STP 06-29-2015: Isolated-to-Scattered Thunderstorms Dotted the High Country and Adjacent Low Elevations

Issue Date: Monday, June 29th, 2015
Issue Time: 9:00 AM MDT

Summary:

Yesterday started out fairly benign, with isolated-to-scattered showers/weak thunderstorms dotting the High Country. As the day progressed into the afternoon hours, intensity began to pick up on a few storms, bringing stronger outflow winds, small hail, and brief heavy rain. During the evening hours, activity increased across the adjacent low elevations of the Urban Corridor, Northeast Plains and Palmer Ridge, with a few storms reaching severe thresholds. Severe storm reports include:

1.5 inch hail: 3 miles S of Country Gardens (Arapahoe)
1.25 inch hail: Briggsdale (Weld), 6 miles NE of Colorado Springs (El Paso), 5 miles SSW of Black Forest (El Paso)
1.0 inch hail: 8 miles SE of Arapahoe Park (Elbert), 1 mile N of Black Forest (El Paso), 3 miles NE of Black Forest (El Paso), 5 miles NNW of Peterson AFB (El Paso), 4 miles NW of Peterson AFB (El Paso), 4 miles SSW of Black Forest (El Paso), 4 miles WNW of Peyton (El Paso), 8 miles NE of Black Forest (El Paso)

No flash flooding was reported.

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FTB 06-28-2015: Uptick in Moisture Leads to an Uptick in Thunderstorm Coverage

Issue Date: 6/28/2015
Issue Time: 9:57 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, CENTRAL MOUNTAINS, SOUTHEAST MOUNTAINS, SAN JUAN MOUNTAINS, AND SOUTHWEST SLOPE.

The upper-level ridge centered over western Utah continues its dominance over the western US today. One main difference over yesterday is that a bit more subtropical moisture has rotated into Colorado under the ridge, pushing precipitable water values slightly above average. This will lead to a slight uptick in thunderstorm coverage today, but, due to mean storm motions from north to south, most will still remain confined to the High Country. An isolated thunderstorm or two will develop during the late afternoon/early evening over the Urban Corridor thanks to outflow boundaries from storms over the higher terrain.

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A feature of note in today’s forecast is a weak shortwave that will move overhead during the early-to-mid afternoon hours. In addition to helping initiate storms over the higher terrain, this will also allow one or two isolated thunderstorms to develop over the Palmer Ridge and southern portions of the Urban Corridor, moving southward with time. With surface high pressure and upper-level high pressure in place, these storms will not last very long as they move away from the preferred terrain of the Palmer Ridge. Additionally, most of the precipitation that falls from these storms will likely not reach the ground due to high cloud bases. Maximum rain rates will be 0.2-0.5 inches/hour.

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.

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Flood Threat Legend

Zone-Specific Forecasts

Urban Corridor and Palmer Ridge:

Mostly sunny, with a couple of isolated thunderstorms possible this afternoon and evening. The main threat from storms will be gusty outflow winds, small hail, and lightning. With high cloud bases, though, much of the precipitation will evaporate before reaching the surface, resulting in maximum rain rates of 0.2-0.5 inches/hour. An outflow boundary moving off of the mountains and over the Urban Corridor will provide the best opportunity for a storm to produce locally heavy rain, though the chances are low. This is accounted for in the low flood threat area. If this situation occurs, maximum rain rates will push to 0.8-1.2 inches/hour.

Timing: 1 PM – 9 PM

Southeast Plains, Northeast Plains and Raton Ridge:

Mostly sunny and hot will be the main story today across these regions. Plains regions near the preferred terrain of the Palmer Ridge, and Raton Ridge near the Southeast Mountains, will hold a chance for an isolated thunderstorm to drift overhead, although chances are slim. Maximum rain rates will be 0.3-0.6 inches/hour.

Timing: 3 PM – 9 PM

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

Mostly sunny early, becoming partly sunny this afternoon as scattered thunderstorms begin to develop over the higher terrain. The main threats from thunderstorms will be gusty outflow winds, small hail, and lightning, but brief heavy rain cannot be ruled out. Most rain rates will be light (0.2-0.4 inches/hour), but a stronger storm or two could produce rain at 0.6-1.0 inches/hour. The San Juan Mountains will be the main region to watch today as the best moisture resides there. Maximum rain rates will be 1.0-1.4 inches/hour for the San Juan Mountains.

Timing: Noon – 8 PM, with a few showers/weak thunderstorms lingering until midnight over southern regions.

STP 06-28-2015: Warmer and Drier East, Isolated-to-Scattered Showers and Thunderstorms Over the High Country

Issue Date: Sunday, June 28th, 2015
Issue Time: 9:00 AM MDT

Summary:

It would be hard to point to a better Saturday than what Colorado experienced yesterday. Due to upper-level high pressure continuing to build across the western US, isolated-to-scattered showers and thunderstorms were confined to the higher terrain. Most storms produced gusty outflow winds, lightning, and brief light-to-moderate rain. Hail observations greater than 0.5 inch were reported in Saguache (0.88 inch) and La Plata (0.70 inch) Counties; no other reports were made yesterday. Abundant sunshine was the main story yesterday for the majority of Colorado’s population – a great way to spend a late-June weekend.

No other flash flooding was reported yesterday.

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Storm Total Precip Legend

FTB 06-27-2015: Showers and Thunderstorms Will Favor the High Country

Issue Date: 6/27/2015
Issue Time: 9:47 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, SOUTHEAST MOUNTAINS, AND RATON RIDGE.

An upper-level ridge has set down roots across the Western US, centered over western Utah. The location of the high pressure center is important, as it will place Colorado under north-northwesterly flow aloft. This will keep storms mainly confined to the high country, with a slight chance of an isolated shower/thunderstorm to stray over adjacent lower elevations of the Urban Corridor (Pikes Peak region and south) and Southeast Plains.

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With upper-level ridging in place, isolated-to-scattered showers and thunderstorms will rely on daytime heating to initiate activity over the mountains. The favored terrain for scattered storms will be the San Juan Mountains and Southeast Mountains, with more isolated coverage over the mountains of the Front Range, Northern Mountains, Southwest Slope, and Central Mountains. Gusty outflow winds and lightning will be the main impacts of storm activity, along with brief moderate-to-heavy rain. Precipitable water is near average, and while some drying is expected today, there will still be enough available for maximum rain rates around 0.8-1.2 inches/hour over the San Juan Mountains and Southeast Mountains. Elsewhere over the high country, maximum rain rates will be 0.4-0.7 inches/hour.

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.

Flood Threat Legend

Zone-Specific Forecasts

Urban Corridor, Palmer Ridge, Southeast Plains, Northeast Plains and Raton Ridge:

Partly sunny near the interface with the higher terrain, mostly sunny further east. A stray, isolated thunderstorm or two will move off of the higher terrain and over adjacent portions of the Urban Corridor (Pikes Peak region and south), Southeast Plains, and Raton Ridge. Otherwise, the rest of the area will stay dry and warm a few degrees over yesterday’s high temperatures.

Any thunderstorm activity will result in mainly gusty winds, lightning, and brief light-to-moderate rainfall. Maximum rain rates will be in the 0.25-0.5 inches/hour.

Timing: 1 PM – 8 PM

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

Isolated-to-scattered showers and thunderstorms will develop around lunchtime over the higher terrain of the Front Range, Northern Mountains, Central Mountains, San Juan Mountains, Southeast Mountains, and Southwest Slope. The best coverage will be across the San Juan Mountains and Southeast Mountains, as discussed above in the main discussion. A few weak thunderstorms will stray over lower elevations, with gusty outflow winds, lightning, and light-to-moderate rainfall being the main threats.

Maximum rain rates around 0.8-1.2 inches/hour over the San Juan Mountains and Southeast Mountains, and elsewhere over the high country will be 0.4-0.7 inches/hour.

Timing: Noon – 9 PM