Issue Date: 8/28/2016
Issue Time: 10:15 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE NORTHWEST SLOPE, NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, GRAND VALLEY, SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, FRONT RANGE, SOUTHEAST MOUNTAINS, URBAN CORRIDOR, PALMER RIDGE, RATON RIDGE, NORTHEAST PLAINS, AND SOUTHEAST PLAINS.

Another unsettled period is expected as an upper-level low shifts eastward out of the 4-corners region and into northern New Mexico. This will provide favorable dynamics for the production of isolated-to-scattered showers/storms across much of Colorado. Much like yesterday, the higher terrain and western slope will see the best coverage, while areas east of the mountains remain in the isolated-to-widely scattered category. A slight increase in moisture (shown well in the chart below), as well as an uptick in instability, will provide a bit more fuel for today’s thunderstorms, keeping the threat of heavy rain in the forecast for areas south of I-70. Even so, the flood threat remains on the low end of the scale, thanks to weak wind shear keeping storm organization/maintenance limited. Most activity will come to an end around 10-11 PM, with a few showers/storms continuing into the overnight and early morning hours thanks to favorable dynamics aloft.

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

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

Isolated-to-widely scattered showers/thunderstorms expected, with the best coverage near the mountains, along the preferred terrain of the Palmer Ridge and Raton Ridge, and across the far Southeast Plains. Most will be garden variety, but a couple will become strong-to-marginally severe, producing bouts with heavy rain, small hail, and strong winds. Maximum rain rates are as follows:

Northeast Plains: 1.5-2.0 inches/hour
Southeast Plains: 1.8-2.5 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 0.8-1.2 inches/hour

Timing: 1 PM – 11 PM, with a few lingering showers/storms into the early morning hours

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

Scattered showers and thunderstorms are expected, with most being garden variety. Better daytime heating today, as compared to yesterday, will bring about a couple more thunderstorms capable of locally heavy rainfall. Maximum rain rates will be:

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

Timing: 11 AM – 9 PM, with a few lingering showers/weak thunderstorms into the early morning hours

Issue Date: 8/27/2016
Issue Time: 9:25 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, AND GRAND VALLEY.

A LOW FLOOD THREAT IS ALSO FORECAST TODAY FOR PORTIONS OF THE SOUTHEAST MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, AND SOUTHEAST PLAINS.

A few degrees of warming aloft will bring slightly warmer afternoon high temperatures across the state, along with a bit of capping to the environment. For the Northeast Plains to the north of I-70, this will act to suppress any shower/thunderstorm chances, keeping the area mostly sunny and warm. Further south, and west over the High Country/Western Slope, isolated-to-scattered showers/storms will overcome the slight warming aloft, owing largely to orographic effects and the passage of a weak, upper-level disturbance. The main impacts from any storm activity today will be gusty winds and lightning, with light-to-moderate rainfall.

With that being said, IPW values (shown above) continue to run about average at Grand Junction (green line), dipping to slightly below average at Boulder (blue line) and Schriever AFB (pink line). There’s enough moisture for some concern over locally heavy rainfall, especially with interacting outflow boundaries that locally enhance moisture content. Steeper terrain and burn scars will be the main focal points for today’s low flood threat areas, as well as urban areas with large amounts of impervious surfaces. For more information on timing and rain rates, 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

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

Isolated-to-widely scattered showers/thunderstorms are expected, mainly along and south of I-70. The best coverage will occur over the Front Range and Southeast Mountains, where orographic effects will play a role in development. Spill over from High Country activity will be the main source of showers/storms over the Urban Corridor, Palmer Ridge, and western portions of the Southeast Plains. Over the far Southeast Plains, a few strong thunderstorms will develop this afternoon/evening, producing strong winds, periods of moderate-to-heavy rainfall, and small hail. Maximum rain rates are as follows:

Urban Corridor and Palmer Ridge: 0.8-1.4 inches/hour
Front Range, Southeast Mountains, and Raton Ridge: 0.6-1.0 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.0 inches/hour

Timing: Noon – Midnight, with a couple showers/weak thunderstorms lingering into the early morning hours

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

A fairly active day is expected, with scattered showers and thunderstorms likely across much of the region. With IPW values around average, widespread heavy precipitation is not expected; rather, the main threats will be gusty winds, lightning, and light-to-moderate rainfall. Locally enhanced moisture from outflow boundaries will provide the opportunity for locally heavy rainfall, and this is taken into consideration with the low flood threat issuance. The best coverage will occur across the higher terrain of the Grand Valley, Southwest Slope, San Juan Mountains, and Southeast Mountains regions. As far as rainfall rates are concerned, most will be 0.25-0.5 inches/hour, with maximum rates of 0.6-1.0 inches/hour.

Timing: 11 AM – 9 PM, with a few lingering showers/weak storms over higher terrain into the early morning hours

Issue Date: 8/26/2016
Issue Time: 9:25 AM

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

A LOW FLOOD THREAT IS ALSO FORECAST FOR PORTIONS OF SOUTHEAST MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, AND PALMER RIDGE.

A LOW FLOOD THREAT IS ALSO FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS.

A somewhat tricky forecast is in the cards today/tonight, thanks to the potential for a few stronger thunderstorms to mix in with otherwise garden variety activity. Currently, a weak shortwave aloft is tracking east-northeastward across Colorado, producing extensive cloud cover across eastern and southern Colorado, along with a few scattered showers/thunderstorms (mainly across the Northeast Plains). Expect these showers/weak thunderstorms to wind down later this morning. As far as moisture is concerned, the IPW chart below shows mainly average moisture for the 3 usual reporting stations (Boulder, Grand Junction, and Schriever AFB); enough for a few locally heavy rainfall reports, but not enough for widespread heavy rain.

Today’s main event, so to speak, will begin early this afternoon as daytime heating and orographic effects help kick off scattered showers/storms across the High Country and Western Slope. These storms will generally move eastward with time, pushing over the lower elevations of eastern Colorado by early-to-mid afternoon. Wind shear and moisture will be sufficient for a few strong-to-marginally severe storms across eastern Colorado, but cloud cover will be a limiting factor. Where clouds can break earliest, allowing the most daytime heating, will be where the strongest storms can occur. Further west, the concern for locally heavy rainfall is mainly limited to the San Juan Mountains and Southwest Slope regions, thus the issuance of the low flood threat area. For more information on timing and rain rates, please see the zone-specific forecast 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, Palmer Ridge, Southeast Plains and Raton Ridge:

Scattered showers/thunderstorms are expected, with a couple strong-to-marginally severe storms mixed in with the garden variety majority. The main threats from stronger storms will be small hail, strong winds, lightning, and locally heavy rainfall. Maximum rain rates are as follows:

Urban Corridor and Palmer Ridge: 0.8-1.2 inches/hour
Northeast Plains and Southeast Plains: 2.0-2.5 inches/hour
Raton Ridge: 1.0-1.4 inches/hour

Timing: Noon – 10 PM, with a few showers/storms continuing until around midnight

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

Scattered showers/thunderstorms are expected during this period, mainly over the higher terrain. Storm motions will help carry a few showers/storms over lower valleys. Most activity will be produce gusty winds and light-to-moderate rainfall, but a bit better moisture/instability over the San Juan Mountains, Southwest Slope, Front Range, and Southeast Mountains will bring the potential for locally heavy rainfall to those regions. Maximum rain rates are as follows:

Southwest Slope, San Juan Mountains, Front Range, and Southeast Mountains: 0.8-1.2 inches/hour
Northwest Slope, Northern Mountains, Grand Valley, and Central Mountains: 0.4-0.8 inches/hour
San Luis Valley: 0.3-0.6 inches/hour

Timing: 11 AM – 9 PM, with a few lingering showers/weak thunderstorms over the higher terrain until midnight

Issue Date: Thursday, August 25th, 2016
Issue Time: 10:20AM MDT

— LOW flood threat for Palmer Ridge, parts of Southeast Plains, Raton Ridge, Urban Corridor and Front Range

The trough that has been affecting Colorado’s weather pattern for the better part of 3 days continues to stay put while small disturbances rotate through it on a daily basis. The water vapor image, below, shows another such disturbance located across western Colorado. As this feature moves east, it will provide favorable dynamics in the form of cool temperatures aloft and mid-level upward motion. With clear skies nearly statewide this morning, temperatures will be able to warm into the 70s and 80s over lower elevation locations. This will be enough to cause scattered to widespread thunderstorm activity mainly over the Palmer Ridge and surrounding areas. A Low flood threat has been posted here. One negative factor today is the relatively dry air in eastern Colorado that will try to advect westward as upslope flow develops by early afternoon. This will likely limit heavy rainfall to the foothills and immediate areas. Due to the cold air aloft, hail up to 0.75 inches will be possible with the strongest storms.

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.