Monday, September 25, 2017
As one center of circulation currently located in Wyoming moves to the northeast, another wave of energy moving southward from British Columbia forms another circulation center in southern Nevada by Wednesday that is cutoff from the jet stream. The cool and unstable northwest flow behind the departing Wyoming storm will continue the chance of afternoon showers today before cool and mostly sunny fall weather graces the Steamboat Springs area for Tuesday.
By later Wednesday, we will begin feeling the effects form the cutoff low which is forecast to move northeastward through the Great Basin as temperatures warm towards normal. Moisture from the south will be pulled northward by the southerly winds on the eastern periphery of the circulation, and the moisture may make it far enough north to produce a chance of light showers in our area by late in the day Wednesday.
Interestingly, on Wednesday, the old Wyoming low is absorbed by fast westerly flow along the Canadian border, and along with continued energy moving southward from Hudson Bay, will help deflect hurricane Maria to the northeast as the jet stream moves eastward across the Great Lakes, sparing the central East Coast form a direct hit.
By Thursday, the Great Basin low is forecast to in central Utah, and waves of energy rotating around the low will combine with increasing moisture from the south to produce increasing chances of showers, with high snow levels, for Thursday and Friday.
Recent model solutions have done away with the ridge of high pressure that was originally forecast for the weekend in favor of some sort of cool trough of low pressure from the Pacific, reinforced with some cold air from the North Pole. And if your thinking that sounds cold, then you are right. Current forecasts, which will almost certainly modify this week due to the recent large forecast model changes, indicate that while we have a chance of showers later Saturday ahead of the front in near normal temperatures, much colder air will arrive sometime on Sunday with showers and lowering snow levels.
While we may not see our first snow in the Yampa Valley then, a reinforcing wave from the northern latitudes crosses the Pacific Northwest coast later Sunday. There is disagreement among the models, with the ECMWF holding the coldest air to our west and north and the American GFS bringing a more consolidated push. The colder solution would bring another round of showers around Monday afternoon, with some snowflakes possible in the city.