Strong cutoff low will be the main weather story this week
A strong upper level storm system will cutoff from the main atmospheric flow/jet stream this week over the Central US, becoming the first strong cutoff low of the autumn season. These systems are typically observed in the transition seasons of Autumn and Spring, and can bring a plethora of weather impacts. One of the signature features in a cutoff low is the entrenchment of cold air, especially in northern stream systems which drop south out of the Pacific Jet and/or Canada. This one, coming from Western Canada, will dive south and east into the mean 500mb low over the Central US and briefly cutoff before being lifted northeast by a generally progressive pattern.
ECMWF forecast model showing the strong cutoff low at 500mb (mid levels of the atmosphere). Notice the upper level low is “cut off” from the main atmospheric flow.
Technical Stuff: From a meteorological standpoint, cutoff low events aren’t overly rare. Yet, they remain impressive each time they occur. The strong surface low developing in response to this system is expected to develop and curve northwest over the North/Central US, while the cold air pool dives south of it and brings below normal temperatures and mid-level height anomalies (colder than normal averages). The result will be potential severe weather on the far south and east periphery of the system, and the potential for isolated frozen precipitation on the north/northwest fringes. The 12z Euro from October 17th shows the system very well, with the mid level heights displaying the upper level low cutoff from the main height field.
What’s it mean for us?: In our area, the system will bring a chance of showers and thunderstorms beginning late Thursday Night and continuing through Friday. There is isolated potential for a strong thunderstorm or two, given the very impressive shear from the upper level cutoff low to our west. However, meager instability is expected to generally mitigate the threat. We can’t completely rule out an isolated strong wind gust or maybe a brief spin up/weak tornado if all the pieces fall into place. Either way, the weather will be unsettled from Thursday Night through Friday, and continuing into Saturday before the cold front moves through. Thereafter, the cutoff low is expected to shift North and East away from the area.
Keep reading for more information on the cutoff low, as well as a peek into the winter season…