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In Brief:
Mild temperatures remain through Sunday with afternoon thundershower chances moving off the mountains. Cooler weather, rain, and even snow chances return early next week.
Forecast Discussion:
Another mild cool front is approaching the state and tapping into some more of the southern jet stream moisture. For Friday afternoon, the front is not here yet, but cool air aloft plus daytime heating will kick off mountain showers. Some of these may move out on the plains in the afternoon when daytime heating is at a maximum (Figure 1). I colored the afternoon 'warm' time with red dashes for a few days in Figure 4. You can see the chances of showers pop up at those times. The front is south of the state Saturday cooling us a bit (Figure 2) (about 5 degrees - Figure 4). Remember, lighting, even from small non-severe storms, is deadly. Respect the bolt.
The Longer Range Forecast:
Afternoon shower chances and nice weather is the pattern through Sunday. The GFS gives most the state at least measurable rainfall through Sunday, but it is not a lot of water except for the northern and central mountains (Figure 5). The GFS keeps Longmont mostly dry to dry through the weekend.
The NAM gives Longmont about 0.1 to 0.2 inch of rain through Sunday afternoon. The GEM gives us 0.01 to 0.05. Convective systems like this are spotty in nature.
Sunday, a strong cold front arrives. The wind shift to the north occurs around 2 pm Sunday. This is powered by a deep mean trough approaching and a short wave out front (two red dashes over Colorado and West Colorado - Figure 3). Weatherunderground.com is giving us about 1/10th to 2/10ths inch of rain Sunday evening.
We cool to the mid to upper 30's F Monday morning. There is a chance the precipitation will fall as snow for a few hours (the purple colored precipitation depiction in Figure 4). For rainfall over the next 10 days (mainly this storm) we are in the 0.75 to 1 inch zone now (it is dropping again!). For snowfall (!) we pick up 3-4 inches from the GFS while Boulder and north Denver see up to 6 inches. Sort of hard to believe, but worth watching.
