FTB 09-13-2017: Last Day under Persistent Ridging Pattern Brings Scattered Showers

Issue Date: Wednesday, September 13, 2017
Issue Time: 10:10 AM MDT

— Flooding is NOT expected today

Today should be the last day of westerly flow under the ridge that has been persistent for the last several days. As the remnants of Irma continue move to the NE over the next 24 to 36 hours, the ridge will finally be pushed east as the west coast trough moves over the state. Currently, clear skies across the majority of the state excluding the northern Mountains. With the ridge overhead, this will help increase high temperatures over the lower elevations today. Precipitable Water (PW) at Denver and Grand Junction was measured at 0.7 inches and 0.78 inches, respectively. This is still a bit above climatology, but down from the last two days. Less moisture paired with lower dew points and drying in the mid-levels, will cause storms to be high-based and limit rainfall totals when compared to the last couple of days. Gusty winds are likely with stronger storms that form due to the inverted-V soundings.

This afternoon, some weak mid-level vorticity will make its way to the state via the west coast trough. While this will help slightly enhance the upslope flow coverage, the limited atmospheric moisture will prevent widespread rainfall in the mountains. The highest coverage of rainfall is expected to be over the southern Front Range, Palmer Ridge and Southeast Plains. The stronger W/SW steering winds aloft, will allow storms to move off the mountains and Palmer Ridge into the Southeast Plains. Dew points over the Southeast Plains are forecasted to be in the 40s and low 50s (east), so gusty winds are likely for the short duration of the storms. Activity will cease a couple hours after sundown with the decrease in instability. Flooding is not expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Front Range, Urban Corridor, Northeast Plains, Palmer Ridge, Southeast Mountains, Raton Ridge, Southeast Plains:

Sunny this morning becoming partly cloudy this afternoon. Shower and thunderstorm activity over the mountains will be greatest over the southern Front Range. Some storms are also expected to form due to convergence along the Palmer Ridge. Max 1-hr rain rates up to 0.6 inches with gusty winds possible. Flooding is not expected.

Primetime: 1PM to 10PM

Northwest Slope, Grand Valley, Southwest Slope, Northern Mountains, Central Mountains, San Luis Valley, San Juan Mountains:

Partly cloudy over the Northern Mountains with sunny skies elsewhere. Higher terrain will become partly cloudy this afternoon with the development of showers and thunderstorms. Highest coverage of rainfall will be in the Northern Mountains, and scattered showers are expected over the San Juans as well. 24-hour rainfall totals up to 0.3 inches (north) and 0.2 inches (south). Flooding is not expected today.

Primetime: 1PM to 10PM