Messy Forecast For the End of the Weekend

You have all probably already heard about the potential for our first Plowable Snow Storm of the season, but what you haven’t heard is what we can expect here in our Neighborhood. This system is still three days out and hasn’t fully formed yet in the Midwest, so the data is a bit sparse, but we have some pretty good ideas along with the model guidance to go off of. First off, here is one model’s suggestion as to what we will see for Sunday Night and through the day Monday.

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From the looks of it right now, the Low Pressure system that will be bringing our precipitation will pass its center over the Great Lakes Region. In meteorology, we call that an inside runner. Usually with an inside runner, we start off with some snowy precipitation as there is still cold air in place, but as the storm tracks to the west of New England, the warm front from the Low Pressure System ends up passing directly over New England allowing warm air to intrude the region and cause the snow to change over to a mix and rain. However, this storm looks like it could end up being a special case, so let’s take a look at a few things.

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This image is from an analysis of Weather Types (WTs) (Weather Patterns seen during a season) in the Northeast by Roller et al (2015). Right now, we are in WT 1 as High Pressure is dominating the Southeast U.S. This storm can be seen as the Low Pressure system over the Midwest. This pattern is mostly seen during a (-PNA) phase, which is what we are seeing now. PNA is a form of teleconnection, which represents the low-frequency tropospheric height variability, as classified in the study of Barnston and Livezey (MWR, 1987). Basically it affects our weather patterns throughout the year based on the position of the jet stream and other factors. This pattern then transitions to WT 2 which sees the Low Pressure system push to the East and North. Most storm tracks tend to go into the Great Lakes Region.

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A look at the current PNA and NAO Indices. A negative PNA and Neutral to Negative NAO suggest stormier weather for the Northeast U.S.

By the end of the weekend, we will see a negative PNA and neutral NAO. This usually suggests stormy weather for the Northeast, but also suggests that inside running storms are likely. That means we are most likely to see a changeover to some mix and rain at some period during the day on Monday as warmer air is pulled into the region. graphic.aspx.png

Above you will see a map of the vorticity in the upper atmosphere. When we look at vorticity, we look for the regions of bright colors, indicating a vorticity maximum. That usually suggests somewhere around the area there will be rising air and the potential for some precipitation (this is one of many factors that influence whether or not precipitation will occur). Looking at this, we see the maximum that is near the center of the Low around the Great Lakes so there is expected precipitation to the west. There is another interesting area around Virginia that suggests some precipitation off the East Coast. There is suggestion that this could be picked up by the low pressure system and form a secondary low off the coast of Massachusetts. That would cause enhanced precipitation over Southern New England leading to higher amounts by the end of the day Monday.

This storm needs to be monitored closely during the next couple of days to fully see what will happen, but either way, expect a messy start to next week!

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