Westward Trend

GFS Friday

GFS MondayIf you read last nights weather update, we told you about two systems that we will be keeping an eye on over the next week. The first one, which is shown above, will move across southern Minnesota on Monday. This will bring rain into the state, before it eventually transitions over to snow Monday night into Tuesday across northern Iowa. This still continues to be the best area for snowfall accumulations of a couple of inches. As this system continues to move off to the east, this is where things will begin to get interesting.

gfs_ptype_slp_east_21As we stated last night, as the low continues off to the east, it will begin to interact with the jet stream. As this low begins to interact with the jet streaks, or areas with the greatest wind speeds in the jet stream, this will help strengthen the low. This is still the case this morning, however, the track of this low is now further to the west. This would now shift the impacts of this system further to the west as well.

GFS FridayHow much further to the west is this low? Well the center of the low is now tracking right over Chicago. This would now shift much of the heavy snow across northern Illinois, and extreme eastern Iowa. While this system is still 6 days away, there will still be time for much to change. With stronger storm systems, westward trends are not uncommon. The question now is just how far west will this trend, or will we see it go back to where it was before?

GFS Friday snowWith such a strong system, comes high snowfall totals. The track of this system will ultimately determine where the heaviest snowfall totals will fall. Track and timing will be key, so we will continue to watch this. So for now, do not buy into any snowfall forecasts.

GEM PrecipThe GEM is also showing a similar scenario where the low will track near Chicago. The GEM also “bombs” out this low. By midnight Wednesday, the low is centered over Kentucky with a pressure of 990mb. As it moves off to the north towards Michigan by Thursday morning, it will have a pressure of 965mb. This is a 25 mb pressure drop in 24 hours. A “bomb” or also called bombogenesis, is when rapid strengthening of an extratropical cyclone takes place by at least 24 millibars over the course of 24 hours. If this low does drop 25mb in 24 hours, it will be classified as a bomb. This rapid intensification of the low, will bring heavy snowfall totals. GEM FridayThe only difference with snowfall totals with the GEM is it continues to produce heavy snowfall as it moves off to the east across Indiana, and Ohio. Comparing the GEM and GFS to the 00z ECMWF, the ECMWF is even further to the west. The ECMWF is tracking the low further to the north, which would then bring snow for much of Iowa, with the heaviest band of snow across central Iowa.

It should also be pointed out that with such a strong low, the pressure gradient will be tight. This will be increasing the winds Thursday and Friday with gusts between 30-40mph. This will lead to blowing snow and reduced visibilities.

We will continue to have to keep a close eye on this system as the very latest westward shift has made things interesting. Many of you will be traveling in the coming week, so you will want to continue to check back here for the very latest developments.


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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