FTB 07-31-2020: Scattered Mountain Storms

Issue Date: Friday, July 31st, 2020
Issue Time: 10:15AM MDT

— Flooding is NOT expected today

Strong northerly flow continues over Colorado today due to the state being stuck between a high amplitude ridge to the west and a departing low pressure system/trough to the east (see satellite image below). This strong flow aloft will cause diurnally-driven storms to move quickly to the south-southeast. Some moisture is present along the plains of eastern Colorado this morning where dew points are near or just above the 50F mark, but the moisture looks shallow. The morning Denver sounding shows abundant dry air aloft with PW similar to yesterday at 0.75 inches. Even more dry air is evident in the Grand Junction sounding (PW = 0.51 inches), indicating storms will favor the eastern portion of the state. The dry air will help mix out surface moisture, and drop dew points into the 30Fs and 40Fs, which will limit the amount of instability that can build and cause storms to have higher bases and produce more gusty winds than rainfall. There will still be enough moisture to fire isolated to scattered storms over the mountain terrains with ample sunshine, and storms should favor the eastern mountains and southern San Juan Mountains for development. Better moisture will remain further south over the Southeast Mountains today, so higher rain rates will be expected here. Storms will have difficulty producing heavy rain due to fast storm motions and the limited low-level moisture, so flooding is not expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Southeast Mountains, San Juan Mountains, San Luis Valley, Front Range, Raton Ridge, Southeast Plains, Palmer Ridge, Urban Corridor, & Northeast Plains:

Isolated to scattered diurnal thunderstorms will fire over the higher terrain and track south-southeast this afternoon. The highest chances for storm coverage will be over the Sangre de Cristo Mountains, and max 1-hour rain rates up to 0.4 inches will be possible. Slightly higher totals might be possible over the western Raton Ridge further south. Flooding is not expected today, but as always, if a storm tracks directly over a recent burn area, there is a chance for flash flooding issues, so use caution if near one. Further north and west, max 1-hour rain rates up to 0.25 inches will be possible. Storms could also produce gusty outflow winds (up to 45mph).

An isolated thunderstorm or two will likely track into the Urban Corridor and plains regions as they move off the mountains, but these storms should dissipate quickly and may produce some strong outflow winds as this occurs. Additionally, some storms may track into the Northeast Plains, but quick storm motion to the south should keep totals around 0.5 inches. No flooding is expected.

Primetime: 1PM to 11PM

Grand Valley, Northwest Slope, Northern Mountains, Central Mountains, & Southwest Slope:

Mostly sunny and warm today with high temperatures possibly reaching 100F for the Grand Valley. Small, isolated diurnal storms are possible over the southern Central and San Juan Mountains, but rain rates should stay under 0.1 in/hr. Storms could produce brief gusts up to 40 mph. Flooding is not forecasted.