Monday, July 31, 2017
The day after my last Thursday forecast predicted another monsoonal moisture surge for today and Tuesday, model forecasts started trending further west with a building western ridge of high pressure. This has come to pass, bringing drier air over the Steamboat Springs area as of yesterday afternoon and keeping storm chances minimal for the first half of the work week.
Meanwhile, Pacific energy will travel in waves over the top of the western ridge and will eventually carve out a broad trough of low pressure over the eastern two thirds of the country by the end of the work week. One of these waves will phase with some cool air sourced from around the Hudson Bay region and bring a fall-like cool front through our area later Wednesday or early Thursday.
Though a much cooler Thursday is very likely, there is disagreement among the models as to the precipitation potential for this event. The wetter models forecast some storms from Wednesday afternoon through Thursday, including Wednesday night, and the drier models just bringing in the cooler air for Thursday. At this point, I would lean toward the drier solutions, though these systems in northwest flow are notorious for digging further west and becoming wetter as the models get a better handle on extent of the cool Canadian air.
Warmer air returns on Friday, but the weekend forecast looks unsettled. In addition to the waves traveling over the ridge in northwest flow, some energy from the southern latitudes moves northward to the northern California coast by late in the work week. Pieces of the resultant low pressure area then move eastward underneath the western ridge and across the Great Basin through the second half of the weekend.
Combined with another cool front in northwest flow timed for mid-weekend, unsettled weather with possibly strong storms are in the forecast for later Saturday and through Sunday.
There is model disagreement as to whether the western ridge stays put early next week for a drier forecast as advertised by the European ECMWF, or moves eastward like the American GFS for a wetter forecast.