Outcome of Eastern Great Lakes Storm Difficult To Forecast

                        Written by: William R. Deedler, Weather Historian 11/29/2011

Well I will have to say, many of the assortment of weather forecast models had our present /11/28-30th/ significant upper and surface low pressure system over the Ohio Valley & eastern Great Lakes pegged well out in time. I started conversing with my fellow meteorologists and weather enthusiasts back on November 19th about this system and it's been a nightmare ever since for the models and forecasters alike.

It wasn't so much a question of something developing as time marched on as much as: what would impact the area (rain versus snow), exactly where it would develop and its timing. And, though things are coming together there are still significant questions on the system. The general public still has a very limited knowledge of what hassles a winter storm can be to forecast. Those common remarks such as: "they were forecasting 2.0" of snow and we got nothing" or "they were forecasting 2.0"-4.0" in my area and I got 6.0" follow many storms." 

First off, "they" includes a hell of a lot more weather forecasters than ever before. Gone are the days from when I started that the forecast was from one general source; the National Weather Service. I can't tell you the amount of times I've heard "they" said this or that and ALL forecasts were attributed to the NWS. The general public in this day and age receives many more opinions out there of what could (or will) happen in just the daily forecasts, let alone days or weeks out.

Secondly, just to give you an idea of the problems still facing the forecaster, the following was taken from an excellent area forecast discussion /AFD/ issued just this Tuesday morning /29th/ from the NWS at DTX on the system and changes still coming in. He gives his educated and expert opinion of what he personally (sometimes with the help of co-workers) interprets the latest models are trying to convey to him on this storm.

"THE MODEL TRENDS EARLY THIS MORNING ARE CLEAR...FASTER TIMING...AND MAIN LOW TRACK MUCH FARTHER EAST...IN BETWEEN LAKE ERIE/ONTARIO. THIS IS IMPORTANT...AS IT WILL ALLOW FOR A FASTER WIND SHIFT TO THE NORTH/NORTHWEST BETWEEN 00-03Z WEDNESDAY...RESULTING IN FASTER CHANGEOVER TO SNOW. THE TOUGH PART OF THE FORECAST IS THE DEFORMATION ZONE WILL LIKELY BE CONSTRICTING TONIGHT...AS THE NOTICEABLY DRIER AIR OVER THE DAKOTAS...MINNESOTA...AND WISCONSIN (SURFACE DEW PTS IN TEENS AND 20S) INFILTRATES THE CENTRAL GREAT LAKES. A VERY SHARP PRECIPITATION GRADIENT LOOKS TO EXIST WITH THE STRONG BUT STRETCHED MID LEVEL DEFORMATION...AND MIDLAND COUNTY LOOKS TO BE ON THE EDGE OF THIS GRADIENT (SEE 00Z CANADIAN MODEL). ON THE FLIP SIDE...THIS LOW LEVEL DRY AIR WILL HELP WITH WET BULBING EFFECTS...INCREASING CONFIDENCE WE WILL SEE SNOW...BUT DBZ IS VERY HIGH UP AND STILL DIFFICULT TO GAUGE HOW MUCH OF THE SNOWFALL WILL BE WASTED DUE TO THE WET GROUND. REGARDLESS...TEMPERATURES EVENTUALLY FALL TO FREEZING AND BELOW...ASSURING THE SNOW WILL BEGIN TO STICK. SKEWING THE FORECAST TOWARD THE COLDER AND CONSISTENT 00Z EUROPEAN...EXPECTATIONS ARE GENERALLY 3 TO 5 INCHES ALONG AND WEST OF U.S 23...WITH 1 TO 3 INCHES EAST. LOOKING AT MOSTLY AROUND 1 INCH TOWARD THE CANADIAN BORDER AND MONROE COUNTY...AS THE MARGINALLY MILDER MARINE LAYER HOLDS ON AND MORE IMPORTANT FOR THE CITY OF DETROIT AND MONROE COUNTY...IT LOOKS LIKE THE MID LEVEL DRY SLOT WILL IMPINGE ON THE AREA...LIMITING THE QPF. JUST ABOUT ALL THE SNOW SHOULD BE DONE BY 12Z WEDNESDAY.


Next: We'll look at why these systems whether days or hours out, can still be such a pain in the butt and could this present system be telegraphing the difficulties of things to come this winter?

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian