Sunday, September 15, 2019
After a spectacular mid-September day yesterday, this Sunday morning is warm and sunny, with temperatures running about 3 F ahead of where they were yesterday at this time. There are three weather systems that will have some impact over northern Colorado this week, with the first later Monday being the weakest and warmest and the last for the end of the work week being the strongest and coldest.
Currently, there is a subtropical disturbance near the Four Corners moving through a ridge of high pressure over the Rocky Mountains, a large and cold storm bringing precipitation to the Pacific Northwest coast and another cold and strong storm in the Gulf of Alaska. While we will see increasing clouds as the subtropical disturbance moves across southern and central Colorado today and Monday, most of the precipitation should be confined to areas to our south, though there will be a chance for a Monday afternoon shower.
Overnight lows should be above our average of 35 F on Monday and Tuesday as the clouds act like a blanket over the earth. The warm airmass will keep our highs a bit above our average of 72 F on Monday before we see some cooling, breezy winds and a good chance of showers on Tuesday as the Pacific Northwest storm is pushed across the Great Basin by the advancing Gulf of Alaska storm.
However, the storm will be deflected to our north as it crashes into and weakens the ridge of high pressure over the Rocky Mountains. Nonetheless, a weak cool front associated with the storm is forecast to push through during the day on Tuesday, with the best chance of showers along the cool front as it pushes through in the afternoon or evening.
Wednesday and the first half of Thursday should be a pleasant between-storms period as the Gulf of Alaska storm moves south along the West Coast on Wednesday and across the Great Basin on Thursday. Clouds will increase during the day Thursday as the breezy to windy southwest flow ahead of the storm draws moisture northward and over our area. Storms will become likely by Thursday afternoon and evening ahead of and along the seasonably strong cold front which is expected to pass through later Thursday.
The storm is forecast to move across Wyoming on Friday, and we will see a continued chance of showers, along with high elevation snow, in the cool, moist and unstable northwest flow behind the storm.
It looks like another nice September weekend is in store following the Friday storm, with another Pacific storm forecast to cross the West Coast around Sunday. The may affect our area around the following midweek period, though there is substantial disagreement among the weather forecast models on the evolution of the storm.