A large spring system is going to bring severe thunderstorms, snow, and near record cold to parts of Colorado on Monday and Tuesday. I'm a little skeptical of some of the huge snow predictions from the National Weather Service, as the storm may track a little too far to the northeast. But since we are still two days out, the track could change... and even a slight shift in the storm track could make a big difference in snowfall amounts. Day-by-day details below...
Rest of Sunday
A few isolated showers and thunderstorms are popping up over the Plains, and isolated rain and snow showers in the mountains, but otherwise, Sunday is turning out to be a warm, quiet, nice day for most areas... the calm before the storm. Another mild day will occur on Monday before dramatic changes occur.
Monday afternoon
As a strong low pressure system approaches from the West, temperatures will still remain mild, with high temperatures across the Front Range metro area and eastern Plains reaching the mid 60's, and high temperatures in the mountains near 9,000 ft. reaching the mid 40's. On Monday afternoon, as the system approaches, the air across the eastern Plains will be warm and unstable, and the approaching cold front will help to spark strong to severe thunderstorms across the region. Far eastern Colorado will be the most likely bet for supercell storms, with even higher chances as you move into Kansas. Lightning, strong winds, and even isolated tornadoes will be possible, especially near the Kansas border. Thunderstorms will be possible in the Denver area as well, but with virtually no severe threat.
The graphic below shows projected values of convective available potential energy (CAPE) for Monday afternoon. Higher convective energy means that moisture can quickly rise from the surface to higher altitudes, due to heating and other forcing mechanisms (in this case, for example, a cold front) thus producing stronger thunderstorms. In laymen's terms, CAPE generally means "thunderstorm potential", with the higher values corresponding to severe thunderstorm potential. Relatively high CAPE values look to extend into far eastern Colorado on Monday. The Storm Prediction Center has extended a "Slight Risk" of severe thunderstorms into this area as well.
Projected CAPE values for Monday afternoon
Storm Prediction Center Outlook for Monday
Heavy snow will begin in the Southern San Juan Mountains on Monday afternoon/evening as well, favoring areas such as Wolf Creek, Purgatory/Durango, and Silverton. Convective snow showers will pop up across the central and northern ranges as well, but due to an unfavorable wind direction from the southwest (and later, the northeast, as the storm turns upslope), most of these areas won't see big snow accumulations.
Monday night
On Monday evening, a strong cold front associated with the storm system will pass through, bringing a rapid drop in temperatures along with an onset of steady precipitation in the Front Range. Heavy snow in the San Juans will spread east toward the Sangre de Christo Range, and will quickly begin in the Front Range after the cold front passes through and winds switch to northeasterly.
Precipitation will initially begin as rain in the Front Range metro area and across the Plains. In the foothills, precipitation will briefly begin as rain, but will quickly change over to snow. In Denver, Boulder, and Ft. Collins... rain should change over to snow between 10 p.m. and midnight, from north to south. Between mid afternoon and midnight, this region will experience a 30 degree temperature drop. On the eastern plains, the changeover to snow will occur later in the night, as temperatures drop from west to east. Snow will continue through the night in the San Juans, but will gradually taper off on Tuesday morning as the storm's energy moves east.
Tuesday
Moderate to heavy snow will continue throughout the day Tuesday for the Front Range, winding down by early evening. The exact track of the storm will determine who receives the heaviest snowfall accumulations. Earlier today, the NWS issued a Winter Storm Warning for most of the Denver/Boulder forecast area, calling for 9-13 inches for the Front Range urban corridor from Denver to Ft. Collins... 8-14 inches for the Front Range foothills and mountains... and 6-11 inches for the eastern Plains.
From looking at the models and data today, I'm a little concerned that the storm may track too far to the north and east for Denver to receive the kind of snowfall totals the NWS and some models are predicting. The latest model runs have trended the storm a little farther to the northeast, focusing the heaviest precipitation over eastern Wyoming, Western Nebraska, and the Dakotas.
Also, from looking at some past storm comparisons, the current system is very similar to a storm that affected the region in early April of 2009. As I remember, the 2009 storm was expected to bring big snowfall totals to Denver, but ended up being a complete bust. Denver received very little snowfall, just barely missing out on the South, while areas farther north such as Ft. Collins received 7-10 inches.
The 2009 storm did track farther east than what models are predicting with the current storm, so Denver isn't going to miss out completely... but it just goes to show how a slight shift in storm track can lead to big snowfall discrepancies, and it is certainly possible that Denver could underperform with this storm if the heaviest precipitation stays to the north. However, a few factors will still favor the Denver metro area to receive significant snowfall... favorable northeasterly winds, very cold temperatures for April (higher snow-to-water ratios), and the upslope effect (rise in elevation "wrings out" more moisture with favorable winds).
As a result, I'm predicting that 6-10 inches of snow will fall in Denver... less than what some are forecasting, but still significant. I'll probably refine this prediction tomorrow based on the storm track (like I said, a slight shift either way can make a big difference). In addition, even though it's April, very cold temperatures will lead to snowpacked roads on Tuesday, in spite of the warm temperatures leading up to the event. This, combined with gusty winds and blowing snow, will make for hazardous driving conditions on Tuesday.
Near record cold will arrive with this system, as high temperatures in Denver on Tuesday will remain in the low 20's throughout the day (similar cold with what we saw in the snowstorm a couple of weeks ago). On Tuesday night, as the system exits to the East, temperatures in Denver will fall to near record levels for April into the upper single digits!
For the mountains and ski areas, most resorts are not in a favorable location to receive big snowfall from a storm like this. Wolf Creek, Silverton, and Purgatory in the Southern San Juans will likely receive big snow totals, along with Monarch, which also does well with this type of upslope set-up. In the Front Range, Eldora should have a nice powder day on Tuesday and Wednesday, but the upslope won't be quite strong enough to produce big snow totals along the Continental Divide at places like Loveland and A-Basin. Areas west of the Divide will be sitting in the snow shadow for this event, so despite what some weather services predict, these areas will not see much snow. Fortunately, that will change later in the week, though.
NWS Snow Probability Forecast for 8 inches or more... notice how the Denver area is right on the southern borderline
Wednesday and Beyond
Active weather is going to continue through the remainder of the week, which is great news as we continue to capitalize on some much-needed moisture this spring. Behind the main system, a series of weather disturbances will move across northern and central Colorado behind a steady, moist northwest flow. Two to three days of persistent snow showers will be likely for the northern and central mountains ranges (especially along and north of I-70), potentially bringing great late season skiing conditions. After Friday, there is uncertainty regarding what the weekend will bring, but the storm track looks to stay active for the near future, so continued snow chances are likely to occur.
In Denver, the post-storm warm-up will be slow, considering its April. Highs will only reach the 30's on Wednesday despite sunny skies, as snowcover will keep high temperatures in check. On Thursday, temperatures will rise into the upper 40's, but an increase in clouds associated with the next weather system will occur, and rain and snow showers will be possible later in the day as a weak disturbance moves through. Temperatures gradually warm through the end of the week into the weekend, but will still remain below average for mid April.
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