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Going back to the beginning of (last week), I posted every day about the issues models were having resolving energy in the northern and southern streams that were converging over the Midwest. Why? Because the signals were there for a major late winter storm. One solution, offered by the GFS, was significantly stronger and colder, even posing the threat of snow. The EURO was less phased regarding the bundling of energy and, while bringing a decent rain, showed little if any snow.

In what I consider to be a significant win for the GFS model, the EURO has flipped to the GFS solution, and it now appears that a potent spring storm will pass through the Midwest with heavy precipitation and wet accumulating snow. Along with the rain and snow, strong winds and progressively colder temperatures are shown feeding into the deepening storm. It leads to what looks to be a very dynamic system.

Notice the 500mb energy on both the GFS and EURO have consolidated in a single closed 500mb low near Chicago Wednesday, April 3rd. Excellent agreement.



Notice the difference in the latest EURO (above) to last Friday's run, (below). That's a whole different animal.

The next 48 hours are not going to be stormy and unpleasant. More on storm impacts below.




There are some very complex issues unfolding, in other words, this whole event and its dynamics are still in the oven, cooking and coming together before our eyes. That means some uncertainty remains regarding the exact track of the surface low, precipitation amounts, and where and how much snow falls. For now, the GFS shows the storm Tuesday around 10:00am with a 993mb surface low Between Quincy and Springfield.

By Wednesday morning, the low has deepened to 980mb and is actually rotating W/SW around the upper air center. The HRRR drops the pressure to 978mb. Strong North winds of 40-50 mph are blowing and snow is falling from eastern Iowa and WC Illinois into Wisconsin. Temperatures Wednesday morning are near freezing, with wind chills in the upper teens to low 20s.

This animation is fascinating as it shows the surface low tracking from EC Missouri to just SE of Chicago. By then, it's absorbing an injection of cold air from the northern stream energy. At that point, the southern and northern branches of the jets combine, and the energy is bundled (phased). The potent surface low is drawn NW where it does a full loop circling through Michigan, Lake Michigan, and Wisconsin, before passing over Chicago for a second time. That is rare to see.

The EURO is pretty much in sync with the GFS, just a hair east. With a tight cut like this, any shifts west or east matter. By the way, the pressure on the EURO was lower than the GFS at 979mb.

What will be massively important to the snow production of this April storm is dynamic cooling. Since cold air is very limited at the surface initially, a process known as dynamic cooling will be required to get cold air and snowflakes to the ground. With an intense and still deepening storm such as this, heavy precipitation rates in the deformation band can get the job done. However, that is highly contingent on the storm phasing as expected and intensifying as a result. Sometimes I've seen last minute alterations (kind of like Lucy pulling the football on Charlie Brown). Less phasing occurs, and the storm takes a track further southeast and is far less impactful here. That remains a critical wild card, but for now is not expected

Precipitation tends to be banded in systems like this, which means some locations may see significantly higher amounts than others. Even so, moderate to heavy totals are likely in most locations, in the range of 1–2 inches.

These are some early projections, with the highest amounts likely in the central and southeast.




Snowfall will be very difficult to determine, with the location of the heaviest snow and timing of the transition uncertain. Melting from below will also eat into accumulations. However, my current thinking is much of the area could pick up 2-5 inch totals. Some places in the north, especially N/NE of the Quad Cities could see 3-7 with locally higher totals near HWY 20. Rain could start mixing with snow in the late morning in the north and change to all snow by evening, gradually spreading south. Snow of varying intensities will continue into Wednesday before tapering off Wednesday night. At some point, winter weather advisories (maybe even warnings) are very likely. These are snow totals that models are currently suggesting. Again, just raw model output, not official forecasts. The GFS for the time being has become very aggressive on totals in the north, with at least a couple inches in all locations.


The EURO. Higher on totals, but still keeps the worst from far NW Illinois into Wisconsin. Still Impressive.


The 3k NAM

The 12K NAM


For my friends in Wisconsin, this has the potential to be a very significant event, with some spots potentially seeing a foot or more of very heavy wet snow, especially in the central and EC sections. Winds of up to 50mph+ along with the heavy weight of the snow could damage trees and power lines, leading to power outages. This needs to be watched in my area as well if the heavier snow can sneak into my northern counties.

Also, as I mentioned last week, with the storm tracking well to the south, we are firmly in the cold sector. N/NE winds will slowly and steadily increase to 40 and 50 mph Tuesday night and Wednesday. Readings 20 below normal (in the 30s) are possible Wednesday afternoon if we get the snow that's shown.

The next 5 days look very fresh. These are the 5-day average temperature departures through Saturday.

Without a doubt, this is not going to be a springlike week. Welcome to April! Roll weather...TS


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