Issue Date: Wednesday, August 17th, 2022
Issue Time: 10:30AM MDT

— A MODERATE/LOW flood threat has been issued for portions of the Southwest Slope, San Juan Mountains, Southeast Mountains and Raton Ridge
— Fire-Burn Forecast Summary: 1 burn area under HIGH threat; 1 burn area under LOW threat; click HERE for more info

There’s a strong High pressure ridge over the western US with a secondary High near the four corners region this morning. Northwest flow aloft should take over today and help push a drier air mass from north to south, which should limit rainfall chances across the northern tier of Colorado. In North Platte’s morning sounding, PW was measured at 1.01 inches with much drier air noted above 700mb. PW at Platteville has dropped to 0.71 inches, so the drying trend is underway. Currently, there is some ongoing cloud cover, fog and light showers over southern and eastern Colorado associated with a departing shortwave and monsoon moisture. With stable conditions forecast over the eastern plains by this afternoon, rainfall is unlikely to develop behind the current wave of showers. The most welcome news is that high temperatures will continue to run below average for most of the state, and the southeast corner could see temperatures up to 15°F below average.

Drier air has also started to work its way into portions of western Colorado with a nice dry pocket noted at 400mb in Grand Junction’s morning sounding. PW is still elevated (1.14 inches) with values estimated near an inch near the southwest border. With mid-level energy, moisture and upslope flow combining again today, another round of scattered to numerous storms are forecast for the central and southern mountains. Storm motion towards the southeast should still be relatively slow and will likely cause some spillover of rain into the San Luis Valley again. The one limiting ingredient to today’s flood threat will be instability with the cooler temperatures, ongoing cloud cover and morning showers. However, with an adequate warm layer depth and some breaks in cloud cover, stronger storms that develop should produce some very efficient rain rates again both in the 1-hour time frame (more isolated) and the longer duration 3-hour time frame. A Moderate/Low flood threat has been issued through this evening with the main flood threats being mud flows and debris slides (mountains), road flooding, excessive runoff and ponding in low-lying areas. These threats increase if storms track over soils that have received a good dose of precipitation over the last couple of days (southern San Juan Mountains, Southeast Mountains and western Raton Ridge).

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, San Juan Mountains, San Luis Valley, Southwest Slope, Central Mountains, Grand Valley & Southeast Plains:

Ongoing rainfall is expected to continue and strengthen with a little daytime heating as they move southeast. Behind this first wave of storms, drier conditions are forecast. Where some higher instability can develop with breaks in the cloud cover, isolated max 1-hour rain rates up to 1.5 inches could be realized. Longer duration rainfall will be the main threat for most areas with max 3-hour rain rates up to 2.5 inches possible. Mud flows, debris slides, road flooding and rises on local streams/creeks could occur, especially if storms track over already saturated soils. A Moderate/Low flood threat has been issued.

Primetime: 11AM to 10PM

Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, Northwest Slope & Northern Mountains:

It should be drier and cooler for these zones today with some isolated precipitation possible over the Palmer Ridge. Isolated storms may also develop over the southern Front Range near the Continental Divide, but storm totals should remain under 0.5 inches. Flooding is NOT expected.

Primetime: 4PM to 9PM

Issue Date: Tuesday, August 16th, 2022
Issue Time: 10:35 AM MDT

— The flood threat will persist into the overnight hours
— A HIGH flood threat has been issued for the Southeast Mountains, Raton Ridge, Urban Corridor, Palmer Ridge, & Southeast Plains
— A MODERATE flood threat has been issued for the Grand Valley, Central Mountains, & Front Range
— A LOW flood threat has been issued for the San Juan Mountains, San Luis Valley, Southwest Slope, Northwest Slope, Northern Mountains, & Northeast Plains
— Fire-Burn Forecast Summary: 4 burn areas under HIGH threat, 4 burn areas under MODERATE threat, 1 burn area under LOW threat; click HERE for more info 

Rain showers are ongoing across portions of central and eastern Colorado with nearly 2 inches of rain in one hour already recorded near Broomfield this morning, and flooding is already occurring according to local storm reports. Midlevel energy continues to build across the state, marked by the “X” in the water vapor image below, and similarly to yesterday, monsoonal moisture continues to wrap around the high pressure (currently centered over the Texas panhandle). PW values of 1.20 and 1.34 inches were measured in Grand Junction and Platteville, respectively, indicating ample column moisture. At the surface, dew points in the low to mid-50s°F (west) and greater than 60°F (east) further shows the depth of moisture present even in the lowest levels of the boundary layer.

This afternoon, upslope flow in association with a deepening surface low pressure is expected to transport additional moisture in from the south and east, creating a pooling effect east of the Continental Divide where moisture can build up against the mountains and adjacent foothills. Instability is forecast to reach values of 1200-1800 J/kg of CAPE for portions of the Eastern Plains, with values ranging from 800-1100 J/kg of CAPE more common over the mountains and west of the Continental Divide. Initially, convective storms producing high rain rates are expected before instability wanes and storms transition to more widespread coverage. Thereafter, storms are expected to produce longer-duration moderate to heavy rainfall across most of southern and central Colorado over a 3-to-6-hour period. Given that west to southwesterly upper-level steering flow is forecast to be weak today, within the range of 5 to 10 mph (west) and 15 to 20mph (east), storms are expected to be relatively slow-moving. Of additional concern are soils that are already saturated from prior days of heavy rainfall; as such, all the aforementioned factors increase confidence in a higher-end flood threat for central and southern Colorado today.

A HIGH flood threat has been issued for portions of southeast Colorado, a MODERATE flood threat for portions of southern and central Colorado, and a LOW flood threat for portions of western and northern Colorado. Urban and small stream flooding are of particular concerns today, similarly to yesterday, with added concerns for excessive runoff, mud flows, and debris slides over steeper terrains that may receive several hours of moderate to heavy rainfall.

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, Central Mountains, Grand Valley, Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, Raton Ridge, & Southeast Plains:

Heavy rainfall is already occurring this morning over portions of the Front Range and Urban Corridor where 1-hour rain rates up to 2 inches have been recorded by local rain gages; this, along with several local storm reports of flooded roads in the area, has prompted the issuance of a Flash Flood Warning for portions of Boulder and Broomfield Counties by NWS Boulder until 11AM. Please refer to the local NWS for further information and warning issuance updates.

As storm coverage increases today, initially convective storms could produce 1-hour rain rates up to 2.25 inches and 3-to-6-hour storm totals of up to 6 inches for portions of the Southeast Mountains, Central Mountains, Front Range, Urban Corridor, Raton Ridge, and western Southeast Plains, warranting the issuance of a HIGH flood threat for these forecast zones. A MODERATE flood threat extends further east into the adjacent plains, further west toward Grand Valley, and further north, where max 1-hour rain rates of 1.75 inches and 3-to-6-hour storm totals up to 4 inches are possible.  Urban and small stream flooding are of particular concerns today, along with excessive runoff, mud flows, and debris slides over steep terrain.

Primetime: Ongoing through Overnight

Southwest Slope, San Juan Mountains, San Luis Valley, Northwest Slope, & Northern Mountains:

Cloud cover overspreads much of western Colorado today, with some light embedded precipitation occurring over some of the higher elevations. Storm coverage should be more limited for these forecast zones today given lesser instability forecast for these zones. That said, storms may be briefly convective initially and produce max 1-hour rain rates up to 1.25 inches, and 3-hour storm totals up to 2.5 inches. Some minor urban and small stream flooding may occur, along with the potential for excessive run off, mud flows, and debris slides over steeper terrain; as such, a LOW flood threat has been issued for portions of the Southwest Slope, San Juan Mountains, San Luis Valley, Northwest Slope, and Northern Mountains.

Primetime: Ongoing through Overnight

Issue Date: Monday, August 15th, 2022
Issue Time: 10:55AM MDT

PM Update (1:30PM MDT): There’s an increasing likelihood for storms to produce high rain rates overnight in eastern Washington County and Yuma County. The High flood threat has been extended into the area where local totals just over 5 inches will be possible. The Moderate threat over the Front Range has been extended slightly west to include the eastern portion of the Northern Mountains where longer duration rainfall could cause some flooding issues later this evening.

— The flood threat will persist into the overnight hours
— A HIGH flood threat has been issued for the Front Range and portions of the Urban Corridor, Palmer Ridge and Northeast Plains
— A MODERATE flood threat has been issued for the Southwest Slope and portions of the Central Mountains, Northern Mountains and San Juan Mountains
— A LOW flood threat has been issued for portions of the Southeast Mountains, Southeast Plains, Northwest Slope and Grand Valley
— Fire-Burn Forecast Summary: 4 burn area under HIGH threat; 4 burn areas under MODERATE threat, 2 burn area under LOW threat; click HERE for more info

There’s a bit of a change to the synoptic pattern today as the 500mb High to our southeast weakens, and the High centered over the Great Basin begins to build a ridge back to the west. A surface Low is also forecast to develop near the Kansas and Colorado border, which should help pull some monsoon moisture south with northerly flow over portions of eastern and northern Colorado. SSW (south) and WSW (north/central) steering flows should remain weak under the ridging pattern, and storms should become more widespread by this afternoon and evening with some daytime heating, the addition of mid-level energy and enhanced convergence over the adjacent plains.

Moisture is on the upswing across the state with a well-defined monsoon moisture plume still rotating around the High (blue and white below). PW was measured at 1.14 inches and 1.04 inches in Grand Junction and Platteville, respectively, which in the 95^th percentile for this time of year! The column of moisture looks impressive in morning soundings, as does the warm layer, so storms should produce some very efficient rain rates with longer duration rainfall and a couple rounds of storms also causing an increase in the flood threat.

Over western Colorado, the flood threat is expected to be greatest over the high terrain in the southwest corner, and a MODERATE threat has been issued. Cloud cover and ongoing rainfall further north may limit the instability that can build, so only a LOW flood threat has been issued for the area and heavy rainfall should be more isolated. Over eastern Colorado, persistent rainfall is anticipated along the Front Range, so a HIGH flood threat has been issued. Additionally, heavy rainfall is likely over portions of the adjacent plains with increased convergence along a developing surface trough and over the Palmer Ridge. A High threat has been issued. There is less confidence of the location and likelihood for heavy rainfall tonight near the eastern border, so a larger MODERATE threat area has been drawn. If storms can move into the area, very high rain rates are expected. The flood threat for eastern Colorado will persist until just after midnight with lighter showers anticipated thereafter. Flood threats today include urban flooding issues (low-lying areas, roads, gulches and small streams), mud flows and debris slides over steeper terrain, and heavy ponding under the storm cores.

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

In addition to the singular thunderstorm, longer duration rainfall may cause some flooding issues along the Front Range. Max 1-hour rain rates up to 2.5 inches and 3-hour rain rates just under 3.5 inches will be possible. This could cause isolated mud flows and debris slides as well as road flooding. A HIGH flood threat has been issued. Over the Southeast Mountains, the Wet Mountains could see 1-hour rain rates up to 1.25 inches, so a LOW flood threat has been issued. For the adjacent plains, high moisture and enhanced convergence could produce 1-hour rain rates up to 2.5 inches (west) and 3.5 inches (east). A HIGH flood threat has been issued, which persists into the overnight hours. Lighter rainfall may linger through tomorrow morning. In addition to heavy rainfall, stronger storms may produce outflow winds and small hail.

Primetime: 1:30PM to 6AM

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

Ongoing rainfall and cloud cover may limit the flood threat north, but where there are breaks in cloud cover and instability can build, storms that develop could produce very heavy rainfall. A LOW flood threat has been issued. Further south, better moisture, instability and lift are forecast, and a MODERATE threat has been issued for the high terrain in the area. Max 1-hour rain rates up to 1.2 inches (north) and 1.4 inches (south) will be possible with the majority of the rainfall falling in the first 30-45 minutes. A couple rounds of storms south could boost storm totals up to 2.25 inches. In addition to heavy rainfall, thunderstorms may produce small hail and strong outflow winds. Flood threats include road flooding, ponding in low-lying areas as well as isolated mud and debris flows. The flood threat should end later this evening with lighter rainfall likely continuing overnight with mid-level energy moving through the flow.

Primetime: 1PM to 6AM

Issue Date: Sunday, August 14th, 2022
Issue Time: 10:30 AM MDT

— A MODERATE flood threat has been issued for the Front Range
— A LOW flood threat has been issued for the Northwest Slope, Grand Valley, Central Mountains, Northern Mountains, Urban Corridor, & Northeast Plains
— Fire-Burn Forecast Summary: 3 burn areas under HIGH threat, 3 burn areas under MODERATE threat, 3 burn areas under LOW threat; click HERE for more info 

This morning, the high-pressure center is located over southwest Oklahoma after shifting slightly southeast overnight. Its position should remain relatively unchanged or shift slightly back west today. As a result, southwest flow for southern Colorado becomes more westerly further north, along with steering speeds in the 10 to 15mph range. A shortwave disturbance is located over northeastern Utah this morning, marked by the “X” in the water vapor image below, and is forecast to track into northern Colorado by early afternoon. This disturbance, in conjunction with instability ranging from 1500-2000 over the northern-central parts of the state, is expected to trigger scattered to numerous storms over primarily the northern half of the state by early afternoon.

Column moisture has increased overall today compared to yesterday, with Grand Junction measuring a PW value of 1.10 inches and Platteville measuring a PW value of 1.02 inches. Additionally, surface moisture has increased, and dewpoint depressions are much shallower today relative to yesterday, indicating deeper boundary layer moisture throughout. Given the increasing southerly wind component with relatively slow steering flow, the highest concern for flooding exists across the northern Front Range where convergence and training storms are most likely. A MODERATE flood threat has been issued for this forecast zone, while a LOW flood threat has been issued for greater portions of northern Colorado.

Isolated to widely scattered storms may also occur over the high terrain south and west of the Continental Divide, with an isolated storm or two also possible over the Palmer Ridge. Given less instability and moisture and higher dewpoint depressions for these areas, NO flooding is expected for the southern half of the state today.

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:

Northwest Slope, Grand Valley, Northern Mountains, Central Mountains, Front Range, Urban Corridor, & Northeast Plains:

A few weak showers are beginning to develop over the far Northwest Slope this morning. By early afternoon, scattered to numerous storms are expected to overspread much of northern Colorado. Max 1-hour rain rates for the Front Range (especially above 7,000 feet) could reach up to 1.75 inches, and 3-hour storm totals up to 2 inches are possible, along with the potential for training storms. A MODERATE flood threat has been issued to reflect these higher rain rates forecast. A LOW flood threat has been issued for the Northwest Slope, Grand Valley, Northern Mountains, Central Mountains, Urban Corridor, and Northeast Plains, where 1-hour rain rates up to 1.25 inches and 3-hour storm totals up to 2 inches are possible.

Primetime: 12PM to Midnight

Southwest Slope, San Juan Mountains, San Luis Valley, Southeast Mountains, Raton Ridge, Palmer Ridge, & Southeast Plains:

Clouds are beginning to build over the higher elevations this morning, with mostly clear skies for the rest of southern Colorado. This afternoon, scattered storms are expected over the higher terrain west of the Continental Divide. However, with much less instability to work with, storms are not expected to be of long duration. A few isolated moderate downpours may occur over the western San Juan Mountains and eastern Southwest slope and produce 1-hour rain rates up to 0.75 inches. A few brief, isolated storms may also develop over the higher elevation ridges and produce 30-minute rain rates up to 0.4 inches. Flooding is NOT expected today.