Three Strikes and You’re Out

19th GFS Accumulated Snowfall

GFS 12z Precipitation MondayThe questions continue to come in if we will have a white Christmas or not. Looking over the model data, there are three chances for snow. Some of them are better than others. The first chance will be Sunday into Monday. This is when a low pressure system will be moving to the northeast out of Oklahoma, and will be tracking across southeast Iowa. There have been some major changes from last night model runs. Last night the models were slower with this low which allowed for little snow. This morning, the GFS and the ECMWF are coming in faster and more north. This will split the state in half. The northwest part of the state will be on the northwest side of the low and will be in the cold sector. This will allow the precipitation to be in the frozen variety. But for the the southeast half of the state, precipitation will be in the liquid form.

GFS Snowfall MondayThe 12z GFS is laying down the snow across northwest and northern Iowa. It is forecasting snowfall totals of 2″ to 4″ with isolated 5″ amounts. The ECMWF is very similar with the track, with the exception of less snow across north central Iowa, places like Mason City.  The ECMWF and GFS are similar with handling extreme northwest Iowa with forecast snowfall totals of 6″ to 8″ with isolated 9″ totals (purple shaded regions above). It is good that we are seeing similarities between the models, but due to the differences from last night runs to today’s runs, a lot will need to be watched.

snow

For now if the current track and timing holds true, a widespread 2″ to 4″ with isolated 5″ totals will be likely Monday. As colder air begins to pull in as the low slides off to the east, rain will begin to transition over to snow, so a rain snow mix transitioning over to snow Monday afternoon into evening for central, northeast, and southwest Iowa will be possible. A wintery mix will be possible for eastern and southeast Iowa, however, not expecting much in the way of accumulations going off current model timing and track.

ecmwf_z500a_sd_us_5To recap, storm system number one will be moving through the Midwest on Sunday and Monday. This will bring a good amount of rainfall and moderate snowfall accumulations across northwest Iowa by Monday. After this system moves out, colder weather but still slightly above average will set in for the remainder of the week. Temperatures will be in the 30’s with lows in the 20’s.

ecmwf_z500a_sd_us_11 After system number one moves out, we will have two more systems on standby. The second one will move through the Midwest around the 19th and the third one around the 24th. This is where the forecast gets messy. Right now, the ECMWF and the GFS are not in agreement with the second system. The ECMWF brings a good amount of snow across Missouri and leaves Iowa high and dry. The GFS is playing devils advocate and gives us a little snow, and leaves Missouri alone.

19th GFSAs you can see from the graphic above which is a combination of the first system which will move through Monday, and the second system, not a whole lot more snow is added to the state. The GFS also differs from the ECMWF by bringing this system in earlier. Because of these major differences it is hard to say what will happen.

WhiteChristmasProbabilityBinned_620_hatSo what is the probability of a white Christmas? Well your chances are better the more north you go. Across northern Iowa you have a 61% to 75% chance of a white Christmas. Across southern Iowa, your chances go down to 26% to 40%.  We have three potential systems in the line up, so if we strike out with all three systems, then we are out of the white Christmas game.  A lot will continue to change between now and Christmas, which is only two weeks away now, so continue to check back here for the very latest on operation white Christmas!

Zach Sharpe

My name is Zach Sharpe. I am the president and forecaster for the Iowa Storm Chasing Network. You can find me on Twitter @Stormchaserzach and on Facebook at: https://www.facebook.com/stormchaserzach/

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