.

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 25, 2013 at 05:31 PM
Yep, I appreciate that! The next couple of hours might be interesting. I'm beginning to worry a little about afternoon traffic, especially on the NE side where the CAD is still firmly entrenched. Timing, timing, timing...
Trent Bullock January 25, 2013 at 05:59 PM
I am in Dacula, its 26-28 degrees on my back porch, I know that not official reading as my thermometer is 12' off the ground on my screened porch. That rain is edging closer and looks like CAD is firm right now. gonna be interesting shortly.
North Georgia Weather January 25, 2013 at 06:00 PM
Thanks Trent! I agree... could be very interesting.
North Georgia Weather January 25, 2013 at 07:21 PM
If we get anything it would be in the next 30 minutes to an hour. Quick... run outside! :-)
Terrie R January 25, 2013 at 08:04 PM
Seriously? (I seem to ask you that a lot!) I would love to see that much snow. Question is first whether it will really happen that way and second, will it come before I have to go in to work! I do not want to get caught at work again when it decides to really snow around here! Been there, Done that back in the early 80's!
Tommy Hunter January 25, 2013 at 08:19 PM
Amazing. All the weather outlets are calling for high 50's to mid 60's next weekend.
North Georgia Weather January 25, 2013 at 09:12 PM
It is, isn't it. Let's see who's gonna be right! :-) 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
North Georgia Weather January 25, 2013 at 09:15 PM
Well Trent, the dry air ate the precip as it got closer. Just our luck. But I'm getting pretty stoked about next weekend, I think it's going to be a fun week tracking this one.
Terrie R January 25, 2013 at 09:20 PM
If I remember correctly, today was forecasted at the beginning of the week to be a high in the mid 50's. They really missed that one!
North Georgia Weather January 25, 2013 at 09:29 PM
:-) It was. When I mentioned on Tuesday that there was a possibility of ice on Friday, they were calling for 53º. My high for the day actually occurred at midnight when I hit 35.7ºF, but for the actual day, I only reached 33ºF. So yes, they were only 20 degrees wrong! 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! :-)
Lori January 25, 2013 at 09:34 PM
So they are saying the system next Friday will not produce any snow? I sure hope we get some :) Thanks for all of your information.
North Georgia Weather January 25, 2013 at 09:47 PM
I was looking at a temperature map of the local area It's in the mid-50's south of the airport and even the mid 40's downtown. 32 here. Shows you the strength of the CAD. Look at it here: http://www.daculaweather.com/images/2013_01/fztp.gif
North Georgia Weather January 25, 2013 at 09:48 PM
They aren't saying anything at all... which is normally the case. I sure hope we get some too Lori! I'm tryin'!
Jimmy Orr January 25, 2013 at 10:53 PM
Folks, you've got to stop listening to those TV weather gurus. When the first inking of bad weather conditions comes up on my radar, I go on-line and see what NGW has to say. I have found Steve to furnish the best what I call play by play of the weather patterns heading our way. Knowing that I would be leaving the house this AM, I begin tracking today's forecast shortly after 5:00 AM. It was right on the money. Apparently the cold air got here but the moisture did not.
North Georgia Weather January 25, 2013 at 10:59 PM
Thank you very much Jimmy! Very kind words! :-)
Tommy Hunter January 27, 2013 at 01:37 AM
Hey Steve, I got my fields plowed today--3 acres worth. It was a BEAUTIFUL day. Now if you can get some snow on them with a slow melt, I'll give you some tomatoes this summer!!
North Georgia Weather January 27, 2013 at 01:31 PM
Here we go... 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.
Sharon Swanepoel January 27, 2013 at 01:42 PM
And this means....? Are we setting up for another weekend scare next week?
North Georgia Weather January 27, 2013 at 01:52 PM
Sounds like a deal Tommy! I love a good tomato, with a little salt, I can eat it like an apple!
Hope Thompson January 27, 2013 at 04:01 PM
I agree Jimmy . He was right with the last snow's when the tv's wasn't saying anything . I check his weather first . Glad he's on here !!
North Georgia Weather January 27, 2013 at 04:52 PM
Not sure yet Sharon. There are two systems coming in this week. The first system coming in Wednesday/Wednesday night that looks like a severe weather event, then Friday/Saturday another cold front brings cold air again. As always at this time of year, there is almost always the potential for winter weather, it's too early to tell right now though. The Euro depicted a potential cut-off low and kept holding energy back, allowing cold air to come in before the precip. Time will tell though. 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
North Georgia Weather January 27, 2013 at 04:54 PM
Thank you Hope! I hope we can get at least one snowfall to forecast this year!
North Georgia Weather January 27, 2013 at 06:57 PM
And Friday.... HA! 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.
North Georgia Weather January 27, 2013 at 07:15 PM
From my buddy Larry in Savannah: " 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!"
North Georgia Weather January 27, 2013 at 07:30 PM
I'll have a new post within the hour regarding this week coming up, but this from the SPC today: 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.
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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