Monday, July 10, 2017
Pacific energy moving eastward from a complex of storms in the Gulf of Alaska has flattened the dominant western U.S. ridge and nudged it eastward, allowing the first significant surge of the Southwestern U.S. Monsoon to reach the Steamboat Springs area this season.
The tropical storm system discussed in the last forecast did indeed turn into hurricane Eugene and contributed to the moistening of the atmosphere over the southwestern U.S. As a result, there is a good chance of wetting rains over the Steamboat Springs area later this afternoon and early this evening. Short range models show another batch of showers that may reach far enough northward to produce more rain around midnight.
As weak Pacific energy moves eastward to our north, drier air moves in behind the wave, and our weather will depend on the outcome of the battle between this dry air to our west and north and the monsoonal moisture to our south and southwest. Current models have a chance of showers for Tuesday and Wednesday as the boundary between the dry and moist air is close to northern Colorado.
By Thursday, the western U.S. ridge rebuilds, bringing drier air across the region under hot temperatures. The strong surface heating will cook any remaining low-level moisture to produce a chance of afternoon storm for the remainder of the work week and into the weekend.
Significant differences between the models arise for the second half of the weekend, with the American GFS further rebuilding the western U.S. ridge and further warming temperatures as cool Canadian air moves southward across the Eastern U.S. The European ECMWF, on the other hand, slides this cool Canadian air westward and tries to phase it with some incoming Pacific energy, flattening the western U.S. ridge and moderating temperatures for the second half of the weekend and early next week.
Thursday, July 6, 2017
A ridge of high pressure centered over the Great Basin will be nudged eastward this weekend by incoming Pacific energy. The weak southerly to southwesterly flow on the west side of the ridge will allow the monsoonal moisture pooling around the Sonora Desert to move northward, increasing mid and upper level moisture over the Steamboat Springs area for Friday and Saturday. The additional moisture will create high-based afternoon and early evening storms that will produce more gusty and erratic wind than rain, and possibly some dry lightening, as the lower levels of the atmosphere remain quite dry.
By Sunday, the Pacific energy traveling over the top of the ridge will interrupt the fledgling monsoonal flow from the southwest, with drier air moving over the area in weak westerly flow. There will still be the possibility of afternoon storms though, as the meager low-level moisture is lifted by the strong surface heating of mid-summer and interacts with some of the grazing Pacific energy to our north.
On Monday, more Pacific energy again pushes the western ridge eastward into the Great Plains, and a better monsoonal tap of moisture appears around Tuesday. While mid and upper level moisture is carried northward by southerly flow on the west side of the ridge, low level moisture may also receive a boost from a tropical storm moving westward south of Baja. Northern Colorado will have a much better chance of wetting rains starting around Tuesday and extending through the work week and into next weekend, as moisture falling from any storm will not encounter the very dry lower-level air present for this weekend.
Longer-range models, as of today, want to keep the monsoonal flow around after next weekend as well, hopefully leading to a far wetter July as compared to June as tropical waves of energy move northward over the Sonora Desert and eventually across the Great Basin.
Monday, July 3, 2017
The wave of energy discussed in the last forecast has moved east of the Steamboat Springs area, and drier air has moved in behind the departing disturbance. There may still be a chance of some afternoon or evening sprinkles later today.
Temperatures will warm further for Independence Day and the work week as a ridge of high pressure builds over the western US. Moisture to fuel any afternoon storms will be sparse for most of the work week as generally light northwest flow keeps hot and dry air over our area.
By the end of the work week and heading into next weekend, incoming Pacific energy is forecast to nudge the western U.S. ridge eastward, placing the ridge axis over the spine of the Rocky Mountains. The weak southerly to southwesterly flow on the west side of the ridge will allow the monsoonal moisture pooling around the Sonora Desert to move northward, though the northward extent of this moisture surge is uncertain.
The robustness of the moisture surge may also be moderated by the incoming Pacific energy traveling over the top of the western U.S. ridge and digging southward into the eastern third of the country. The cooler air to our east may nudge the western ridge back westward which would interrupt the fledgling monsoonal flow over Colorado.
The end result is the hot and dry conditions forecast for the work week will be followed by some increasing moisture and the chance of afternoon storms heading into weekend.
Thursday, June 29, 2017
A trough of low pressure over the northern plains has brought cooler temperatures to the Steamboat Springs area today. A trailing wave will bring the last cool front in this series through the area overnight, leading to a chilly morning with even the possibility of some frost. The National Weather Service forecast for the Park Range even has the mention of snow flurries for tonight! Still-tender plants in low-lying areas might need to be protected tonight and Friday night with the unseasonably cool temperatures.
As the trough moves eastward, a ridge of high pressure will return to the western states, bringing drier air and strongly warming temperatures for the weekend.
Meanwhile, another Gulf of Alaska storm has mixed with some subtropical moisture and will weaken as it crosses the Great Basin on Sunday. By the time the trough moves over Colorado later Sunday into Monday, the increased moisture and upward motion associated with the trough will bring increasing chances of showers, with the associated clouds moderating the hot temperatures.
A western ridge rebuilds behind the early week storm, bringing hot temperatures for Independence Day. There may be a chance of some afternoon showers, but they should be isolated and brief.
By midweek, the numerical models disagree with the evolution of the western ridge. The American GFS insists on further amplification, bringing even hotter and drier weather to the western states for the rest of the work week, while the European ECMWF has a weakening ridge which allows some Pacific energy to move inland. This would result in more seasonable temperatures with the possibility of afternoon showers starting around midweek.
Monday, June 26, 2017
A ridge of high pressure over the Intermountain West will allow temperatures to rise above normal for today and Tuesday with very little chance for precipitation. A storm currently in southern British Columbia will mix with some cool western Canadian air as correctly forecast by the American GFS last week and bring a series of cool fronts through the Steamboat Springs area starting Wednesday and persisting through the first part of the weekend.
These fronts will be dry, with some breezy westerly to northwesterly afternoon winds. Temperatures will be close to or slightly below normal leading to gorgeous and comfortable summer days with cool nights for the rest of the work week and heading into the weekend.
A transient ridge of high pressure is forecast to translate over the western states for the second half of the weekend, allowing hot temperatures to return around Sunday and heading into the new work week. There is also a weak subtropical disturbance moving through this ridge, leading to a slightly better chance of clouds and possibly some precipitation on Sunday.
With summer weather firmly entrenched, I’ve been looking at the longer-range forecast models to get an idea of when our summer monsoon season might arrive. While there currently is some moisture pooling around the Sonoran Desert, it appears it won’t get here until around the following weekend when southwesterly flow is predicted to become better established over the western states.