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 Post subject: Precip is in the Forecast to Start October
Post Posted: Oct 1, 2018 12:09 pm 
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Partly to mostly cloudy day across the state today as moisture from Tropical Storm Rosa is advected across CO. Rosa is currently just off the central Baja coast and will move into AZ Tuesday as a Tropical Depression. Today we will see a chance for afternoon showers and isolated thunderstorms with best chances along and west of the Divide, but still a chance for some precip in the foothills and along the Urban Corridor this afternoon and evening. Any precip amounts expected to be on the light side in the local area. As Rosa moves into northern AZ on Tuesday, much better precip chances for western CO along and west of the Divide Tuesday afternoon and evening. Models currently keep precip west of the Divide, so little if any precip expected in our foothills on Tuesday, but southwest CO could receive up to an inch of precip on Tuesday.

For later this week, the upper level pattern has changed. The Rex Block in the Pacific has moved north into Alaska which has allowed a upper level trough to anchor off the West Coast this week. Systems will be able to drop down from the Gulf of Alaska and then into the western U.S. later this week into early next week. First such system will move across CO late Wednesday into Thursday. Precip looks likely from Wednesday evening into Thursday morning across much of eastern CO including our foothills. Models suggest generally 0.10 to 0.25 inches will be possible with the snow level near 12,000 ft, so we could see some decent snow on higher peaks to remind us of what is ahead. Next system moves into CO Friday afternoon into Saturday morning as snow level lowers to 8000-9000 ft, so higher foothill areas could see our first dusting. The next and more powerful system is forecast to become a closed upper low near the 4 Corners area late Sunday and move across CO into Monday afternoon. This system could bring snow levels down to 6000 ft on Monday on drop 2-5 inches of snow at higher elevations. Given the time of year and normal model adjustments, I would not take this to the bank just yet, as the last system could have some significant adjustments before it actually arrives. The good news is the change in our upper level pattern will allow more systems to transit across CO over the next 7-10 days.

September ended with just 0.95 inches of precip, so our 13 consecutive month with below average precipitation. In looking at past records, found an interesting trend. From 1993 to 2000, Conifer Mountain had an average snowfall in September of 5.8 inches, and 6 out of 8 years has snowfall in September. From 2001 to 2010, the average September snowfall was 2.3 inches, and 5 out of 10 years had snowfall in September. From 2011 to 2018, the average September snowfall was 0.1 inches and snowfall occurred on 2 out of 8 years. Yes, our planet is getting warmer, our climate is changing and the snow season is becoming shorter.

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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: Precip is in the Forecast to Start October
Post Posted: Oct 2, 2018 12:28 pm 
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Mostly cloudy day today as moisture from former tropical system Rosa moves across the state. Remnants of Rosa currently over central AZ but precip extends into CO as showers and isolated thunderstorms will be possible across much of CO through this evening. Heaviest precip will remain along and west of the Divide where up to an inch of precip will be possible, while locally less than 0.10 of an inch will be possible. Snow level should remain above 14,000 ft today. Temps should be near average today.

Models persist in keeping a much more active weather pattern over the western U.S. through early next week as systems move from the Gulf of Alaska into the Great Basin and across CO. Next system to bring precip to CO is forecast for Wednesday night into Thursday morning as a upper trough passes to our north and brings a back door cold front into eastern CO Wednesday afternoon/evening which will usher in upslope flow east of the Divide and bring 0.25 to 0.50 inches of precip to our foothills according to latest models as snow level lowers to near 12,000 ft which should put a nice dusting of snow on higher peaks. Wednesday will be the last warm day for a while. The remainder of Thursday will be cool with some isolated showers possible through the afternoon and evening hours.

Next system will move into CO Friday afternoon into Saturday morning. ECMWF is much wetter with this system than the GFS, but as usual will favor the ECMWF until proven otherwise. ECMWF brings 0.25 to 0.50 inches of precip to much of our foothills while GFS would bring less than 0.10 inches. ECMWF would bring snow level down to near 8000 ft while GFS would keep snow level above 10,000 ft. Precip should taper off during the day on Saturday with just a few isolated showers as temp remains below average.

Models then dig a much more powerful upper trough into the Great Basin on Sunday. As usual, models have different solutions on the intensity and track of the upper trough. GFS develops a closed upper low but much farther north over ID and keeps the majority of precip and cold air north of CO, while the ECMWF develops a closed upper low over the 4 Corners area and moves across CO on Monday. The result would be not much precip for eastern CO with the GFS solution and a snow level above 8000 ft, while the ECMWF would bring 0.5 to 1.0 inches of precip to foothill areas with snow level down to 5500-6000 ft by Monday morning, so a big difference in our local weather where the ECMWF would drop 4-8 inches of snow above 8000 ft. Time will tell how this evolves, but could be our first taste of winter.

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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: Precip is in the Forecast to Start October
Post Posted: Oct 3, 2018 1:42 pm 
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Sunny to partly cloudy day today across the state as temps run near to slightly above average. This looks to be the last warm day for a while as models bring a long range upper trough over the Western U.S. beginning late this week and should extend through next weekend, while a upper ridge will move over the Eastern U.S. and create very warm conditions next week. So on to the specific forecast ahead. In general, models are in good agreement through Saturday, then some big differences show up for next week, so that forecast remains much more uncertain. The overall trend of much cooler weather with some precip is in both models, but the details still differ significantly.

Strong southwest flow aloft will keep gusty winds going today over the mountains and into the foothills through this evening. A back door cold front will push into eastern CO this evening and bring cooler and moist air from the plains up into the foothills. Precip is expected to develop sometime between 6 pm and 9 pm across portions of eastern CO and into the foothills with some isolated thunderstorms. Precip will persist overnight and into Thursday morning with snow level near 12,000 ft. Precip amounts look to be mostly in the 0.10 to 0.25 inches in our local area with higher amounts possible across the eastern plains. Foggy conditions may be present in the foothills tonight into Thursday morning. Conditions should clear during the day from the foothills eastward, but precip will move into western CO and should remain mostly along and west of the Divide through Thursday evening. Only a slight chance for a few showers in the foothills Thursday afternoon and evening but mountain areas could see some decent precip as snow level rises to near 14,000 ft.

Next system will move into CO Friday afternoon into Saturday morning. Models suggest this to be a fairly quick moving band of precip that will move into the foothills sometime between 3 pm and 6 pm and be mostly east of the area by midnight. Looks to be another 0.10 to 0.25 inches of precip for most areas, but snow level could lower to near 8000-9000 ft and be the first dusting of snow for higher foothill areas. Temps on Friday will be near average. Conditions should improve during the day on Saturday with breezy southerly winds and temps below average. Precip will begin to move into western CO late in teh day on Saturday ahead of next system.

Here is where models begin to diverge. GFS and ECMWF bring upper level trough into the Great Basin on Saturday into Sunday. Precip will extend from the Divide west late Saturday into Sunday morning with snow level near 10,000 ft. GFS then moves upper trough progressively across CO on Monday while the ECMWF digs a closed upper low over Arizona on Monday. Both models bring some initial precip over eastern CO Sunday afternoon into Monday morning with snow level possibly down to 8000 ft. GFS clears precip out of CO on Tuesday while the ECMWF keeps closed low over 4 Corners region and brings more precip to most of CO Tuesday afternoon into Wednesday morning with snow level 8000-9000 ft. Hoepfully models will better converge on a solution late this week so precip and snow amounts can become more specific.

Both models keep the long wave upper trough over the Western U.S> through next weekend, which will keep temps below average and create some additional precip chances later next week into next weekend.

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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: Precip is in the Forecast to Start October
Post Posted: Oct 4, 2018 12:36 pm 
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Sadly, not much precip fell last night across eastern CO, but hopefully more to come....

Showers and thunderstorms currently moving across western CO along and west of the Divide with snow level 12,000-13,000 ft. Little if any of this precip is expected to make it east of the Divide, and activity should diminish later this afternoon. Temps should be near average today. Strong southwest winds aloft will continue to generate gusty southwest winds from the foothills west, and gusty southerly winds on the eastern plains.

Friday should start out mostly sunny, then clouds will increase as upper level trough will bring a band of precip across CO during the day. Precip will move into western CO Friday morning, and then into the foothills and eastern CO Friday afternoon and evening. Snow level should be near 9,000 ft with this band, so only highest foothill areas may see a dusting of snow. Precip amounts look to remain mostly below 0.10 inches in foothill areas. Precip should exit by around midnight with mostly clear conditions by Saturday morning. Temps on Friday should also be near average and gusty southwest winds will persist.

For the weekend into early next week, models are beginning to come into better agreement. On Saturday, upper trough will dig into the Great Basin and bring associated precip to western CO mostly west of Vail Pass by afternoon with snow level 10,000-11,000 ft. As this upper trough deepens, southwest flow aloft will increase oevr CO and create some gusty southwest winds over the mountains and into our foothills. On Sunday, upper trough will become a closed circulation with the center along the AZ/UT border. Precip will move into western CO Sunday morning and move into eastern CO Sunday afternoon with snow level 11,000-12,000 ft. Models suggest best precip chances for our foothills will be Sunday afternoon into Monday morning as snow level lowers to near 8000 ft. During the day on Monday the upper level system will become an open trough and move slowly across CO, so that showers will be possible on Monday as snow level remains between 8000 and 9000 ft. At this time models generate between 0.25 and 0.50 inches of precip in our local area, so that would translate to 2-4 inches of snow possible above 8000 ft Sunday night into Monday. Given the warm temps on the ground, I would not expect much in the way of travel concerns in the foothills from this snow if it develops. Probably just some wet and possible slush on roads above 8000 ft, just wet below. Temps will remain below average from Saturday through Tuesday, so some good weather for fires and watching football/baseball this weekend. Hopefully everyone has made the seasonal transitions necessary as we head into winter. Mountain areas may see 5-10 inches of snow above 10,000 ft, so travel across higher mountain passes may have winter driving conditions.

For the remainder of next week, models suggest a secondary system will move from the northwest across CO late Tuesday into Wednesday, which will renew precip chances across CO Tuesday into Wednesday morning. Models suggest precip will be mostly light with heaviest amounts in the mountains with snow level near 8000 ft. As upper trough remains over the Western U.S. temps will remain below average all of next week. Later next week another upper level trough is forecast to dig down from the northwest across CO and bring more precip chances late Thursday into Friday afternoon with snow level possibly down to 7000 ft, and this upper trough may import moisture from a tropical system off Baja, but too early for details on that. The good news is that we have precip in the forecast through the end of next week, so a good start to Fall from a moisture perspective. Forecast for next weekend looks mostly dry with temps on the cool side of average.

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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: Precip is in the Forecast to Start October
Post Posted: Oct 5, 2018 1:44 pm 
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Frontal band is currently moving into western CO with showers and isolated thunderstorms and snow level 10,000-11,000 ft. Precip will move into our foothills and onto the plains later this afternoon with precip beginning between 4 pm and 7 pm. Could be a few heavy showers and isolated thunderstorms as band moves through until about 10 pm to midnight. Latest models now suggest some upslope flow after midnight that may produce some light precip in the foothills through about 6 am Saturday. Snow level may drop down to about 8000 ft tonight so a dusting to an inch or so of snow possible in higher foothill areas tonight. Temps will be near average until cold front moves through then cooler tonight.

Conditions should clear out Saturday morning but temps will remain below average with a crisp Fall day in store. As next system moves into the Great Basin later on Saturday, some precip will be possible west of Vail Pass Saturday afternoon into Sunday morning with snow level near 10,000 ft. Models coming into better agreement, and overall trend is to slow down incoming system as it becomes a closed upper low over the Great Basin on Sunday, then over AZ on Monday and into NM on Tuesday. It appears precip will come in distinct waves for eastern CO. First wave will move into eastern CO Sunday afternoon into Monday morning with snow level lowering to 7000-8000 ft Monday morning. Things then clear out during the day on Monday with a few isolated showers as snow level remains between 8000-9000 ft, and then second wave of precip will move in during the day on Tuesday into Wednesday morning with snow level 7500-8500 ft. Models suggest 0.25 to 0.50 inches of precip with each wave, so that would translate to 2-4 inches of snow above 8000 ft with each wave. Still with warm ground temps, I doubt primary roads will be anything beyond wet to slushy, while dirt roads may accumulate some snow. Higher mountain areas will likely see more significant snow with 5-10 inches possible, so higher mountain roads may have winter driving conditions from late Sunday into Wednesday morning. Temps will remain below average statewide Monday through Friday.

Later next week things are a bit more uncertain. Models bring another upper trough down from the northwest into the Great Basin late next week and also want to bring the remnants of hurricane Sergio up over the Southwest and Colorado. Depending on whether these two features phase together will determine how much, if any, precip CO will get late next week. If they phase nicely, could be a fair amount of precip, and if they stay out of phase we may see no precip. It currently looks like if we do get any precip it would be late Thursday into Friday evening. For next weekend, depends on the model. GFS keeps CO dry with temps near average while the ECMWF brings another upper trough over with showers and cooler temps.

_________________
"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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