Weather slowly turns more seasonable for the week ahead

Thursday, August 10, 2017

A ridge of high pressure in British Columbia is sandwiched between a strong storm in the Gulf of Alaska and a broad trough of low pressure over the eastern two thirds of the country. Energy traveling southward from western Canada along the east side of the ridge has brought a series of cool fronts through the Steamboat Springs area this past week. Additionally, a weak area of low pressure off the northern California coast has supplied a steady stream of moisture for our area, and this combined with the cool fronts has brought significant moisture to the Yampa Valley.

Additional cold air dropping into the Gulf of Alaska first elongates the storm located there southward before moving it eastward early in the next work week. As this happens, the old low pressure area off the northern California coast gets kicked east-northeastward on Friday. Brief ridging occurs over our area on Friday ahead of that leading to a slight chance of afternoon storms.

However, pieces of the old California low will move over our area on Saturday and Sunday, and combine with a couple more surges of cool air from the north to increase the chance of storms for both days again.

There is a fair bit of uncertainty for early next week with respect to the evolution of the Gulf of Alaska storm. At one point it looked like drier westerly flow would overspread the area as the storm traveled to our north, but now there are indications that some of the storm will be left behind off the California coast. It is not clear whether our area will experience a moist southwest flow, which would produce storms for Monday and Tuesday, or a drier westerly flow.

For what it’s worth, models currently agree that the midweek period will be drier, though the following weekend may be affected by energy left off the California coast that eventually propagates inland.

Unsettled and cool for the week ahead

Monday, August 7, 2017

A ridge of high pressure over British Columbia, a large trough of low pressure over the eastern two thirds of North America and a small, diffuse trough of low pressure located off the northern California coast will influence our weather this week.

A number of cool fronts will pass through the Steamboat Springs area this work week courtesy of the generally northwest flow between the ridge to our west and the trough to our east. Additionally, upper level energy and moisture will periodically eject across the Great Basin from the diffuse low off the northern California coast, creating an active weather regime for Steamboat Springs this work week.

The exact timing of the cool fronts from the north and energy from the west are difficult to forecast due to their subtle nature. Generally active weather with cooler than average temperatures are expected this week as the weather pattern is fairly constant, with breaks between the periods of active weather.

By the end of the work week, a powerful storm that was spinning in the Gulf of Alaska begins to move toward the Pacific Northwest coast. This storm will not only kick the nearly stationary northern California low well to our northwest, but will also force the Pacific Northwest ridge eastward.

There will be a brief battle between another surge of cooler to our north and the building ridge of high pressure around Friday, with current model solutions bringing warming and some drying to northern Colorado by the weekend as the ridge eventually wins the battle. Though the weather will dry considerably, there will still be a chance of afternoon storms for the weekend as residual moisture is heated and lifted.

There is considerable uncertainty with regards to the Gulf of Alaska storm and how it may affect our weather for the following work week.

Mostly dry before unsettled weather appears heading into next week

Thursday, August 3, 2017

A weak and dry cool front has passed through the Steamboat Springs area early this morning as cool air from western Canada was pulled southward along the east side of a building Gulf of Alaska ridge. Smoke from the Montana wildfires was also brought southwards over our area in the north-northwest flow producing the current hazy conditions.

Northern Colorado will be affected by three distinct weather regimes over the next week; a couple more weak cool fronts currently timed for Saturday and Sunday mornings, a tongue of dry air to our northwest associated with the Gulf of Alaska ridge, and a diffuse area of low pressure off the coast of northern California.

Drier air has spread over our area behind this morning’s cool front, and will remain in place until the next weak cool front on Saturday. As is the case today, there is not much moisture associated with the Saturday wave, but there may be some afternoon and evening storms as weak upper-level forcing moves over the area before the drier air briefly returns overnight.

The second weak front for Sunday will be a bit stronger and moister, yielding better chances for afternoon storms.

By Monday, we begin to feel the influence of the low pressure system off of Northern California as energy begins to eject eastward across the Great Basin. These waves will not only carry moisture and energy over our area starting later Monday and lasting through the work week, but will also mix with several more weak surges of cool western Canadian air still moving southward along the east side of the Gulf of Alaska ridge for a good chance of wetting rains each day.

The old Northern California low pressure system is forecast to move across the Great Basin and be east of our area by around next weekend, though the timing is uncertain as models disagree with how quickly cold air drops into the Gulf of Alaska and moves the ridge of high pressure eastward towards the Intermountain region.

Models agree on eventually returning drier air over our area when this happens, though perhaps briefly, as pieces of the new Gulf of Alaska storm may begin affecting our weather soon after that.

Warm and mostly dry work week until fall-like cool front arrives for Thursday

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.

After a drier Thursday, rain chances increase for the weekend and early next week

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.

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8 September 2018

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