No major change to what I’ve been outlining since Monday for the weekend as of now. There will likely be revision of the details in the next couple days as the storm comes into better focus. Heavy snow for the Northeast corner of Georgia, more rain than anything else for MOST of Atlanta, but still the risk of some ice accumulation North and East of the perimeter, but especially Hall County and adjacent areas.
As I’ve noted previously, the computer models often do not handle temperature predictions well in a “wedge” (CAD) event like this associated with a “Miller A” winter storm system, they are often too warm. And as I said since NOAA has made changes to the models to try to improve them, it will take a few years for us to learn their new quirks, strengths and weaknesses.
Over the years I’ve tried to educate on how the equations only need to be off the mark by a degree or less for the forecast to go from good to bad. The normal and to be expected margin of error is GREATER than that.
STORM IN QUESTION UNDERWAY TODAY FROM TEXAS EAST:
Remember that some typical flooding of the usual suspect creeks and streams will be possible and with soggy soils and winds gusting over 30 mph at times some trees might fall causing a few scattered power outages. Rain totals of 2-3 inches expected on average.
As always the lines of demarcation for precipitation TYPE are not "magic walls in the sky". They are more a transition ZONE from one type of precipitation to another that is at least 15 miles wide but sometimes only miles and other times 30 miles depending on storm structure, track and 3D thermodynamics. And naturally they can move North OR South even at the last minute.
Since we KNOW the weekend weather will be wet and cold even if there is no ice or snow anywhere, why not do what ya gotta do by end of day Friday and bunker down safe and sound on the weekend. That’s my plan, That’s always my plan. Better safe than sorry. Plan for the worse hope for the best.
Accumulation of ice of a tenth to a quarter of an inch is possible mainly Northern Hall County and adjacent areas. However, as I said the amounts and locations will likely change in future forecast updates. I'll have them on the radio Friday through Sunday and next week as needed.
SURFACE WEATHER CHART SATURDAY:
SURFACE WEATHER CHART LATE SATURDAY NIGHT INTO SUNDAY:
ESTIMATED AVERAGE RAINFALL ENDING MONDAY MORNING:
MODEL NOTES:
Models differ greatly on where the best evaporative cooling will take place, some say only the NE corner of the state, others say all the way to downtown Atlanta or even South of the airport and to Athens. No way to know which will be right but it makes deciding where to draw the rain vs. ice line very difficult and subject to unexpected changes one direction or another once the rain starts falling in earnest. The synoptic set up is classic with the low tracking east near the Gulf Coast and with high pressure centered over PA to feed colder drier air down the east slopes of the mountains to meet the warm moist air coming in from the South and West where it overrides and lifts up on top of the cooler drier air (”over-running or isentropic lift).If the majority of models are right the warm air will mostly win out and its just a cold rain for the majority of the area, but if the numerical weather prediction equations UNDER estimate the strength of the wedge then the system will over-perform and more of the area will get some ice. As I’ve pointed out for years now the margin of error is very tiny, and the NORMAL error in modeling much larger which is why, unless you are located “in the heart of a system” instead of near the edges its a fine line between being on target or the forecast dart being off into the wall. In the middle of a system forecasts are on more solid ground because the air mass is more uniform. But on the edges like we are so often in Georgia thanks to terrain, geography and storm tracks its more iffy.
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