There's been a lot of excitement (good and bad) around some of the GFS modeled snowfall forecasts with the snow event tonight and tomorrow. While its been producing some impressive totals for not just Boulder and Fort Collins but the entire metro Denver area... just how likely is this to occur?
For reference, below is its 18z forecast. It has 10 - 14" across the Denver area, with upwards of 15" for Boulder, and an east to west 8 - 12" up around Fort Collins:
MOST other data continues to suggest this isn't the most likely scenario, at least for Denver. The play, it seems, is for a northern bias with the heaviest snow as we've been outlining all week.
Here's a look at where other models are as of this afternoon or evening, depending on when their latest run was available.
The midday run from the European has 0.35" to 0.5" QPF for Denver. Assuming no melting (and there will be melting) this would equate to 4 - 8" of snow for Denver which is pretty in line with our 3 - 7" forecast. The CLEAR bias here is to paint the heaviest totals north and northwest of Denver:
The latest SREF model has 6" for Broomfield (pictured below), 4" for Denver International Airport, and 4.5" for south Denver.
The HRRR model, which has been very consistent today also has from 0.35" to 0.5" liquid for Denver, but shows much of that falling in the form of rain or mix initially. For snow, it's got about 3 - 5" for Denver through 3pm tomorrow. Again, much heavier totals with QPF upwards of 1" northwest of Denver!
The NAM continues to play games. This morning it tracked everything north, given virtually no snow to Denver and only about an inch to Fort Collins. By its midday run, we saw it pull things south bumping Fort Collins up near a foot for totals, but still only 1 - 3" for Denver.
Tonight, it continues to show this as a NON EVENT for Denver. Some very impressive QPF numbers up north, but south of I-76... meh. To me this scenario is definitely on the table for Denver, and perhaps more likely than a boom?
Still, look how vastly different it looks now as compared to how it did this morning (below). Finally its in the same camp as most other models.
Our evening gamblers only show about a 30% chance that the GFS forecast is correct for Denver. So the answer to the post's question I suppose is yes... a boom on the table, but it's not entirely likely that we'll be eating it. This is even with a generous snow/liquid ratio, which with the melting likely to occur may be hard to achieve in most areas.
For Boulder and Fort Collins however? Still a better than 60% chance you break the 6" mark with this storm. We shall see!
In the end, it'll do what it's going to do. We've got rain and snow falling already this evening and so changing the forecast would be a bit late to the game anyway. Given where most data sits tonight, we feel pretty good about where we sit, and even up north melting may be a bigger concern for our forecast than a boom in some areas. It sure feels like this storm has a surprise or two up its sleeve, but the probability of that coming in a form of a GFS boom for Denver? Perhaps not great.
The NWS has included the entire urban corridor in the Winter Weather Advisory now. It goes into effect at 10pm and expires at 6pm on Thursday. Most of us won't be going anywhere, but for those that need to commute for any reason, plan on winter travel conditions later tonight and be safe.
As a reminder, here's our forecast from earlier today.