Issue Date: Sunday, June 7th, 2015
Issue Time: 9:00 AM MDT

Summary:

The moisture shield of former Hurricane Andres maintained its presence over Colorado yesterday, providing fuel for scattered showers and thunderstorms. The main band of large-scale lift stayed just west of Colorado into Utah, and this helped mitigate the potential flash flood risk, especially considering the relative quick storm motions. Even so, heavy rainfall from stronger storms produced street flooding across the Denver Metro area, and brief Flash Flooding was reported yesterday evening on a few roads in southeast portions of Archuleta County.

As far as severe storm reports are concerned, the following was reported to the local NWS offices:

62 mph Thunderstorm Wind Gust: 2 miles S of Alamosa

Tornado: 3 miles S of Thurman

For a statewide overview on yesterday’s rainfall, be sure and check the Storm Total Precipitation map below.

Issue Date: Saturday, June 6th, 2015
Issue Time: 9:00 AM MDT

Summary:

The moisture shield shed by now-defunct Hurricane Andres reached Colorado yesterday, increasing precipitable water to 150-200% of normal for June 5th, thanks to a deepening low pressure trough over the West Coast. This sent the moisture Colorado’s way in the southwesterly flow, accompanied by multiple disturbances that fired off showers and thunderstorms throughout the day, overnight, and into this morning. Strong-to-severe thunderstorms were fairly common over the Urban Corridor, Northeastern Plains, Palmer Ridge, and Southeastern Plains, producing heavy rain, hail, and a few tornadoes. As far as severe storm reports are concerned, the following was reported to the local NWS offices:

1.0-inch hail: 3 miles SW of Strasburg and Ponderosa Park
1.50-inch hail: 1 mile S of Parker
1.75-inch hail: Genoa and 5 miles ENE of Shamrock
Tornado: 4 miles SSW of Arickaree School and 6 miles E of Parker

Due to heavy rainfall produced by stronger storms, street and intersection flooding was reported across portions of the Urban Corridor. No other reports have been made at this time.

Issue Date: Friday, May 5th, 2015
Issue Time: 9:00 AM MDT

Summary:

FLOOD WARNINGS/ADVISORIES CONTINUE FOR PORTIONS OF THE CACHE LA POUDRE RIVER, SOUTH PLATTE RIVER, SOUTH BOULDER CREEK AND LITTLE THOMPSON RIVER.

Very high dewpoints, approaching 60 to 65 F over eastern Colorado fueled a very impressive array of strong and severe thunderstorms. Action began along the Palmer Divide in the early afternoon where slow moving, or even stationary thunderstorms first began to cause hail. The first cell, by Elizabeth, CO, caused an outflow boundary that jump-started a wave of cells lasting into the afternoon, evening and even overnight hours. The following severe weather was observed:

Tornadoes

At least two separate supercells produced tornadoes. One near Simla, and the other near Berthoud. Both were well documented on various social media outlets. There was some reported damage with the Simla storm, and both were certainly quite impressive for Colorado tornado standards.

Hail

Though it is not enjoyable when big hail damages and destroys objects on our property, the incredible amount of hail in yesterday’s storms saved many from a much more serious flooding threat. Hail takes time to melt and add to runoff, and can be a huge difference maker in preventing flooding. For example, one CoCoRaHS observer noted that about 25% of the total reported rainfall, came from hail! Yesterday’s list of hail reports is lengthy and covers many cities and counties in the Palmer Divide, Northeast Plains and Urban Corridor areas. Some of the more impressive reports include:

• 2.75 inches in Simla, breaking windows and severely damaging cars
• 2.5 inch in Lyons
• 1.5 inch in Loveland
• Many reports of 0.5 to 1.0 inch hail lasting up to 30 minutes

Heavy Rainfall

Thunderstorm rainfall increased in intensity as the evening wore on. Early storms were capable of producing about 1.0 – 1.25 inches per hour. During the late afternoon and early evening, max 1-hr rainfall rates increased to about 1.7 inches per hour. However, this does not do justice in describing short-term rainfall, which was well observed on the Urban Drainage ALERT network. Several gauges picked up 0.35 to 0.50 inches of rain in 5 minutes! Fortunately, most individual storm updrafts were only sustained for 30-45 minutes.

The highest 24-hour rain total came from the tornadic cell near Berthoud where several observers noted over 3 inches of rain. Several other 2 inch + reports were received from Boulder and Larimer counties. Many other locations in the Northeast Plains, Urban Corridor and Palmer Ridge experienced anywhere from 1 to 1.8 inches of rain.

For estimated rainfall in your area, be sure to check out the rainfall map below. NOTE: hail contamination caused severe overestimates in rainfall amounts. For example, radar estimates of the Berthoud storm (Larimer/Boulder counties) were in the 5-7 inch range, while highest observed values were around 3.5 inches. This is also likely the case with the Simla cell (Elbert County).

 

Issue Date: Thursday, May 4th, 2015
Issue Time: 9:00 AM MDT

Summary:

FLOOD WARNINGS/ADVISORIES CONTINUE FOR PORTIONS OF THE CACHE LA POUDRE RIVER, SOUTH PLATTE RIVER, AND SOUTH BOULDER CREEK.

With dry air aloft, it took a fairly substantial amount of moist, upslope flow to provide the fuel for isolated-to-scattered thunderstorms to develop yesterday. The Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, and portions of the Southeast Plains received this influence and in return produced a show of strong-to-severe thunderstorms. Action got started in the mid-afternoon hours over the Front Range, Palmer Ridge and Urban Corridor and winded down overnight across the Northeast and Southeast Plains. The storms produced bouts with moderate-to-heavy rain, large hail, and strong winds. Take a look at the severe storm reports:

1.0 inch hail: Bennett, 5 miles ENE of Centennial, 14 miles SSE of Fort Collins, 2 miles N of Elizabeth, 3 miles WNW of Evergreen, 5 miles E of Parker, SW Arvada, Aurora, 4 miles E of Elizabeth, 1 mile S of Agate, and 3 miles NNE of Larkspur

1.25 inch hail: 5 miles W of Country Gardens, Centennial, Loveland, 3 miles SSW of Elizabeth, 1 mile NW of Louviers, and 3 miles ESE of Perry Park

1.5 inch hail: 5 miles S of Bennett, 8 miles S of Manilla Village, 1 mile NE of Loveland, 2 miles N of Kiowa, 4 miles N of Elizabeth, and 3 miles WSW of Ponderosa Park

1.75 inch hail: 4 miles E of Elizabeth, 3 miles SSE of The Pinery, 3 miles NE of Franktown, 5 miles SE of Parker, 5 miles SE of Franktown, 4 miles NNW of Larkspur, and 3 miles N of Ordway

2.0 inch hail: Elizabeth

2.5 inch hail: 3 miles ENE of Elizabeth

Due to the effects of hail on radar, the radar-estimated STP map below is likely contaminated and shows higher total precipitation than what was actually observed. From CoCoRaHS, these are the highest observed rainfall totals:

Weld County: 1.28 inches
Jefferson County: 0.83 inches
Douglas County: 0.71 inches
Larimer County: 0.64 inches
Arapahoe County: 0.60 inches

No flash flooding was reported yesterday.