This week starts warm with mountain showers

GRAND JUNCTION, Colo. (KKCO) - Showers and thunderstorms this evening can be locally heavy at times. They will track toward the south and fade to an end before midnight - most of us will be drying by 10 PM.

Our Next 24 Hours

A few showers and thunderstorms are possible this evening through about 10 PM. Locally heavy rainfall is possible. We’ll cool through the 80s away from any showers. Closer to the showers, you can be 10-15 degrees cooler. Overnight, we’ll be partly cloudy to mostly clear. Low temperatures by morning will be near 59 degrees around Grand Junction and 54 degrees around Montrose. Monday will be mostly sunny to partly cloudy. Showers and thunderstorms will be few, and most of us will stay dry. Those showers and storms that do form will generally be pinned to the mountains, where they can be heavy. High temperatures will be near 91 degrees around Grand Junction and 88 degrees around Montrose.

This Week’s Weather Maker

High pressure centered west of us will be the main feature influencing our weather this week. That high pressure will gradually shift eastward and its influence on us early this week will be different from its influence on us later in the week. Two things to know about high pressure: first, air tends to sink in regions of high pressure; second, wind around high pressure flows clockwise. While the high pressure is centered over Nevada, west of us, we get a north-to-south wind flow around its eastern edge. The sinking air suppresses rain, but the wind from the north will blow up the north-facing slopes of the mountains. That upslope wind will help to generate some showers and thunderstorms along the northern slopes of the mountains. Those showers will likely stay pinned to the mountains, so they’ll be isolated if they exist at all, otherwise.

Our Weather Maker On The Move

That high pressure will shift east of us late Wednesday and Thursday. The clockwise wind flow means a south-to-north wind into our area that will carry monsoon moisture into Colorado. A low pressure trough in the upper levels of the atmosphere will set up along the West Coast, and that will help funnel the moisture and prompt the lift in the atmosphere necessary to generate more widespread showers and thunderstorms for Thursday and Friday.