Well, well. What a change a day or two makes. Monday the NWS was calling for 56 degrees on Friday. Tuesday, when I mentioned the possibility of ice on Friday, the NWS was calling for 53 degrees. Today they are calling for 36 and I expect that to be lowered even further.
Here's the scenario. A strong arctic high pressure system that has brought bitterly cold temperatures to the north and northeast, will start to slide eastward today. As it does, the clockwise rotation of the air around this high will cause cold air to ride down the east side of the Appalachian mountains (known as Cold Air Damming or CAD). The very cold dense air can't go west so it's forced south down the east side of the mountains.
As this happens, a clipper type of shortwave (a bundle of energy in the atmosphere) comes riding down from the northwest Thursday night. As it does, a warm moist flow in the mid-levels begins to overrun the cold dense air below. If it's above freezing at the mid levels (which it is forecast to be maybe around 40 degrees or so) the precipitation falls as rain. But as it reaches the very cold arctic air at the surface (20s), the rain begins to freeze.
Depending on how warm that warm-nose of air is and how thick the cold air is, the precipitation will either fall as freezing rain or sleet for us. It won't be cold enough for snow (at least not right now), so sleet and freezing rain will be our main threat. Models are showing a very cold dense CAD developing, with temps dropping into the 20s Thursday night. Cold rain falling into those temps will cool the surfaces rapidly through evaporative cooling and cause the rain to freeze to anything it touches. I believe Friday morning (assuming the models continue on their present course) will be absolutely treacherous over north Georgia.
Here's another issue. The ground over most parts of north Georgia is very saturated right now. At this time of year, evaporation from the soil is slow at best. What that means is if the trees get enough ice on them, they are more likely to fall due to the wet, loose soil.
This could be one of the worse ice storms we've had in many years. I will be making updates here when I have new updates. I am expecting watches and warnings to begin to go up within the next six hours.
Much more to come...
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A week out, strictly climo or close to it, and/or they are going with the GFS. Today, the GFS feel a little more in line with the idea of a cut-off low in the far SW. The Euro is holding back the energy and then ejects it our direction. That map I showed several comments ago would be caused by a big cut-off low traveling across the northern Gulf coast, taking a negative tilt as it crosses the panhandle of Florida and across south Georgia. That would put us in the favorable spot for a deformation zone and BOOM. Lots of moisture and lots of cold make for a big snow. Some meteorologist look back on the winter storm on 1/7/88 as an analog. Here's a great study done by the NWS to explain what happened. http://www.erh.noaa.gov/gsp/localdat/TechAttachments/ta2001-02.pdf
This morning the Hydrometeorological Prediction Center said this about the forecast: WILL NOT BELABOR THE BOTTOM LINE FOR THE CONFIDENCE IN THIS MEDIUM RANGE FORECAST: IT IS VERY LOW. Patterns are changing again. Will go through a warm up before the system next weekend, and back to the cold, and this next batch should be colder. February is going to be our month for winter and it will be a roller coaster ride, but I think it's going to be fun. Hey Tommy! You shouldn't be surprised about next weekend! :-)
Look at it here: http://www.daculaweather.com/images/2013_01/fztp.gif
I sure hope we get some too Lori! I'm tryin'!
THE BOTTOM LINE FOR THE PERIOD IS A THERMAL ROLLER COASTER, WITH MUCH ABOVE NORMAL TEMPERATURES OVER THE EAST DAY 3, FOLLOWED BY ANOTHER ARCTIC OUTBREAK OVER THE CENTRAL AND EASTERN STATES DAYS 4-6, THEN A PRONOUNCED CHINOOK OVER THE NORTHERN PLAINS BY DAY 7.
Looks like we weren't too far off from the ice. I know we had ice over on the Harbins side of Dacula, it anyone else had some I'd love to hear where it was! NWS write up of the event: http://www.srh.noaa.gov/ffc/?n=icestorm_01252013
AS FRONT EXITS THE REGION...A SHORTWAVE SKIRTS ACROSS NORTHERN GEORGIA EARLY FRIDAY...AND WITH A COOLER AND DRIER AIR MASS IN PLACE...THERE IS A SMALL POSSIBILITY FOR WINTER PRECIPITATION. MODELS SUGGESTING MOISTURE ASSOCIATED WITH THE FEATURE WOULD ENTER FAR NORTH GEORGIA LATE THURSDAY...AND QUICKLY SPREAD EASTWARD...GENERALLY ACROSS THE FAR NORTHERN TWO TIERS OF GEORGIA COUNTIES...AND QUICKLY EXIT AFTER SUNRISE FRIDAY. FOR NOW...HAVE GONE AHEAD AND INCLUDED MENTION OF THE SNOW/FREEZING RAIN/MIX PRECIPITATION...BUT ACCUMULATIONS LOOK BE EXTREMELY LIGHT.
" There's no question that having had three winters in a row with a major snow in Atlanta, (don't forget that 3/1/2009 had a 4.2" fall at Atlanta, itself) as well as a total of six 1"+ snows, lead to a way above normal three year period. The total was a whopping 16.6"! That was the first time since the three winter period of 1892-1893 through 1894-5 that Atlanta had three winters in a row with at least one major S/IP!! How often has Atlanta had 16.6"+ of S/IP over just three winters? Well, the last time was in the early 1980's, thanks mainly to a combo of SnowJam '82 and the 3/24/1983 snow. 19.3" fell 1981-2 through 1983-4. Prior to that, one has to go all of the way back to 1896-7 through 1898-9 to find the last three winter period producing that much S/IP! (when 16.9" fell). The record highest by far was for 1892-3 through 1894-5, when a whopping 29.8" fell!! Each of those three winters had at least one 6"+ S/IP and one winter had two 4+"'s!"
DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0330 AM CST SUN JAN 27 2013 VALID 301200Z - 041200Z ...DISCUSSION... THERE IS REASONABLE AGREEMENT AMONGST THE LATEST SUITE OF GUIDANCE THAT A POWERFUL AND HIGHLY AMPLIFIED UPPER TROUGH WILL MAKE RAPID PROGRESS TOWARD THE ERN SEABOARD THROUGH LATE D4/WEDNESDAY. A MID LEVEL WIND MAX IN EXCESS OF 100KT IS FORECAST TO ROTATE THROUGH THE BASE OF THE TROUGH FROM THE TN VALLEY TO THE MID ATLANTIC COINCIDENT WITH THE ADVANCING COLD FRONT ACROSS THESE AREAS. MODELS ALSO SUGGEST THAT LOW AND DEEP-LAYER MOISTURE WILL INCREASE RAPIDLY IMMEDIATELY AHEAD OF THE FRONTAL ZONE WITH ECMWF DEPICTING A PLUME OF AT LEAST 1.5 INCH PW VALUES EXTENDING AS FAR NORTH AS PHL AREA BY WEDNESDAY EVENING. QPF AND VERTICAL MOTION FIELDS FROM LATEST EURO AND GFS MODELS SUGGEST A CONTINUATION AND/OR RESURGENCE OF CONVECTION ALONG NEARLY THE ENTIRE FRONT AMIDST INTENSE CLOUD-BEARING SHEAR. WHILE CAPE ACROSS MUCH OF THE RISK AREA WILL REMAIN LOW...EXPECT BOUNDARY LAYER WARMING/MOISTENING TO BECOME SUFFICIENT ENOUGH TO SUPPORT THE DOWNWARD TRANSPORT OF HIGH MOMENTUM AIR TO THE SURFACE WITH DAMAGING WINDS EXPECTED TO ACCOMPANY THE PASSAGE OF THE CONVECTIVE LINE.
Possible severe coming in Wednesday/Wednesday night, I think this will mostly be a potential high wind events as strong upper level winds may be drawn toward the surface. A good soaking rain should be in store (see if we can muddy up that garden for you Tommy!) with almost 1.5" of rainfall if we're lucky. NWS is downplaying the light snow Thursday night but are bringing up the potential for Saturday night. THIS MIDWEEK EVENT APPEARS TO BE OF BIGGEST CONCERN THROUGH THE THE EXTENDED PERIOD. THE UPPER TROUGH REMAINS ACROSS THE EASTERN U.S. THROUGH THURSDAY AND INTO EARLY FRIDAY...WITH A MUCH WEAKER DISTURBANCE MOVING THROUGH THE BASE OF THE TROUGH. WITH A COOLER AIR MASS IN PLACE...ALONG WITH THE MOISTURE INFLUENCE...IT IS POSSIBLE FOR SNOW FLURRIES OR LIGHT SNOW...ESPECIALLY ACROSS THE NORTH GEORGIA MOUNTAINS OVERNIGHT THURSDAY INTO FRIDAY. THE RUN TO RUN MODEL TRENDS IS TO PULL THIS SYSTEM FURTHER NORTH... KEEPING THE BEST MOISTURE NORTH OF THE TN/GA BORDER. FOR NOW...HAVE OPTED TO CONTINUE MENTION OF THE LIGHT WINTER PRECIP. NO ACCUMULATIONS ARE EXPECTED AT THIS TIME. ... continued
THE UPPER TROUGH CONTINUES TO PERSIST INTO THE WEEKEND...WITH ANOTHER SHORTWAVE IMPACTING NORTH GEORGIA LATE SATURDAY INTO SUNDAY. LIKE WITH THE EARLIER DISTURBANCE...MOISTURE IS LIMITED AND THE ARCTIC AIR MASS REMAINS IN PLACE. HAVE OPTED TO GO WITH SLIGHT CHANCE RAIN OR SNOW SATURDAY NIGHT...AND SLIGHT CHANCE SNOW FLURRIES EARLY SUNDAY FOR FAR NORTH GEORGIA. BEHIND THIS SYSTEM...HIGH PRESSURE BUILDS INTO THE REGION INTO EARLY THE FOLLOWING WEEK.
http://www.cnn.com/video/?hpt=hp_t3&buffer_share=016eb&utm_source=buffer#/video/us/2013/01/22/dnt-vt-snow-rollers-wcax.wcax
"I agree this is not a prime tornado setup, but given the very strong dynamics I think there is a pretty good chance of at least a few embedded QLCS tornadoes lasting well into the night across the South, with maybe even one or two supercell tornadoes ahead of the main line, especially in AR/LA early tomorrow evening. Despite the poor timing here in GA, this is such a dynamic system even a noon passage of the line Wednesday could result in a fain amount of problems from wind. This looks like one of the better January severe setups in a while, maybe not from a tornadic standpoint, but there will likely be a ton of wind reports."