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 Post subject: Weather Outlook into Late december
Post Posted: Dec 11, 2017 1:33 pm 
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The story of our December weather is the large scale upper level blocking ridge along the West Coast, which is dominating the weather pattern across the entire U.S. leaving the western U.S. dry and warm, and creating cold and snowy conditions across most of the U.S. east of the Rockies. These high amplitude patterns are fairly common during La Nina seasons, and these large scale blocking patterns tend to remain in position for weeks to months at a time.

Currently, upper level ridge axis is over the Great Basin, creating warm and dry conditions across CO. Temps will be well above average today and Tuesday across the state with no precip expected. Fire danger will be elevated over much of eastern CO, with Red Flag Warnings in effect across the far eastern plains today. Tuesday will feature similar conditions, so no big changes between today and Tuesday expected.

By Wednesday, upper level ridge positions shifts westward back along the West Coast, which will allow a system to slide down from western Canada and skirt CO late Wednesday into Thursday. An associated cold front will move south across CO Wednesday afternoon/evening so expect cooler temps on Wednesday, closer to seasonal norms. Some light snow will be possible Wednesday night into Thursday morning, mostly over higher mountain terrain, but a few flurries may be possible in the foothills with a dusting of snow possible as snow level lowers to 5000-6000 ft Thursday. Temps will be much cooler Thursday with below average readings for much of eastern CO, near average across western CO.

Temps climb back above average on Friday under mostly sunny skies statewide. Next system from the Gulf of Alaska pushes through upper ridge position into CO on Saturday. This will again bring cooler temps and a chance for some light snow across much of CO on Saturday. Amounts will be light, with perhaps a few inches over the mountains, and a dusting to an inch possible in the foothills and eastern CO. Temps will be below average on Saturday.

From Sunday into most of next week, upper ridge builds back over the Great Basin which should keep CO mostly dry and temps are expected to remain above average through Friday. Models suggest cooler temps with a chance for snow next weekend as upper ridge builds up into Northwest Canada and allows a system to drop south over CO from Alberta. It does not appear any major snowstorms are on tap for CO through xmas at this time.

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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 into Late december
Post Posted: Dec 12, 2017 12:47 pm 
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Another warm and dry day across our state as upper level ridge remains parked over the Great Basin. Some signs of hope that this pattern will be changing over the next week or so though... Temps will be 10-20 degrees above average today statewide with mostly light winds, except some gusty northwest winds on the far eastern plains this afternoon and evening.

On Wednesday, upper ridge will move westward and allow a system to slide down from western Canada into CO Wednesday evening into Thursday. Temps will be cooler on Wednesday, close to seasonal norms and some gusty northwest winds will be possible across the state. Precip will move into the northern and central mountains between 6 pm and 9 pm Wednesday evening and into the foothills between 9 pm and midnight with snow level near 5000 ft. Snow will continue overnight and spread into the Urban Corridor and adjacent plains into Thursday morning, creating a slick Thursday morning commute for most. Snow level will be below 4000 ft by Thursday morning, and temps will remain below average during the day as snow persists through Noon, then begins to diminish into flurries in the afternoon, then clears Thursday night. For snow amounts, mountain areas may see 2-6 inches with heaviest amounts along and north of I-70, while foothill areas may see 1-3 inches, and a trace to an inch or so along the Urban Corridor. Expect Thursday morning commute to be slick with ice and snow over most local roads Wednesday night into Thursday morning. Roads should improve by Thursday afternoon.

Friday should be another dry day with some gusty northwest winds across many areas of the state. Temps will be back close to seasonal norms for most areas.

Next system will move from the Gulf of Alaska into CO Friday night into Saturday. System looks pretty similar to our Thursday system so expect temps and snow amounts to be close to Thursday. Snow looks to move into mountains after midnight on Friday night and spread into eastern CO during the day on Saturday as snow level remains below 4000 ft. Thus temps will be below average on Saturday, and snow amounts look to range from 2-6 inches in the mountains, to a trace to 2 inches over the foothills and Urban Corridor/plains. Roads may become slick during the day on Saturday, especially in the mountains and foothills.

Sunday looks to remain dry as temps remain below average.

For next week, models suggest a significant change in the upper level pattern. Monday into Tuesday will be dry statewide as temps remain near average. Later next week, models suggest large upper level ridge will retrograde westward into the Pacific and northward towards Alaska and create a Omega blocking pattern that will place a large upper level trough over the Western U.S. If this pattern come to fruition, CO would see very cold temps as arctic air would plunge south over much of the Western U.S. and this would bring much wetter conditions to much of the West, including periods of snow over CO. Models still have some differences in how this pattern will evolve, so the eventual position of the upper trough will dictate how cold and how much snow would come to CO from Thursday next week into xmas weekend. The good news is this is hopefully signaling a significant change in the upper level pattern that will allow snow to come to CO, which we are in need of. I will anxiously continue to follow how this evolves.

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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 into Late december
Post Posted: Dec 13, 2017 4:58 pm 
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First surge of cooler air moved over CO this morning, so temps today near seasonal norms versus the record high temps yesterday. Upper level trough currently bringing snow to the northern Rockies and upper Great Basin will move over CO this evening into Thursday. Latest high resolution models show snow moving into northwest CO after 4 pm, then moving into the foothills between 6 pm and 9 pm with snow persisting overnight from the mountains to the Urban Corridor. Heaviest snow will be from 9 pm through 6 am Thursday in the foothills, and will be enough to snarl the morning commute. For snow amounts, latest HRRR brings from 0.25 to 0.50 inches to the mountains and foothills, with lesser amounts farther east. Snow level will begin around 6000 ft this evening and then lower to below 4000 ft after midnight. For snow amounts, looks like 2-6 inches in the northern and central mountains, 1-4 inches in the foothills and Palmer Divide, with up to 6 inches in favored locations, and 1-3 inches over the Urban Corridor with lesser amounts farther east. Roads will likely become snow and ice packed tonight making for a slower and slick commute Thursday morning. Snow will begin to diminish Thrusday morning after 9 am turning to flurries after Noon, and then clearing after 6 pm. Temps will be well below average on Thursday statewide.

Friday will bring mostly sunny skies and temps warm back to near average.

The next system will approach CO from the northwest on Saturday. Clouds will increase during the day as temps remain near average. Models differ a bit on this system, with GFS and NAM splitting the energy in the upper level trough, while ECMWF keeps all of the energy together as upper trough moves over CO. Thus, GFS and NAM have light snow amounts over CO while the ECMWF has much more snow. Will have to wait and see how things evolve, but either way expect much cooler temps Saturday into Sunday, with snow likely Saturday afternoon into Sunday morning, just depends how much at this point.

For next week, models really not sure what will transpire at this point. Early in the week models agree CO will remain mostly dry with temps near seasonal norms. Later next week, models have very different solutions. GFS keeps upper level ridge along the West Coast and brings a series of systems across CO late Thursday into next weekend, while the ECMWF develops a large and deep upper level low over the Great Basin and brings it towards the 4 Corners by next weekend. Not sure which way this one will go. Models have had very different solutions the past few days, so confidence in any solution is very low at this point. Will just have to wait and see how things evolve.

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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 into Late december
Post Posted: Dec 14, 2017 1:18 pm 
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Nice to finally see some snow, about 1-3 inches for most foothill areas, with generally less than inch across the Metro Area. A few lingering flurries will be possible this afternoon, then clearing overnight with cool temps, so any moisture left on roads likely to freeze. Some gusty northerly winds likely across portions of eastern CO from the Divide east, so potential for some blowing and drifting snow into this evening. Winds should diminish overnight.

Mostly sunny day on tap for Friday with temps at to slightly above average.

Models are a bot confused on the next system. GFS and now the ECMWF split the majority of energy with incoming upper level trough way south into southern AZ Saturday into Sunday, while the NAM and WRF keep the majority of energy farther north and develop a closed upper low near the 4 Corners by Sunday morning. Hence, GFS and ECMWF would bring very little snow to CO, while NAM and WRF bring much higher snow amounts Saturday evening into Sunday morning. Not quite sure which way this one will go, so for now will wait and see what model solutions look like tomorrow. Given the high amplitude upper ridge along the West Coast, I am beginning to favor the GFS and ECMWF, but it could go the other way as well. In general temps will be near seasonal norms on Saturday, then cooler on Sunday.

For next week, models have come into better agreement that early next week will be dry with temps near average. Both the GFS and ECMWF keep the upper level ridge off the West Coast, far enough to allow systems to move southeast from the Gulf of Alaska across CO late next week into next weekend. First system would move across CO Thursday with decent snow and much colder temps, then leave Friday cool but dry. Next system would bring more snow and even colder temps to CO on Saturday with the possibility of snow persisting into Sunday, with very cold temps. This forecast is very promising for a white xmas across much of CO, but too early to get too excited about it. Sure would love some fresh snow for xmas to head out x-country skiing and snow shoeing though.

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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 into Late december
Post Posted: Dec 15, 2017 6:16 pm 
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Sunny and mild day across the state today as temps rose a bit above average most areas.

Well, as models hinted earlier, next system will be a bust for CO. Upper level trough moving through the Pacific Northwest today will dive into the Great Basin on Saturday and then dig farther south into southern AZ/NM on Sunday. This will leave most areas of CO with little if any precip from this system. Some cooler air will move into CO Saturday night into Sunday morning, but not much else from this system. Temps Saturday will be close to seasonal norms for most areas. Sunday will be mostly sunny as temps remain on the cool side of average, but a pretty nice day for mid December.

For next week, a flat upper level ridge will be over the Great Basin leaving CO dry with temps above average Monday through Wednesday. Some breezy westerly winds will be present at times in the mountains and foothills. Models continue to bring an upper level trough from the Pacific Northwest into the Great Basin and then across CO Wednesday night into Thursday. Precip would move into western CO Wednesday night with snow level 5000-6000 ft then move into eastern CO during the day on Thursday morning as snow level lowers to plains level. Snow would persist into Thursday afternoon then dissipate by Thursday evening. At this time models would bring 4-8 inches to the mountains, 1-4 inches in the foothills and a trace to 2 inches to the Urban Corridor and plains. Some very cold air would follow bringing temps down to or below zero by Friday morning. Still a ways before this system arrives, so forecast could change between now and then. Models then keep CO dry Friday into next weekend, but with very cold temps keeping things below freezing for several days. Sadly, the latest forecast keeps the xmas weekend dry and cold as upper level ridge remains parked along the West Coast. Models suggest this pattern will remain through the end of the year, so little if any snow expected between xmas and New Years for all of CO.

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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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