Issue Date: Monday, July 26th, 2021
Issue Time: 9:30AM MDT

— A MODERATE flood threat has been posted for parts of the San Juan Mountains
— A LOW flood threat has been posted for parts of the Southeast Plains, Raton Ridge, Southeast Mountains, Central Mountains and Southwest Slope
— An afternoon forecast update is possible today for the Southeast Plains

As shown in the water vapor image below, a notable area of dry air is working into northeast Colorado from the northeast. Denver’s PW this morning dropped to 0.79 inches and could drop a little more during the day. A distinct dry layer was noted on the North Platte (NE) morning sounding, which implies little to no rainfall coverage over northeast Colorado today. Moving southward, a marked disturbance was noted over southeast Colorado, just south of the dry air. With only weak steering flow from the north, this disturbance is expected to setup a moisture convergence zone over the Southeast Plains today that could produce very heavy rainfall rates. This is partially mitigated by the relatively low precipitation chances (50-60%) and scattered coverage of the storms. Nonetheless, a LOW flood threat is warranted here. Moving west, plenty of moist air remains over southern and southwestern Colorado with the Grand Junction morning PW coming in at 1.08 inches, along with a surface dewpoint of 61F, very high even for this time of year. Some drying will occur along the Continental Divide as the aforementioned dry layer spills over the higher terrain. Nonetheless, we expect numerous thunderstorms again along the climatologically favored San Juan Mountains as well as the Elk Mountains. A MODERATE flood threat has been posted for the western San Juans, mainly for the higher probability of multiple heavy rainfall cores. In surrounding regions, a LOW flood threat has been posted.

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 Plains:

Scattered thunderstorms likely this afternoon with the highest coverage in the far southeast, along the Kansas border. Max 1-hour rainfall up to 3.0 inches possible, which could produce isolated flash flooding. A LOW flood threat has been posted for parts of the region. The threat of heavy rainfall will persist into the late evening and possibly early overnight hours. An afternoon forecast update is possible, if a higher threat appears warranted.

Primetime: 3PM through 2AM

San Juan Mountains, Southwest Slope, Grand Valley, Central Mountains, Raton Ridge, San Luis Valley and Southeast Mountains,:

Numerous showers and thunderstorms again today, with the highest coverage over the San Juan Mountains, Elk Mountains as well as southern parts of the Sangre de Cristo mountains. Max 1-hour rainfall up to 1.3 inches possible, with max 24-hour totals up to 2.2 inches especially over the San Juans. A MODERATE flood threat has been posted for the San Juans with a LOW flood threat in surrounding areas. Threats include isolated flash flooding, debris slides and mud flows. With consistent precipitation over the recent days, base river flows have increased so small creek and tributary flooding will also be possible today.

Primetime: 12PM through 11PM

Northwest Slope, Northern Mountains, Urban Corridor, Northeast Plain, Palmer Ridge and Front Range:

Generally drier today, but isolated to widely scattered showers and thunderstorms possible in the afternoon and evening especially over the higher terrain and foothills. Max 1-hour rainfall up to 1.0 inch (east of Continental Divide) and 0.8 inches (west of Continental Divide). Flooding is NOT expected today, but nuisance street ponding is possible.

Primetime: 12PM through 9PM

Issue Date: Sunday, July 25th, 2021
Issue Time: 10:10AM MDT

— A MODERATE flood threat has been issued for the Grand Valley, Southwest Slope, San Juan Mountains, Central Mountains, Front Range, Southeast Mountains and Raton Ridge
— A LOW flood threat has been issued for portions of the Northwest Slope, Northern Mountains, Urban Corridor, Palmer Ridge, Northeast Plains and Southeast Plains

The busy rainfall season continues. Visible satellite imagery below shows cloud cover over the northern portion of the state associated with the ongoing monsoon moisture surge, which is helping to generate some isolated, light showers over the western border this morning. There is also a noticeable drier air mass over the southwest corner as indicated by the lack of cloud cover (orange dotted oval). This may help to reduce the storms coverage over this region today. Not much change in the overall pattern, but the area of Low pressure from yesterday should have less of an influence on the overall pattern as it continues its westward progression. With the High pushing slightly north, due to the movement of the Low, steering flow over the state will really be lacking today. What that means is that storms will likely be anchored to the high terrains, remain nearly stationary, and pulse in intensity. So, while less coverage of the heavy rainfall is anticipated, storm cores will still be able to drop a lot of rain over an area.

PW at Grand Junction was measured at 1.08 inches, so storms over the western elevated terrains will again have the potential to produce around an inch of rainfall over a short duration. Cloud cover also seems to be clearing out fairly easily with the daytime heating, which will let instability build for stronger storm cores. Over the eastern mountains, the heavy rainfall threat also continues with PW increasing towards the southern border. Numerous rounds of rainfall over the last 5 days across the mountains will support soils producing excessive runoff as well as mud flows and debris slides. For these reasons, the MODERATE/LOW flood threat continues.

There are also flooding concerns over the eastern plains where a dryline sets up with a lee trough. There is a high likelihood of storms popping along the northern portion of it by mid-afternoon. With PW over 1.50 inches, dew points in the 60Fs and slow steering flows, storms that develop have the potential to produce VERY heavy rainfall. Outflow boundaries may aid in triggering additional convection over the denoted LOW flood threat area. Flooding concerns include local stream/creek flooding, arroyo flooding, road flooding and heavy field ponding.

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:

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

Heavy rainfall is likely again by early this afternoon over the high terrains. While heavy rainfall is likely to be less widespread, nearly stationary storms will help to increase local precipitation totals. Over western Colorado, max 1-hour rainfall rates up to 1.75 inches (central), 1.50 inches (south) and 1 inch (north) will be possible. Isolated storm totals up to 3.25 inches will be possible and most likely within the central portions of the mountains.

To the east, max 1-hour rain rates up to 1.75 inches will be possible along with storm totals up to 3.25 inches. Less coverage of rainfall is anticipated over the northern Front Range, but rain rates up to 0.50 inches will be possible with the more isolated storms that do develop.

A MODERATE/LOW flood threat have been reissued. Saturated soils will again increase the flood threat today as excessive runoff and mud flows/debris slides become more likely. Other threats include road flooding and local stream/creek flooding. Most of the storms should come to an end around 11PM with lighter rainfall activity into the morning early hours.

Primetime: 11AM to 2AM

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

A dryline sets up over the Northeast Plains, and some storms will likely pop along it by mid-afternoon. Due to the high moisture environment and slow-moving nature of the storms, VERY heavy rainfall is possible with max 1-hour rain rates up to 3.5 inches. Additional storms may develop further south with outflow boundaries through tonight. Storm totals up to 4 inches may be possible, which could cause local creek/stream flooding, road flooding, arroyo flooding and field ponding. In addition to heavy rainfall, the convection may produce damaging outflow winds and some hail. A LOW flood threat has been issued.

Primetime: 3PM to 11PM

Issue Date: Saturday, July 24th, 2021
Issue Time: 10:30AM MDT

— A MODERATE flood threat has been issued for the Southwest Slope, San Juan Mountains, Central Mountains and Front Range
— A LOW flood threat has been issued for portions of the Southeast Plains, Northwest Plains, Urban Corridor and Palmer Ridge, as well as the higher terrains of the Southeast Mountains, Northern Mountains, Grand Valley, Raton Ridge and Northwest Slope

The satellite imagery below shows a lot of cloud cover over the northern portion of the state behind a cold front that came through. Accompanying this cloud cover is a slightly drier air mass, and PW over Denver has dropped to 0.96 inches this morning. Between these two factors, rainfall chances will be lower today north of I-70. Best chance for storms to develop over this region will be where the sun can break through and build some instability, so likely over the Flat Top region. Thus, the Low flood threat has been extended northwards into this area. Overall, there is a much lower threat for downpours over this area when compared to yesterday; however, if storms can develop, anticipate some local, heavy rainfall.

The main focus for the heavy rainfall potential today is across southern Colorado. With the Low just south of the border near the Four Corners area, steering flows will be from the east today. That means that more rainfall should be expected over the Southwest Slopes as storms move off the higher elevations. PW at Grand Junction and Albuquerque continues to be over an inch, which is still well above normal for this time of year. That means that storms should again be efficient rainfall producers with the moist surface layer, and local rainfall totals up to 3 inches will be possible in the Moderate threat areas drawn below. With saturated soils from the last 24 to 96-hours of precipitation (see SPM), an increase in runoff is likely, which could cause some flooding of local streams. Soils will likely also be less stable with all of the rainfall, which could lead to more mud flows and debris slides where the heavy downpours develop. Thus, a MODERATE/LOW flood threat has been issued.

In addition to another day of monsoon rainfall across the mountains, there is a possibility of some thunderstorms capable of producing heavy rainfall along the orange dotted boundary shown below. This front is forecast to drop south throughout the day, where it may encounter some stronger instability and high moisture. In similar fashion to yesterday, storms that develop on it will likely be nearly stationary and the extra convergence along the boundary could produce high rainfall totals. The Low flood threat has been extended eastward.

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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:

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

Another round of monsoon moisture fueled storms are forecast today with the steering flow changing to more easterly. Max 1-hour rain rates up to 1.75 inches will be possible along with isolated storm totals up to 3 inches. This will most likely occur in the MODERATE flood threat areas drawn above. This could cause road flooding, local stream flooding and mud flows/debris slides over the steeper terrains. This is especially true over areas with saturated soils, so use extra caution around these areas. The flood threat should come to an end a couple hours after sunset, though some rainfall may linger into the early morning hours over the San Juan Mountains. The interior of the San Luis Valley could see isolated totals up to 0.50 inches once again.

Primetime: 11AM to 2AM

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

Some low-end severe thunderstorms will likely develop along the cold front as it drops southwards today. This could produce local heavy rainfall this afternoon and evening along with some small hail and damaging outflow winds. Max 1-hour rain rates up to 1.50 inches and local storm totals up to 3 inches would be possible. Storms will likely linger into the early morning hours, but the flood threat should come to an end a couple hours after sundown.

Primetime: 2PM to Midnight

Northern Mountains, Northwest Slope and Grand Valley:

Without much instability being able to form with the ongoing cloud cover, rainfall chances are much lower over this area today. If some sun is able to break through (most likely west), some heavy rainfall producing storms would be likely. Max 1-hour rain rates up to 1 inch (west) and 0.75 inches (east) would be possible. Some light showers will be possible over the Northwest Slope this evening, but flooding is NOT forecast. For the most part, it should be a cooler day with high temperatures reaching into the upper 70Fs to low 80Fs for the mountain valleys and upper 80Fs to low 90Fs for the Northwest Slope.

Primetime: 3PM to 11PM

Issue Date: Friday, July 23rd, 2021
Issue Time: 10:05AM MDT

— A MODERATE flood threat has been issued for the San Juan Mountains, Central Mountains, Grand Valley, Northwest Slope, Southwest Slope and Front Range
— A LOW flood threat has been issued for Southeast Mountains, Palmer Ridge and Urban Corridor

Not much change in the overall pattern this morning with the High continuing to pull above average moisture northward. This is helping to create some cloud cover over the western border and Northern Mountains this morning, which may be producing some light precipitation as well. Throughout the day, the High will begin to be displaced to the northwest as a Low traverses westward from Texas. This will produce more easterly steering flows south and more westerly steering flows north for the storms that develop today.

PW at Grand Junction was measured at whopping 1.27 inches, which is about the highest the maximum moving average gets during monsoon season. At Denver, PW was measured at 1.14 inches, which is still equally impressive. Both soundings indicated high moisture from the surface to the upper layers, which means storms that develop today will be very efficient rainfall producers once again. The upper-level pattern will help storms remain more stationary in nature and pulse-like in intensity once again. Highest coverage of rainfall west should be over the south/central high terrains, and to the east rainfall should favor the Front Range and Palmer Ridge with more limited coverage over the Southeast Mountains. Some additional storms are also possible over the Urban Corridor and Northeast Plains this evening.

Saturate soils are a concern over the mountains today as they can lead to excessive runoff and an increased threat for mud flows/debris slides if a storm moves overhead (unstable ground). In addition to this threat, storms are expected to produce intense rain rates again with decent instability forming over the Front Range and portions of the San Juan Mountains for convection. For the reasons stated above, another MODERATE flood threat has been issued. Scroll down for more details about the flood threat over your region.

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: 

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

Widespread, heavy rainfall producing storms are forecast again this afternoon and evening, so the MODERATE/LOW flood threat continues. Max 1-hour rain rates up to 2.25 inches with local totals up to 3.50 inches will be possible by morning in the MODERATE threat areas. Best chance for the higher accumulations will be over the San Juan Mountains or near the Continental Divide (central/north). The interior of the San Luis Valley may see up to 0.40 inches of rainfall. Flash flooding of local streams, mud flows and debris slides will be possible with the stronger storms that develop and over areas with saturated soils (mountains). This includes recent burn areas, so please head over to the FBF for the elevated threats issued for today. Most rainfall should end just after midnight, but light showers may linger over the high terrains through early tomorrow morning.

Primetime: 12:30PM to 4AM

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

Isolated storms will likely develop over the Palmer Ridge early this evening, and additional storms are possible north (westerly steering flow) with better coverage of rainfall overall compared to yesterday. Max 1-hour rain rates up to 2 inches (north) and 1.75 inches (south) may be possible, which could cause flooding of local streams, roads and low-lying areas. A LOW flood threat has been issued. The flood threat should end later this evening, but some rainfall may linger over the northern Urban Corridor/northern Northeast Plains overnight.

Primetime: 2PM to 1AM