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 Post subject: Weather Outlook Through Late November
Post Posted: Nov 10, 2017 12:56 pm 
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The upper level pattern that appears to remain established through much of November has an upper level trough over the Pacific Northwest, with a mean upper level ridge along the Rockies, then another upper level trough over the eastern U.S. This long wave pattern is fairly typical of a La Nina pattern, so we may get used to seeing this pattern for much of our Fall and Winter this season. This pattern will bring a lot of precip to the Pacific Northwest down into northern CA, but keep conditions relatively dry across the central and southern Rockies. Models suggest this pattern will remain in place through the end of November.

Specifically, CO will see a lot of dry and mild days with his pattern, but small changes will occur as Pacific systems skirt to our north. Mostly, as these systems pass to our north we will see increased winds ahead of them, then slightly cooler temps after they pass. Any precip would be mostly confined to the northern and central mountains, with some exceptions if a more vigorous system slides farther south.

For the weekend ahead, mostly dry conditions expected statewide Saturday. A system will skirt to our north Saturday, which will increase westerly winds over the mountains and foothills from tonight into Saturday afternoon. No precip expected in CO and temps will remain near average Saturday, then lower a few degrees on Sunday. Skies should remain mostly to partly sunny each day.

For next week, upper ridge builds over CO early next week, so temps will rise above average Monday through Wednesday. Models suggest another system will skirt to our north late next week, which will bring strong westerly winds on Wednesday, then a chance for some mountains precip Thursday into Friday with temps cooling back to near average or below average Thursday into Friday. GFS has precip on Thursday in the mountains, while the ECMWF holds it off until Friday, but either way it will only be a light and brief shot of moisture.

Next weekend looks dry and mild statewide. The following week (Thanksgiving Week) models suggest a chance for some precip Monday and then again Thursday, but any precip currently looks to remain on the light side, but that could of course change.

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 Post subject: Re: Weather Outlook Through Late November
Post Posted: Nov 12, 2017 7:41 am 
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Not a lot to write about regarding weather in CO except for mostly sunny skies and mild temps this weekend. Sunday temps will be slightly cooler than Saturday but still above average. Some gusty westerly winds will be possible tonight in the foothills as a mountain wave is likely to form.

For the week ahead, mostly sunny skies and temps will climb well above average Monday through Thursday. Breezy westerly winds will be possible in the mountains and foothills at times as well. Models suggest a system will move into CO late this week and bring a chance for precip across much of the state. GFS is faster and weaker while the ECMWF is slower and wetter with the system. Will use ECMWF guidance for now which would bring precip into western CO Thursday night into Friday morning with snow level near 8000 ft and then precip moves into eastern CO during the day on Friday, as snow level lowers to near 6000 ft by Friday afternoon. Currently looks like several inches of snow will be possible in the mountains, while only a few inches in the foothills. Precip should be mostly done by evening with clearing overnight.

Weekend looks mostly dry with cool temps on Saturday returning to near average on Sunday under mostly sunny skies.

For the following week of Thanksgiving, models suggest dry conditions will prevail across CO with temps at or above average and dry conditions expected to persist into the weekend.

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"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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 Post subject: Re: Weather Outlook Through Late November
Post Posted: Nov 13, 2017 12:36 pm 
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Another warm and mild day across the state, with temps today reaching near record levels in many parts of the state. Some gusty westerly winds will be possible at times in the mountains and foothills as moderate flow aloft persists over CO. Tuesday will be a near repeat of Monday with mostly sunny skies and warm temps near record levels once again. A weak system skirts to our north Tuesday night into Wednesday, which will brings some gusty westerly winds and cool temps back to near average values on Wednesday under mostly sunny skies statewide.

GFS is trending towards the ECMWF as usual, so models now in better agreement on system later this week. Prior to system arriving, southwest flow aloft will increase over the state on Thursday, so expect some strong southwest winds in the mountains and foothills on Thursday, and temps will once again be well above average statewide. Some showers will be possible across far western CO late in the day on Thursday with snow level near 12,000 ft. The big change will occur on Friday as Pacific systems moves across CO. Precip will spread to the Divide by Friday morning with a snow level near 10,000 ft. Precip will intensify during the day on Friday and slowly move east to near the Front Range Crest by Noon as snow level lowers to near 8000 ft. Best chance for precip across eastern CO will come Friday afternoon into Friday evening, but models suggest precip will remain on the light side east of the Divide as winds aloft remain westerly. Snow level will lower to near 6000 ft by Friday evening when best precip chances will be in the foothills. For snow amounts, mountains will likely see 6-12 inches above 10,000 ft, while foothills may see 1-4 inches above 6000 ft, and mostly rain east of the foothills. Conditions clear overnight with cool temps expected Saturday morning.

For the weekend, mostly sunny skies both days with temps below average on Saturday, warming to near average on Sunday.

Next week models suggest will remain dry and mild with little if any precip statewide, and temps likely to remain above average most if not all of the week, providing good travel weather for Thanksgiving travelers across CO. Pretty limited for early season skiing however.

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"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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 Post subject: Re: Weather Outlook Through Late November
Post Posted: Nov 14, 2017 1:45 pm 
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Warm and breezy day across much of the state with temps 5-15 degrees above average across the state. Weak system skirts to our north tonight which will bring cooler air into much of CO on Wednesday, so temps will return to near average values Wednesday. No precip expected statewide today through Wednesday.

Latest models still have differences, and the trend is to delay the incoming system. GFS is still faster and drier while the ECMWF is slower, deeper and wetter. As usual my preference is the ECMWF guidance with somewhat lighter precip amounts. Using this approach, Thursday will be another warm and windy day as flow aloft becomes quite strong from the southwest. Winds will reach the 25-50 mph range in the mountains and foothills, creating high fire danger across much of the state without snow on the ground. Clouds will increase Thursday afternoon across western CO leading to a chance for showers by Thursday evening west of Vail Pass with snow level above 10,000 ft. Precip become widespread Thursday night along and west of the Divide with snow level near 10,000 ft. Precip intensifies during the day on Friday from the Front Range Crest westward as snow level lowers to near 8000 ft. Precip continues and moves east into eastern CO Friday evening into Friday night as snow level lowers to 6000 ft overnight. Precip will come to an end early Saturday morning. Models suggest copious snow amounts in the mountains above 10,000 ft with 1-2 feet possible by Saturday morning, with 6-12 inches above 8000 ft along and west of the Divide. Travel across mountain passes may become difficult late Friday into Saturday morning. For our foothills, snow amounts depend on which model you believe. GFS would keep snow amounts below 2 inches, while the ECMWF would have snow in the 3-7 inch range, so my best guess is for 2-5 inches of snow in the foothills above 6000 ft, so roads could become slick Friday night into Saturday morning above 7000 ft.

Saturday looks cool but mostly sunny with temps remaining below average. More sun on Sunday as temps warm back to near average values.

Next week continues to look dry and mild across the state. Perhaps a few mountain showers Tuesday, but nothing significant. Temps will be near average values Monday through Wednesday, then above average late next week, but dry statewide through Friday. Latest models suggest a chance for some precip next weekend.

On the climate side, SST anomalies have further decreased in the eastern Pacific with the weekly ONI of -1.1 in the Nino 3.4 region, which is in the moderate La Nina range. More confidence is building in there will be a weak La Nina this Fall and Winter, with a slight chance we could see a moderate La Nina for a portion of the season. The upper level pattern that has formed in November is a traditional La Nina pattern, with a high amplitude ridge over the western U.S. that has kept CO drier and warmer than average. In addition, there is a strong negative MJO pattern which would keep CO dry through the remainder of November into early December. Assuming this pattern remains for much of the Fall and Winter, much of CO will remain drier than average with above average temps. Normally, there will be brief breaks in this pattern where the upper ridge axis moves back over the Pacific, which allows cold systems to come down from Western Canada across CO. Otherwise, CO will likely see mostly northwest flow aloft as systems move to our north. The northern and Central mountains can get average snowfall from this pattern, while the rest of CO receives less than average snowfall. Of course every La Nina is different, so we will just have to wait and see how things transpire.

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"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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 Post subject: Re: Weather Outlook Through Late November
Post Posted: Nov 15, 2017 1:12 pm 
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Mostly sunny day statewide with temps near seasonal normal values. For Thursday, expect near record temperatures along with increasing southwesterly winds over the High Country and foothills through the day. Wind speeds should reach the 25-50 mph category by Thursday afternoon with higher gusts possible. High winds will extend into Thursday night and Friday morning. Models suggest a very powerful Fall storm will move from the Pacific Northwest into CO Thursday night into Saturday morning. A very strong jetstream of 130-150 knots will move over CO during the day on Friday, which will create strong dynamics and strong westerly winds over the Mountains and foothills. The only lacking component from this system for eastern CO is upslope flow. Flow aloft is so strong from the west that surface winds will likely remain westerly for the duration of this system, which will limit precip amounts east of the Front Range Crest. Along and west of teh Front Range Crest mountain areas will receive copious amounts of precip.

Models hold precip off now until about midnight Thursday night when precip spreads into western CO, mostly west of Vail Pass with snow level neat 10,000 ft. By Friday morning precip has spread to along and west of the Divide as snow level remains near 10,000 ft. It is during the day on Friday into Friday night that strongest dynamics move over CO, so precip will intensify during the day on Friday along and west of the Front Range Crest as snow level lowers to near 8000 ft by Friday late afternoon. Westerly winds of 30-60 mph will accompany snow in the High Country, making travel across mountain passes difficult. There are still differences in precip amounts in the foothills between the American and European models. American models keep precip between 0.25 and 0.5 inches of liquid, while the ECMWF has almost an inch. Given the lack of a good upslope wind component, it is difficult to get high snow amounts in our foothills, yet given the very strong dynamics I could also see slightly higher precip amounts. We will likely see a good burst of snow as the cold front and upper trough move over our area Friday evening. Timing currently looks like heaviest precip will be from 3 pm through 8 pm Friday in the foothills, which may impact late commute traffic. Given the warm temps this week, initial snow will likely melt on roads below 9000 ft until heavier snow and colder temps progress through the evening, so road conditions may deteriorate rapidly after 6-7 pm Friday. Snow level lowers to 6000 ft by 9 pm as precip begins to diminish with clearing by Saturday morning. For snow amounts, here is what I am now thinking:

Mountains above 10,000 ft: 1-3 feet
Mountain Valleys: 6-14 inches
Foothills and Palmer Divide: 2-6 inches

Travel in the mountains will remain difficult through Saturday morning, then improve. Some road closures and power outages will be possible in mountain areas.

The rest of the day Saturday should be mostly sunny and cool, as temps remain below average. Sunday should also be mostly sunny with temps returning to near average values.

For next week, models agree weather should be mild and mostly dry Monday through Wednesday with a chance for some mountain flurries on Tuesday. Temps should be near average. Late next week models now diverge with the GFS bringing cold temps and snow to CO Thursday into Friday, while the ECMWF keeps temps warm and CO dry until Friday night with some light precip possible. Since the cold and snow are a new twist from the GFS, will side with the more consistent ECMWF but will need watching for Thanksgiving travelers.

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"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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 Post subject: Re: Weather Outlook Through Late November
Post Posted: Nov 16, 2017 1:26 pm 
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Warm and breezy day across the state as temps will run 10-20 degrees above average today. Record high of 80 in Denver (set last year) will not likely be broken, but some records may be today across the state. Powerful Pacific system that is bringing very heavy rain to portions of the West Coast will being clouds into western CO later today. Southwest winds aloft will also increase through the day causing gusty surface winds in the mountains and foothills with speeds in the 25-50 mph range with higher gusts possible. Winds will persist overnight and into Friday. Models overall have some into pretty good agreement, with the ECMWF lowering precip amounts in the foothills which seems more reasonable given westerly flow, and produce copious precip amounts west of the Front Range Crest.

Forecast brings precip into western CO overnight, mostly after midnight along and west of the Divide with snow level near 10,000 ft. Precip and westerly winds will intensify during the day on Friday along and west of the Front Range Crest as snow level remains near 10,000 ft, lowering to near 8000 ft by late Friday afternoon. As cold front and upper trough move through CO Friday evening, bursts of moderate to heavy precip will be possible as snow level lowers to 6000 ft by late evening, and down to 4000-5000 ft by midnight. Most precip should end around midnight with clearing by Saturday morning. As front passes Friday evening, winds will shift to northwesterly and remain very strong into Saturday morning, creating blowing and drifting of snow. Travel through the mountains will be difficult from Friday afternoon into Saturday morning with delays, traction laws and road closures possible. All models now keep precip amounts in the foothills below 0.25 inches, so high winds will be the bigger issue in the foothills versus snow. Here are my updated snow amounts:

Mountains above 10,000 ft: 1-2 feet with up to 3 feet on west facing slopes
Mountain Valleys: 6-16 inches
Foothills: 1-4 inches

Roads will be warm initially, so lots of melting before snow begins to stick. In the foothills that may be until after 6-8 pm above 8000 ft, but as temps drop rapidly Friday night any moisture will likely freeze overnight as temps drop into the teens by Saturday morning.

Weekend looks dry statewide, cool temps on Saturday warming to near average Sunday.

For next week, Monday looks warm and dry, then a weak system skirts to our north and brings some light precip to the mountains Monday night into Tuesday morning. Dry with temps near average Tuesday, then warm and dry on Wednesday. Models keep Thanksgiving Day dry and mild statewide now. GFS brings precip into CO Friday with snow down to 6000 ft while the ECMWF holds precip off until Saturday, so we will have to wait and see how that plays out.

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"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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 Post subject: Re: Weather Outlook Through Late November
Post Posted: Nov 17, 2017 9:10 am 
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Powerful Pacific system has begun to bring precip to CO from the Front Range crest westward this morning, with snow level above 10,000 ft. Strong southwest winds will reside over CO much of the day today, as 130-150 knot jetsream moves across the state. Precip intensity will pick up through the day with snowfall rates of 1-2 inches per hour in the mountains. Cold front is currently over Utah and will move east through the day, moving into the foothills around 6 pm this evening. Snow level will remain at or above 10,000 ft until cold front moves through, then snow level will rapidly lower to 8000 ft by 7 pm and down to 6000 ft by midnight. Foothills may receive some light precip during the day, especially the western edges but precip will remain light until front moves through. Moderate to heavy band of precip is expected with and just behind front, so heaviest foothills precip will be from 6 pm through 10 pm, then precip diminishes after midnight, with clearing by morning. Winter Storm Warning is in effect for mountain areas above 8000 ft through 5 am Saturday. For snow amounts, latest models keep 1-2 feet possible in the mountains above 10,000 ft, with 6-14 inches over mountain valleys above 8000 ft. In our foothills, still looks like 1-4 inches will be possible above 8000 ft, with only a dusting to an inch or two below 8000 ft. Mountain roads mostly wet below 10,000 ft but as heavier snow moves in this afternoon, travel in the mountains will become difficult as 30-50 mph winds will create whiteout conditions that will persist into tonight. Initial snow in our foothills will likely melt, but as heavier snow bands move through this evening roads may become snow and ice packed above 8000 ft.

Weekend looks dry with cool temps Saturday and near average temps Sunday.

For next week, temps looks to remain at or above average all week. Weak system will bring some mountains showers Monday night into Tuesday, but dry elsewhere. Wednesday through Friday looks dry statewide with temps above average, so good travel weather for Thanksgiving travelers. Both GFS and ECMWF now keep CO dry next weekend as well with temps remaining on the warm side of average. GFS brings precip to CO early the following week, but will have to wait and see how that evolves.

_________________
"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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