Issue Date: Tuesday, July 17th, 2018
Issue Time: 09:25AM MDT

— A MODERATE flood threat has been issued for portions of the Palmer Ridge, Southeast Plains and Northeast Plains as well as the recent burn scars over the San Juan Mountains and Southeast Mountains

 — A LOW flood threat has been issued for the San Juan Mountains, Southeast Mountains, Raton Ridge, Front Range and Urban Corridor

Much cooler start to the day with cloud cover over a large portion of the state thanks to the MCS that moved through the NE panhandle into KS overnight. Today the low pressure over the Pacific Northwest will start to migrate to the east breaking down the ridging pattern to our west. This will push some upper disturbances (marked in orange) over the state, which will provide lift for more widespread thunderstorm activity this afternoon. Over the eastern plains, low level easterly winds will pull in plentiful moisture with dew points reaching the mid 50Fs to 60F later this afternoon. That means paired with sunshine, CAPE will also be able to build throughout the day. So as the storms fire over the higher terrains this afternoon and move into the adjacent plains, they will move into a favorable severe weather environment. Storms are expected to merge into a line, which will be capable of producing large hail and strong winds. With PW values well over 1 inch, (Denver’s sounding had a PW value of 1.15 inches) local, heavy rainfall is expected. A Low and Moderate flood threat have been issued. Storms that track over burn scars should be monitored closely as there is high confidence rain rates will exceed 0.5 inches/hour.

Over the San Juan Mountains, subtropical moisture is able to hold on for one more day. The GEFS is projecting PW values greater than 1 inch this afternoon, which means there is a threat for flash flooding again this afternoon with burn scars being the most susceptible. A Low flood threat has been issued with the recent burn scars under a Moderate flood threat. Storms will likely fire around noon with upslope flow and the flood threat should diminish as instability decreases after sundown. Further north over the Central and Northern Mountains, afternoon thunderstorm activity will be much more isolated. Over the adjacent valleys, a few storms may wander across the border from Utah, but 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:

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

Upper disturbance moving in with the low over the Pacific Northwest will help trigger more widespread thunderstorm development this afternoon. With high dew points, the flood threat returns to the Front Range, Southeast Mountains and eastern plains. Max 1-hour rain rates up to 1.1 inches are possible to the west. With deeper moisture over the plains, max 1-hour rain rates up to 2 inches are possible with local totals exceeding 2.3 inches. Threats include local stream and road flooding with debris slides and mud flows possible over the higher terrains. Burn scars will be especially susceptible to flooding, so a Moderate flood threat has been issued for those. A Low/Moderate flood threat has been issued for these regions. Storms over the eastern plains will also be capable of producing large hail and damaging winds.

Primetime: 1PM to 1AM

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

High PW values over the San Juan Mountains means another day for a Low flood threat with a Moderate flood threat for the burn scars. Max 1-hour rain rates up to 1 inch are possible. This could trigger mud flows and debris slides along with local stream flooding. Further north, storms will be more isolated in nature. A couple thunderstorms may move into the lower elevations from Utah. Max 1-hour rain rates will be closer to 0.5 inches/hour. A couple light showers may linger over the San Juan Mountains into the night, but the flood threat will end after sundown.

Primetime: 1PM to 8PM

Issue Date: Monday, July 16, 2018
Issue Time: 09:20AM MDT

— A HIGH flood threat has been issued for the Burro/416, Spring Creek, Junkins and Hayden Pass burn scars

— A MODERATE flood threat has been issued for the San Juan Mountains, Southeast Mountains, Raton Ridge and Chateau burn scar

 — A LOW flood threat has been issued for the Northeast Plains, portions of the Front Range, Urban Corridor and Palmer Ridge and Weston Pass burn scar

After a busy night of ongoing thunderstorms and moderate rainfall, there will be some fog and lingering showers to start this morning. The thick fog can be seen the visible satellite imagery below as well as some of the rain showers over the Southeastern Plains. Both should begin clearing after some heating later this morning. Today, some drier air begins to make its way in from the north. It won’t quite make it to southern Colorado, so the subtropical moisture will remain south of the green axis in the image below.

Under the influence of the ridge (slow steering winds), this will allow for another round of heavy rainfall over the southern mountains and Raton Ridge with more isolated activity over the Southeast Plains. Between the high moisture and antecedent rainfall, burn scars will be susceptible to flash flooding again today, which includes mud flows and debris slides. A High/Moderate flood threat has been issued for the higher terrains and burn scars. The entrainment of the dry air should limit rainfall totals on the north side of the moisture axis, but still expect showers and thunderstorms over the northern mountains this afternoon. The storms to the north will be more isolated in coverage when compared to yesterday and will produce some gusty winds. Though more isolated and less intense, thunderstorms that track near fresh burn scars should be monitored closely as it can take as little as 0.25 inches/hour to trigger flash flooding. Thus, a Low flood threat has been issued for the Weston Pass burn scar.

 

Lastly, a shortwave will move near or across the northeast corner of the state overnight, which would bring a line of organized convection to the Northeast Plains. Threats include severe hail and gusty winds after 11PM with local, heavy rainfall. With high PW values and slow moving storms there is the potential for flash flooding. A Low flood threat has been issued for this area.

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

Drier air will begin to work its way in from the north, which should lower rainfall rates this afternoon over the higher terrains. Max 1-hour rain rates up to 1 inch are possible across the southern Front Range and Urban Corridor, so a Low flood threat has been issued. Threats include local stream and road flooding with debris slides and mud flows possible over the higher terrains. Burn scars will be especially susceptible to flooding. A Low flood threat has been issued for portions of some of these regions. Elsewhere over the high terrains, max 1-hour rain rates will be closer to 0.5 inches.

Primetime: 1PM to 11PM

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

Subtropical moisture remains over southern Colorado, and with slow steering winds, heavy rainfall is likely again this afternoon. Special attention should be shown to burn scars in this area as mud flows and debris slides are likely. Max 1-hour rain rates up to 1.2 inches/hour are possible, so flash flooding is likely over this area along with mud flows and debris slides – especially with antecedent moisture. Showers and thunderstorms may linger overnight, but the flood threat should not. A Moderate flood threat has been issued.

Primetime: 1:00PM to Midnight

Palmer Ridge, Southeast Plains, Northeast Plains:

More isolated showers are expected this afternoon over the eastern plains. Overnight, a shortwave and associated convection may move over the northeast portion of the state. Should this occur, this would bring max 1-hour rain rates of 2 inches/hour. Slow storm motion and high moisture would lead to local totals exceeding 3 inches. A Low flood threat has been issued for flash flooding of streams and low-lying roads. Isolated showers and thunderstorms may linger through early tomorrow morning.

Primetime: 11PM to 8AM

Issue Date: 7/15/2018
Issue Time: 8:30 AM

A HIGH FLOOD THREAT HAS BEEN ISSUED FOR THE SPRING, WESTON PASS, AND CHATEAU FIRE BURN AREAS.
A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE NORTHERN MOUNTAINS, FRONT RANGE, SOUTHEAST MOUNTAINS, CENTRAL MOUNTAINS, URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, SOUTHEAST PLAINS, AND RATON RIDGE.
A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS, NAMELY THE 416 FIRE, BURRO FIRE, AND WEST FORK COMPLEX BURN AREAS.
A LOW FLOOD THREAT SURROUNDS THE AREAS MENTIONED ABOVE, AND INCLUDES PORTIONS OF THE NORTHWEST SLOPE AND GRAND VALLEY.

The stage is set for scattered-to-widespread thunderstorms to impact Colorado today, with plenty of moisture available for heavy rainfall. An upper-level disturbance (denoted by the red line in the water vapor image below) has shifted yesterday’s high pressure to the east, and centered a plume of deep moisture (green arrow) over Colorado. This plume of moisture will shift east a bit through the day, placing many of the state’s burn scars under the gun for heavy rain, as well as the Urban Corridor. At the surface, a cold front is advancing through eastern Colorado, with easterly flow behind the front expected to push dewpoints in the upper-50s and low-60s back into the foothills. Altogether, these moist conditions set the stage for showers/thunderstorms capable of heavy rainfall.

The bulk of shower/thunderstorm activity will occur over the area outlined by the low flood threat, with drier air limiting storm coverage over the far Northwest Slope and far Southeast Plains. Between those two drier regions, showers/thunderstorms will begin to ramp up between 11 AM and Noon, with coverage increasing through the afternoon and into the evening hours. Much of the activity will diminish after sunset, with a few showers/thunderstorms lingering into the early morning hours across the Urban Corridor, Palmer Ridge, Raton Ridge, and eastern plains.

Burn scars and urban locations are the main areas to watch today for potential flash flooding issues, due to impervious soil/man-made surfaces exacerbating runoff. Recent/ongoing fires, such as the Spring, Weston Pass, Chateau, Lake Christine, Abode, 416, and Burro will need to be watched closely for mud flows, debris slides, and flash flooding issues. The Urban Corridor will likely see flooding issues underneath strong storms, especially in poorly drained locations, such as low-lying intersections, neighborhood streets, and low points in highways bordered by concrete barriers.

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:

Scattered showers/thunderstorms are expected today/tonight, with plenty of moisture available for efficient precipitation processes. Storms will get their start around lunchtime, increasing in coverage through the afternoon/early evening, decreasing in coverage after sunset as temperatures cool. A few thunderstorms are expected to continue into the nighttime/early morning hours. Maximum rain rates are as follows:

Urban Corridor and Northeast Plains: 1.0-1.5 inches/30 minutes
Palmer Ridge and Southeast Plains: 0.8-1.3 inches/30 minutes
Raton Ridge: 0.5-1.0 inches/hour

Timing: Noon – 11 PM, with a few showers/thunderstorms continuing into the overnight/early morning hours.

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

Scattered showers/thunderstorms are expected today/tonight, capable of heavy rainfall. Burn scars deserve careful attention, especially the Spring Fire, Chateau Fire, and Weston Pass fire; high threats have been issued for those scars. Flash flooding in steep terrain, burn scar flash flooding, mud flows, and debris slides are the potential impacts. Maximum rain rates are as follows:

Front Range, Southeast Mountains, and Central Mountains: 1.2-1.6 inches/hour
Northern Mountains, San Juan Mountains, and Southwest Slope: 0.8-1.2 inches/hour
Grand Valley: 0.6-1.0 inches/hour
San Luis Valley: 0.5-0.9 inches/hour
Northwest Slope: 0.2-0.5 inches/hour

Timing: 11 AM – Midnight for the Front Range and Southeast Mountains, 11 AM – 10 PM for all other regions. A few showers/thunderstorms will linger into the early morning hours over the Front Range, Southeast Mountains, San Juan Mountains, and Southwest Slope.

Issue Date: 7/14/2018
Issue Time: 7:40 AM

A MODERATE FLOOD THREAT IS FORECAST FOR THE 416 FIRE AND BURRO FIRE BURN AREAS IN THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS REGIONS.
A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, GRAND VALLEY, NORTHWEST SLOPE, NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, FRONT RANGE, AND SOUTHEAST MOUNTAINS, WITH THE MAIN FOCUS ON RECENT/ONGOING BURN AREAS.

The mid-level high centered over southwest Colorado this morning is expected to shift eastward in response to an approaching mid-level trough today/tonight. This shift will bring moisture currently over Arizona and Utah into western Colorado, setting the stage for another day/night of scattered showers/thunderstorms over the High Country. Due to the depth of moisture associated with the moist plume, heavy rainfall will once again be a threat. Additionally, with the high pressure center centered near the area, steering flow will be weak, meaning showers/thunderstorms will by slow-movers, increasing the residence time of any rainfall. For these reasons, a Moderate Flood Threat has been hoisted for the 416 Fire and Burro Fire burn areas, as well as a broad low threat area across much of the High Country.

To the east of the mountains, temperatures will be on the rise, with high temperatures a few degrees warmer than yesterday’s readings. A couple isolated thunderstorms cannot be ruled out for locations adjacent to the Front Range and Southeast Mountains over the Urban Corridor and western portions of the Northeast/Southeast Plains, or for the preferred terrain of the Palmer Ridge and Raton Ridge. The main threats from any thunderstorm activity will be gusty winds and lightning, with periods of light-to-moderate rainfall. Relatively dry air below cloud bases will evaporate much of the precipitation before it reaches the surface. For more information on rain rates and timing, please see the zone-specific 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

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:

Mostly sunny and hot, with high temperatures a few degrees warmer than yesterday’s readings. A couple isolated showers/thunderstorms will dot areas near the Front Range/Southeast Mountains over the Urban Corridor and western portions of the Northeast/Southeast Plains, as well as the preferred terrain of the Palmer Ridge and Raton Ridge. The bulk of storm activity will produce more gusty winds than rain due to relatively dry air below cloud bases. Maximum rain rates are as follows:

Northeast Plains: 0.2-0.4 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 0.3-0.7 inches/hour
Southeast Plains: 0.5-0.9 inches/hour

Timing: 3 PM – 10 PM

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

Scattered showers/thunderstorms are expected today/tonight, beginning around lunchtime, and continuing into the nighttime hours as a weak disturbance keeps showers (and a few thunderstorms) going well past sunset. Relatively slow storm motions and the deep moisture plume require the issuance of a moderate flood threat area for the sensitive burn scars of the 416 Fire and Burro Fire, with a broad low threat area for much of the High Country (with the focus on burn scars). Maximum rain rates are as follows:

Northwest Slope and Northern Mountains: 0.4-0.8 inches/hour
Grand Valley, Southwest Slope, Central Mountains, and San Juan Mountains: 0.6-1.2 inches/hour
Front Range and Southeast Mountains: 0.4-0.6 inches/hour
San Luis Valley: 0.2-0.4 inches/hour

Timing: Noon – Midnight, with a few lingering showers into the early morning hours over the higher terrain of the Southwest Slope, San Juan Mountains, Grand Valley, and Central Mountains regions.