Issue Date: 7/23/2016
Issue Time: 10:20 AM

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

Current analysis shows the expansive upper-level high being flattened by an upper-level shortwave trough moving across the northern US. This has turned the flow aloft over Colorado to a more westerly direction, which will eventually result in drier air being ushered in from the west. At this time, though, that drier air sits across northern and western Utah, leaving IPW values elevated across Colorado. Eventually, the drier air will make its way into northwestern Colorado, likely this afternoon. The drier air will help reduce the coverage and intensity of any isolated-to-scattered storm activity over those areas.

There will still be plenty of residual monsoonal moisture elsewhere, with the 4 normal reporting stations hovering between 0.75 inches and 1 inch. Moisture reinforcement will come to the eastern plains behind a surface cool front, as well. Generally speaking, there will be enough fuel for thunderstorms to produce localized heavy rainfall, so a low flood threat will be issued again this period. Overall, coverage and intensity will be less than previous days, except for over the plains where a few isolated strong-to-severe thunderstorms are expected. Please see the zone-specific forecast discussions below for more information about timing and rain rates.

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

Isolated-to-scattered showers and thunderstorms are expected, with the main threats being gusty winds, locally heavy rainfall, and lightning. Storm coverage and intensity will be less than previous days, but a few will be strong enough to warrant flooding concerns, especially considering antecedent soil conditions. Otherwise, it will be a hot day, with temperatures climbing into the 90s and low 100s. Maximum rain rates are as follows:

Urban Corridor: 0.8-1.2 inches/hour
Palmer Ridge: 1.0-1.5 inches/hour
Northeast Plains and Southeast Plains: 1.0-2.0 inches/hour
Raton Ridge: 0.4-0.8 inches/hour

Timing: Noon – 11 PM, with a few showers/storms continuing over the plains into the early morning hours.

Front Range, Southeast Mountains, Northern Mountains, San Juan Mountains, Central Mountains, and Southwest Slope:

Isolated-to-scattered showers and thunderstorms are expected as residual moisture fuels another unsettled day across the High Country and Western Slope. The higher terrain will see the most activity, with storm motions carrying storms over lower valleys. Storms will move quicker than yesterday, which will act as a limit on the flood threat. Maximum rain rates are 0.6-1.2 inches/hour. Antecedent conditions from the past few days of rainfall are a concern, especially in steep terrain areas where enhanced runoff issues are greatest.

Timing: Noon – 10 PM

Northwest Slope and Grand Valley:

Mostly Sunny with only a couple isolated thunderstorms. Drier air will reach these regions first, likely by early this afternoon. This will reduce the rain rate potential, so no flood threat is warranted. Otherwise, temperatures will be warmer than normal.

Timing: 1 PM – 9 PM

San Luis Valley:

The main weather story today will be the sunny skies to start, turning to partly sunny as scattered showers/storms develop over the surrounding high terrain. A few showers/storms will move overhead, with maximum rain rates of 0.6-0.8 inches/hour.

Timing: Noon – 9 PM

Issue Date: 7/22/2016
Issue Time: 10:20 AM

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

Two main features in the larger scale atmospheric pattern will bring about another day of monsoon-driven showers and thunderstorms. The strong upper-high centered over the central US will shift westward today, while an upper-level shortwave trough will move onshore the Pacific Northwest and track to the east across the Northern US. These two features will funnel monsoonal moisture across Colorado through today/tonight, fueling another period of unsettled weather. The spark will be provided by a weak disturbance rotating across the state from the southwest. Overall, a general lack of wind shear and instability will keep most storms garden variety, with the main threats being locally heavy rainfall and gusty winds (up to 40-50 mph). IPW values continue to hover around/above the 1 inch mark, so activity will produce rainfall efficiently.

The strongest storms, relatively speaking, will occur across the Northeast Plains, Palmer Ridge, and northeastern portions of the Southeast Plains. In that area, instability and shear will be sufficient for a couple strong-to-marginally severe thunderstorms. The main threats from these storms will be strong winds, hail up to 1.5 inches in diameter, and locally heavy rainfall. For more information, 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, and Palmer Ridge:

Isolated-to-scattered showers and thunderstorms are expected this afternoon and evening, with a few continuing into the overnight hours over the plains. The main threats from any storm activity will be locally heavy rainfall and gusty outflow winds. A couple isolated strong-to-marginally severe storms are possible, mainly over the Northeast Plains and Palmer Ridge. The main threats would these storms will be heavy rainfall, hail up to 1.5 inches in diameter, and strong winds (50-60 mph). Maximum rain rates are as follows:

Urban Corridor: 0.8-1.4 inches/hour
Palmer Ridge: 1.2-1.6 inches/hour
Northeast Plains: 1.5-2.0 inches/hour

Timing: 1 PM – Midnight

Southeast Plains and Raton Ridge:

Isolated-to-widely scattered showers/thunderstorms are expected. Coverage will be best near the higher terrain of the Southeast Mountains, and near the preferred terrain of the Palmer Ridge. One or two isolated storms will become strong over far northeastern portions of the Southeast Plains, with small hail, strong winds, and locally heavy rainfall being the main threats. Maximum rain rates are as follows:

Southeast Plains: 1.2-1.6 inches/hour
Raton Ridge: 0.4-0.6 inches/hour

Timing: 1 PM – 1 AM

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

Another period of unsettled weather on tap with scattered showers/thunderstorms expected. Activity will begin to develop around 11 AM – Noon, increasing in coverage through the afternoon and early evening, and then diminish after sunset. Locally heavy rainfall is likely underneath thunderstorms, and slow-moving storms are a concern. Antecedent conditions also deserve attention, as runoff will be enhanced and unstable soils may result in mud/debris flows/rock slides. Maximum rain rates for the Front Range, Northern Mountains, and Central Mountains will be 0.8-1.2 inches/hour, with 0.6-1.0 inches/hour for all other regions.

Issue Date: Thursday, July 21st, 2016
Issue Time: 10:42AM MDT

— LOW flood threat for parts of Central Mountains, Northern Mountains, Grand Valley, San Juans and Southwest Slope
— LOW flood threat for parts of Front Range and Palmer Ridge

This morning’s water vapor image, below, appears quite similar to yesterday’s. At face value. However, important details emerge upon closer inspection. The most notable difference in the past 24-hours is the ridge centered southeast of Colorado will bulge out noticeably to the west. The main implication of this is essentially turning off the monsoon spigot. That said, plenty of residual moisture remains this morning so heavy rainfall storms will be had once again. However, parts of the far southwest will see some notable upper-level drying. Thus, the main region for heavy rainfall storms will shift northward today and roughly straddle the I-70 corridor of the western slope. The second important difference today is that the steering flow will all but cease to exist as the ridge axis moves almost directly overhead. Regarding heavy rainfall, this has a pro and con component. On the one hand, a lack of storm motion will allow for very heavy short-term rainfall at a given location. On the other hand, lack of shear means that downdrafts and updrafts will have a hard time separating. The ultimate effect of this is that today we are looking for sub-hourly heavy rainfall that could lead to isolated flood problems. Lastly, antecedent rainfall amounts of 2-3 inches in the past 72 hours suggest runoff will be more effective today. In all, a Low flood threat captures these factors.

A severe storm cannot be ruled out across the far eastern parts of the state in the early to late evening. However, odds are slim and hail up to 1 inch and wind up to 55mph should be the bigger threat compared to heavy rainfall. Given the very low odds, a flood threat is not warranted in this region today.

 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.

Issue Date: 7/20/2016
Issue Time: 9:50 AM

A MODERATE FLOOD THREAT IS ISSUED FOR PORTIONS OF THE NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, GRAND VALLEY, AND NORTHWEST SLOPE.

A LOW FLOOD THREAT IS ISSUED FOR SURROUNDING AREAS, INCLUDING PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, AND NORTHEAST PLAINS.

The continued stream of monsoonal moisture into the region is easy to pick out in the water vapor image below. With a strong high centered over the south-central US and an upper-level trough off the West Coast, west-southwest flow aloft continues over Colorado, pulling subtropical moisture into the state. Moisture values are comparable to yesterday’s values, albeit slightly less east of the mountains. The moisture content will set the stage for another unsettled day, widespread over the mountains, with more isolated-to-widely scattered coverage over adjacent lower elevations.

Showers and thunderstorms will get a slightly later start today, awaiting the influence of daytime heating and the arrival of the next disturbance out of western NM/eastern AZ. Initial development will begin over the High Country and Western Slope, moving off the mountains and over the Urban Corridor and adjacent plains during the early afternoon hours. Activity will continue into the late evening hours, diminishing across most locations by midnight. A lingering shower or two may continue over the higher terrain into the early morning hours. For more information regarding 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

Urban Corridor, Northeast Plains, and Palmer Ridge:

Isolated-to-scattered showers/thunderstorms are expected during the afternoon and evening, coming to an end between 10 PM and midnight. Slow-moving storms and locally heavy rainfall are a concern, thus the low flood threat. Other threats from storms include gusty winds and dangerous lightning. Maximum rain rates 0.8-1.4 inches/hour.

Timing: 1 PM – Midnight

Southeast Plains and Raton Ridge:

Isolated-to-widely scattered showers/storms are expected, beginning during the early afternoon and continuing into the evening hours. The best coverage will occur along and near the higher terrain of the Southeast Mountains, with more isolated coverage to the east. Maximum rain rates are 0.6-1.2 inches/hour. Strong winds and lightning are the other threats.

Baca, Prowers, and eastern portions of Bent, Las Animas, Kiowa, and Cheyenne Counties will stay mainly dry.

Timing: Noon – 11 PM

Northwest Slope, Northern Mountains, Central Mountains, and Grand Valley:

Scattered-to-widespread showers and thunderstorms are expected, capable of producing heavy rainfall. IPW values are highest across western Colorado, and moisture transport will shift the axis of deepest moisture across the moderate flood threat area. Repeated rounds of showers/storms, as well as slow-moving storms, are the main concern. Maximum rain rates are 1.0-1.6 inches/hour. Gusty winds and dangerous lightning will attend thunderstorms.

Timing: 11 AM – Midnight

Front Range, Southeast Mountains, San Luis Valley, San Juan Mountains, and Southwest Slope:

Scattered-to-widespread showers and thunderstorms are expected over the higher terrain, with more isolated-to-scattered coverage for lower valleys. Slow-moving storms are a concern when coupled with locally heavy rainfall. Gusty winds and lightning will also attend thunderstorms. Maximum rain rates are 0.8-1.4 inches/hour.

Timing: 11 AM – 2 AM