For the third time in less than two weeks a significant spring storm will spread a hefty helping of precipitation to the Front Range in the coming days. Initially it will be all rain across the Plains Sunday and during the day Monday, but we are concerned about a change-over to snow Monday night into early Tuesday for the lower elevations. Let’s take a look at the storm timeline and how much May snow everyone can expect!
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At a Glance:
- Another somewhat slow-moving and wet storm system will impact the Front Range Sunday into Tuesday
- Widely scattered rain showers and a few thunderstorms possible Sunday afternoon into Sunday night
- The main event with this storm will be Monday afternoon into Tuesday with widespread precipitation expected
- Snow levels generally remain above 7000 feet Sunday and Monday, but will most likely fall to include Boulder and Denver Monday night
- More than a foot of snow possible in the Foothills, with light accumulations expected across the Plains as well (though uncertainty is high in exactly how much)
A
s of Sunday morning, another bout of unsettled weather is knocking on our door! A flattened Pacific trough will slowly dig southward across Colorado from Sunday into Tuesday bringing an extended period of precipitation chances to the Front Range.
This incoming storm doesn’t have a lot going for it as the overall strength and dynamics are on the lower end of the spectrum. However, as is always the case for these spring storms, there are a few important factors to consider in the coming days. A key facet of this event will be its influx of deep moisture and, more importantly, the long duration. Precipitation chances will exist from Sunday afternoon all the way into Tuesday night. Given the weak nature of everything, we certainty don’t expect precipitation to be falling the entire time, with some flare ups suggested for Sunday afternoon into the nighttime and then again on Monday into Tuesday. The main event, that is when most of the widespread and heavier precipitation will fall, will likely come late Monday afternoon into early Tuesday.
All things considered, this should be another 1″ (or more) precipitation event for much of the Front Range. For those counting, it will be our third such system in just under two weeks! This is just typical May weather for our area. The GFS model is predicting anywhere from 1 to 2″ of precipitation for the area by Wednesday morning (below left). The NAM is fairly similar (below right). The Euro model is coming in a shade lower, but not much.
GFS (left) and NAM (right) model precipitation amounts for this event by Wednesday morning
Overall, we’re happy to see such good model agreement on precipitation amounts! This makes that aspect of the forecast easier and less of a concern for us. Unfortunately, notable model differences remain on the TYPE of said falling precipitation. It’s nearly mid-May, but yes, we’re still talking about the chance of snow! There has been considerable model variation over the last few days in regards to how much cold air will accompany this system, with the GFS model being plenty cold enough to produce significant snow across the Denver Metro area by Tuesday night (6+”). For example, the GFS model-derived snowfall forecast from last evening’s run is shown below.
Up until today the GFS has been a very cold outlier, with competing models such as the Euro predicting a strictly rain event for the lower elevations. However, we have witnessed some convergence in the temperature forecast of late. The GFS has warmed up a little, but other models have shifted colder. Uh oh! We now believe that snow is a likely possibility across the Denver and Boulder area. We’re just going to have to wait a little bit for that colder air to arrive.
As it stands now as of Sunday morning, snow levels are likely to remain at or above 7000 feet elevation Sunday, Sunday night, and during the day Monday. It’s not until Monday night when the coldest air will get drawn into the Front Range and snow levels will drop down towards 5000 feet. Conveniently, this is also the time when we expect the best forcings to overlap across the Front Range with widespread precipitation falling. This all spells out a chance of everyone seeing some snow.
The GFS, NAM, and HRRR models are all turning cold enough for accumulating snow across the lower elevations late Monday night into Tuesday morning, with even several inches of snow possible. Snow could begin mixing in before sunset Monday evening.
The Euro still stubbornly sits a few degrees too warm and produces mainly rain or a rain/snow mix that doesn’t amount to much. However, right now as we see it, the Euro has become a warm outlier and thus our forecast will lean towards the colder solutions.
So what does this all mean? Well, for the Foothills above 7500 feet elevation, this means a very high probability of significant accumulating snow. There may be light accumulations Sunday evening into Monday morning (up to 3″) in these areas, but overall most of the expected snowfall will occur Monday afternoon into Tuesday morning. Storm total accumulations will likely range from 7 to 14″ above 7500 feet elevation. Those highest-end amounts will be above 8500 feet east of the Continental Divide. The rest of us will have to wait until Monday night for temperatures to turn cold enough for snow. The coldest solution (the GFS outcome) would produce upwards of 4 to 8″ even in Boulder and Denver by Tuesday morning. The warmest solution (the Euro outcome) could see some areas struggle to even mix over to snow with almost no accumulation. Needless to say, uncertainty is high at the moment, but we do think some light snow accumulations will be possible, especially given the overnight timing of the cold air and heaviest precipitation overlapping. For now we’ll go with a trace to 4″ across the Plains, mainly on grassy surfaces with roadways remaining just wet or barely slushy. We do caution that we aren’t quite sure if most areas will see the lower end amounts in that range, or the higher end. Our preliminary snowfall forecast map for the event is shown below.
Hopefully we see models come into better agreement on the temperatures in the coming runs before things get going late in the day Monday. They almost always do. Check back for our final storm forecast Monday morning when we hope to pass along a higher confidence forecast.
Happy Mother’s Day to all the moms out there and have a good rest of the weekend!
We discuss Boulder and Denver weather every single day on BoulderCAST Premium. Sign up today to get access to our daily forecast discussions every morning, complete six-day skiing and hiking forecasts powered by machine learning, access to all our Front Range specific weather models, additional storm updates and much more!
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