Issue Date: Wednesday, July 14th, 2021
Issue Time: 10:15AM MDT

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

The visible satellite imagery below shows the shortwave from yesterday to our north (orange “X”), which will continue to move to the east throughout today. An associated northerly surge of surface winds has started to move south over the eastern plains this morning, which is expected to increase surface moisture behind it. In addition, a surface Low over the plains today will help to reinforce surface moisture over this area on its east and north sides. Due to the shortwave’s passage, the 500mb High has been pushed south and west, which has allowed for a nice plume of moisture to move northward. Currently over western Colorado, an upper-level disturbance is combining with the moisture plume to produce showers over the southwest corner of the state. Throughout the day, this upper Low is forecast to move eastward and produce extra lift out in front of it. All in all, plenty of moisture and lift over the state for widespread rainfall.

Moisture has already increased quite a bit over western Colorado, and PW at Grand Junction was measured at 1.11 inches. Over Denver, PW remains around 0.80 inches, but is expected to increase to over an inch by later this afternoon. This well above average moisture will set the stage for heavy rainfall producing storms today, so a Moderate/Low flood threat has been issued. As far as the evolution of rainfall development, the ongoing storms over southwest Colorado are expected to increase in intensity with a little daytime heating and spread into the Central Mountains. Training storms will likely produce some higher totals over the southern San Juan Mountains, so a Moderate flood threat has been issued. The eastward movement of the upper-level disturbance will also help to produce widespread storms over the Southeast Mountains by early afternoon. Activity is anticipated to spill into the adjacent plains, and overnight rainfall is forecast for the Southeast Plains. Best chance for heavy rainfall over the plains will occur later this evening along the aforementioned SW to NE oriented boundary from this morning.

In addition to the storms south, numerous storms are expected to develop over the Front Range with post-frontal upslope flow. Decent CAPE is also forecast due to slightly better daytime heating. This means that some stronger thunderstorms may develop as the storms move off the mountains with the northwesterly steering flows. In addition to some hail and strong outflow winds, high surface moisture will allow storms to produce very high rainfall rates. So, a Moderate flood threat has been issued for road, small stream/creek and low-lying area flooding issues over the Urban Corridor and foothills.

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

Storms are anticipated to pick up in intensity and coverage by early afternoon. Best coverage of storms is anticipated over the Central and San Juan Mountains. Max 1-hour rain rates up to 1 inch will be possible with storm totals up to 1.5 inches. A Moderate flood threat has been issued. Further north, better instability may develop, which would allow for some thunderstorm activity later this afternoon. Storm movement will be more northerly during this period as the ridge builds to the west. Max 1-hour rain rates up to 1 inch will be possible with these storms, so a Low flood threat has been issued. Threats today over the steeper terrains include mud flows and debris slides as well as local stream/creek flooding and road flooding.

Primetime: 12PM to 12AM

Front Range, Southeast Mountains, Palmer Ridge, Raton Ridge & Urban Corridor:

Numerous storms are anticipated to develop over the eastern high terrains this afternoon. Max 1-hour rain rates up to 1.25 inches (north) and 1 inch (south) are possible. This could cause mud flows and debris slides as well as road flooding over the steeper terrains. As storms move into the Urban Corridor, max 1-hour rain rates up to 2 inches will be possible, which could cause road, low-lying area and intersection flooding issues. A Moderate flood threat has been issued.

Primetime: 1PM to 11PM

Northeast Plains & Southeast Plains: 

As storms move off the mountains and into the plains this afternoon, they will be moving into higher surface moisture. If the storms can make it into the plains before the instability drops off, max 1-hour rain rates up to 2 inches will be possible. Best chance for heavy rainfall will be along the left over cold front boundary that stalls out over the far eastern plains, which could make storms more stationary in nature. These storms may produce road flooding, field ponding and local stream flooding issues. Other threats from storms include hail and damaging outflow winds. Storms will likely linger into the early morning hours over the Southeast Plains, but the flood threat should drop off around midnight. A Low flood threat has been issued.

Primetime: 6PM to Midnight

Issue Date: Tuesday, July 13th, 2021
Issue Time: 9:30AM MDT

— A LOW flood threat has been posted for parts of the San Juan Mountains and Southeast Mountains

As expected, changes are in the air over Colorado today. As shown in the visible satellite image, below, one easily seen difference since yesterday morning is the expansive deck of mid-level clouds seen mainly across northern and central Colorado. These clouds were mainly located in a narrow layer roughly 15-18k feet above the surface, as seen in both the Denver and Grand Junction soundings. They are associated with multiple disturbances, of monsoon origin, that have raised Precipitable Water to about 0.8 inches at both Grand Junction and Denver. For most areas (as mentioned in yesterday’s Outlook) it will take time to moisten the boundary layer to make it conducive for heavy rainfall. Additionally, the cloud deck will significantly impede instability for most of the state leading to a light to moderate intensity rainfall this afternoon and evening, so no complaints there.

There are two areas that we are watching for heavy rainfall chances. The first will be the climatologically favored San Juan Mountains and Southeast Mountains, where instability will locally exceed 1,000 J/kg this afternoon. Rain rates have been on the higher side of our model guidance the past two days and today’s guidance has significantly increased compared to yesterday. Thus, a Low flood threat is warranted for these areas through early evening, before instability quick diminishes and precipitation transitions to a more gradual rainfall. The second area is in the Northeast Plains where a cool front/outflow boundary has moved in from the northeast. To the north of the boundary, only limited instability is expected. To the south, higher instability will support the chance of strong-to-severe thunderstorms that will be capable of heavy rainfall and damaging winds. However, the limiting factor is strong SE steering winds aloft that will limit point rainfall. Thus, rainfall rates are expected to stay just below flood thresholds.

Finally, the change to more westerly flow aloft will finally clear out the smoky skies a bit today, as will any 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:

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

Scattered to numerous showers and thunderstorms developing, with better coverage for elevations above 7,500 feet. Max 30-minute rainfall up to 0.8 inches and max 1-hour rainfall up to 1.2 inches in southern areas, where a Low flood threat has been posted for isolated flash flooding, debris slides and mud flows. Further north, max 1-hour rainfall up to 0.7 inches is possible. Gusty winds could accompany the stronger storms, especially over northern areas.

Primetime: 12PM to 9PM

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

Partly to mostly cloudy early, then isolated to scattered showers and thunderstorms possible this afternoon. Max 1-hour rainfall up to 1.5 inches in the east and 0.8 inches for the foothills and adjacent areas. Damaging winds will be possible with the stronger storms over the Northeast Plains. However, flooding is NOT expected today.

Primetime: 1PM to 10PM

Issue Date: Monday, July 12th, 2021
Issue Time: 8:45AM MDT

— Flooding is NOT expected today

A “persistence” pattern remains overhead for today, with PW at Grand Junction and Denver holding in the 0.50 – 0.57 inch range. Slightly more moisture was noted at mid-levels today, which will increase storm coverage across the entire higher terrain compared to yesterday. However, even so, only isolated to perhaps widely scattered storms are expected, with the highest coverage continuing to be in the San Juan Mountains and Southeast Mountains along the New Mexico border. As shown in the water vapor image, below, a much more active day of rainfall is expected tomorrow as a slow-moving pool of monsoon moisture enters Colorado from the west. But for today, flooding is NOT expected.

The big story today continues to be the smoky skies across all of Colorado, arising from dozens of new and ongoing wildfires in MT, ID, OR and WA. A rough count this morning showed 26 wildfires in Montana alone, with a few exceeding 10,000 acres in size. Some reduction is smoke is expected tomorrow as our steering flow changes to more westerly and rainfall removes some ash particles from the sky.

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:

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

Becoming partly cloudy, hot and continued smoky and hazy skies. Isolated to widely scattered showers and thunderstorms are expected early afternoon through the evening hours. Max 1-hour rainfall 0.3 inches, except up to 0.6 inches along the New Mexico border. Flooding is NOT expected today.

Primetime: 1PM to 9PM

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

Hazy conditions will continue today with the ongoing fire activity. Isolated to perhaps widely scattered storms are possible over the higher terrain above 8,000 feet today. Max 1-hour rainfall up to 0.3 inches possible. Flooding is NOT expected today.

Primetime: 1PM to 8PM

Issue Date: Sunday, July 11th, 2021
Issue Time: 8AM MDT

— Flooding is NOT expected today

Northerly flow from the combined High/Low pattern aloft pulled in a lot of smoke over state yesterday, which produced a noticeable haze by the afternoon hours. That smoke is still here this morning, and visible satellite (below) shows this feature as a gray hue over the western states. A couple stronger plumes of smoke affecting Colorado are marked by the dashed lines. A rinse and repeat pattern is forecast today for precipitation chances and high temperatures, so another mild weather day is ahead. PW was measured around 0.50 inches both east (DEN) and west (GJT), and a weak moisture plume was noted over the mountains. This minimal moisture paired with larger-scale subsidence, should only allow for a couple isolated, weak storms to develop over the mountains this afternoon and evening. Better concentration of the PW plume is across the southern border, so the southern San Juan and Southeast Mountains have the best shot at seeing some measurable rainfall today. Northerly steering flow should keep the weak storms anchored to the mountains with all rainfall activity ending just after sundown. Flooding is NOT forecast.

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

Hazy conditions will continue today with the ongoing fire activity. A couple isolated, weak storms are possible over the mountains again this afternoon. Best chance for rainfall will be over the Front Range/Palmer Ridge intersect, Southeast Mountains and southern Raton Ridge. Isolated storm totals up to 0.40 inches (south) will be possible with most storms producing only virga. Brief, localized wind gusts will also be possible over the Southeast Mountains. High temperatures will be a couple degrees warmer than yesterday with upper 80Fs for most of the lower elevations and low to mid-80Fs for the mountain valleys. Flooding is NOT forecast.

Primetime: 1PM to 9PM

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

Near surface smoke is expected to be strongest west of the Continental Divide over these forecast regions. Despite the smoke, high temperatures should still be able to climb in the upper 90Fs and possibly reach 100F (localized) over the lower elevations. Mountain valleys’ high temperatures will reach into the mid-80Fs. Best chance for an isolated, weak storm or two will be over the southern San Juan Mountains and along the Continental Divide over the southern Central Mountains. Max 1-hour rain rates up to 0.60 inches will be possible (south). Plenty of virga is also forecast due to the dry surface layer. Flooding is NOT forecast.

Primetime: 1PM to 9PM