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 Post subject: Dry and Warm to Start the Week, Precip on Track Thu/Fri
Post Posted: Mar 20, 2017 11:25 am 
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Another Red Flag day today in the foothills. Dry and warm weather will persist across the state today with low RH values and gusty westerly winds in the foothills. Isolated showers may develop along and west of the Divide this afternoon with snow level above 10,000 ft. A weak cold front may bring some cooler temps to astern CO on Tuesday, although still above average. In addition, isolated showers will be possible in the mountains and a few may move into the foothills and plains Tuesday afternoon and evening as snow level remains above 10,000 ft. Wednesday looks like another warm and dry day statewide with gusty westerly winds in the mountains and foothills, so another critical fire weather day.

Finally, models are suggesting a high probability for a good soaking for eastern CO late Thursday into Friday. Models are in good agreement that a Pacific system will move into the 4 Corners region late Thursday and then move east into southeast CO by Friday morning. If this track holds up, much of eastern CO could see 1 to 2 inches of precipitation, but with most of our Spring systems, the eventual track will determine the amount of precip for various regions of CO. ECMWF and now the GFS have been consistent the past few runs on this track, so confidence is growing. Assuming this track holds, precip would move into western CO during the day on Thursday with snow level 7000-8000 ft as precip moves to about the Front Range Crest by afternoon. As upper and surface low move into southeast CO overnight, precip moves into eastern CO as snow level lowers to near 7000 ft. This would keep precip as rain for most of eastern CO with snow limited to the foothills and mountains and strong northerly winds would accompany precip. Precip would gradually move east during the day and exit the state by evening. For snowfall, foothills could see 8-16 inches above 7000 ft with up to 2 feet in favored areas at higher elevations while mountains could see 6-16 inches above 8000 ft. This would be the wet and heavy Spring variety, but laden with much needed moisture. Urban Corridor and plains could see 1-2 inches of welcome rain. I will keep my hopes up that this system tracks as models suggest. The fear is that these systems can track farther north or south which would significantly reduce precip amounts for us.

For the weekend, Saturday looks dry and mild statewide. Another system is forecast to move across CO on Sunday, bringing a chance for more precip mostly along and west of I-25. Mountains would have the best chance for precip with snow level near 8000 ft, while foothills may see some light precip Sunday afternoon and evening.

For next week, models then suggest another potentially strong system moving into CO late Monday into Wednesday morning. Snow levels with this system could lower into the 6000-7000 ft range, and bring another 1-2 inches of precipitation to portions of the state, so foothills could see another 6-18 inches of snow next week. Models keep the wet trend going late next week with a system late Thursday into Friday, then more precip Saturday into Sunday. Hopefully this trend becomes reality which would greatly reduce fire danger.

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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: Dry and Warm to Start the Week, Precip on Track Thu/Fri
Post Posted: Mar 21, 2017 1:46 pm 
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Temps running a good 10 degrees below yesterday, yet still well above seasonal norms. A bit more moisture in the air as well today across eastern CO, helping to ease fire danger a bit. As weak upper level system moves across CO today, showers and isolated thunderstorms will be possible from the mountains to the plains. Best chances for precip will be along and north of I-70. The danger will be from any lightning activity that could start fires. Precip should end by sunset with clearing overnight.

Wednesday looks dry and warm statewide. As upper level system begins to move into the Great Basin, southwest winds aloft will increase over the state, bringing stronger southerly surface winds to the mountains and foothills, persisting into Thursday that will increase fire danger.

Models continue to track upper level trough to the 4 Corners region by Thursday afternoon, then strengthen system into a closed upper low and move it into southeast CO by Friday morning. The biggest change from today's model runs is a slight delay in precip. This remains a very favorable track for precipitation across CO, especially eastern CO. At the surface, precip will move into western CO during the day on Thursday with snow level near 9000 ft. As surface low deepens over southeast CO Thursday night, precip will move into eastern CO with snow level lowering to 6500-7000 ft. Precip will continue during the day on Friday, moving east of the Urban Corridor by Friday evening. Strong northeast winds will develop across eastern CO Thursday night through Friday morning in the 25-50 mph range. As for precip, models suggest copious amounts in the 1 to 3 inch range across eastern CO depending on the model. Snow level during the day on Friday should remain near 6000-7000 ft, so believe most areas below 6000 ft will see only rain or a rain/snow mix with no accumulation. Above 7000 ft, foothill and mountain areas could see 6-18 inches of snow, with up to 2 feet possible above 9000 ft. Temps will remain relatively warm, so snow will be of the very wet and heavy Spring variety, good news for moisture, but could cause some power outages. Because of warm temps during the week, snow will initially have a hard time sticking on pavement, but believe roads will be snow and ice packed Friday morning above 8000 ft with slush down to 7000 ft. Roads could be very slick as initial melting likely to freeze as heavier snow continues. Roads should improve during the day on Friday as warmer temps aid in melting. Precip should end in teh foothills by late afternoon Friday, and end across the plains by midnight. Some areas could see dense fog Saturday morning with such moisture on the ground.

Saturday looks dry and mild statewide. Weak system will move across CO on Sunday, bringing light precip from the mountains to the Urban Corridor with snow level near 8000 ft. Currently looks like 1-3 inches will be possible in the mountains, and a trace to 2 inches in the foothills.

For next week, models are currently not in very good agreement. The good news is that both GFS and ECMWF bring a significant system to CO next week. The GFS brings the system across Tuesday into Wednesday on a similar track to this weeks storm. The ECMWF is much slower and would impact CO late Wednesday into Friday morning as an upper level low moves slowly to our south. Each model would bring an additional 1-2 inches of precip to much of eastern CO. ECMWF solution would bring snow down close to 5000 ft, so if this solution verifies it could be a major Spring snowstorm for eastern CO. Still too early to tell which way this system will go, but in general prefer the slower and deeper ECMWF solution given the time of year. Thus, if you belive in old weather proverbs, March certainly entered like a lamb, and appears will exit like a lion.

In other interesting weather news, a very strange thing has happened in the eastern Pacific Ocean. As our earlier La Nina condition has begun to transition to a Neutral ENSO pattern, a very warm plume of water has developed off the coast of South America, with ONI values of +2.1 in Nino 1+2 region. This has caused severe flooding in parts of Peru the past 2 weeks. This kind of rapid change is unprecedented since 1950 when records began for ENSO. Models now suggest that the entire Pacific will transition to weak El Nino conditions later this Spring and Summer and potentially become a moderate El Nino by Fall. I looked back at ENSO records, and there has only been one other period when ENSO went from El Nino to La Nina and back to El Nino in successive tears, which was the period from 1963-1965. In those years, Denver had average snowfall during the first El Nino, above average during the La Nina the following year, and below average snowfall during the second El Nino, which is opposite of what one would expect. Closer to home, when we begin to transition to El Nino conditions in the Spring, this usually is associated with above average precipitation from March through June. I am hoping this becomes the case this year so we can ease the current fire danger levels.

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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: Dry and Warm to Start the Week, Precip on Track Thu/Fri
Post Posted: Mar 22, 2017 2:19 pm 
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Yet another warm and dry day across CO with low RH values and gusty westerly winds creating high fire danger. Temps will be 10-15 degrees above average today. One more scary fire weather day to get through on Thursday before moisture arrives. Red Flag Warning has already been issued by NWS for Thursday in the foothills as warm temps and gusty southwest winds will combine with low RH values. Temps Thursday will be again well above seasonal norms.

Models have remained mostly on track with incoming system. Upper level low track remains into the 4 Corners Thursday afternoon and into southeast CO Friday morning. As this system is a quick moving system, precip will be fast and furious. Latest trend in models has been slightly less precip but lowering snow level to near 5000-6000 ft by Friday morning. Precip still scheduled to move into western CO during the day on Thursday with snow level near 9000 ft. Strong southwest winds will occur in the mountains and foothills, and strong southerly winds expected on the plains Thursday. There will be a slight chance for thunderstorms to develop Thursday afternoon mostly along and east of I-25, with a slight risk for severe thunderstorms across far eastern CO. Precip is forecast to move into the foothills between 6 pm and midnight Thursday, and become heavy between midnight and 8 am Friday. Snow level will begin around 8000 ft and lower to 5000-6000 ft by Friday morning. Snowfall rates of 1-2 inches per hour will be possible at times, along with northerly winds of 25-50 mph, so very difficult driving conditions Thursday night into Friday morning. Fore precip amounts, most models still in the 1 to 2 inch range, with the ECMWF at the higher end. This will translate to 6-18 inches of snow for most foothill areas above 8000 ft with lesser amounts at lower elevations. Snow will be tough to accumulate below 6000 ft due to warm temps this week on roadways. Above 8000 ft roads likely to become snow and ice packed and very slick. Precip will diminish after about Noon on Friday and move east quickly. Roads should improve during the day on Friday as warm temps aid in melting, and we should see clearing Friday night with cooler temps.

Saturday remains dry and mild statewide. Next system brings precip to western CO Saturday night and spreads east to eastern CO during the day on Sunday with snow level 7000-8000 ft. Mountains may see 2-4 inches while foothills could see a trace to 2 inches.

Models still trying to resolve the pattern for next week. Details remain uncertain, but the general theme is another large and slower moving upper low will impact CO sometime from Tuesday afternoon through Thursday evening. As this appears to be slower moving system, it has the potential for heavy precip across much of CO with snow level somewhere between 6000 and 8000 ft. Details hopefully will emerge by the weekend. Models suggest a wetter and cooler pattern will continue next weekend and into the following week which will greatly reduce fire danger.

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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: Dry and Warm to Start the Week, Precip on Track Thu/Fri
Post Posted: Mar 23, 2017 10:11 am 
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One last high fire danger day for a while. Dry and warm day across eastern CO with a Res Flag Warning in place for most of eastern CO including the foothills as southwest winds of 15-35 mph will be likely today. Showers will move into western CO during the day, mostly along and west of Vail Pass this morning, moving east to the Divide this afternoon with snow level 9000 - 10,000 ft. Isolated thunderstorms will also be possible across the far eastern plains this afternoon and evening, with severe storms possible farther east into western KS and NE.

For the upcoming change in our weather, models remain consistent with the track of the system, System currently over southern UT and will move into western CO this afternoon, then become a closed upper low over southeast CO tonight and move into southwest KS Friday morning. This system is a fast mover which will limit precip amounts, but intense precip will occur tonight into Friday morning. Precip is expected to move into the foothills sometime between 7 pm and 10 pm tonight and spread east overnight. Heavy precip is expected between midnight and 6 am Friday, then precip will begin to diminish Friday morning as system moves farther east. Precip should end by Noon in the foothills and Urban Corridor, and end by afternoon across the eastern plains. Models suggest snow level will be near 9000 ft this evening, down to 7000-8000 ft by midnight, and down to 5000-6000 ft by Friday morning. In conjunction, strong northerly winds of 25-50 mph will develop tonight into Friday morning, so driving will be very difficult across eastern CO tonight through Friday morning. GFS and NAM now suggesting closer to an inch of precip, while the ECMWF has remained very consistent with 1-2 inches of liquid precip possible. Snow ratio with this storm will be in the 8:1 to 10:1 ration due to warm temps and high moisture content. Snow accumulation will be best above 6000 ft, with highest accumulations above 7000-8000 ft. Here are my best estimates for snowfall accumulations:

Mountains: 2-6 inches
Foothills and Palmer Divide above 7000 ft: 6-16 inches
Urban Corridor: 2-5 inches with highest amounts on west and south side or Metro area
eastern plains: trace to 2 inches

Believe roads above 7000 ft will become snow and ice packed overnight, with very slick conditions due to melting and re-freezing. Roads below 7000 ft may be slushy to wet overnight. Blizzard conditions may occur overnight into early Friday morning due to strong northerly winds and blowing snow. Conditions should improve rapidly after 09:00 am Friday morning with warmer temps and some sun which will quickly melt snow and winds will gradually diminish.

Saturday should be dry and mild statewide. Weak system will move across CO Saturday night into Sunday, so a chance for showers will occur in the mountains Saturday night and spread into eastern CO during the day on Sunday. Snow level looks to be in the 7000-8000 ft range with 2-5 inches possible in the mountains, and 1-3 inches possible in the foothills.

For next week, models remain a bit unclear on what will transpire. In general an upper level low will wander into the Desert Southwest early next week and bring precip to CO as it moves slowly east Tuesday into Wednesday. Snow level currently looks to be near 7000-8000 ft, and this system could bring heavy precip to portions of CO, as it may have a tap of moisture from the Gulf of Mexico. Details hopefully to emerge by this weekend. Later next week, GFS brings more precip to CO Thursday into Friday, while the ECMWF holds precip off until Saturday. The good news is that models suggest the global upper level pattern will remain conducive to additional moisture into CO into mid April, which will significantly reduce fire danger.

_________________
"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: Dry and Warm to Start the Week, Precip on Track Thu/Fri
Post Posted: Mar 23, 2017 2:54 pm 
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Last update on the incoming system before the fun begins....

Showers have intensified across western CO, now along and west of the Divide with snow level 9000-10,000 ft. Upper level trough currently moving across western UT and should remain on forecast track stated earlier. Latest HRRR model hold precip off in the foothills until 09:00-10:00 pm and then becomes heavy by 11:00 pm to midnight and remains heavy through 6:00 am to 7:00 am Friday. Snowfall rates of 1-2 inches seem likely with periods of 2-3 inches per hour possible. All this combined with 25-50 mph winds will create whiteout conditions overnight into Friday morning. NWS will likely upgrade Winter Storm Watch to either a Winter Stomr Warning or Blizzard Warning for the foothills and Palmer Divide. As upper level winds will remain more northerly than northeasterly, Palmer Divide and southern JeffCo foothills will be more favored for upslope enhancement of snowfall. Latest HRRR snowfall model has 12-15 inches for this area through Friday morning. Thus, any travel above 7000 ft will be quite difficult from midnight through about 9 am Friday, as roads will become snow and ice packed with ice underneath. With heavy snow and winds road crews will have a very difficult time keeping up overnight, so would expect roads to not be well plowed until later Friday morning. Snow will be very wet and heavy which can cause power issues, but believe strong winds will help in some ways to keep heavy snow off lines and trees, but it could also bring down some trees, so be prepared for possible power outages.

Snow and wind will diminish quickly late Friday morning, with clearing by afternoon, so roads should improve quickly by late morning into afternoon. There cold be temporary road closures and traction restrictions above 7000 ft as well. Possible flight delays and cancellations at DIA, mostly due to winds and poor visibility early Friday morning. Great day to work from home if that is a possibility.

Stay safe, and thanks Mother Nature for the very needed moisture.

_________________
"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: Dry and Warm to Start the Week, Precip on Track Thu/Fri
Post Posted: Mar 24, 2017 7:41 am 
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A rather bewildering storm. It set up just as models predicted, but precip did not materialize as models forecast. Heaviest precip band is now along and east of I-25, so foothills should see improving conditions this morning. I measured 6 inches on Conifer Mountain, which seems to be the highest snowfall report so far from NWS. Southwest mountains got 9-18 inches past 24 hours, but overall precip was over-forecast by all models. Strong northerly winds will continue through about Noon and then begin to subside as well as many locations reporting gusts to 50-60 mph along the Urban Corridor and plains. Primary roads look to be mostly in good shape, mostly wet with some slush.

_________________
"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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