Issue Date: Monday, July 9, 2018
Issue Time: 09:10AM MDT

— A LOW flood threat has been issued for the Burro and 416 burn areas

The center of 500mb ridge is currently over the Nebraska, Colorado and Wyoming intersect. The subtropical moisture on its west side has shifted westward out of Colorado as seen in the water vapor imagery below. Drier air has worked its way in on the east side of the high and the Precipitable Water measurement at Denver this morning was 0.74 inches. Flow aloft will be from the east over eastern Colorado, so this should keep the dry air in place and downward motion should nix thunderstorm activity over the lower elevations. Any clouds or isolated storms that form this afternoon will be over the mountains due to the eastward motion aloft.

As the center of the ridge continues its eastward progression today, small disturbances over Utah and Wyoming may work their way into the northwest corner of the state, which would help trigger some showers and thunderstorm activity. Further south over NM/AZ, the disturbance marked in the image below may also graze the southwest corner of the state as it propagates to the WNW around the high. If it makes it into the state, this would affect the southern San Juan Mountains by helping to enhance upslope flow thunderstorms. Precipitation Water in Grand Junction is still quite high, but dry air in the lower levels will reduce the intensity of the rain rates this afternoon when compared to the last couple of days. There is still a chance for a thunderstorm or two to move over the 416 and Burro burn areas with intensities greater than 0.25 inches/hour, and these rates would be enough to trigger mud flows and debris slides. Thus, a Low flood threat has been issued for the two burn areas. Elsewhere over the western mountains, rain rates will remain under flood threat criteria.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Dry air will continue to be pulled into these areas from the east, which should limit thunderstorm coverage this afternoon to the mountains. Not expecting anything more than a few isolated thunderstorms and showers over the higher terrains. Max 1-hour rain rates up to 0.1 inches/hour are possible, but virga and brief windy conditions are more likely. High temperatures should be similar to yesterday with mid to upper 90Fs over the lower elevations. Flooding is not expected today.

Primetime: 3PM to 8PM

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

A couple disturbances may move into the northwest and southwest corners of the state as they propagate around the high pressure this afternoon. If this occurs, this would enhance the chance for showers and thunderstorms over the northwest corner of the state. Rain rates would be under 0.1 inches/hour for these storms. The best chance for thunderstorms this afternoon is again over the San Juan Mountains. Rain rates of these storms are forecast to be up to 0.5 inches/hour (less intense than the previous few days), but if they were to move over a burn area, flash flooding could occur. The main threats would be mud flows, debris slides and local stream flooding. A Low flood threat has been issued for the 416 and Burro burn scars. Elsewhere, flooding is not expected.

Primetime: 2PM to 10PM

Issue Date: 7/8/2018
Issue Time: 7:15 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS TODAY, NAMELY THE 416 FIRE, BURRO FIRE, AND WEST FORK COMPLEX BURN AREAS.
A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, CENTRAL MOUNTAINS, GRAND VALLEY, NORTHWEST SLOPE, NORTHERN MOUNTAINS, FRONT RANGE, AND SOUTHEAST MOUNTAINS, MAINLY DUE TO RECENT/ONGOING FIRE BURNS.

Today will be nearly a repeat of yesterday as the large-scale conditions change little and moisture remains trapped underneath the upper-level ridge. The High Country will once again see scattered showers/thunderstorms focused over the higher terrain, drifting over adjacent lower valleys with time. Most storms will be along and west of the Continental Divide, with more isolated coverage expected over the mountains east of the Continental Divide. The focus areas for the flood threat today, as yesterday, will be the numerous fire burn areas across the High Country, with the highest threat over the sensitive 416 Fire and Burro Fire burn areas.

East of the mountains, the main weather story will be another day of hot temperatures, with highs similar to those experienced Saturday. A couple late-afternoon/evening storms will be possible over the Urban Corridor, Palmer Ridge, and western portions of the Northeast Plains. This activity will be driven by the peak of daytime heating, and will be isolated in coverage. Gusty winds, lightning, and light-to-moderate rainfall will be the main threats.

NOTE: Due to technical difficulties beyond our control, the flood threat map today will be a static image and not zoom-able as usual. We apologize for any inconvenience this may cause, and we will do everything we can to have this fixed ASAP.

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, Northeast Plains, Southeast Plains, and Raton Ridge:

The heat will be the main weather story for most, with high temperatures similar to yesterday’s readings. Another weak surface boundary will take shape on a line roughly from Castle Rock to Briggsdale, which will provide enough convergence, coinciding with peak heating, for a few isolated, high-based storms over the Urban Corridor and western portions of the Northeast Plains and Palmer Ridge. Gusty winds, lightning, and light-to-moderate rainfall will be the main impacts. Any storm activity will diminish as the sun fades, ending around 9 PM. Maximum rain rates will be 0.4-0.6 inches/hour.

Timing: 2 PM – 9 PM

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

Another day of scattered showers and thunderstorms are on tap for the higher terrain along and west of the Continental Divide, with more isolated coverage for the higher terrain east of the Divide. Storms will drift in a generally southwestward direction over adjacent lower valleys. Precipitable water values will remain above normal, providing showers/storms with enough moisture for efficient rainfall production. Much of that moisture is confined to the mid-levels, however, so evaporation below cloud bases will reduce the actual rain rates at the surface. All in all, it is another day where burn scars need to be monitored. Maximum rain rates are as follows:

Northern Mountains, Northwest Slope, Grand Valley, and Central Mountains: 0.5-0.7 inches/hour
Front Range and Southeast Mountains: 0.4-0.6 inches/hour
Southwest Slope and San Juan Mountains: 0.5-0.9 inches/hour
San Luis Valley: 0.15-0.35 inches/hour

Timing: Noon – 9 PM, with a couple lingering storms into the early morning hours

Issue Date: 7/7/2018
Issue Time: 8:15 AM

A HIGH FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS, NAMELY THE 416 FIRE AND BURRO FIRE BURN AREAS.
A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SAN JUAN MOUNTAINS, NAMELY THE WEST FORK COMPLEX BURN AREAS.
A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, CENTRAL MOUNTAINS, GRAND VALLEY, FRONT RANGE, AND SOUTHEAST MOUNTAINS, MAINLY DUE TO RECENT/ONGOING FIRE BURNS INCLUDING THE SPRING, CHATEAU, ADOBE, SUGARLOAF, AND WESTON PASS FIRES.

The Rocky Mountains provide an incredible backdrop for pictures and events, but today they will also be the reason behind a dichotomy of weather regimes across the state. Strong high pressure aloft has settled over the region, with the 500 mb center over northwest Colorado. This high pressure has started today with abundant sunshine across the state, as seen in the visible image below. As the day warms up underneath the sunshine, orographic lift will take shape alongside the heat, working on residual moisture trapped underneath the ridge to force scattered showers/thunderstorms over the mountains. The bulk of precipitation will occur over the higher terrain of the Southwest Slope and San Juan Mountains due to the best moisture residing there, and that’s where we find the High/Moderate flood threats for today/tonight. The 416 Fire and Burro Fire are under the High Threat, due to it taking as little as 0.2-0.3 inches/hour rainfall to cause flash flooding, debris slides, and mud flows in, and immediately downstream of, those recent burns. Elsewhere across the High Country, scattered showers/thunderstorms are expected, mainly over the higher elevations, drifting with time over adjacent lower valleys.

East of the mountains, the heat is on. High temperatures will climb well into the 90s across elevations below 6000 feet or so, and into the upper 80s/near 90 across the slightly higher terrain of the Palmer Ridge and Raton Ridge. Due to northeasterly flow aloft, showers/thunderstorms over the higher terrain will not drift over the lower elevations east of the mountains, so skies will be dominated by sunshine and perhaps a few fair weather cumulus clouds during peak afternoon heating.

The *only* chances for a shower/storm will be 1) over the far northern reaches of the Urban Corridor where a southward shift in the high pressure center would bring weak, westerly flow to the northern Front Range, allowing for a storm to drift over the area, and 2) Over the Raton Ridge where southerly surface flow may result in marginally enough lift to produce an isolated, brief thunderstorm during the afternoon/early evening. Both of these scenarios have about a 15% chance of occurrence.

For more information on timing and rain rates, please see the zone-specific forecast discussions below.

NOTE: Due to technical difficulties beyond our control, the flood threat map today will be a static image and not zoom-able as usual. We apologize for any inconvenience this may cause, and we will do everything we can to have this fixed ASAP.

Today’s Flood Threat Map

Zone-Specific Forecasts

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

Hot with abundant sunshine is the name of the game today, with high temperatures climbing a few degrees above yesterday’s readings. A few fair weather cumulus near the higher terrain will bubble during the afternoon, and perhaps an isolated, high-based thunderstorm or two may impact the Raton Ridge and far northern portions of the Urban Corridor. Maximum rain rates from any storm activity over the northern Urban Corridor and Raton Ridge will be 0.3-0.6 inches/hour.

Timing: 4 PM – 9 PM

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

Scattered showers and thunderstorms will impact the region today, mainly over the higher mountain terrain where orographic lift will aid the work of daytime heating in producing convective development. The bulk of precipitation will fall across the higher terrain of the Southwest Slope and San Juan Mountains, thanks to their coinciding with the best moisture. Cumulus clouds will start to develop later this morning, with showers/thunderstorms ramping up during the early afternoon. The peak of activity will coincide with the peak in daytime heating, with storms diminishing after sunset. Maximum rain rates are as follows:

Northwest Slope: 0.2-0.4 inches/hour
Northern Mountains, Front Range, Grand Valley: 0.5-1.0 inches/hour
Central Mountains and Southeast Mountains: 0.7-1.1 inches/hour
Southwest Slope and San Juan Mountains: 0.7-1.0 inches/hour
San Luis Valley: 0.2-0.4 inches/hour

Timing: 11 AM – 9 PM, with a few lingering showers/storms over the Southwest Slope, San Juan Mountains, and Grand Valley into the early morning hours.

Issue Date: 7/6/2018
Issue Time: 10:35 AM

— A HIGH FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE SAN JUAN MOUNTAINS, INCLUDING THE 416 AND BURRO FIRE COMPLEXES.
— A MODERATE FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE SOUTHEAST MOUNTAINS AND CENTRAL MOUNTAINS, PARTICULARLY AREAS IN AND NEAR THE SPRING CREEK, CHATEAU, ADOBE, AND WESTON PASS BURN AREAS.
— A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, CENTRAL MOUNTAINS, SAN LUIS VALLEY, AND SOUTHEAST MOUNTAINS.

Even as a strong mid-level ridge becomes even more strongly entrenched over Colorado today, a surge of subtropical moisture will bring a heavy, slow-moving shower and thunderstorm threat this evening and tonight. Atmospheric moisture levels were approaching the 90^th percentile at Grand Junction this morning, indicative of an atmosphere primed for widespread rainfall. Moisture is even expected to increase today as the remnants of a tropical wave that spent much of the week over the Gulf of Mexico continues to drift west-northwestward around the south side of the upper-level ridge. This pattern is therefore not typical of the monsoon, but still involves the potentially troubling combination of tropical moisture and strong midsummer heating. In addition, a couple of subtle shortwaves are forecast to ripple around the periphery of the ridge, potentially enabling more widespread and persistent thunderstorm activity (see figure below).

The bulk of the threat today comes from the potential for slow-moving storms atop current and old burn scars, primarily across the southern 1/3^rd of the state. The main focus area today is across the Burro and 416 fire areas, where forecast models are in near-unanimous agreement that some thunderstorm activity will occur today. While a widespread soaking rain is not expected, brief heavy rainfall rates of up to 1” per hour will pose a flood threat in and around recent burn areas, where exposed soil, ash, debris, etc. could be quickly swept up in any rain that occurs. In addition, the lift from one or more shortwaves this evening could maintain storm activity into the overnight hours, with some guidance indicating that storms may linger well into tomorrow morning. This is therefore a long-duration threat with potentially significant consequences near active burn scars in the southwestern portion of the state, necessitating a High flood risk today.

A Moderate risk has also been issued for the active Adobe, Weston Pass, Chateau, and Spring Creek fire areas to account for the expected low coverage of thunderstorm activity (isolated to scattered), but with the potential for rainfall rates in excess of 0.5”/hour, which would be more than sufficient to cause some isolated mud flows and debris slides. More broadly, the high terrain of the southern portion of the state has been included in a Low risk for today to account for two potential flood risks today: the chance of isolated rainfall rates of up to 1” per hour in steep terrain and over a handful of old burn scars (e.g., the West Fork Complex in Hinsdale and Mineral counties), as well as the threat of several hours of continuous moderate rainfall overnight, which could cause some notable rises on local creeks and streams. For the most part, however, consequential flooding is expected to be centered around the burn areas.

For more information on timing and rain rates, 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

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

Clouds will begin building this morning and scattered thunderstorms are expected this afternoon as moisture moves in. Rainfall rates may broadly be expected to range from 0.1” to 0.5” per hour but may locally reach or exceed 1” per hour. Higher terrain may be expected to see the most storms today and tonight, but notable rainfall may also be possible in the high deserts of the San Luis Valley and Grand Valley.

Primetime: 12PM to 9AM tomorrow

Northwest Slope, Northern Mountains, and Front Range:

Largely sunny and hot today over the northwestern and northeastern portions of the state, with highs into the 90s °F across the low country and 60s and 70s °F in the mountains. Expect increasing cloudiness this afternoon as storms form across the mountains, but expect just a very isolated storm risk today.

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

Largely sunny and hot today over the eastern portion of the state, with highs into the 90s °F across the low country and 60s and 70s °F in the mountains. Expect increasing cloudiness this afternoon as storms form across the mountains, with the chance for storms on the plains increasing from north to south. Very isolated storms are possible but unlikely in the northern Urban Corridor out to the northeast corner, with better chances from Denver and the Palmer Ridge south to the NM border. Any storms that get going may be capable of producing isolated pockets of rainfall up to 1” per hour.

Primetime: 2PM to 10PM, possibly until 3AM across the Southeast Plains