1:15 PM, Friday, May 18, 2018
Parts of the Front Range region are in for a lot of rain today and Saturday, with wet snow above treeline. There are two phases of rainfall expected. Phase one will be in the form of showers and thunderstorms this afternoon and evening, some producing intense rain and hail.
Phase 2 (after a possible lull during the night) will come later tonight and Saturday with a soaking rain. It’s possible that not all areas will get a heavy soaking rain. The chances are greater north of Denver than they are south of Denver. I’d say the additional heavy rain is likely over Weld and eastern Larimer counties into southeastern Wyoming. But the risk of additional heavy rain exists throughout the Denver-Boulder area later tonight and tomorrow. Where the heavy rain hits there could be more than a month’s worth by Saturday evening (an average May brings about 3 inches total in Boulder and 2-3 inches in Denver).
Watch out for localized street flooding and the potential for creeks to spread out of their channels in some places. The Saturday morning Farmers Markets may be in for the second wet Saturday in a row.
For those interested, the GFS is a good, reliable model but not always the best at resolving the terrain influences. That one brings heavy rain to the entire Front Range region from the Denver area to Cheyenne. Many of the models that have better terrain representation (the NAM and different versions of the WRF) keep the most intense rainfall amounts just to the north an east of the Denver-Boulder area (but watch out Fort Collins and Greeley). I wouldn’t dismiss the GFS solution even though I’m a little suspicious. Stay alert.