Issue Date: Tuesday, August 8, 2017
Issue Time: 10:10AM MDT

Summary

Moisture paired with several mid-level disturbances made for nearly continuous rain yesterday. Despite heavy cloud cover and cooler temperatures (temperatures were close to the lowest record high at DIA), the shortwaves were strong enough to fire multiple rounds of showers and thunderstorms. There was even some snow over the higher peaks! The first round of showers began in the morning with the first disturbance and low convective temperatures. Throughout the day, the precipitation was more tropical like than our typical heavy rainfall scenarios. With high dew points, the 24-hour totals were more impressive than they looked on radar with low reflectivity producing 30-min rain totals close to a half inch. In the evening and overnight hours, a cluster of showers formed over the adjacent plains and began to move south overnight. The final showers of this feature are exiting over the Kansas border this morning.

The multiple rounds of rain yesterday accumulated to create high storm totals for low temperatures and lack of instability. Over the Front Range, two SNOTEL sites recorded an inch of rain. Over the Southeast Mountains, 1.01 inches was recorded in an hour over Custer County. A CoCoRaHS station in Lincoln County recorded 2.63 inches. Radar estimates in this area were as high as 3.5 inches with overnight totals. There were two flood advisories yesterday, but as of this morning, there were no flood reports. We will continue to monitor the Arkansas River basin over the next couple of days as saturated soils and widespread rainfall will contribute to rising water on already elevated flows.

The most interesting report yesterday was near the Wet Mountains where there were several reports of funnels yesterday afternoon. Often times, mountains create their own circulations. The low-level winds are moving in one direction, while the mid-level winds are moving in another. This creates a rotation on a horizontal axis. If this vortex is located near an updraft (like yesterday), it can tilt from horizontal to vertical. With enough moisture in the air, condensation will occur making the funnel visible. For a funnel to form, you don’t always have the presence of a severe thunderstorm mesocyclone.

Issue Date: Monday, August 7, 2017
Issue Time: 11:00 AM MDT

Summary:

As storms began to build over the mountains in the early afternoon, the first set of storms fired over the western slope. The SW corner of the state was the center of action yesterday, but lower Precipitable Water (PW) favored strong winds more than heavy rainfall. The initial wave of convective storms east of the Continental Divide favored the areas that were able to produce higher instability from less cloud cover. Two of those places were along the higher terrain of the Palmer and Raton Ridge. Towards the evening hours, a second batch of thunderstorms developed further north over the Urban Corridor and Northeast Plains with the help of strong low-level moisture, a mid-level vorticity maximum and upper-level jet support. The thunderstorms on the eastern plains formed two clusters north and south of the Palmer Ridge with the cluster to the north producing the heavier showers. The northern mesoscale convective system (MCS) moved south/southeast throughout the night and eventually exited the state this morning. There were several Areal Flood Advisories throughout the day.

Over the Western Slope, storm totals were less than Saturday. Gusty winds accompanied the thunderstorms with a 55 mph gust recorded at the airport in Rifle. The Lily Pond SNOTEL site recorded the highest observation for the 24-hour period at 0.7 inches. Over the Southeast Mountains, the Apishapa SNOTEL site recorded 1.2 inches yesterday with 1-hour rainfall totals of 0.5 inches. Over Colorado Springs, storm totals were estimated at 2.5 inches with a CoCoRaHS station recording 1.94 inches. The most impressive rainfall was over Kit Carson County where the cluster of storms formed in the evening hours. A CoCoRaHS station recorded 6.2 inches of rain and another station nearby recorded 4.06 inches. Radar estimates of 1-hr rain rates are as high as 3 inches. Road and ditch flooding was reported near Burlington. There were no other flood reports as of this morning, although rain amounts in that range definitely caused flooding over the county.

To see how much precipitation fell in your area, take a peek at the State Precipitation Map below.

Issue Date: Sunday, August 6, 2017
Issue Time: 10:10 AM MDT

Summary:

An active weather pattern remains in place over Colorado, as scattered to numerous thunderstorms formed again yesterday. The trough located across the plains and weak jet streak near Colorado continue to usher in shortwaves that amply the diurnal weather patterns and help continue showers overnight. Precipitable Water (PW) values over 1 inch over the eastern plains and southwest corner of the state helped supply moisture to the thunderstorms yesterday. While atmospheric conditions were again marginal for a flood threat, storms produced high efficient rainfall rates. Storms formed over the high terrain midafternoon yesterday, and by late afternoon made it over the adjacent plains. Outflow boundaries from the initial storms helped create low-level convergence and more low-level moisture for other thunderstorms formation. Moisture advection from Utah with the west/southwest flow helped trigger numerous thunderstorms over the western slope as well.

Over the higher terrain in the eastern portion of the state, storms favored the Front Range. Urban Drainage and Flood Control District (UDFCD) mesonet recorded 24-hour rain totals as high as 0.87 inches over the mountains. Over the western slope in the higher terrains, rain rates were just under 1 inch with the highest recorded storm total being 1.15 inches. Radar estimates were as high as 1.8 inches. There was a Flood Advisory and Flash Flood Warning for Garfield County during early in the evening hours. Rainfall totals of 1.8 inches created mud flows and flash flooding along Government Creek near Rifle, Colorado. A mud flow also occurred in Rio Blanco. A heavy rainfall report was recorded in Redlands, Colorado for 0.86 inches of rain. Radar estimates were 1.5 inches over this area.

Over the plains, the highest precipitation producing storms were over Crowley and Otero County. Otero County had a CoCoRaHS gage captured 2.15 inches. Radar estimates were as high as 2.5 inches. In the Denver Metro area, rain gages captured 0.87 inches in 30-minutes, but 1-hour rainfall totals were under 1 inch. Further south over Douglas County, a flood advisory was issued, where 1 inch of rain was recorded at a CoCoRaHS station. There were no storm reports over the eastern portion of the state as of this morning.

To see how much precipitation has fallen in your neighborhood, scroll down and take a look at the State Precipitation Map.

Issue Date: Saturday, August 5, 2017
Issue Time: 11AM MDT

Summary:

In Colorado, we are frequently impressed by thunderstorms that “overachieve” given the atmospheric conditions. Such was the case on Friday. Despite marginal moisture and relatively fast storm steering winds, isolated pockets of heavy rainfall were observed. Overall, precipitation coverage was highest across the Grand Valley, San Juans, Northeast Plains and Southeast Plains. West of the Continental Divide, over 1 inch of rainfall was estimated to have fallen across Mesa, Montrose and Garfield counties. Several debris flows were reported in those counties, along with flooded streets in Carbondale (Garfield County).

Farther east, most storms were cruising along at 25+ mph, which generally limited rainfall rates. However, once enough storms form in proximity to each other, they change the local steering winds and localized heavy rainfall can result. Over 1.5 inches of rainfall was estimated (highest official gage reports just under 1 inch) east of Pueblo. An Areal Flood Advisory was issued in the early evening. Fortunately, flooding was not reported as of this morning.

In addition to the rainfall, a few reports of large hail (up to 1.5 inches near Wetmore) and gusty winds (62 mph report at the Denver International Airport) were reported in association with the strongest thunderstorm cells.