Major cool down coming for US September 18-20, and potential for early and widespread frost/freezes north of I-80

Long range models have continued to indicate the potential for an abnormally cold airmass to head towards the US as we get into next week. The pattern this week will be cool over the eastern US, but ridging will rebuild over the eastern US, and a trough will begin to develop over Alaska in about a week, and that will lead to high pressure over western Canada. With that, we will see a very sharp low pressure area dig in between the ridge over western Canada and an area of over the canadian maritimes. This will force an area of low pressure to come out of Manitoba and Saskatchewan and dive east- southeastward into the upper midwest and upper great lakes, and with this system there will be significantly more cold air than with this previous low pressure area that moved through and produced severe weather from the central plains to the northeast. Initially, in the long ranges, the models had indicated the potential for snow over the upper midwest, but that seems a bit overdone due to the typical trough bias in models like the GFS. However, the model guidance and the pattern at 500 millibars supports such a cold snap to occur, and with this cold airmass will likely be some severe weather, as is typical with strong fall cold fronts. The effects of this set-up will be lots of cold and early season freezes and frosts. mainly north of I-80, and if this occurs, it could mean the end to the growing season over the northern and central plains. Highs will likely struggle to get out of the 50s over the upper midwest and northeast. Over the southeast, the high temperatures will probably tumble from the summer-like heat from 80s and 90s that will dominate later this week, to at least the 70s, and even 80s further south towards the Gulf coast. Overall, this potential cool down looks even more significant than the current one, and with this airmass we need to keep an eye out for the potential for severe weather, due to the typical nature of these strong fall-like frontal boundaries. If this scenario unfolds, it could put an end to summer for most of the country, lead to the end of the growing season for areas along and north of I-80, and it may be a precursor of what is to come as winter approaches.