SPM 07-30-2017: Dangerous Debris Flows Cause Evacuations

Issue Date: Sunday, July 30, 2017
Issue Time: 09:55AM MDT

Summary:

Cloud cover limited the northern extent of the heavy rainfall yesterday along the Front Range. Further south, storms began to fire over the higher terrain by 1PM. Another area along the Northeast Plains and eastern Palmer Ridge began to fire in the early afternoon where there was plentiful sunshine. Some storms were able to move off the higher terrain later in the afternoon favoring the higher terrain of the Palmer Divide. Overnight, the storms merged over the Southeast Plains in the high moisture environment and slowly moved SE exiting the state early this morning.

Over the western mountains, a CoCoRaHS station in La Plata County recorded 2.09 inches over the 24-hour period. Another report came in from Delta County where 1.25 inches in 90 minutes. There was a debris flow reported in Mesa County at 4:20PM over Routh 330 between mile marker 7 and 8. Storm totals were estimated around 1.8 inches.

In the Southeast Mountains, a station in Teller County recorded 1.16 inches. Over this area, radar estimates were as high as 1.8 inches. There were several Flash Flood Warnings and Advisories over this area over the course of the day. Just west of Walsenburg, 1.03 inches had fallen by 3:40PM. The rain here continued throughout the afternoon and evening making for dangerous conditions. At 6:35PM, a debris flow had cover portions of a road in Custer County near Wetmore, which is near the Junkins burn scar. There was debris reported all along highway 165 from Mckenzie Junction to mile post 6. By 7:15PM there was 3-4 feet of water over the Hardscrabble Creek Bridge in Wetmore. The evacuation of Wetmore and Greenwood began as the bridge was expected to fail (it did not fail).

In the adjacent plains over the south, there were a few more Flash Flood Warnings and Areal Advisories. At 6:30PM, there was 7-8 inches of water coving the road in Pueblo. A CoCoRaHS station in Pueblo recorded 1.34 inches. Near Peterson AFB, 0.6 inches was recorded falling in a 30 minute period. Storm estimated totals were as high as 2.8 inches. Over the SE Plains where the cluster of storms dropped precipitation both over the north and south. Over the north and south just over 5 inches had accumulated. A couple CoCoRaHS stations were able to capture some of the heavier rainfall. One was over Cheyenne County that recorded 3.02 inches, and the other over Otero County that had 2.74 inches.

To see how much rain fell in your neighborhood the last 24-hours, check out the State Precipitation Map below.

Storm Total Precip Legend

FTB 07-29-2017: Moisture Remains Intact for More Heavy PM Rainfall

Issue Date: Saturday, July 29th, 2017
Issue Time: 10:35AM MDT

— MODERATE/LOW flood threat for Palmer Ridge, Northeast Plains, Urban Corridor, Front Range, Southeast Plains, Southeast Mountains, Raton Ridge, Central Mountains, San Juan Mountains and Southwest Slope

Water Vapor imagery below shows some isolated embedded showers over the mountains, with cloud cover over nearly the entire state. This cloud cover will begin to break up after strong daytime heating and should not inhibit the formation of thunderstorms today over the eastern plains. Precipitable Water (PW) values at Denver this morning were 1.21 inches and 1.17 inches at Grand Junction. Values are as high as 1.4 inches are over the Southeast Plains. This moisture is expected to stick around with the southerly and southeasterly surface winds. Some of the drier air in northern New Mexico is expected to mix into the Southeast Mountains, which will cause showers to be more isolated (but not less threatening) in nature.

Over the mountains, expect continued showers over the Central Mountains as diurnal heating will lead to an upslope flow pattern. Other storms will begin to fire early this afternoon favoring the southern mountains for the stronger convection. Storm motion will be slow once again, but eventually the storms will push off the mountains later this afternoon and move to the N/NE. Over the Southeast Plains, a boundary will set up this afternoon, which will be located in an area of high instability. Shear will be weak, so most storms should not become severe. However, slow storm motion under the ridge will allow storms to heavy precipitation along the boundary. Once again, sufficient instability will allow storms to continue well after sunset. Lingering showers could persist through about 4AM.

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.

Flood Threat Legend

Zone-Specific Forecasts:

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

Partly cloudy early with showers then scattered to numerous showers and thunderstorms developing by early afternoon. Highest coverage will be where sun is able to break through the clouds. Max 1-hr rainfall up to 2.3 inches (adjacent plains) and 1.1 inches (mountains). 3-hour rainfall up to 4 inches over the plains will support a Moderate flood threat. Threats include mud flows, debris slides, field ponding and small stream and road flooding. The threat is expected to continue over night once again.

Primetime: 1PM to 4AM

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

Mostly cloudy with scattered showers over the Central Mountains. These should increase in intensity this afternoon. Heavier rainfall is expected over the San Juan Mountains with max 1-hr rainfall up to 1.1 inch. 3-6 hour rainfall amounts up to 2.2 inches are possible. A Moderate flood threat has been posted with threats including isolated mud flows and debris slides over saturated soils.

Primetime: 12:30PM to 10PM

SPM 07-29-2017: Slow Moving Storms Drop Widespread Precipitation

Issue Date: Saturday, July 29, 2017
Issue Time: 09:55AM MDT

Summary:

As expected, there were two separate areas of action yesterday. The first was over the high country and the second was along a boundary over the eastern plains. There were several Areal Flood Advisories and a couple Flash Flood Warnings. Over the mountains, the thunderstorm activity favored the San Juan Mountains, Central Mountains, Southeast Mountains and southern Front Range. 24-hour rain totals from CoCoRaHS stations were as high as 1 inch with radar storm total estimates at 2 inches. The San Miguel Sheriff’s Office reported a debris flow across CO 62 and CO 145 due to the steady rainfall over the course of day.

As storms began to sluggishly move off the higher terrain, the southern Urban Corridor was favored due to the enhanced lift of the Palmer Ridge. The UDFCD Willow Creek gage captured 1.1 inches in 30-min. In El Paso County, a CoCoRaHS station reported 1.75 inches of rain. Storm totals were estimated by radar to be as high as 3 inches. Outflow boundaries helped trigger additional thunderstorm activity, but most of these storms were short-lived.

Further east over the plains, storm motion was slow and storms eventually made their way to the SE corner of the state. CoCoRaHS gages captured up to 1.6 inches of rain, with radar estimates up to 5 inches. A Flash Flood occurred over Las Animas County at 10pm with 2 feet of water reported over the roads. Activity over the mountains began to dissipate around 11PM and the cluster of storms over the SE corner of the state moved out early this morning.

To see how much rain fell in your neighborhood the last 24-hours, check out the State Precipitation Map below.

Storm Total Precip Legend

SPM 07-28-2017: Heavy Rainfall Streak Alive And Well

Issue Date: Friday, July 28, 2017
Issue Time: 10:45AM MDT

Summary:

The long streak of heavy rainfall days that we have witnessed in Colorado was alive and well on Thursday. Although rainfall coverage and intensity took a noticeable downtick compared to Wednesday, scattered to locally numerous activity was still observed. The highest concentration of storms during the afternoon was once again along the Palmer Ridge, stretching southward though the Southeast Mountains and Raton Ridge areas. Highest rain gage observations recorded about 1 inch of rainfall with most of that falling in about an hour or less. Radar-based estimates suggest up to 1.5 inches fell locally in these regions.

A secondary areas of high coverage was in the San Juan Mountains where up to 0.75 inches was common. Though, a few higher elevation SNOTEL sites measured over 1 inch of precipitation. A rock slide was reported in Hinsdale County in the late afternoon hours along Highway 30.

During the late evening hours, a few rogue storm cells crossed into northeast Colorado from Wyoming. These produced locally very heavy rain, to the tune of 2.25 inches per hour and up to 3.5 inches in a 90 minute period. A few flash flooding (and a severe thunderstorm) warnings accompanied this activity.

In all, a handful of Flash Flood warnings and Areal Flood advisories were issued for eastern Colorado yesterday afternoon and evening.

Finally, it will be amiss of us not to point out that the Great Sand dunes USGS gage measured 0.79 inches of rainfall yesterday. This represents about 10-12% of its annual average rainfall.

For rainfall estimates in your area, check out our new State Precipitation Map below.