Issue Date: 9/5/2015
Issue Time: 9:05AM

—NO FLOOD THREAT TODAY

Coloradoans, or Coloradans, whichever you prefer, awoke to partly sunny skies this Sunday with streaks of mid and high clouds seen east of the Continental Divide. Although the dynamics of the atmosphere have not changed much since yesterday, a substantial import of dry air has lowered precipitable water values from the 0.8 – 1.1 inch range this time yesterday to the 0.5 – 0.8 inch range today (see chart below). A strong jet stream remains overhead, and with it there will be forcing for upward motion. However, without any appreciable instability, we only anticipate a few widely scattered showers and perhaps a very weak, brief thunderstorm in the far southwest corner of the state. Otherwise, the good weather will provide a nice opportunity to enjoy the outdoors on this Labor Day weekend.

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, jump below the map.

Zone Specific Forecasts

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

Partly to mostly sunny today and seasonably warm with highs in the 50s in the higher terrain to the mid-90s F in the lower elevations of the Arkansas River valley. Scattered showers will be possible across the higher terrain from the mid-afternoon through early evening hours. However, max 1-hour rainfall rates will be limited to 0.2 inches or less due to weak instability. Flooding is not expected today. Strong winds, up to 50 mph, will be possible in the higher ridges of the Front Range through the early afternoon.

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

Partly cloudy with widely scattered showers and stray weak thunderstorm possible, mostly across the south and central portions of the area. Max 1-hour rain rates up to 0.25 inches will be possible. Flooding is not expected today. High temperatures will range from the 50s in the higher terrain to the upper 80s in the Colorado River lowlands.

Issue Date: 9/5/2015
Issue Time: 9:00AM

—NO FLOOD THREAT TODAY

The atmosphere has only subtly changed form over the past 24 hours. An unseasonably strong trough has now entered the North American west coast, as shown in the water vapor image below. This large disturbance is continuing to direct strong moisture transport from the subtropics into the southwest United States. Morning precipitable water (PW) values have increased into the 0.8 to 1.2 inch range. This, by itself, would suggest the possibility of a heavy rainfall threat. However, a 100 mph jet stream is positioned over Colorado today, which will lead to storms motions of 35 to 45 mph. Further, instability will once again be very minimal. Altogether, there will once again be showers and a few weak thunderstorms today, but heavy rainfall will be very unlikely and flooding is not expected.

For today, we expect the ongoing rainfall over southwestern Colorado to intensify and grow in coverage. Once again, rainfall will have a difficult time moving into the eastern plains due to the downsloping flow, but a few showers and a weak thunderstorm will be possible over the Southeast Plains. Hourly rain rates up to 0.5 inches will be possible across the San Juans, Central Mountains, Southeast Mountains and Raton Ridge. Total 24-hour rainfall amounts of up to 0.7 inches will possible locally. As such, there is no flood threat 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, jump below the map.

Zone Specific Forecasts

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

Partly to mostly cloudy today and seasonably warm with highs in the 50s in the higher terrain to the lower 90s F in the lower elevations of the Arkansas River valley. Scattered thunderstorms will be possible closer to the mountains from the mid-afternoon through early evening hours. However, max 1-hour rainfall rates will be limited to 0.4 inches or less due to weak instability. Flooding is not expected today. Scattered showers may continue into the overnight hours.

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

Partly to mostly cloudy with scattered showers and weak thunderstorms developing, mostly across the south and central portions of the area. Max 1-hour rain rates up to 0.5 inches will be possible. Thunderstorms will weaken by early evening, but showers may continue overnight. Flooding is not expected today due to the lower rainfall intensities. Due to a strong jet stream overhead, gusty winds will be possible over the higher ridges.

Issue Date: 9/4/2015
Issue Time: 9:55AM

—NO Flood Threat Today

An unseasonably strong trough is positioned over the North American west coast, as shown in the water vapor image below. This large disturbance is helping to direct strong moisture transport from the subtropics into the southwest United States. Morning precipitable water (PW) values are in the 0.6 to 0.9 inch range, while surface dewpoints range from the mid-40s to the low-50s. Early in the summer, such a combination may have resulted in a heavy rainfall threat for Colorado. However, in early September, with a lower sun angle and weaker solar heating, there will simply not be enough instability for heavy rain today. Another negative factor is the fast steering level flow, resulting in storm motions of 30 to 40 mph.

We expect the ongoing rainfall over western Colorado to slightly intensify and grow in coverage. Rainfall will have a difficult time moving into the eastern plains due to the downsloping flow. Across the west, rain rates up to 0.75 inches will be possible along the south face of the San Juans, where instability will be greatest. Elsewhere, rain rates up to 0.5 inches will be possible. Total 24-hour rainfall amounts of up to 1.5 inches could occur over the Western Slope, Central Mountains and San Juans. However, flooding is not expected due to the lower rainfall intensities.

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, jump below the map.

Zone Specific Forecasts

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

Mostly sunny to partly cloudy today and seasonably warm with highs in the 50s in the higher terrain to the lower 90s F in the lower elevations of the Arkansas River valley. Scattered thunderstorms will be possible closer to the mountains from the mid-afternoon through early evening hours. However, max 1-hour rainfall rates will be limited to 0.6 inches or less due to weak instability. Flooding is not expected today. Scattered showers will continue into the overnight hours.

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

Partly to mostly cloudy with scatter showers and thunderstorms developing and/or intensifying. Max 1-hour rain rates up to 0.75 inches will be possible over the San Juans, with 0.5 inches elsewhere. Thunderstorms will weaken by early evening, but showers will continue overnight. Flooding is not expected today due to the lower rainfall intensities. However, up to 1.50 inches of rainfall could occur for isolated regions by tomorrow morning.

Issue Date: 9/3/2015
Issue Time: 8:51 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, GRAND VALLEY, CENTRAL MOUNTAINS, NORTHERN MOUNTAINS, NORTHWEST SLOPE, AND FRONT RANGE.

Stuck between an upper-level ridge over the central US and an upper-level ridge over the Pacific Northwest, Colorado will be under the influence of southwesterly flow through today and tonight. A disturbance embedded in the flow will work across the state from southwest to northeast through the afternoon/evening, accompanied by an increase in monsoonal moisture. This will kick off scattered showers and thunderstorms across the mountains, Urban Corridor, and Northeast Plains, with more isolated coverage across the Southeast Plains, Palmer Ridge, and Raton Ridge. Looking at the IPW graph below, the steady increase of moisture since the arrival of yesterday’s monsoonal disturbance is evident, and the pattern will continue today.

The heavy rain threat is a bit higher today as compared to yesterday across the mountains due to increasing moisture and better upper-level support, but steering winds will keep storms moving at a decent clip, limiting the overall flood threat. Lower elevations east of the mountains show a bit of an Inverted-V atmospheric profile, meaning gusty winds and lightning will be the main threats, with rain rates staying below flash flooding thresholds. For more information on rain rates and timing, be sure and check the zone-specific discussions below.

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, jump below the map.

Zone-Specific Forecasts

Urban Corridor, and Northeast Plains:

Scattered showers and thunderstorms are expected, producing mainly gusty winds and lightning, with brief bouts of moderate rainfall. With an inverted-V atmospheric profile in place, maximum rain rates will stay below flash flooding thresholds so no flood threat is warranted. Maximum rain rates will be 0.4-0.7 inches/hour over the Urban Corridor, and 0.-9-1.2 inches/hour over the Northeast Plains.

Timing: 1 PM – 10 PM along the Urban Corridor, and 3 PM – Midnight across the Northeast Plains.

Raton Ridge, Palmer Ridge, and Southeast Plains:

Partly sunny skies will be in place today with the increase in moisture from the monsoonal disturbance. Isolated showers/thunderstorms are expected, with the best opportunity near the mountains. Rain rates will be low, maximizing at 0.3-0.6 inches/hour.

Timing: 2 PM – 9 PM

Front Range, Northern Mountains, Northwest Slope, Central Mountains, San Juan Mountains, Southwest Slope, and Grand Valley:

Scattered-to-widespread showers and thunderstorms expected, capable of locally moderate-to-heavy rainfall. Storm motions will be quick enough to limit the overall flood threat, so only a low flood threat is warranted. Maximum rain rates will be as follows:

Front Range: 0.6-1.0 inches/hour
Northwest Slope, Northern Mountains, and Central Mountains: 1.0-1.8 inches/hour
Grand Valley, Southwest Slope, and San Juan Mountains: 0.8-1.2 inches/hour

Timing: 11 AM – 10 PM, with isolated-to-scattered showers/weak thunderstorms lingering into the early morning hours.

San Luis Valley and Southeast Mountains:

Isolated thunderstorms expected, otherwise a mostly cloudy day is in store. Rain rates will be low, generally in the 0.2-0.4 inches/hour range.

Timing: Noon – 10 PM