Issue Date: Friday, August 10th, 2018
Issue Time: 09:15AM MDT

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

Morning storms over the Northeast Plains to start Friday. This thunderstorm complex will continue to crawl south/southwest throughout the morning producing lightning, gusty winds and light-to-moderate rainfall. Similar to Wednesday morning, some additional convection may initiate as the sun begins to heat the surface, but it shouldn’t make it further south than the Palmer Divide. Max 1-hour rain rates up to 0.7 inches are possible, so not expecting any flooding. The visible satellite imagery below again shows the heavy subtropical moisture remaining to our south (below the green line). The north/northeast upper-level flow will continue today, so showers and thunderstorms should be confined to the higher terrains. This flow may also pull in a little extra moisture to the far southwest corner of the state near the CO/NM border throughout the day. In spite of this, there will still be quite a spread between the temperature and dew point. This is anticipated to promote gusty winds rather than heavy rainfall this afternoon.

Convection will return to the southwest corner of the state this afternoon, which will bring another day of measurable rain to the San Juan and Central Mountains. The only difference from Thursday is the center of action will shift a little further west. Storm motion will be fairly swift to the south/southwest, and with dry soils, widespread flooding is not foreseen. However, rain rates will be high enough to trigger mud flows and debris slides over the 416 and Burro burn areas if a storm tracks directly over a recent scar. A Low flood threat has been issued for these areas. Over the Southeast Mountains and Southern Front Range, shower and thunderstorm activity will be more isolated. Similar to yesterday, storm formation will be greatest along or near the Continental Divide. An isolated storm is also possible where the Southern Front Range and Palmer Ridge intersect. Decreases in surface moisture over this area should keep rain rates low enough that they won’t pose a threat to the burn scars in the region. Storm activity over the mountains should decrease with sundown with all activity ending a couple of hours after that.

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.

Issue Date: Thursday, August 9th, 2018
Issue Time: 08:55AM MDT

— A LOW flood threat has been issued for the Spring Creek, Hayden Pass and Weston Pass burn scars

Beautiful start to the morning with abundant sunshine across the state. Today, the center of the 500mb high pressure will continue expand over the Great Basin bringing dry and hot conditions to the western US. Colorado will remain under northerly flow aloft with a bit of an easterly component, which should keep the showers and thunderstorms this afternoon confined to the higher terrains. A couple shortwaves were noticed in the water vapor imagery this morning rotating around the high. These will help increase coverage of storms later today and may help fuel showers after the sundown. Subtropical is expected to remain south of the green line in the image below. Thus, widespread flooding is not anticipated, and dry low-levels will help limit rainfall rates.

The shower and thunderstorm activity will kick off over the mountains around 1PM this afternoon. Highest totals by tomorrow morning will likely be along the east-west oriented ridges and along the Continental Divide. The activity today is expected to shift more to the west, in conjunction with the passing shortwaves, which will bring some much needed rainfall to the eastern San Juan and Central Mountains. A few showers may even track into the outer fringes of the San Luis Valley, which is well below average for this season. Guidance indicates some showers may linger over the eastern San Juans and Central Mountains through midnight, which would help put 24-hour totals near the 1 inch mark. To the east, storms are again likely over the southern Southeast Mountains, though there is a slight chance an isolated storm may form near the Palmer Ridge.

With the entrainment of arid air into the low-levels, thunderstorms are expected to produce some gusty winds and dangerous cloud to ground lightning more than heavy rainfall. Max 1-hour rain rates up to 0.8 inches are possible, which would put burn scars at risk for mud flows, debris slides and flash flooding. A Low flood threat has been issued for the Hayden Pass, Weston Pass, and Spring Creek burn scars.

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:

Southeast Mountains, Central Mountains, Raton Ridge, San Juan Mountains, San Luis Valley, Front Range, Palmer Ridge:

Shower and thunderstorm activity should shift westward today. The strongest convection this afternoon will be along or near the Continental Divide and over the southern Southeast Mountains. Some showers might move into the outer fringes over the San Luis Valley as well. Max 1-hour rain rates up to 0.8 inches are possible along with gusty winds. By tomorrow morning, 24-hour totals up to 1 inch are possible over the eastern Central and San Juan Mountains favoring the east-west oriented ridges. A Low flood threat has been issued for the Hayden Pass, Weston Pass and Spring Creek burn scars. These rain rates have the potential to trigger mud flows, debris slides and localized flash flooding if a storm tracks over a recent burn scar.

Primetime: 1PM – 12AM

Northeast Plains, Southeast Plains, Urban Corridor:

With the north and somewhat easterly flow aloft, showers and thunderstorms should be confined to the higher terrains this afternoon. This means plenty of sunshine and hot temperatures today. Most cities over the eastern plains will near the century mark. Further west along the Urban Corridor, temperatures will be closer to 90F. A few higher clouds may be found this afternoon near the Palmer Ridge area with some broken clouds over the far eastern plains.

Northern Mountains, Northwest Slope, Southwest Slope, Grand Valley:

High temperatures will continue to run a few degrees above average for August. Dry air will keep the northern high terrains from receiving any measurable rainfall this afternoon. With the passing shortwave and mountain convection, broken cloud cover will be likely over the Grand Valley and Southwest Slope this afternoon and overnight. This may help keep low temperatures a couple of degrees higher than normal. Near surface smoke looks to decrease quite a bit as well with the exception of the far southwest corner of the state where the West Guard and Plateau fires continue to burn. Flooding is not expected.

Issue Date: Wednesday, August 8th, 2018
Issue Time: 09:00AM MDT

— A LOW flood threat has been issued for the Spring Creek, Hayden Pass and Junkins burn scars

The center of the 500mb high begins its migration to Nevada today. As the ridge builds over the Pacific Northwest, dry air will begin to be entrained into the state with more of a northerly flow aloft. This will also keep the subtropical moisture south of Colorado. This is expected to reduce the thunderstorm activity this afternoon; however, there is enough residual moisture under the ridge to initiate storms over the higher terrains. Currently, a shortwave over the Northeast Plains helped provide lift for some overnight thunderstorm and shower activity and is marked with the orange “X” below. This disturbance will linger to the south/southeast over the plains through the early afternoon before eventually making its way into Kansas. Moderate rainfall and thunder are being reported now along with gusty winds and small hail, but flooding is not expected with these storms. With high dew points in the area (60F+), localized totals up to 1.4 inch are possible.

With more of a northerly flow aloft, storms separate from the ongoing plains convection, should be confined to the mountains with isolated activity over the adjacent plains. The Denver sounding this morning showed moisture beginning to drop, and PW was measured at 0.88 inches. Thus, the most likely area for thunderstorm development this afternoon is along the southern Front Range, Southeast Mountains and Palmer/Raton Ridges. Though some more isolated, short-lived storms are possible further north. Storm motion will be to the south at about 15-20 mph, so widespread flooding is not expected. Over western Colorado, dry air and the 500mb high confining subtropical moisture south, should nix the chances for measurable rainfall again this afternoon.

Fresh burn scars over the Southeast Mountains will be susceptible to mud flows and debris slides this afternoon. It can take as little as 0.5 inches/hour to trigger the aforementioned threats and flash flooding if a storm tracks directly over a scar. Due to rain rates up to 0.8 inches/hour being possible, a Low flood threat has been issued for the Junkins, Hayden Pass and Spring Creek burn areas. Elsewhere, flooding is not expected.

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:

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

Ongoing convection on the plains will continue through early this afternoon. Dew points in the 60Fs will promote heavy rainfall, but storm motion should prevent flooding. Max 1-hour precipitation rates should stay below flood threat criteria, though localized storm totals up to 1.4 inches are possible. Small hail and gusty winds are also possible. To the west, expecting convection to initiate over the higher terrains again this afternoon. Southerly storm motion should keep the storms over the mountains with isolated activity over the adjacent plains. Max 1-hour rain rates up to 0.5 inches (north) and 0.8 inches (south) are possible. A Low flood threat has been issued for the recent burn scars over the Southeast Mountains.

Primetime: 1PM – 10PM

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

Starting to heat up some more today, though hazy conditions from the smoke will likely knock down high temperature a couple degrees. The latest HRRR run indicates that the northerly flow aloft will start to cut off the inflow of smoke overnight. However, it will stick around to limit visibility today. Rainfall chances are slim to nil over the higher terrains today, though some cloud cover is expected this afternoon.

Issue Date: Tuesday, August 7th, 2018
Issue Time: 09:30AM MDT

— A MODERATE flood threat has been issued for the Spring Creek, Hayden Pass and Junkins burn scars

— A LOW flood threat has been issued for Palmer Ridge, Southeast Mountains, Raton Ridge and portions of the Southeast Plains, Front Range and Urban Corridor

Fog can be seen on the visible satellite imagery below, but that should burn off fairly quick this morning as heating occurs. The lack of cloud cover means that instability will be able to build again for another round of severe thunderstorm activity this afternoon. The upper-level high pressure center remains elongated over CA/AZ/NM/TX with a little northward movement today. Similar to yesterday, storms will be confined to the eastern half of the state and favor the southern Front Range, Palmer Ridge and Southeast Mountains for initiation under upslope flow. Also expecting some thunderstorms to fire off the Cheyenne Ridge, and an isolated storm or two may move into the Northeast Plains by the early evening.

As far as the dynamical set up, looking at something similar to yesterday with a few minor differences. Another shortwave is expected to move through the area this afternoon, but it is not quite as strong as yesterday and may not reach eastern Colorado at peak heating. This would reduce the widespread thunderstorm activity over the adjacent, eastern plains. Instability will drop off a bit, but shear will increase some. The 12Z sounding shows the freezing level has dropped, which brings back the threat of large hail. In regards to low-level moisture, dew points remain high again today with the area beneath and to the east of the green line at least in the 50Fs. The Southeast Plains and Raton Ridge already have dew points in the 60Fs, which is extremely high for August. Some of this surface moisture may mix out, but steady east/southeast surface flow would only allow the dew points to drop off by a couple of digits at the most. Overall, the atmospheric environment is more than sufficient for some large, severe thunderstorms again this afternoon.

Threats for Tuesday include large hail, damaging winds and heavy rainfall. Guidance shows the heavy rainfall threat should remain south of the Palmer Ridge. While storm motion will be fairly quick to the southeast, saturated soils from yesterday may help to increase runoff and field ponding over the adjacent plains. There is also an increased threat for any storms that track over urban areas as the impervious surfaces will increase runoff and ponding in low-lying areas. The southern Southeast Mountains look a bit more active today when compared to yesterday, which will put recent burn scars at risk for flash flooding. A Moderate flood threat has been issued for the Spring Creek, Junkins and Hayden Pass burn scars due to high confidence rainfall rates in the area will exceed 0.5 inches/hour. Mud flows, debris slides and flash flooding of local streams are all possible for storms that track over these areas, or for any heavy rainfall over high terrains. A Low flood threat has been issued for the Front Range, Urban Corridor, Northeast Plains and Southeast Plains.

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:

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

Looking like a similar set up to yesterday. However, some reduced dew points over the northern portion of the state will limit the heavy rainfall threat to the Palmer Ridge and south. Increased runoff is likely today for any storms that track over urban areas or the same areas as yesterday (see SPM). Threats today include heavy rain, damaging winds and large hail. Max 1-hr rain rates up to 1.1 inches/hour are possible west with 1.4 inches/hour possible east of I-25. Some clusters of thunderstorms may linger overnight on the eastern plains, but max 1-hr rain rates should remain below flood threat criteria. The recent burn scars over the Southeast Mountains have a Moderate flood threat due to high confidence max 1-hr rain rates will exceed 0.5 inches/hour over the area. Debris slides, mud flows and flash flooding are all possible with the threat for the mountains ending after 10PM. A Low flood threat has been issued for the Palmer Ridge, Southeast Mountains, Raton Ridge and portions of the Southeast Plains, Front Range and Urban Corridor.

Primetime: 1PM – 4AM

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

Tuesday is looking a lot like Monday with the mercury rising a couple of ticks. Lots of reports of haze over western Colorado this morning. Increased smoke from the fires will continue today with the northerly flow aloft, which will reduce visibility and may knock a couple of degrees off the high temperature. Rainfall chances are confined to the higher terrains along the Continental Divide this afternoon, but no measurable rainfall is forecast. Expected some broken clouds to form over the higher terrains this afternoon with clear skies elsewhere.