The remnants of Hurricane Rosa will bring rain showers to most mountains on Tuesday through Wednesday while snow levels stay very high. On Thursday, Friday, and Saturday, additional showers and cooler air could combine for snow to fall on ski areas. And by early next week, more snow could accumulate, potentially down to the elevation of many mountain towns.
Short Term Forecast
Tuesday morning’s radar image shows a blob of rain over southern Arizona. This is associated with the moisture from the former Hurricane Rosa, and it’s heading in our direction.
The moisture over Colorado is actually near record levels for this date. The graphic below shows the average and record dew points (a measure of moisture) for Grand Junction, Colorado. The thin red line at the top of the image is the record-high dewpoint for each date (January 1 on the left, December 31 on the right). Circled in red is the dew point as of Monday night, which is a record for this date.
When we have a very high amount of moisture, the chances for precipitation are also high. When we combine a high amount of moisture with storm energy to help lift the air, the moisture is converted to precipitation.
And that’s what we will expect today … on Tuesday and Tuesday night, expect many rain showers across the mountains of Colorado with rain totals likely exceeding one inch in some spots.
Because the moisture on Tuesday will be associated with the remnants of Hurricane Rosa, temperatures will be warm. The freezing level (map courtesy of CAIC) will be around 14,000 feet, which means that the only snowflakes will be at the peaks of Colorado’s highest mountains, generally well above the elevation of ski areas.
Following the showers on Tuesday and Tuesday night, we will see additional showers on Wednesday, though likely less frequent than Tuesday as the moisture from Hurricane Rosa will head to the east of Colorado.
However, the remnants of Hurricane Rosa aren’t the only game in town.
Another storm is spinning to the west of California, and as this system slowly moves to the east, it will bring us additional precipitation on Thursday.
The good news for us snow lovers is that it will be colder on Thursday, with the freezing level closer to 11,000 feet (green and tan colors in the map below), so any precipitation that does fall on Thursday could be in the form of snowflakes near the summits of many ski areas.
To close out the week, cooler air should arrive on Friday and Friday night, and this could bring a burst of snow to the central and northern mountains.
Recap – Tuesday rain showers, Wednesday fewer rain showers, Thursday rain and snow showers, Friday cooler with rain and snow showers over the northern half of Colorado.
Saturday might be drier for at least part of the day as we will be in between storms.
Then the coolest air of the fall will arrive sometime on Saturday night or Sunday, and the cool air will stick around through at least the next week.
The model-averaged temperature forecast for Wolf Creek (in the southern mountains) shows high temperatures (blue bars) dropping from Saturday to Sunday and then staying chilly through the middle of October. Do not take these numbers as absolutes, rather notice the cooling trend.
The precipitation forecast from Sunday through next week is good but uncertain. What I mean is that it’s very likely that the mountains and many towns will see cool air and snow, but we will not know the exact timing of the snow for many days.
The average of 51 versions of the European weather model show the best chance for snow at Wolf Creek starting on Sunday and continuing through Tuesday, with lower but real chances for the rest of next week.
The wind direction from Sunday through much of next week will be from some version of southwest, south, or southeast, and this will generally favor snowfall in the southern and eastern mountains. Again, though, there is a ton of uncertainty in the forecast, so this is just an early estimate.
Finally, the 10-day multi-model snow forecast shows what we’ve been talking about, namely a good chance for snow for many of Colorado’s mountains (as well as Utah, Wyoming, and Montana).
And NOAA’s temperature outlook from October 7-11 corroborates the likelihood of snow with colder-than-average temperatures likely around the US Rocky Mountains.
Peering far into the future, most models show that the cool air will hang around through at least the middle of October, which would be good news for snowmaking crews as they could start to ramp up.
Snowmaking efficiency depends both on temperature and moisture, with the ideal situation being cold temperatures and low moisture. It’s too early to know about the moisture content of the atmosphere two weeks into the future, but at least cool or cold temperatures look likely through mid-October.
Thanks for reading … next update on Wednesday, October 3 (I will be posting daily from now through the end of April)!
* October 18 in Colorado Springs
* October 25 in Golden
* November 7 in Boulder
* Early November in Summit County
* November 28 in Vail
* December 5 in Denver
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