wxgeek's weather-Warmer Weekend, Cold and Snowy Next Week

12 Apr 2013 16:55 #1 by RenegadeCJ
Update Sun Apr 14

Using latest 1200Z model guidance, still lots of uncertainty with our upcoming system. Seems to be the trend this year that models hint at a significant storm, and then as it gets closer, lots of differences in the model output leading to lots of uncertainty in the forecast. The NAM appears to be the nay-sayer with this system, while the GFS, ECMWF and WRF are more bountiful with precip. Basically not an easy forecast, as it depends on where the frontal boundary sets up. If this boundary remains farther north like the NAM suggests, snow amounts would be pretty low. If the boundary pushes farther south towards the Plamer Divide like other models suggest, more snow. I will base the forecast below primarily on the GFS, but know if the NAM solution verifies, snow amounts would be less than half of what I show below.

Upper level trough will dig into the Great Basin overnight tonight into Monday, then drift slowly east through Thursday morning across CO. Precip moves into western CO tonight west of the Divide with snow level from 5000-6000 ft neay the WY border rising to 7000-8000 ft along I-70 and up to 9000-10,000 ft near US 50. Precip pushes east into the foothills and plains during the day on Monday, with snow levels by Monday evening near 5000-6000 ft along I-70 and 7000-8000 ft along US 50. Could be some moderate to heavy snow at times Monday into Monday night. Models indicate a bit of a break during the day on Tuesday with precip moving mostly north of I-70, some light precip possible south to the Palmer Divide. Snow levels on Tuesday 5000-6000 ft near the WY border, 7000-8000 ft along I-70 and up to 10,000 ft along US 50. Precip remains lighter and mostly north of I-70 Tuesday night, some light precip south to the Palmer Divide. Next significant push of precip will come during the day on Wednesday as upper trough begins to move across the state. Snow to become moderate to heavy during the day on Wednesday and presist into Wednesday night. Snow level down to plains level north of I-70 rising to near 6000-7000 ft along US 50, so mostly a snow event on Wednesday across eastern CO. Snow finally dissipates by Thursday morning.

For snow amounts, not an easy forecast. There will likely be large differeneces across relatively small areas. In general, here is my best guess for the entire period from Sunday night to Thursday morning:

Mountains west of the Divide: 12-24 inches
Foothills: 8-16 inches (highest amounts north of I-70 and above 8000 ft)
Banana Belt: 4-9 inches
Palmer Divide: 6-12 inches
Urban Corridor and plains: 4-10 inches

At lower elevations below 7000 ft, roads should remain mostly wet during this event, until Wednesday into Wednesday night when snow and ice will be possible on roads down to plains level. Above 7000 ft, roads will be a combination of wet, slush, snow and ice packed at various times. Overnight temps will be lower so snow and ice more likely during overnight hours. Wednesday and Wednesday night will have the coldest temps, so snow and ice packed roads more likely. Remember, Spring snow, so wet and heavy laiden with moisture.

Thursday and Friday look mostly dry with warmer temps. Chance for nmore precip Saturday, then dry and warmer Sunday.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".
Update Sat Apr 13

Relatively nice day across the state today with mild temps and mostly dry conditions with some breezy south to westerly winds, especially from the foothills west. A fast moving upper trough and associated cold front will move across CO tonight. Cold front will bring moderate to heavy snow with strong westerly winds to the mountains, which has caused the NWS to issue a Winter Weather Advisory for much of the High Country from 6 pm today through Noon Sunday. 6-12 inches of snow are expected west of the Front Range Crest (a line from Longs Peak to Mt. Evans to Kenosha Pass). As the front moves through, foothills are likely to see a brief period of snow tonight between 9 pm and 4 am, with sonmewhere between a dusting to an inch or two. Snow level expected to be between 5500 and 6500 ft. Sunday should be mostly dry in the wake of the front, with cool temps and breezy west to northerly winds.

Then the weather will get interesting from Sunday night into Thursday morning. Models are in pretty good agreement on the upcoming system, but the nuances of the system will dictate the where and how much part of the snow forecast. In general, a deep upper level trough will dig from the Gilf of Alaska into the Great Basin on Monday, then slowly move east across the southern Rockies through Wednesday. At the surface, a low develops over southwest CO on Monday, then translates into southeast CO Tuesday through Wednesday. A stationary frontal zone will drape across northern CO, and pulse southward into southern CO at times from Monday night into Thursday morning. Along and north of this boundary, snow will be moderate to heavy at times. South of the boundary, only light snow or no precip. The snow level will lower rapidly across this boundary, with snow levels below 5000 ft north of the boundary, rising to 8000-9000 ft south of the boundary. So where this boundary ends up settling will determine snowfall amounts across the state. Latest model guidance has the boundary north of I-70 most of the day on Monday, but moves it south to about US 50 Monday night into Thursday. Based on the latest model guidance, here is how the forecast looks to evolve:

Snow develops across western CO (west of the Divide) Sunday night into Monday morning. Snow level ranges from 6000 ft near the CO/WY broder to near 7000-8000 ft along I-70, and up to near 9000-10,000 ft along US 50. Snow fills in basically north of I-70 by Monday evening and drops south Monday night to near US 50. Snow levels on Tuesday look similar to where they were on Monday, maybe 500 ft lower. Tuesday night is when the stationary front moves farther south so snow levels drop to near plains level north of I-70 and near 6000 ft along US 50. Snow continues during the day on Wednesday across the state with snow levels down to near 5000 ft state wide. Snow finally comes to an end by Thursday morning. Now the big question is how much snow. Based on model liquid equivalent output, mountains west of the Divide could see 2-3 feet of snow from Sunday night through Thursday morning. For our foothills, amounts could range from 10 to 30 inches for ths same period. Highest amounts likely above 8000 ft and north of I-70. Amounts below 8000 ft will be tough, as most precip Monday and Tuesday may either fall as rain or melt. Snow accumulations for areas below 8000 ft will come Tuesday night into Thursday morning, so perhaps 8-16 inches for foothill locations below 8000 ft, and 6-12 inches for the Urban Corridor and plains. Hopefully amounts can be refined with future model runs. The bottom line for this upcoming system is to be prepared for en extended duration of precip, mostly snow, that has the potential to cause power outages and road closures. This system will be a typical Spring storm, with heavy wet snow. The good news there is that with warmer temps roads will be more wet and slushy than ice and snow packed below 8000 ft, and high water content snow which is great for our moisture deficit. The down side of this type of snow is the capability to snap tree limbs and power lines, and it is much tougher on the back when shoveling.

Models show mostly dry conditions Thursday and Friday, with some precip chances next weekend.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

Showers moving from the northwest will continue over the High Country and foothills with some moving into the Urban Corridor and Plains later this afternoon and evening. Snow level around 7000-8000 ft today. Not much accumulation expected outside the High Country where 1-3 inches is possible. A dusting to an inch posisble across higher elevations in the foothills.

Saturday will be warmer, mostly dry and breezy. Temps Saturday expected to climb above seasonal norms, which has been rare this past week. Breezy southwest winds in the foothills, and south to southeast winds on the plains, increasing in the afternoon and evening. A cold front is expected to drop south into northern CO Saturday night and will bring decent snow to the High Country west of the Divide, where 3-6 inches is possible overnight. Only a slight chance for snow in the foothills Saturday night with snow level 6000-7000 ft. Sunday will be cooler in the wake of the cold front, with some showers possible, mostly over higher terrain. Winds become northerly on Sunday.

Weather then takes a colder and snowier turn beginning Sunday night, and persisting into Wednesday. Upper level trough from the Gulf of Alaska will dig into the Great Basin Sunday night and hang around over the central/southern Rockies through Wednesday. This will bring cold temps and periods of snow to all of CO. Snow moves into western CO Sunday evening and moves east to about the foothills overnight. Snow level looks to be 5000-6000 ft Sunday night. Snow increases across all of CO Monday with the snow level raning from 5000 ft near the WY border to 8000-9000 ft near the NM border. Snow continues Monday night into Tuesday with snow level down to plains level across eastern CO, and near 7000-8000 ft over southwest CO. Snow looks to persist Tuesday night into Wednesday morning with snow level down to plains level across the state. So models are forecasting nearly non-stop snow from Sunday night into Wednesday morning. The likely reality is that there will be periods of snow through the preiod. Some areas may not see any breaks, while other areas may have short breaks in the snow. Models are currently outputting up to 2 inches of liquid equivalent between Sunday night and Wednesday morning, with highest amounts being over the mountains and foothills. I could esaily see 1-2 feet of snow over the mountains, and 8-16 inches of snow across the foothills during this period, with the possibility of higher amounts. Residents should begin to prepare for a long duration snow event. At this time amounts do not look to cause serious issues, but that could change over the weekend. Warmer temps this weekend will create warm roads, so initial snow to melt and create ice underneath as additional snow falls and temps remain below freezing. Commutes early next week could be on the slick and slow side.

The good news is that fire danger will remain quite low across most of the state through next week, and the additional moisture is much needed. We should all remember that April is climatologoically the snowiest month of the year in the foothills. Yes, many of us are ready for Spring warmth, but this cool and snowy weather help to keeps the fire danger lower and helps to replenish our drinking water supplies.

_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

Too bad future generations aren't here to see all the great things we are spending their $$ on!!

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13 Apr 2013 18:07 #2 by RenegadeCJ
Bump for April 13 update

Too bad future generations aren't here to see all the great things we are spending their $$ on!!

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14 Apr 2013 14:34 #3 by RenegadeCJ
Bump for Sun April 14 update

Too bad future generations aren't here to see all the great things we are spending their $$ on!!

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