Sunday 9:15am: Snowfall totals and Frost Advisory Live Blog
The next 24 hours will be critical across the state, in particular the northern Front Range. Right now, there are flood warnings/watches, tornado watches, and winter storm warnings.
It'll be a mixed bag of precipitation type overnight. Bottom line is that more water is to fall and the flooding threat will be foremost in our attention.
Through evening, the heaviest storms with flooding rains will remain over the eastern plains. These storms have the potential to also produce tornadoes, hail and wind damage in addition to flooding. The rain will be measured in inches in many areas.
Meanwhile, rain/thunder/snow will develop over southern Colorado and will be moving toward the Front Range. This activity is what will bring another 1 to 3 inches of precipitation to the metro areas through Sunday morning.
This will be a mix of rain and snow statewide overnight. Regardless of rain versus snow, it's a lot of water headed toward the area and flooding will continue to increase.
As discussed in previous posts, we have known for days that a lot of water will fall over the region this weekend. That remains on track. Further, we discussed the potential for snowfall that also remains on track. Let's break down the snowfall forecast a bit more now.
For Denver, we will see rain chances through mid-evening, then a transition to snow chances late evening and overnight. For many neighborhoods there will be a sloppy mess of slushy snow in the morning. For those above 6,000 feet the transition to snow will happen earlier than for the city.
Snowfall amounts will not be spread out equally as with a traditional winter storm. This storm will have pockets of heavy snow versus areas of no snow due to its convective nature -- expect a wide range of snowfall across the area.
Any one of us in the metro area has the chance for 5 to 10 inches. However, some will get that and others will not due to the isolated nature of the heaviest snow. Breaking down the probabilities, you can see here the chances for 1, 4, 6, and 12 inches of snow:
You can see by those probabilities, that getting more than 4 or 6 inches becomes increasingly undrealistic until you get to about the 10 to 12 inch range...hence the chance for 5-10" in Denver and along the Front Range.
However, snow ratios will be 3:1 to 7:1 overnight, which limits the build-up of snow totals. Factor in also the warm ground temperatures and rapid melt of the snowfall. Many will wake-up to a lot less snow than what actually fell overnight.
The forecast snowfall amounts in yesterday's post will increase a bit to account for convective nature of tonight's snow. Further, any adjustment made to fit nicely with the probabilities, but keeping in mind the idea of rapid melting with low snow ratios. Here's the breakdown, 2 - 6" for Denver, 4 - 8" across the Palmer Divide, at 6 - 12" for the foothills west of the city, and along the Wyoming border and northward.
The short range models that handle these more convective systems with greater detail follow the hit-and-miss nature of the highest snowfall totals. For example, here's the HRRR running through 4am Sunday morning. You can see what I mean by, the hit-and-miss nature to the snowfall.
The bulk of the precipitation will fall through the night, then become more scattered throughout the day as the system slides passed us. We will continue to dry off heading into Monday.
This is a great deal of moisture regardless of which form it takes. Most of the northern Front Range can't handle any more water so flooding from here on out is inevitable. If you are in a flood prone area, please stay safe and alert.