South Wisconsin May Get Crushed with Late Season Snow

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The latest GFS is showing over a foot of snow for southern Wisconsin and far eastern Iowa. This comes as a fast moving storm system appears to absorb additional moisture to provoke additional snow amounts.

Before I go any further: This image may be produced with 10:1 ratios, which would be higher than what is being shown here. The keyword is 'MAY', because a comparison to other 10:1 ratio images yielded different results. That said, I am treating this image as a 10:1 ratio image in order to not get everyone's hopes up too high.

Anyhow, I would expect a realistic scenario to be 1-4 inches in southern Wisconsin, with another 2-4 in Pennsylvania. I really don't know with the difference in images using the exact same data, which should yield the same results.

Possible Weekend Snow Update at 4:00 PM CDT

Southwestern Low May Ignite Severe Weather in Plains

The ECMWF is projecting that a large low pressure system will swing into the Southwest and likely ignite some showers and storms if it should progress eastward into the Plains.
There isn't too much I can say about this storm system, but the jet stream appears to be latched onto the system, which would increase tornadic shearing and the overall intensity of the system.

Snow Event Potential This Weekend

A storm system is expected to bring a snow event to the Lower Great Lakes and lower part of the New England region. This image portrays 500mb relative vorticity values. For a refresher, positive vorticity values indicate low pressure systems. So, as you can see, there is an area of higher vorticity values in lower Iowa, which is the system we are watching for possible snow.
The system should quickly shift eastward and weaken in the process. Despite this, expect snow values to quickly increase in the North Ohio and New England regions, as the Atlantic Ocean enhances the moisture content of the system.

Here is a snow map valid for April 29 off the 12z GFS model. It has been showing snow in the area for a while. As you can see, a good 6 inches of snow is being forecasted in Pennsylvania off this system, with 2-4 inches in north Ohio and around the 6 inch swath.
Just for kicks, let's imagine that this snow is going to have a 10:1 ratio (10 inches of snow = 1 inch of liquid). Now, 10:1 ratios are uncommon in early and late season snowfalls, so take a look below.

This is a 5 day accumulation map.

Andrew

Severe Weather Possible Thursday

I am monitoring the potential for some hazardous or potentially severe weather in the Plains come Thursday. Looking at the image above, there is a vorticity maximum in northeastern New Mexico, suggesting the presence of a low pressure system. It looks like it will be negatively tilted, with the highest vorticity values pointing towards the southeast. This negative tilt will add to much needed instability if storms want to develop.
A lack of jet stream support and stronger vorticity values is leading me to assume that this will not be a big event. I am not seeing sufficient jet stream winds to indicate that this storm will be strong enough to cause a more large-scale event, and that this may be a slightly more localized event.

Instability values will be pretty impressive with CAPE values exceeding 3000 j/kg in Kansas and Missouri, as well as parts of Oklahoma. Again, this storm system is not looking too strong, so maximum instability is going to be around what is shown here. Considering the system is in northeastern New Mexico, the system should move in a general east-northeast direction, giving the Oklahoma/Kansas areas the first shots at severe weather potential.

Here is the reason storms may struggle to form. A huge storm-suppressing cap of warm air will be over the darkest shades of blue, meaning that a lot of instability will be needed to break this. As of now, it looks like a good 3000 j/kg of CAPE will be necessary to break the cap and then produce severe storms. This is about the maximum instability being offered by the so-so storm system.

When it comes down to it, the instability will probably cancel out the cap and ignite some storms. The question is, will these storms be severe, and could they be tornadic? I would not go as far as to forecast that, but using these indications, I would say that some severe storms are possible, but lack of major shearing is discouraging for tornado potential.

Andrew