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Freezing Rain, Sleet Possible Thursday Night

Friday morning could be absolutely treacherous over north Georgia.

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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North Georgia Weather January 28, 2013 at 12:31 PM
OK... one more comment for this blog post. 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
North Georgia Weather January 28, 2013 at 12:32 PM
... 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.
North Georgia Weather January 28, 2013 at 12:35 PM
The discussion is here: http://www.daculaweather.com/4_afd_ffc.php
North Georgia Weather January 28, 2013 at 03:19 PM
Pretty cool! 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
North Georgia Weather January 28, 2013 at 05:26 PM
A comment from a local meteorologist this morning about the storms on Wednesday: "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."

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