, 2012 at 12:28 PM
Steve - I thought I told you I wanted 74 and sunny for Christmas. ;)
North Georgia Weather December 23, 2012 at 12:28 PM
Here's roughly how close we'll get to accumulating snow with this first system on Christmas: http://www.daculaweather.com/images/2012_12/snow.gif
North Georgia Weather December 23, 2012 at 01:20 PM
Birmingham is getting very concerned ON CHRISTMAS DAY THROUGH EARLY WEDNESDAY MORNING...THE THREAT OF TORNADOES AND DAMAGING STRAIGHT LINE WINDS LOOKS TO BE INCREASING AND POSSIBLE NOW FOR ALL OF CENTRAL ALABAMA. THE BEST TIME FRAME FOR POSSIBLE SEVERE WEATHER COULD START AS EARLY AS 2 PM CHRISTMAS AFTERNOON IN THE WEST WITH THE THREAT SPREADING EASTWARD THROUGH THE EVENING. THE THREAT COULD LAST THROUGH AT LEAST 2 AM WEDNESDAY MORNING IN THE EAST. ALL INTERESTS SHOULD CONTINUE TO MONITOR THE LATEST FORECASTS REGARDING THIS SYSTEM...AS CHRISTMAS DAY PLANS WILL BE IMPACTED. .SPOTTER INFORMATION STATEMENT... ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT WILL BE NECESSARY CHRISTMAS DAY THROUGH EARLY WEDNESDAY MORNING.
North Georgia Weather December 23, 2012 at 02:45 PM
New Year storm talk from my buddy Larry: "I'm definitely liking that the last three GFS runs have been centered on a weak, N GOM to ~Jacksonville track and consistently for 1/1-1/2. For N GA, this is about as optimal a track as can be had for the best shot at a sig. snow. So, to stay in the ballgame, I hope this continues. However, it isn't cold enough at 850 on two of the three runs. So, getting it cold enough might be a challenge. I'm sticking with a 25% chance for the bulk of N GA to get a significant wintry event (1"+ S/IP and/or 0.25"+ ZR) near 1/1-1/2. For 9-10 days out, those are pretty respectable odds."
North Georgia Weather December 23, 2012 at 03:04 PM
Atlanta HWO released a few minutes ago... ...SEVERE THUNDERSTORMS WILL BE POSSIBLE CHRISTMAS NIGHT INTO EARLY WEDNESDAY MORNING... A STRONG STORM SYSTEM WILL BE DEVELOPING OVER THE LOWER MISSISSIPPI VALLEY TUESDAY BRINGING WIDESPREAD RAIN AND A FEW THUNDERSTORMS TO MUCH OF NORTH AND CENTRAL GEORGIA CHRISTMAS DAY THROUGH WEDNESDAY MORNING. VERY STRONG SURFACE LOW PRESSURE WILL MOVE INTO NORTHERN MISSISSIPPI BY LATE CHRISTMAS DAY...AND INTO NORTHERN TENNESSEE BY WEDNESDAY MORNING. AN ASSOCIATED COLD FRONT WILL MOVE FROM WEST TO EAST ACROSS NORTH AND CENTRAL GEORGIA CHRISTMAS NIGHT. INSTABILITY AND VERTICAL WIND SHEAR WILL INCREASE ACROSS THE REGION CHRISTMAS NIGHT AND WILL BE ENOUGH FOR ISOLATED SEVERE THUNDERSTORMS TO DEVELOP...MAINLY ACROSS WESTERN GEORGIA BETWEEN 10PM AND 3AM LATE TUESDAY NIGHT...AND ACROSS EASTERN GEORGIA BETWEEN 3 AND 9 AM WEDNESDAY MORNING. AS THIS IS A DEVELOPING SITUATION PLEASE STAY TUNED TO THE LATEST UPDATES.
North Georgia Weather December 23, 2012 at 04:20 PM
NCEP Operational Status Message Sun Dec 23 15:01:00 2012 GMT NOUS42 KWNO 231500 ADMNFD SENIOR DUTY METEOROLOGIST NWS ADMINISTRATIVE MESSAGE NWS NCEP CENTRAL OPERATIONS COLLEGE PARK MD 1457Z SUN DEC 23 2012 CRITICAL WEATHER DAY STATUS... THERE IS A POTENTIAL FOR CWD BEGINNING 12Z TUE 12/25 THROUGH 12Z FRI 12/28 AS AN AREA OF LOW PRESSURE AND ASSOCIATED PCPN/MOISTURE MOVES ACROSS SOUTHERN AND EASTERN REGIONS.
North Georgia Weather December 23, 2012 at 05:46 PM
A Critical Weather Day is defined as: DEFINITION: A critical weather event is defined as any of the following occurring on/near the coast of or within the United States and its territories (including Puerto Rico, the Virgin Islands and Guam): 1. A widespread tornado outbreak; 2. A storm system causing a major precipitation event; 3. A severe cold-season storm affecting a large area with widespread heavy snow, freezing rain, or blizzard conditions; or 4. A tropical system threatening the coastline or producing excessive rainfall after moving inland.
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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