Issue Date: 8/17/2015
Issue Time: 9:48 AM

A MODERATE FLOOD THREAT IS ISSUED FOR PORTIONS OF THE NORTHEAST PLAINS, SOUTHEAST PLAINS, PALMER RIDGE, URBAN CORRIDOR, AND FRONT RANGE.

A LOW FLOOD THREAT IS ISSUED FOR PORTIONS OF THE SOUTHEAST PLAINS, PALMER RIDGE, URBAN CORRIDOR, FRONT RANGE, RATON RIDGE, SOUTHEAST MOUNTAINS, AND SAN JUAN MOUNTAINS.

In what has been a string of fairly active weather, today/tonight will feature the grand finale for areas east of the Divide. The environment is bringing together ingredients favorable for severe weather and heavy rainfall. A seasonably strong shortwave trough will rotate across the Rockies today, pushing into the northern US plains by tomorrow morning. This shortwave is accompanied by a jet streak, and both will bring favorable broad-scale lift/deep-layer shear for strong/severe thunderstorms to eastern Colorado. Additionally, the approach of the trough will push a cool front through Colorado, providing a source of low-level convergence and wind shear, and southeasterly flow ahead of the front continues to transport in abundant low-level moisture.

The prime areas for strong/severe thunderstorms will be along and south of the I-70 corridor, from the Front Range to the CO/KS border. A few strong storms will be possible north of that line, but south is where the most action will occur. Narrowing down this further, wherever the cool front is located, that will be the best corridor for severe thunderstorms capable of large hail, damaging winds, and a couple tornadoes. At this time, that appears to be across the Palmer Ridge, southern extents of the Urban Corridor, and central/northern portions of the southeast plains, but all areas in the general area outlined in the first sentence of this paragraph will have an environment favorable for strong-to-severe storms thanks to available moisture, instability, and deep-layer shear.

West of the Continental Divide, on the other hand, will see the downtick experienced yesterday continue through today and tonight. Isolated-to-widely scattered showers and thunderstorms are expected, developing over the higher terrain initially and drifting over valleys with time. The most active regions will be across the southern half of the area, namely in the San Juan Mountain, Central Mountain, and Southwest Slope regions. Drier air will begin working south behind the passing cool front late this afternoon/evening, effectively ending thunderstorm chances behind the front. The front will push out of the area by early Tuesday morning.

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, and Raton Ridge:

Scattered strong-to-severe storms are likely, especially for the areas outlined in the discussion above. With abundant moisture available, heavy rain is also likely, with maximum rain rates as follows:

Urban Corridor, Raton Ridge, and Front Range: 1.0-1.8 inches/hour
Northeast Plains: 2.0-2.5 inches/hour
Southeast Plains: 2.5-3.0 inches/hour

A thunderstorm complex is currently ongoing across the Southeast Plains/Raton Ridge. Today’s main activity timing: 2-3 PM – 11 PM, with a few thunderstorms continuing into the early morning across the plains.

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

Isolated-to-widely scattered showers and thunderstorms expected this afternoon and evening, before winding down after sunset. Locally moderate-to-heavy rainfall is possible across the San Juan Mountains, Central Mountains, and Southeast Mountains. Maximum rain rates break down like this:

Northern Mountains, Northwest Slope, Grand Valley, San Luis Valley, Central Mountains, and Southwest Slope: 0.4-0.8 inches/hour
San Juan Mountains: 0.6-1.0 inches/hour
Southeast Mountains: 0.8-1.2 inches/hour

Timing: 11 AM – 9 PM

Issue Date: 8/16/2015
Issue Time: 9:30 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHEAST PLAINS, PALMER RIDGE, AND SOUTHEAST PLAINS.

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE URBAN CORRIDOR, PALMER RIDGE, NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, FRONT RANGE, SOUTHEAST MOUNTAINS, RATON RIDGE, AND SAN JUAN MOUNTAINS.

For today, the main focus will shift to areas east of the mountains as the most active regions due to a passing mid-/upper-level shortwave disturbance. The disturbance will flatten the ridge, cooling temperatures aloft and providing a source of broad-scale thunderstorm support for areas along and east of the Continental Divide. Near the mountains, low-level moisture has been eroded slightly this morning with westerly flow, but should rebound this afternoon as low-level flow turns east-southeasterly once again. The best instability will be in place over the Northeast Plains, Palmer Ridge, and Southeast Plains, with slightly less over the Urban Corridor, Front Range, Raton Ridge, and Southeast Mountains. With the ingredients in place, heavy rainfall will be a threat with thunderstorms, especially considering expected slow storm motions due to weak steering winds aloft. A couple of thunderstorms will become severe, with the main threats being strong winds and large hail, but an isolated tornado cannot be ruled out near the Cheyenne Ridge.

The Northwest Slope, Grand Valley, Southwest Slope, San Juan Mountains, and San Luis Valley will be on the edge of the upper-level support, so terrain-based, isolated-to-scattered thunderstorms will be the main player in those regions. Rain rates will vary, so 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

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

Scattered thunderstorms are expected to develop this afternoon, continuing through the evening and into the overnight hours. A few will become severe, mainly across the Northeast Plains and Palmer Ridge regions, producing large hail and strong winds. As stated above, as isolated tornado cannot be ruled out near the Cheyenne Ridge. Maximum rain rates will vary:

Urban Corridor and Front Range: 1.0-2.0 inches/hour
Northeast Plains, Palmer Ridge, and Southeast Plains: 2.2-3.0 inches/hour
Raton Ridge and Southeast Mountains: 0.8-1.4 inches/hour

Timing: Noon – 11 PM, with a few thunderstorms lingering into the early morning hours

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

Isolated-to-scattered showers and thunderstorms, with the best relative coverage across the Northern Mountains, Central Mountains, and San Juan Mountains. Locally heavy rainfall will be possible across portions of the Northern Mountains, Central Mountains, and San Juan Mountains, and this has been accounted for in the low flood threat area. Maximum rain rates are as follows:

Northern Mountains, Central Mountains, and San Juan Mountains: 1.0-1.5 inches/hour
Northwest Slope, Grand Valley, Southwest Slope, and San Luis Valley: 0.4-0.75 inches/hour

Timing: Noon – 8 PM

Issue Date: 8/15/2015
Issue Time: 10:05 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE PALMER RIDGE, NORTHEAST PLAINS, SOUTHEAST PLAINS, SAN JUAN MOUNTAINS, FRONT RANGE, NORTHERN MOUNTAINS, AND CENTRAL MOUNTAINS.

Another day of isolated-to-scattered showers and thunderstorms is on tap today. Storms will be more numerous over the higher terrain than lower elevations, but regardless of location, all stronger storms will hold the threat of producing locally heavy rainfall. Underneath the upper-level ridge, the large-scale environment is basically neutral for today, but daytime heating will combine with residual moisture to produce thunderstorms, much like yesterday. Also like yesterday, weak steering winds aloft will lead to relatively slow storm motions, providing the opportunity for storms to rain over one location for an extended period of time.

For the lower elevations of eastern Colorado, outflow boundaries from mountain convection will be the main source of forcing for thunderstorms, with a few being the result of strong solar heating. Either way, ample moisture will make heavy rain a threat from any thunderstorm. Other threats include strong winds and lightning, with one or two thunderstorms becoming marginally severe producing wind gusts greater than 55 mph. It looks like the Urban Corridor may be spared the heavy rain threat today, as drier low-level air is in place along the interface with the mountains due to downsloping winds. If the westerly component remains in place through the afternoon, light-to-moderate rain and gusty winds will be all that thunderstorms can muster over the region. For more information on rain rates and timing, please see 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, Northeast Plains, Raton Ridge, Palmer Ridge, and Southeast Plains:

Isolated-to-scattered thunderstorms are expected, with the best coverage over the Palmer Ridge and Southeast Plains regions. Maximum rain rates will vary, so here is the breakdown:

Urban Corridor: 0.4-0.8 inches/hour
Palmer Ridge, Northeast Plains, and Southeast Plains: 1.5-2.5 inches/hour
Raton Ridge: 0.8-1.2 inches/hour

Timing: 1 PM – 10 PM, with a couple thunderstorms lingering until midnight, or just after, across the Plains.

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

Scattered thunderstorms expected over the higher terrain, with more isolated coverage over the lower valleys. The best relative coverage will be over the San Juan Mountains, Central Mountains, Northern Mountains, and Front Range. Maximum rain rates vary:

Northern Mountains, San Juan Mountains, Front Range, and Central Mountains: 0.8-1.4 inches/hour
Southeast Mountains and San Luis Valley: 0.4-0.8 inches/hour
Southwest Slope, Northwest Slope, and Grand Valley: 0.3-0.6 inches/hour

Timing: Noon – 10 PM

Issue Date: 8/14/2015
Issue Time: 9:30 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, FRONT RANGE, SAN JUAN MOUNTAINS, SOUTHEAST MOUNTAINS, URBAN CORRIDOR, PALMER RIDGE, RATON RIDGE, AND SOUTHEAST PLAINS.

The high pressure ridge will remain anchored over Colorado today, but subtle changes from yesterday will make the difference in today’s forecast. The main difference is that there is really no disturbance expected to track over Colorado. Instead, the main driver behind today’s thunderstorm activity will be daytime heat working on residual moisture under the ridge. Put simply, the activity will favor the higher terrain (especially early in the afternoon), with only a few thunderstorms moving over/developing above the Urban Corridor, Palmer Ridge, and Southeast Plains regions.

Underneath the ridge, weak flow aloft will allow for slow storm motions. This, combined with precipitable water values near, or above, an inch, will allow for heavy rainfall to impact a localized area for an extended period of time. Tempering the flood threat, though, is that instability is fairly low with warm mid-/upper-levels, so intense convection will be difficult. With all things considered, the low flood threat is warranted. For more details regarding rain rates and timing, please see 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. **OUR MAPPING SERVICE IS EXPERIENCING TECHNICAL DIFFICULTIES THIS MORNING. THE MAP WILL BECOME INTERACTIVE AS SOON AS THEIR ISSUES ARE RESOLVED. WE APOLOGIZE FOR THE INCONVENIENCE.**

Zone-Specific Forecasts

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

Isolated-to-widely scattered thunderstorms are expected, mainly near the higher terrain. Further east over the Southeast Plains, a couple of isolated thunderstorms will develop during the late afternoon/evening thanks to outflow boundaries from mountain convection moving into the moist environment. Maximum rain rates will vary…

Northeast Plains: 0.6-1.0 inches/hour
Urban Corridor and Palmer Ridge: 0.8-1.2 inches/hour
Southeast Plains and Palmer Ridge: 1.2-2.0 inches/hour

Timing: 1 PM – 10 PM, with a thunderstorm or two lingering until midnight over the Southeast Plains.

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

Scattered thunderstorms are expected over the higher terrain, with the best coverage expected over the Northern Mountains, Front Range, Central Mountains, Southeast Mountains, and San Juan Mountains. Maximum rain rates will vary…

Northwest Slope, Grand Valley, and Southwest Slope: 0.25-0.5 inches/hour
Northern Mountains: 0.6-1.0 inches/hour
Front Range, Central Mountains, and Southeast Mountains: 1.2-1.8 inches/hour
San Juan Mountains and San Luis Valley: 0.6-1.0 inches/hour

Timing: 11 AM – 10 PM