- Oct 27, 2019

WINTER WEATHER UPDATE ON COMING SNOW...

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WINTER STORM UPDATE # 5

This is the 5th in what will be a series of posts on the potential of hazardous winter weather in the Midwest just before Halloween. This includes 2 threats, cold and snow.

We are now at a point where it's fair to say most of us are going to be seeing our first accumulating snow of the season. It comes in two waves. The first round comes Monday night, a 2nd stronger wave is due in Wednesday night and Halloween. The purpose of this post is to keep you updated on the latest trends for planning purposes. It is not a forecast yet. Do not focus on snow amounts even though you will see some some, they are going to change and are nothing more than model output at this point, or what we call guidance.

The first system now has moderate to high confidence. The only question is, (and it's a big one) is how much rain there is to start, and how soon any rain transitions to all snow? With the ground still being warm some of the snow is going to melt or settle. It's possible that roads could stay mainly snow-free limiting transportation impacts unless it really comes down at a good clip. The best chances for accumulations will be on grassy and elevated surfaces where the cold air can undercut. Here are what the models are showing for accumulations Monday night. Keep in mind what I just said about settling. For example, it might snow 2" but accumulate only an inch. It's kinda hard to know Joe.

The GFS

The 3k NAM

The 12K NAM

The Weather Prediction center shows these odds for at least an inch.

The NWS in Des Moines put out this snowfall forecast.

The NWS in the Quad Cities has this for chances of snow greater than 1". I think these might be a little on the low end.

The next shortwave trough to impact the area is currently situated over the northern portions of the Northwest Territories. As this vorticity anomaly dives southward, part of the energy will somewhat separate/elongate with one area following the upper low over south central Canada with another piece digging southward into the Rockies and carving out a deep longwave trough. This southern energy will eventually move towards Iowa Wednesday into Thursday. Differences remain over the past 24 hours at 500mb with the EURO farther north than today's GFS on the center.

The latest GFS/GEFS have come into better agreement showing the upper low likely passing over southern Iowa if not south of the state and the surface low passing south as well, the cold air will remain entrenched over Iowa mid to late this week. This continues to lead to high confidence in below normal temperatures averaging between 15 and 25 degrees below normal for late October into early next weekend.

Wednesday night it's likely that snow or a rain snow mix will develop, particularly over the south. However, as earlier mentioned, the cold air will remain over Iowa and most model soundings during Wednesday night through Thursday night would have the column cold enough to support snow over much if not all of my forecast area. Again, it appears likely that a Halloween snow is in the works and it could be heavier than the first round earlier in the week. However, there is time for the forecast track to changes so it will be a couple more days before any detailed snow amounts can be accurately issued. Anyway, if you combine the 2 systems this is what you get for total snow accumulations ending Friday.

The GFS