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.
Thursday, July 27, 2017
The Steamboat Springs area finally received some beneficial rainfall from one of Southwest U.S. Monsoon surges that have been passing through the last few weeks. Around a half inch of rainfall was recorded in several locations around the city from Tuesday night through Thursday afternoon, with the town waking up to a rare steady rain Wednesday morning.
Activity will decrease today, but rain chances increase again later on Friday as the northern California low pressure system talked about in the last forecast begins it’s eastward trek across the Great Basin. Some energy ejects out ahead of the storm and moves over our area later Friday, increasing chances of rainfall Friday afternoon and evening.
After the ejecting wave passes, the northern California storm moves bodily into the Great Basin on Saturday, pushing the ridge of high pressure over the western states eastward. Another monsoonal surge appears on the the western periphery of the ridge, and embedded sub-tropical waves will once again increase the chances for locally heavy rainfall Saturday afternoon and evening.
Model disagreement makes Sunday’s forecast uncertain with the northern extent of the sub-tropical moisture battled by some dry air to our north. There could be another chance of locally heavy rain on Sunday or it could be drier than Saturday.
By Monday, there is model agreement that another robust surge of monsoon moisture and energy will begin and last through Tuesday. If the energy moves as far north as currently forecast, Steamboat Springs has a good chance of locally heavy rain for both days.
Longer range models have the western ridge retreating back westward as energy over the eastern two thirds of the country interrupts and reverses the eastward progress of the ridge. Much drier air is advertised for the rest of the work week and heading into the following weekend. This may spell the end of our monsoon season as the two week forecast has the strengthening westerlies of our next season moving southward. If this occurs, it will suppress any northward moving moisture and energy from the southern latitudes to our south.
Monday, July 24, 2017
The U.S. Southwest Monsoon will be re-invigorated tomorrow, a day faster than advertised in the last forecast. Currently, a storm off the West Coast has split, with the northern part of the wave forecast to move along the northern U.S. border during the week while the southern part loiters over the northern California coast until midweek.
Meanwhile, a well defined wave of energy from the tropics is currently moving northward in southern Arizona, and will conspire with some energy ejecting out of the northern California storm to bring a good chance of rainfall, some locally heavy, for the entire state of Colorado on Tuesday.
While this complex will move east of the Steamboat Springs area by early Wednesday, additional energy ejecting out of the northern California storm will keep a good chance of rain for Wednesday as well, though the chances are less robust than Tuesday. But stronger and sparser storms are possible later Wednesday and Wednesday night courtesy of a very weak cool front grazing our area from the wave moving along the northern U.S. border.
Eventually by Thursday, the northern California storm will penetrate inland and move northwest of Colorado, displacing the ridge of high pressure over the Rocky Mountains eastward. This keeps a weak monsoonal moisture plume over Colorado in the southerly flow on the west side of the ridge, for a continued chance of rains on Thursday.
Drier air is advertised heading into and likely through next weekend, though there is some mid and upper-level moisture that will likely not lead to significant precipitation, but may moderate the hot summer temperatures by partially blocking the sun.
Thursday, July 20, 2017
Though the rainfall from the current Southwest U.S. Monsoon has only amounted to a few tenths of an inch over the past two days in the Steamboat Springs area, we will have more chances today and Friday for locally heavy rainfall, including the overnight periods.
Subtle waves of energy moving northward in the monsoonal moisture plume make local forecasting difficult, but current model forecasts have one of these waves phasing with some energy moving across the northern U.S. and traveling over our area later on Friday. This should give us our best chances for locally heavy rainfall Friday evening and overnight.
The westerly flow behind Friday’s wave will return drier air to northern Colorado for the weekend and into the early part of next week. Along with a building ridge of high pressure over the Intermountain West, there should be minimal chances for afternoon storms on Saturday, with a better chance on Sunday.
The drier air will stick around until Wednesday, keeping precipitation chances low, before a storm off the Pacific Northwest coast elongates to the south along the West Coast. This will promote southwesterly to southerly flow that is forecast to bring another monsoonal surge of moisture over Colorado. Some energy ejecting out of the West Coast trough of low pressure may provide a focus for stronger storms on Wednesday, with continued chances of more rains through the rest of the work week as the monsoonal plume of moisture remains mostly intact.
The evolution of the West Coast trough will dictate whether we see drier air for next weekend or a continuations of the moist conditions.
Monday, July 17, 2017
A storm off the coast of British Columbia has mixed with some cool air from western Canada, and a piece of the storm will travel across the northern U.S. border through today. Energy associated with this wave has flattened the dominant western ridge of high pressure that was over the Steamboat Springs area this past week and may provide a focus for a round of afternoon storms today.
Some drier air will follow for Tuesday as the western ridge tries to rebuild, though there will still be a slight chance of afternoon storms.
By Wednesday, the parent storm near British Columbia begins to move eastward, with energy ejecting out ahead of the storm nudging the flattened western ridge eastward and opening the door to a robust surge of monsoonal moisture from the south.
We should have a good chance of wetting rains on Wednesday and Thursday, including the overnight periods, with locally heavy precipitation possible, as embedded subtropical waves move through the moisture plume and phase with some passing energy from the eastward-moving British Columbia storm to our north.
Drier air is advertised to encroach on our area by the weekend in the westerly flow behind the passing storm to our north. Though we will still have a good chance of storms on Friday, the drying air should lead to a downturn in precipitation chances heading into the weekend.