Posted: 5:20 pm Friday, January 6th, 2017

Winter Storm Warning 

By Kirk Mellish

The models have more or less finally come together but differ greatly on amounts, types and locations of rain, snow, sleet and freezing rain.

In summation of what I think, the usual: Most of the snow far north metro, most of the rain far south metro. A mix at times for everyone, and eventually flakes for everyone but they will be a disappointment inconsequential for many. However, the drop in temps by early Saturday will mean whatever falls turns to ice.

Models showing nothing in Atlanta and models showing 10 inches of snow in Atlanta are the outliers, so while either extreme could prove right in the end, I am forecasting using a multi-model ensemble approach along with pattern recognition, trends, and experience to make my forecast call.

Obviously timing, amounts, and locations are subject to future changes just as any other forecast anytime of year!

So expect fine-tuning right through the event.

My total accumulation ESTIMATE for Metro Atlanta is now 1/2 inch to 3 inches ON AVERAGE with isolated totals over 4 inches, especially NE suburbs.

Not going to lie, with the Atlanta area right on the rain/snow line and the models groups split between a dusting or even less OR at least a couple inches the potential for a big forecast bust egg on face is huge with this one.

screen-shot-2017-01-05-at-2-44-31-pm

 

SURFACE WEATHER MAP FRIDAY 7pm:

92fndfd_init_2017010612

SURFACE WEATHER MAP 1am Saturday:93fndfd_init_2017010612

SURFACE WEATHER MAP 7am SATURDAY:

94fndfd_init_2017010612

SURFACE WEATHER MAP 7pm SATURDAY:

96fndfd_init_2017010612

 

CHANCE OF AT LEAST ONE INCH OF SNOW by SATURDAY AM:

screen-shot-2017-01-06-at-5-04-47-pm

CHANCE OF AT LEAST 4 inches by 1pm SATURDAY:

screen-shot-2017-01-06-at-5-07-35-pm

 

SNOWFALL ESTIMATE FROM NOAA/Winter Prediction Center:

wpc_snow_72_50_atl

NWS:NDFD SNOW/SLEET ACCUMULATION ESTIMATE: 

ndfd_snow_atl_9

WINTER PREDICTION CENTER NOAA/NCEP GUIDANCE:

day1_psnow_gt_04

So a robust Miller A snow system for most of North Georgia with AVERAGE amounts from one half inch to 3 inches on average. There will always be exceptions with some getting more than forecast and others getting less than forecast.

IN-BETWEEN THE BLUE DOTS IS WHERE MODELS HAVE BEEN MOST CONSISTENT FOR SOME AMOUNT OF SLEET/SNOW:

screen-shot-2017-01-05-at-5-02-27-pm

NEAR those dots there will be a huge gradient or change from just rain to a little snow and from just a bit of snow to a significant amount. The lowest amounts near and south of the bottom dotted line. Average totals 1/2 to 3 with spots getting 4+.  But precisely where the most will fall no man nor model knows, we just give our best estimate. Mostly rain south of the lower blue dot line.

Look at the SHARP RAZOR edge the metro is on between the rain/snow line Friday evening, as little as one degree aloft could make a big difference in what happens at your house or place of work or mine:screen-shot-2017-01-05-at-5-07-22-pm

***AND that line may end up in reality being 30 miles farther North OR South of the model depiction, that is within the normal margin of error. So you can plainly see for yourself the difficulty of the forecast challenge.***

OUTSIDE chance someone gets a little thunder/lightning with this system.

UNLESS the system fizzles out or becomes more intense than the model consensus. Stay tuned.

ROADS AND TIMING THE ONSET… tricky part, right now daytime precipitation Friday looks of little consequence until around or after 4pm for the Metro. But that could change obviously.  I would plan on not being on the roads to play it safe by or after dark Friday through Saturday.  Peak snow/sleet looks to come after 10pm  give or take a few hours through early morning Saturday.

REMEMBER: Meteorologists are in the business of forecasting the state of the atmosphere not road conditions; models don’t predict road conditions or road temps.

POWER LOSS… is not expected at this time but some models suggest an increase in freezing rain or ice, especially southwest Metro south of I-20 to I-85/75 Southside.

noaad1

 

ndfd_ice_atl_9

If you have not read the previous posts on this system, please do so for more details/background.

A SIMILAR STORM FROM THE PAST (analog) demonstrates how in any winter storm there is potential for some to be happy and some to be angry with what they get, because amounts are not evenly distributed even in a CORRECT FORECAST, nearby places can go from zero to a nice amount and back again, so there is a lot of potential for heartbreak with such a narrow band of accumulations as you can see from Jan 28, 2014:

screen-shot-2017-01-05-at-11-43-29-am

The point I am trying to make, which I shouldn’t have to, is that no model and no forecaster can get the lines exactly right or tell you how much at your office, on this road, or in your backyard.

“Official” Atlanta snow amounts from the past of at least 3:

screen-shot-2017-01-05-at-5-17-21-am

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