Multiple rounds of strong storms possible this weekend

A well advertised weather pattern, featuring a large ridge over the Central United States and building heat in the Northeast US, will come to fruition this week. Temperatures will increase fairly dramatically as the end of the week and weekend approaches, with high temperatures reaching into the middle to upper 90s from Friday through Sunday. In addition to the discussed heat has been a well advertised threat for strong and severe thunderstorms.

Along the top of the mentioned ridge will come several atmospheric disturbances, riding along the ridges periphery as the jet stream is shoved to the north with the ridges development. The positioning of the ridge over the Central US suggests these disturbances will slide from Southern Canada, through the Great Lakes, and into the Northeast states late this week and weekend.

While this period has been highlighted for quite some time as featuring the potential for strong and severe thunderstorms, considerable uncertainty remained in regards to the details of individual disturbances. Forecast models struggle mightily with these details, especially on the periphery of large heat ridges, because the disturbances themselves are convective in nature.

Nevertheless, forecast models have begun to focus on a disturbance approaching the Northeast US on Friday with the potential for strong to severe thunderstorms throughout the Northeast States on Friday afternoon and evening. Global (and some shorter term) models agree that a significant surge of mid and upper level wind shear will accompany the disturbance, acting to effectively form thunderstorms in an unstable environment.

NAM model showing the area of favorable wind fields on Friday with the northwest flow highlighted in yellow.

NAM model showing the area of favorable wind fields on Friday with the northwest flow highlighted in yellow.

The storms are likely to form over New England later on, and then shift southeastward during the afternoon and evening hours. This is where details become important. Forecast models currently depict a textbook “Northwest flow” severe weather event. The name is derived exactly as  you may think — thunderstorms advect toward the Northeast US on a northwest to southeast flow in the mid levels of the atmosphere.

But the exact details of how the convective system evolves will be critical to the forecast. A broader and slower trough could lead to storms remaining further north and discrete over New England. A faster and more compact trough could lead to an organized Mesoscale Convective System diving southward toward New England and the NYC Area/Long Island later on Friday. These details, as you might have guessed, won’t be determined for another day or two.

For now, the Storm Prediction Center has placed much of New England in a Slight Risk for severe thunderstorms on Friday. Another severe weather event is possible on Monday as a cold front — and yes, associated favorable wind fields — approaches the area. Instability is again forecast to increase with a northwest to southeast advection of storms yet again.

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