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 Post subject: Warm Weekend, Then Snow Monday into Tuesday
Post Posted: Mar 24, 2018 1:44 pm 
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Mostly sunny and warm day across the state, and breezy in some areas. Temps running 5-15 degrees above average most locations. Sunday will be similar across the state with a few more clouds and southwest winds will increase as upper level trough moves into the Great Basin. A few showers will be possible over higher terrain Sunday afternoon with snow level 9000-10,000 ft. Temps will remain 5-15 degrees above average.

Big change coming Monday into Tuesday as upper level trough moves into the 4 Corners region and associated cold front moves south over CO during the day on Monday. Showers will move into northwest CO Monday morning with snow level near 6000 ft. Precip will move into the the foothills and Urban Corridor Monday afternoon and evening with snow level near 7000 ft initially. Precip will intensify Monday night into Tuesday morning and then diminish late Tuesday morning. Snow level will lower to near 4000 ft by midnight, so most areas will see accumulating snowfall by Tuesday morning. Heaviest snow will be from about 8 pm Monday through 4 am Tuesday. Models are in pretty good agreement on this system, so confidence is relatively high. Precip is expected to be in the 0.5 to 1.0 inches of liquid equivalent, so this would translate to 5-10 inches of snow for this time of year in the foothills, with 3-7 inches possible across the Urban Corridor. Mountains may not see as much snow from this event, with heaviest snow from the Divide east, with 4-8 inches possible. It currently looks like commute back up the hill Monday should be mostly ok, as initial snow likely to melt until about 7-8 pm due warm conditions. Road conditions will likely deteriorate quickly late Monday evening through Tuesday morning, with ice forming underneath snow, so expect a much slower commute Tuesday morning with traction laws likely in effect. Conditions should improve quickly Tuesday morning as precip moves south, so roads should be fine by Tuesday afternoon/evening. Temps will remain below average on Tuesday.

Earlier forecasts had upper level trough hanging around, but now models move upper trough out Tuesday, and a northwest flow aloft moves over CO for the remainder of the week. A disturbance will move to our north Wednesday into Thursday and create chances for precip Wednesday into Thursday morning, mostly along and west of the Divide and north of I-70. Snow level will be near 8000 ft Wednesday, lowering to 6000 ft Wednesday night into Thursday morning. Foothills could see a dusting to an inch or so of snow Wednesday night. Temps on Wednesday should be near average.

Thursday and Friday should be dry statewide, with temps near average on Thursday, and rising above average on Friday. Dry weather should extend into the weekend, as temps rise well above 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: Warm Weekend, Then Snow Monday into Tuesday
Post Posted: Mar 25, 2018 3:03 pm 
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Another mostly sunny and warm day across CO, with some gusty southerly winds at times. A few isolated showers will be possible from the Divide west today mostly north of I-70 with snow level near 10,000 ft. Red Flag warning in effect across much of south central and southeast CO today. Temps running 5-15 degrees above average for most areas.

Latest models continue the trend of changing our weather Monday into Tuesday. Upper level trough currently over the Great Basin will split into 2 pieces, with a northern branch and a southern branch that will be the primary branch and develop a closed circulation over southwest AZ on Monday, then moves across southern AZ and NM on Tuesday. This is not an ideal track for a good Spring snowstorm for eastern CO, but models develop a surface low over southeast CO that will help pull down cooler air from the north and create enough of an upslope component to provide a good shot of precip from Monday afternoon into Tuesday morning from the Divide east to along the I-25 corridor. Models bring some precip into northwest CO tonight into Monday morning associated with northern branch of upper trough, but most of CO will remain dry until Monday afternoon between 3 pm and 6 pm with snow level near 7000-8000 ft. Precip then looks to become moderate to heavy at times from 6 pm Monday through about 3 am Tuesday, then precip will diminish and move south Tuesday morning. Snow level will lower to 4000-5000 ft after midnight into Tuesday morning. Models continue to output from 0.5 to 1.0 inches of liquid equivalent, so snowfall totals should be in the 4-10 inch range for areas above 6000 ft from the Divide to the foothills. Areas below 6000 ft may see 2-5 inches of snow. For road conditions, I still believe roads will remain mostly wet Monday afternoon through about 7 pm Monday, then begin to slush and become snow and ice packed after 9 pm Monday through Tuesday morning above 6000 ft. Thus tough travel in the mountains and foothills Monday night into Tuesday morning. Roads below 6000 ft may be wet with some slush and snow pack. Conditions should improve quickly Tuesday morning as sun helps melting, so roads should be fine by Tuesday afternoon, although temps will remain below average on Tuesday.

Models differ a bit for the next system. GFS is faster and brings precip into CO during the day on Wednesday with snow level near 6000 ft, then moves precip out by Thursday morning, while ECMWF brings precip in Thursday morning through Thursday evening and lowers snow level down to 4000 ft. Not sure which model is correct, but either way not a lot of snow for the foothills, maybe a trace to 2 inches, while mountain areas could see 3-7 inches. Temps likely to remain near to slightly below average Wednesday and Thursday.

Friday and Saturday look to remain mostly dry, with teps near average. Next system will bring precip to CO Saturday night into Sunday afternoon with snow level near 6000 ft. Mountains should receive bulk of precip, so perhaps a dusting to an inch of snow above 6000 ft in the foothills.

For next week, GFS brings cold and snow to much of CO Monday into Tuesday, while the ECMWF keeps things mostly dry with temps near normal. GFS keeps precip chances most for next week while the ECMWF builds a ridge over CO with warm and dry weather. No idea which way this will go at this point, but Spring is a tough time of year for numerical weather models, eventually they will likely come into alignment.

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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: Warm Weekend, Then Snow Monday into Tuesday
Post Posted: Mar 26, 2018 11:42 am 
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Fairly nice start to the day, but that will be changing. NWS has issued a Winter Weather Advisory for the foothills and Palmer Divide as well as southern mountains. Rather complex evolution of the upper air pattern over CO will transpire today into Tuesday. Upper level trough currently in the Great Basin will split, one branch staying to our north while the majority of energy goes into a southern branch, which will develop a closed upper low over southwest AZ this afternoon/evening. Normally such a split is the kiss of death for precipitation over CO, but in this case models suggest a deformation zone aloft will form over CO this afternoon as a surface low develops over southeast CO. This combination is forecast to have precipitation develop from late this afternoon through Tuesday morning from the Divide east to the western edge of the CO plains. Much of the precipitation may be convective in nature, especially this evening so isolated thunderstorms will be possible, and snowfall rates of 2-3 inches per hour may develop in some areas. The main issue with this type of system is that precipitation amounts will vary greatly, so that some areas get towards the high end of precipitation amounts, while some areas not that far away may get little if any precipitation, so a tough forecast overall. In general, models suggest showers will develop after about 3 pm from the Divide to the I-25 corridor with snow level near 8000 ft initially. Precip will intensify after 6 pm and snow level will lower to around 6000 ft with some moderate to heavy snowfall above 6000 ft from 6 pm through about midnight. Snow level lowers to 4000-5000 ft overnight but precip will diminish after midnight and gradually move farther south. Heaviest precip will be along and south of I-70 for this system, with southern mountains receiving the highest snowfall amounts. For our local area, foothills and Palmer Divide should see 4-8 inches of snow above 6000 ft, with some isolated pockets up to 12 inches, and some isolated pockets of 1-2 inches. Urban Corridor areas should see 2-5 inches of snow, with highest amounts being along western and southern areas at higher elevations. Southern mountains could see 6-14 inches of snow. This will be out typical west and heavy Spring variety, with good moisture content. Roads should remain fine through 6 pm, then deteriorate rapidly above 6000 ft as heavier snowfall creates ice and snow packed roads, so the sooner you can get home the better this evening. Roads will become difficult overnight into Tuesday morning, so expect slow going Tuesday morning, but roads will improve quickly as sun melts snow, and should be fine by Tuesday afternoon.

Next system will move into CO Wednesday evening into Thursday morning. This system will track from the northwest, so heaviest precip will be along and north of I-70. Precip will move into the mountains Wednesday evening with snow level near 6000-7000 ft, and move into eastern CO Wednesday night into Thursday morning as snow level lowers to near 4000 ft. Precip amounts east of the Divide will be fairly light, so only a dusting to 2 inches expected in the foothills, with 3-7 inches possible in the mountains. Conditions will improve during the day on Thursday, but a few lingering showers will be possible in the mountains and foothills through Thursday evening. Temps will remain on the cool side of average Wednesday and Thursday.

Friday and Saturday look mostly dry as temps return to seasonal normal values. A few showers over the mountains may be possible, but dry elsewhere. Models have switched in that GFS keeps things relative dry Sunday into Monday, while the ECMWF brings a decent system across CO, so weather on Eastern Sunday is still in doubt.

Later next week models agree dry and mild weather Tuesday through Thursday, then a chance for precip late next week into next weekend.

_________________
"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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