Return of southerly flow clears smoke but re-establishes the monsoon

Thursday, August 27, 2015

The current storm is now just east of our area, and showers should linger through the rest of the day before clearing overnight.

The upper level flow weakens considerably behind this storm and stays weak through Saturday, interrupting the monsoonal moisture feed from the south that lead to the current storm. Incidentally, and not quite how I forecasted last week, the lingering smoke this past weekend was not purged from the area until the flow shifted from the northwest to the south this past Tuesday. We did get some brief clearing last Friday night, but smoke returned as the northwest flow moved smoke from the active wildfires to our northwest back over the area.

But the weak upper level flow is forecast to increase again Sunday from the southwest as a large storm currently off the West Coast moves eastward early in the weekend and is deflected by the persistent western ridge. This storm will drag a very weak cool front through the area later Sunday, and combined with the increasing moisture from southwest flow ahead of the storm, should contribute to a much greater chance of storms Sunday afternoon.

The increased chance of afternoon storms should be present on Monday as well, before the rebounding of the deflected western ridge dries the atmosphere a bit, leading to decreasing chances of afternoon storms each afternoon for most of the work week.

Another similar storm is forecast to be off the West Coast around midweek, and current model solutions again have the storm deflecting the western ridge and dragging a weak cool from across the region around the end of the next work week. As is forecast to happen this Sunday, the chance of afternoon showers should increase again sometime during Labor Day weekend.

Monsoon returns after another cool front Saturday

Thursday, August 20, 2015

The fall-like cool fronts that pushed through our area Tuesday and Wednesday will be followed by another two similar fronts Saturday and Sunday mornings before the western ridge rebuilds. Temperatures will rebound and monsoonal moisture will return early in the next work week.

Meanwhile, our hazy smoke-filled skies will likely continue today and tomorrow before a storm currently off the Pacific Northwest coast drags a cool front over our area early in the day Saturday as it moves eastward. This will be followed by a trailing wave early Sunday morning that will reinforce the cool conditions.

Wildfires were reported around Maybell and Craig earlier in the week, and it seems likely at least some of the smoke in the Yampa Valley could be attributed to those now-contained fires. But our current northwest flow is passing over the active wildfire regions in the Pacific Northwest, and that is likely contributing to the haze as well.

The smoke should be cleared from the area by the first front Saturday morning. After the second front passes through the area on Sunday, the persistent western ridge rebuilds, bringing seasonably warm temperatures by Monday and allowing monsoonal moisture from the south to move over the area by later in the day Tuesday. This pattern will bring the chance of storms each day under warm temperatures through the following week, as has been typical for most of our summer.

Longer term, the battle between summer and fall continues as additional energy forms strong storms near the Gulf of Alaska. These storms will interact with the still-strong western ridge, with the stronger storms able to penetrate the ridge enough to interrupt the summer weather with fall-like weather.

Autumn-like front now timed to arrive Tuesday

Friday, August 14, 2015

The western ridge responsible for our persistent monsoonal weather regime this summer is forecast to break down starting tomorrow as a series of Pacific shortwaves cross north of our area this weekend. Then, the first Autumn-like front is forecast to move through the area on Tuesday, bringing windy conditions and dry air with noticeably cooler temperatures.

But first, warm days with the chance of afternoon storms bringing the possibility of locally heavy rainfall will exist for today and more so tomorrow. A storm currently off the coast of northern California will move mostly north of our area late Saturday quickly followed by another wave of cooler air early Sunday that will keep temperatures slightly cooler under possibly cloudy skies.

Concurrently, an unseasonably strong storm in the Gulf of Alaska will cross the Pacific Northwest coast by Monday and turn our winds back to the west during the day. Dry air is forecast to be near our area on Monday, and a small shift in the flow may keep the day dry or continue the chance of afternoon storms.

The American GFS has drastically changed since yesterday’s forecast, and now agrees with the European ECMWF that the mostly dry southern part of the front should pass through the area on Tuesday. Northwest winds will initially be strong on Tuesday along and behind the front, but should moderate through the week as temperatures begin to recover on Wednesday and reach near normal by Thursday.

Additional dry waves passing north of our area will keep similar conditions through the weekend, though there is uncertainty with respect to the strength of another moderately strong wave currently timed for the end of next weekend. However, with models now agreeing on some sort of Gulf of Alaska ridge building around then and keeping the western trough intact, dry and cool conditions will likely persist.

Hints of Autumn appearing in numerical solutions

Thursday, August 13, 2015

Our weather for the next week looks to begin with the persistent summer monsoon having upper-level flow generally from the south or southwest around a Great Basin ridge. The week will end with a series of cool fronts that veer the flow to the west.

The weather through Saturday should be typical of the summer with warm days and the chance for afternoon storms. A storm currently off the coast of northern California will move mostly north of our area late Saturday quickly followed by another wave of cooler air early Sunday that will keep temperatures cooler than normal on Sunday. Additionally, these weak fronts will flatten the Great Basin ridge and may invigorate our typical afternoon storms for the weekend.

Concurrently, a seasonably strong storm moving southward this weekend along the West Coast from the Gulf of Alaska will turn our winds back to the southwest by Monday, warming temperatures to normal and continuing the chance of afternoon storms.

As this storm crosses the coast and begins to move eastward across the Great Basin on Tuesday, significantly drier air will move into the area by Tuesday or Wednesday, followed by a mostly dry frontal passage Thursday or Friday. This storm should lead to noticeably cooler temperatures by the end of the work week, and these cool temperatures will be reinforced by next weekend as another Pacific Northwest wave moves over the region.

There is considerable model uncertainty for next weekend and after that as the American GFS forecasts a building ridge in the Gulf of Alaska while the European ECMWF shows much less, if any, ridging. Incidentally, the Gulf of Alaska ridge is a typical feature of an El Nino event, and I’ve found that while the American GFS may be early in predicting pattern changes, the model often is correct in forecasting an eventual pattern change. It will be interesting to see how that forecast evolves over the next few weeks.

Weekend will dry out after Friday’s moisture surge

Thursday, August 6, 2015

After a pleasant day today, a wave currently near Baja will bring a surge of monsoonal moisture over the Steamboat Springs area tomorrow and tomorrow night. Showers may start as early as noon Friday and may contain locally heavy rainfall by the afternoon. The showery weather with possibly locally heavy rain should last for most of the night.

This wave will be followed by a second wave currently off the coast of California. Even the short range model predictions disagree with the southern extent of this wave as it moves eastward and stays mostly north of our area. There is a chance that showers may linger during the morning hours, but forecasts call for clearing by the afternoon as the departing northern wave drags drier air over the region.

While Saturday afternoon will likely stay dry, there will be a chance of the usual brief afternoon storms from Sunday through Tuesday. Another round of monsoonal moisture from southerly flow around the periphery of a building Great Basin ridge is forecast to cover the state by Wednesday, leading to possibly heavy rain showers on Wednesday and likely afternoon storms on Thursday.

Concurrently, another Pacific storm is forecast to be around the Northwest Coast midweek. There is considerable model uncertainty with respect to the interaction between this wave and the Great Basin ridge, so the forecast for the following weekend is uncertain.

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