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 Post subject: Possible Big Spring Storm Friday into Saturday
Post Posted: Apr 16, 2018 1:07 pm 
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I realize by opening a new post related to this storm, I have likely jinxed it, so apologies up front if this thing fizzles, you can blame it all on me... And yet it is pretty rare for models to latch onto something this far out in Spring and then be persistent with it, so I am hopeful models are correct.

For today, a warm and dry day expected across the state with temps running a good 10 degrees above average in most areas. Southwest winds will increase this afternoon and has created high fire danger across much of south central and southeast CO today with Red Flag Warnings in effect. Upper level trough currently moving onto the West Coast will move into the Great Basin overnight and across the northern and central Rockies on Tuesday. Main impact from this system will be wind for CO. Southwest winds will increase overnight into Tuesday morning with speeds in the 30-60 mph range in the mountains and foothills. Winds become westerly Tuesday afternoon as cold front passes through the state, but speeds remain very strong in the 30-60 mph range through Tuesday evening. Limited precip in CO from this system, with precip confined to mountain areas along and west of the Front Range Crest during the day on Tuesday with snow level near 6000 ft. Mountain areas could see 1-4 inches of new snow, but dry elsewhere. Temps will reach near average values by Noon, then decrease as cold front moves through with blustery conditions Tuesday afternoon and evening.

Wednesday and Thursday should remain dry a supper ridge builds over CO in-between systems. Temps should be near seasonal norms each day. Southwest winds will increase late in the day on Thursday, which may prompt more Red Flag Warnings in areas absent snow.

Then we move on to our possible big Spring storm. This may be our one and only this year, so I hope Mother Nature makes the most of it. Latest models have slowed the system down a bit, which bodes well for more precip for CO. The track remains very favorable with closed upper low developing west of the 4 Corners region Friday morning, then the upper low moves across southern CO into southeast CO by Saturday morning and then into western OK Saturday afternoon. Ahead of this system, High pressure develops over the Northern Plains and allows an influx of moisture from the Gulf of Mexico with southeast winds into CO late Thursday into Friday morning, which may create some light precip over eastern CO Thursday night into Friday morning with snow level near 10,000 ft, so light rain and drizzle possible from the eastern plains into the foothills. By Friday afternoon, upper low moves into south central CO and winds become northeasterly over eastern CO as snow level lowers to near 8000 ft. Precip could become heavy at times Friday afternoon into Friday evening. Friday night into Saturday morning is when storm will reach maximum intensity with heavy precip across most of eastern CO from the Divide east and snow level will lower to near 5000 ft. Precip will remain heavy through Saturday morning, then begin to taper off by Noon, with partial clearing Saturday afternoon. Models currently output 2-3 inches of liquid equivalent across much of eastern CO including our foothills, so if models have a handle on this, areas above 8000 ft could see 16-24 inches of wet, heavy Spring snow. Still a little uncertain how much snow areas below 6000 ft will see, as rain may not turn to snow until between 6 pm and midnight Friday. I would expect Metro Areas to get 4-10 inches of snow, mostly on grassy surfaces as roads may remain mostly wet to slushy. In the foothills, expect winter driving conditions from Friday afternoon through Saturday morning, as ice forms under heavy snow making travel difficult. Power Outages may also become an issue in foothill areas due to heavy Spring snow on trees and power lines.

Sunday looks dry statewide, but temps will likely remain below average with snow and wet ground in place.

For next week, upper level ridge builds over CO Monday through Thursday which should keep temps on the mild side. Models suggest the chance for isolated afternoon showers and thunderstorms each day next week, as enough low level moisture remains in place and with more intense daytime heating leading to some convection. Snow level should remain above 10,000 ft, so mostly rain with some graupel and small hail possible over higher terrain of the mountains and foothills. This pattern appears it will remain in place through next weekend, so expect mild temps with isolated afternoon and evening showers possible, a little prelude into our summer weather pattern.

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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: Possible Big Spring Storm Friday into Saturday
Post Posted: Apr 17, 2018 1:29 pm 
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Very windy day across the state today with southwest winds of 30-60 mph across much of the state with some higher gusts. Red Flag Warnings and High Wind Warnings cover most of eastern CO from the foothills east including South Park. Cold front is just entering western CO as winds have begun to turn northwesterly behind front. Precip will also occur behind front along and west of the Divide today as snow level lowers to 6000 ft behind front. The bad news is that winds will simply turn direction (northwesterly) and remain as strong or stronger behind front through this evening. Temps ahead of front are well above average, but will quickly drop as front passes. Mountain areas will see 1-4 inches of snow through this evening, then clear overnight.

Wednesday is looking dry with temps near average and much lighter winds. Thursday will see warmer temps, but winds will begin to increase, from the south across eastern CO and from the southwest from the foothills west, so more fire weather concerns for much of CO on Thursday.

Trend in models past 24 hours is to diminish strength of incoming system somewhat, which means slightly warmer temps and less precip. This is part of the natural evolution of models, so will need to see a few more runs before this trend becomes the actual forecast. Models still bring closed upper level low from the 4 Corners region across the CO/NM border and into the TX Panhandle region, which remains a favorable track for Spring precip in CO. The influx of Gulf air and moisture on Thursday will warm and moisten air over eastern CO, which may keep snow only above 6000 ft for most of this storm. Latest models bring precip from southwest CO to eastern CO Thursday night into Friday morning with snow level near 10,000 ft. Precip intensifies over much of CO during the day on Friday as snow level lowers to near 8000 ft by Friday evening. Precip continues overnight into Saturday morning as focus of precip shifts to east of the Divide and snow level lowers to near 5500- 6000 ft. Precip will begin to diminish Saturday morning through Noon, with partial clearing and some lingering flurries through Saturday evening as snow level rises to 8000 ft on Saturday. Models have decreased precip output from yesterday, with 1-2 inches across much of eastern CO, which would result in 8-16 inches of snow above 8000 ft. Still very uncertain how much if any snow will fall below 6000 ft Friday night into Saturday morning at this point. With warm temps this week and higher snow levels, not sure how bad roads will get below 8000 ft as well. Of course, models may make some more adjustments, so stay tuned for the latest.

Further on down the road, models suggest mostly dry and mild conditions Sunday. For next week, a much more summer like pattern is appearing, with temps likely to remain above average, but decent precip chances each afternoon and evening with isolated showers and thunderstorms possible with snow level above 10,000 ft. Models suggest better precip chances and cooler temps next weekend as a weak upper lvel trough moves over the state, so snow level could lower down to 8000-9000 ft.

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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: Possible Big Spring Storm Friday into Saturday
Post Posted: Apr 18, 2018 2:50 pm 
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Mostly sunny with light winds today and temps near average, a fine Spring day overall. On Thursday, southerly winds will increase across the state, southeasterly over eastern CO and southwesterly along and west of the foothills. Temps will be above average, so this will prompt renewed fire weather concerns. Clouds will begin to increase especially along and west of the Divide.

On Friday, models move upper level closed low from just west of the 4 Corners Friday morning along the CO/NM border into south central CO by Friday evening. Precip will move into western CO along and west of the Divide late Thursday night into Friday morning with snow level 8000-9000 ft. By Noon, precip will move into much of eastern CO and intensify through Friday evening with snow level near 8000 ft. Precip becomes the heaviest across eastern CO Friday evening through Saturday morning as snow level lowers to 5500-6000 ft. Precip will persist through about Noon on Saturday, and then begin to diminish with some lingering showers through Saturday evening. Snow level Saturday will be near 6000 ft Saturday morning rising to 8000 ft by Saturday afternoon. Models have settled on between 0.5 and 1.5 inches of liquid for most areas of CO today, which is good Spring moisture, but not as much as earlier advertised. Hence, snow amounts now only look to be in the 6-14 inch range for mountain and foothill areas above 8000 ft. At present time, I do not believe roads will be much of an issue below 6000 ft, should just remain wet. Between 6000 and 8000 ft there could be some slush and snow pack on roads, with heavy snow and ice above 8000 ft Friday evening into Saturday morning. Not the real big Spring storm many had hoped for, but good moisture to help reduce fire danger for a while.

Sunday looks dry and mild statewide.

For next week, weak system brings cooler air and some precip into CO Monday with snow level 9000-10,000 ft. Tuesday and Wednesday will see afternoon and evening showers and thunderstorms mostly over higher terrain, with temps near average. Models suggest drier and warmer conditions Thursday 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: Possible Big Spring Storm Friday into Saturday
Post Posted: Apr 19, 2018 1:58 pm 
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Breezy to windy and warm day across the state today. Southerly winds of 20-45 mph will persist through this evening, them diminish some overnight. Upper level low is centered over southern Nevada currently, and is forecast to track into southern UT tonight and then across CO on Friday. A couple of things have happened to this system. First is the overall intensity is not that strong and will become more of an elongated circulation center as it passes through CO. Next is the influx of moisture, air moving into CO has originated over the Great Plains versus the Gulf of Mexico, so relatively dry air. The end result will be a good dose of Spring moisture, but not a monster Spring storm. Since the system is not that intense, the core is warmer, so snow levels will be slightly higher than our usual Spring storms. Thus the forecast is expected to go like this....

Clouds will increase over western CO this afternoon ahead of system, and some showers will develop late this afternoon into this evening along and west of Vail Pass with snow level near 10,000 ft. Precip will intensify along and west of the Divide overnight as snow level lowers to near 8000 ft. Some showers will be possible early Friday morning across portions of eastern CO as well. Because it is Spring and this system has good dynamics, isolated thunderstorms will also be possible across much of CO as thus system passes through, especially Thursday night through Friday evening. Models suggest flow aloft will remain southerly during the day on Friday, so heaviest precip will be associated with baroclinic band ahead of low center that will move slowly from west to east across the mountains and then into the foothills Friday afternoon into Friday evening, and this band is where thunderstorms will be most likely. Snow level will remain near 8000 ft during the day on Friday, and then begin to lower as precip moves into eastern CO Friday evening and night down to 5000-6000 ft. Heaviest precip in the foothills will be from about 3 pm Friday through 6 am Saturday. Better upslope flow will develop across northeast CO from Friday evening through Saturday morning, so thunderstorms less likely during this time. Precip should begin to diminish from west to east Saturday morning, turning to showery conditions Saturday afternoon as snow level rises to near 8000 ft. So for snow amounts, here are my thoughts:

Mountains: 6-18 inches
Foothills above 8000 ft: 6-14 inches
Foothills between 8000 ft and 6000 ft: 4-8 inches
Areas below 6000 ft: trace to 2 inches on grassy surfaces

Roads are expected to remain mostly wet, perhaps some slush below 6000 ft. Biggest impact will be above 8000 ft where roads are likely to become snow and ice packed Friday evening into Saturday morning, so travel restrictions and delays/closures will be possible in the foothills and mountains. Snow will have high moisture content and be very heavy, so power outages may be possible due to downed trees and limbs on power lines. All roads should be mostly wet by Saturday afternoon.

Sunday is expected to be dry statewide with temps near average.

For next week, a weak system will move to our north on Monday which will increase precip chances over higher terrain, but snow level near 12,000 ft. Temps will be above average most areas. Tuesday will be cooler with temps near to slightly below average, and only slight precip chances. Wednesday, temps recover to near average, and isolated showers and thunderstorms will be possible in the afternoon mostly over higher terrain with snow level above 10,000 ft. Thursday and Friday will be warmer as temps climb above average, and isolated afternoon showers and thunderstorms will again be possible over higher terrain.

By next weekend, temps will remain above average, but decent precip chances exist Saturday afternoon through Sunday afternoon as upper low to our west will enhance moisture into the state.

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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: Possible Big Spring Storm Friday into Saturday
Post Posted: Apr 20, 2018 7:39 am 
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Quick look at the situation this morning shows upper level low over south central UT with precip band out ahead over western CO this morning with snow level 9000-10,000 ft. A few bands out ahead over the foothills this morning, but main activity will wait until after Noon. Previous forecast mostly on track for today, except for heaviest precip period. Latest HRRR model shows primary precip band moving into the foothills between Noon and 6 pm today, with isolated thunderstorms possible and snow level down to 8000-9000 ft. After 6 pm, upslope flow will prevail and more steady type precip will occur over eastern CO as snow level lowers to 5000-6000 ft after midnight. Precip persists through Saturday morning, then some break up but with flurries lingering in the foothills though Saturday evening as snow level rises to 8000 ft Saturday afternoon.

Previous snow amounts still on track for today, but with heavy precip this afternoon roads above 8000 ft could become slick in heavier snow bands, and remain slick through Saturday morning. Models also show good chance for thunderstorms across the eastern plains this afternoon with some storms approaching severe limits.

Moisture will help reduce fire danger for a bit and help with the green up.

_________________
"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: Possible Big Spring Storm Friday into Saturday
Post Posted: Apr 20, 2018 1:32 pm 
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Well, system has decided to slow down a bit today, low center still over southeast UT, but western CO now starting to transform into wrap around precip over the mountains as frontal band out ahead has begun to wash out, except near the CO/NM border and into NM where active thunderstorms exist. Front Range has mostly resided in dry slot out ahead of system, but that will change a little later. Latest HI-Res models bring upper low center into south central CO this evening and into southeast CO tonight. Latest HRRR now suggests heaviest precip in foothills will be from this evening into Saturday morning as upslope flow develops and wrap around precip moves into eastern CO on north side of upper low. Now believe most of our snow will occur from 5 pm through 5 am in the foothills, with 4-8 inches possible above 8000 ft, and some areas may see up to 12 inches. Precip should diminish Saturday morning with some clearing by late morning, then some flurries possible into Saturday afternoon, but little if any additional accumulation expected after 9 am Saturday. Roads mostly remaining wet at this point, so they should remain that way through about 6-8 pm then as heavier snow develops roads will begin to accumulate snow with ice developing underneath, so expect very slick road conditions tonight into early Saturday morning above 7000 ft. Roads should remain mostly wet below 6000 ft.

_________________
"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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