Issue Date: Tuesday, July 28th, 2020
Issue Time: 10:55AM MDT

— A MODERATE flood threat has been issued for the Spring Creek burn area

— A LOW flood threat has been issued for the eastern Northern Mountains, eastern Central Mountains, Front Range, southern Urban Corridor, eastern San Juan Mountains, Southeast Mountains, Raton Ridge, Palmer Ridge, Northeast Plains, and Southeast Plains. This includes the Decker burn area.

Today, Colorado is located just downstream of a shortwave trough (orange “X”), which will move from west to east across the state today and increase chances for more rain. Portions of this shortwave are causing lift and generating showers over the northwestern part of the state this morning, which are visible on the water vapor satellite image below. As this shortwave moves eastward during the day today, it will continue to cause rising motion and help initiate more storms over the mountains. The most widespread coverage looks to be north, associated with this feature, but more scattered storms are expected over the southern high terrain. These storms are expected to intensify as the wave moves eastward and into the plains of eastern Colorado this afternoon where higher moisture will exist.

The monsoon moisture that has been focused over Colorado the last several days is still in place, which can be seen by the blue shading on the water vapor satellite image below. PW remains above normal in the Denver (0.93 inch) and Grand Junction (0.98 inch) soundings this morning, and dew points remain in the 50Fs for many valley locations of the mountainous west and along the plains east of the Divide. However, behind the trough, drier air is moving in quickly, which will limit shower activity over western Colorado and the western mountains after the wave moves through. Over the eastern San Juan Mountains, the scattered storms may be able to produce slightly higher rain rates. Due to saturate soils and 4-day totals over 3 inches, a half inch in an hour or two span may help trigger mud flows and runoff into already high local rivers and streams.

Mid and upper-level winds will be increasing today as the shortwave moves across Colorado. This will cause storm motions to be fairly quick (20-40 mph), especially over the northwestern part of the state. However, this increased wind shear will likely allow storms to go more upscale and organize, especially over the eastern plains. Additionally, outflow boundaries from storms could help trigger additional convection in a high moisture environment. With more diurnal heating expected in this area, additional instability could build and provide additional fuel for heavy rain. So a Low flood threat has been issued over the Palmer & Raton Ridge and portions of the Northeast & Southeast Plains.

The Low threat has been extended over the Southeastern Mountains due to heavy rainfall the last few days helping to saturate soils. An additional 0.75 inches will be possible today, which could be enough to trigger isolated mud flows and debris slides if storms track over the more unstable soils. A Moderate flood threat has been issued for the Spring Creek burn area due to storms potentially being able to drop a quick 0.50 inches of rainfall over already unstable soils. Storms will push into the plains by early evening, so this is not an overnight threat for the burn area.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Northern Mountains, Central Mountains, San Juan Mountains, Southeast Mountains, & Front Range:

Numerous showers and thunderstorms are expected to develop over the high terrain and quickly move east. Max 1-hour rain rates up to 0.5 inch are possible over the high terrain near the Continental Divide. Due to multiple storms tracking over the same area, 0.75 inch of rain over a couple hours is possible. This falling on already moist soils, especially over the southern Front Range, could cause flash flooding and debris slides over steep terrain. A Low flood threat is expected over these high terrain regions.

Due to plenty of antecedent rain over the Spring Creek, a moderate flood threat is expected. Storms that fire over these locations could cause flash flooding, debris slides, and mud flows.

Primetime: 11AM to 8PM

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

Over the plains east of the mountains, max 1-hour rain rates up to 1 inch are possible as storms go upscale and tap into increased moisture. Downslope winds just east of the Continental Divide will limit storm strength over the northern Urban Corridor. Storms should favor the higher Palmer & Raton Ridges, but outflow boundaries could initiate additional storms over the Northeast/Southeast Plains. A Low flood threat has been issued for these areas.

Primetime: 12PM to 11PM

Southwest Slope, Grand Valley, San Luis Valley, & Northwest Slope:

Some showers and storms may fire over the higher terrain, but flooding is not expected today due to drier air moving in aloft and storms moving east of these regions quickly. Max 1-hour rain rates should stay under 0.5 (0.25) inches for mountain (valley) locations.

Issue Date: Monday, July 27th, 2020
Issue Time: 10:45AM MDT

— A HIGH flood threat has been issued for the 416 burn area
— A MODERATE flood threat has been issued for the San Juan Mountains and the Spring Creek/Decker burn areas
— A LOW flood threat has been issued for the Central Mountains, southern Front Range, Southeast Mountains, Raton Ridge, and Southeast Plains

Fairly heavy cloud cover and fog over eastern Colorado to start the day, but some drier air has start to work its way into the mid-levels from the north. This can be visibly seen in the water vapor imagery (below) over northwest Colorado. An upper level trough and associated vorticity maximums (orange X’s in eastern CO/KS) will start to move slowly to the SSE throughout the day. This feature will produce more northerly flow across the northern border and eastern plains, and will help put a cap on afternoon convection over the majority of the eastern plains. PW values have also dropped slightly because of this at Grand Junction and Denver (0.92 inches and 0.85 inches, respectively). Still expecting some scattered storms to fire over eastern Colorado further south with the vorticity maximum/convergence area, and along the Raton Ridge. With slow steering winds, higher moisture in the area, and possible increased runoff from rainfall yesterday, a Low flood threat has been issued.

The shifting Low will cause the more southerly flow aloft over western Colorado to become more southwesterly. In turn, this will pull in higher moisture and mid-level energy into the area, including the southern Southeast Mountains, for another round of widespread, afternoon rain. Clearer skies over northwest New Mexico indicated that some instability may be able to form over the San Juan and southern Southeast Mountains later this afternoon for some weak thunderstorms, which could produce higher rain rates. With the drier air to the north, widespread showers and weak thunderstorms should stay south of I-70 for the most part over western Colorado. Over the last 72-hours portions of the San Juan Mountains and elevated regions south of them have received between 1.5 inches to 2.5 inches (more isolated), and some observations are nearing 3 inches. With higher rain rates anticipated this afternoon over saturated soils (increased runoff), the Moderate flood threat has been re-issued. With south facing slopes again likely to receive the heaviest rainfall, a High threat for the 416 burn area due to increased likelihood for heavier rainfall today. Threats include flooding of smaller rivers and local streams as well as the continued threat for mud and debris flows. Again, the latter can occur even with the rainfall is over. Reminder, that as the rainfall continues to accumulate over this event, it will take less precipitation to cause flooding issues and mud flows/debris slides.

Tonight, the rain south over the western San Juan should shift east, to areas along and near the Continental Divide, as the Low over California starts to rotate around the High. This will bring overnight rainfall chances back to the northern Southeast Mountains, so a Low flood threat has been issued. Since the Spring Creek and Decker burn area already had flash flooding issues yesterday and received ample rainfall, a Moderate threat has been issued due to an increased risk in mud and debris flows as well as runoff if storms form or track overhead.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

San Juan Mountains, Southeast Mountains, Southwest Slope, Central Mountains, Front Range, Raton Ridge, & San Luis Valley:

Some heavier, widespread rainfall will be possible again this afternoon over the southern and eastern San Juan Mountains. 1-2 hour totals up to 0.75 inches or a quick 0.5 inches in 30-min will be possible with the stronger storms that develop. By morning, rain totals up to 1.5 inches will be possible in the Moderate area. With saturated soils, there’s an increased risk for mud/debris flows as well as local river/stream flooding from rainfall today. A High threat has been issued for the 416 burn area due to both the afternoon rainfall possible and totals by morning. Continue to watch local rivers and streams closely. The Navajo River reached 4.72 ft yesterday, nearing it’s 5.1 ft record, so flows remain elevated and are expected to quickly increase in areas that receive the heaviest precipitation. 24-hour totals along the southern end/edges of the San Luis Valley could reach 0.5 inches.

Over the Central, southern Front Range, and Southeast Mountains, long-lasting rainfall will be likely again today and tonight. Totals over the Central Mountains, southern Front Range, and northern Southeast Mountains up to 1.25 inches will be possible by morning; thus, the Low flood threat with a Moderate flood threat over the Spring Creek burn area. Over the southern Southeast Mountains, some stronger storms will be possible this afternoon/evening. Max 1-hour rain rates up to 0.75 inches will be possible, so a Moderate flood threat has been issued for the Spring Creek burn area in case these brush the southern end of the scar.

Primetime: 11AM to 4AM – This is an overnight threat!

Northern Mountains, Northwest Slope, Grand Valley, Urban Corridor, Southeast Plains, Palmer Ridge, & Northeast Plains:

Best chance for flooding today will be over the Southeast Plains with most other areas over eastern Colorado remaining dry and cool. If some instability is able to build in the Southeast Plains, mid-level energy/convergence could help break the cap and produce some stronger thunderstorms. Totals up to 1.75 inches will be possible, and if storms track over areas that received some of the heavier rainfall yesterday, increased field ponding and flooding of low-lying roads will be possible. A Low flood threat has been issued.

Very scattered storms are possible over the northwest corner of the state this afternoon. Max 1-hour rain rates up to 0.25 inches will be possible over the elevated regions. As the Low over California rotates around the High, some mid-level energy will move across this area tomorrow morning bringing showers and cooler temperatures. Flooding is not expected.

Primetime:

11AM to 9PM (Southeast Plains)

12PM to ongoing (Northwest)

Issue Date: Sunday, July 26th, 2020
Issue Time: 10:15AM MDT

— A HIGH flood threat has been issued for the Spring Creek and Decker burn area
— A MODERATE flood threat has been issued for the 416 burn area
— A MODERATE/LOW flood threat has been issued for the Southeast Mountains and parts of the San Juan Mountains, Central Mountains, Front Range, Urban Corridor, Palmer Ridge, Southeast Plains, Northeast Plains and Raton Ridge

— Afternoon update possible today

Today is expected to be one of the most active days for heavy rainfall across Colorado thus far this warm season. Let’s get right to the details. As shown in the water vapor image, below, many factors will be at play today, but as is often the case for Colorado, the most important one is by far moisture. This morning’s sounding analysis showed the following PW around the region: 1.24 inches at Denver, 1.02 inches at Grand Junction, 1.55 inches at Dodge City, 1.49 inches at North Platte (NE) and 1.25 inches at Albuquerque (NM). These values are well above seasonal normal, with a moist atmosphere extending from the surface to the tropopause. The high moisture content is the result of an extended plume of monsoonal moisture that has basically saturated the atmosphere from top to bottom over the past 48-72 hours. In addition to the monsoonal moisture, which typically favors areas west of the Continental Divide, a cool front is moving into eastern Colorado from the north. Although not particularly strong, it will provide just enough additional focus for boundary layer lift and increase storm coverage mainly over the Palmer Ridge and areas further south. Extremely heavy rainfall will be possible with this situation across the southeast quadrant of Colorado. A High flood threat is warranted for the Decker and Spring Creek burn scars with dangerous debris slides and mud flows possible over these areas, and just downhill from them. A Moderate flood threat is warranted for large parts of southeast Colorado, with the threat persisting well into the overnight hours. The only hesitation in going for a High flood threat is that cells are not expected to be particularly well organized, and the very heavy rainfall duration should generally be less than an hour. However, multiple rounds of very heavy rainfall are likely. Thus, an afternoon update will be possible today to address any increase in hazards.

In areas further west, the San Juan Mountains are again under a Moderate flood threat today as moist soils will contribute to increase runoff efficiency. With the consecutive days of heavy rainfall, the threat of mud flows and debris slides will increase today. Note that these can occur even when the rainfall is over.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Partly cloudy then scattered to widespread showers and thunderstorms forming over the higher terrain and then spreading into the lower elevations. Max 1-hour rainfall up to 3.1 inches (east0 and 1 inch (west). Max 3-hour rainfall up to 4.7 inches (east) and 2 inches (west). Flash flooding will be possible under the strongest cells, with debris slides and mud flows likely over the steeper terrain.

A High flood threat has been issued for the Decker and Spring Creek burn scars for this afternoon and evening. Dangerous mud flows will be possible over these areas.

A Moderate/Low flood threat has been issued for most of the region.

Note that isolated heavy rainfall will continue over the Southeast Plains well into the evening and overnight hours.

Primetime:
12pm-6am

San Juan Mountains, Southwest Slope, San Luis Valley, Central Mountains, Front Range, Urban Corridor, Northern Mountains, Grand Valley:

Partly cloudy then scattered to widespread showers and thunderstorms forming over the higher terrain and then spreading into the lower elevations. Max 1-hour rain rates up to 2.2 inches (east of the Continental Divide) and up to 1 inch (west of the Continental Divide).

A Moderate flood threat has been issued for isolated flash flooding, debris slides and mud flows in the San Juan Mountains and Central Mountains. Small stream flooding could be an issue over the San Juan Mountains, just like on Saturday.

Primetime:
12pm-9pm (west)
12pm-1am (east)

Northwest Slope:

Partly cloudy then isolated to scattered showers and thunderstorms possible this afternoon. Max 1-hour rainfall up to 0.6 inches. Flooding is NOT expected today.

Issue Date: Saturday, July 25th, 2020
Issue Time: 10:15AM MDT

— A HIGH/MODERATE flood threat has been issued for the San Juan Mountains. This includes the 416 & Decker burn area. This threat continues overnight!

— A LOW flood threat has been issued for the Southwest Slope, Central Mountains, southern Front Range, Southeast Mountains, southern Urban Corridor and far Northeast/Southeast Plains. This includes the Lake Christine and Spring Creek burn areas.

Western Colorado and the mountains are starting the day with heavy cloud cover. The moisture stream and embedded energy is continuing to stream in from the south, which is helping produce morning rainfall over portions of the Southwest Slope, Grand Valley, and Central Mountains. Western portions of the San Juan Mountains picked up another 0.50 to 1 inch yesterday (isolated totals closer to 1.5 inches), and gages in local streams and rivers are starting to rise. So, with steady rainfall continuing today and for the area, saturated soils will become a concern for increased runoff into local streams and mud/debris flows.

The evolution of the rainfall and storms will look similar to yesterday. Expect an uptick in rainfall coverage over the mountains by mid-day with the diurnal flow pattern. Extra mid-level energy is plenty (orange X’s), so rainfall is expected be widespread in the moisture rich environment. Then, storms will start to spill into the adjacent plains by early afternoon as Hurricane Hanna and passing trough to the north helps displace the High slightly westward. Additional storms will likely fire over the eastern plains as a shortwave moves through the flow with plenty of outflow boundaries in the area helping provide supplementary lift. A second wave of rainfall arrives for the overnight hours, and the axis of precipitation will shift eastward. This will put the northern Southeast Mountains and eastern San Juan Mountains under a flood threat overnight.

As for moisture and instability, not much change in the former. Soundings and dew points show elevated values, so this will keep rainfall efficiency higher. Instability will be limited over the mountains with the cloud cover, so stronger thunderstorms will again be most likely over the eastern plains. A Low flood threat has been issued for the eastern plains as training storms have caused localized flood issues the last couple of days. There is still the chance for isolated, weak thunderstorms over the mountains (slight breaks in the cloud cover), which would cause increased runoff with slightly higher rain rates. This is especially true if they track over an area with already saturated soils.

The main threat from this system over the southern mountains is the multiple days of steady rainfall. This will likely lead to flooding of local streams/creeks and mud flows/debris slides as the soil becomes unstable over the steeper terrains. A HIGH threat has been issued for the western San Juan Mountains for this reason, and highest rainfall totals are expected on the south facing slopes. This HIGH threat includes the 416 burn area. A Moderate threat has been issued for all of the San Juan Mountains and Decker burn area as the rainfall axis shifts to the east overnight.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

San Juan Mountains, Southeast Mountains, Southwest Slope, & San Luis Valley:

Heavy rainfall will allow 48-hour totals to reach close to 3 inches over the western San Juan Mountains by morning. Small rock slides were already being reported yesterday, so the main threat over the next few days will be mud/debris flows from the saturated soils. Also, expect more rapid rises in local creeks/streams with the increased runoff. A HIGH flood threat has been issued for this region, which includes the 416 burn area.

As the plume of moisture and instability shifts east overnight, morning totals up to 1.25 inches will be possible over the northern Southeast Mountains and eastern San Juan Mountains. This could cause flash flooding issues over the Decker burn area, a Low/Moderate threat has been issued for this region. Looks like the San Luis Valley will also get some much needed rainfall, and isolated totals up to 0.50 inches are possible.

Primetime: 11AM to 8AM – This threat continues overnight!

Northern Mountains, Central Mountains, southern Southeast Mountains, Front Range, Raton Ridge, Southeast Plains, Palmer Ridge, Northeast Plains, & Urban Corridor:

Perhaps some better instability can build over these regions, and 1-2 hour totals up to 1 inch will be possible. A Low flood threat has been issued, which includes the Spring Creek and Lake Christine burn areas. Rather than an individual thunderstorm causing flash flooding, higher 24-hour totals may cause soils over the burn areas to become unstable.

Over the eastern plains (Northeast Plains & northern Southeast Plains), training storms will be possible again. These very high totals can cause local flash flooding issues as storms often continuously fire along outflow boundaries. Thus, the threat includes the high moisture area all along the eastern border as it is difficult to predict the outflow boundaries.

Primetime: 11AM to 8AM

Northwest Slope & Grand Valley:

These are the two areas that won’t see as much rainfall today, but light showers should be expected. Totals up to 0.50 inches will be possible along the higher terrains in both regions. So, over the Northwest Slope closer to mountains over the elevated plateaus. Flooding is not expected here.

Primetime: 11AM to 11PM