Issue Date: Tuesday, June 19, 2018
Issue Time: 10:20AM MDT

— A MODERATE flood threat has been issued for portions of the Northeast Plains, Palmer Ridge and Southeast Plains

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

The visible satellite imagery below shows some lingering high clouds from the overnight, heavy rainfall. While it may take a bit to burn off this cloud cover, breaks in the clouds indicate this is a likely scenario (at least over some areas). Breaks in clouds over Weld and Morgan County should be monitored closely because where the sun can shine through, instability can build for another round of severe thunderstorms this evening. Models indicate a boundary from the north setting off storms over the Urban Corridor tonight in the high moisture environment. If these or any other storms track over the area that received heavy rainfall yesterday, increased runoff and flooding is likely due to saturated soils. The loaded gun sounding at Denver this morning shows quite a cap, but upper level atmospheric support this afternoon should help break it. With freezing levels at 8957 feet and a humped hodograph, there will be a large hail threat and possibly a tornado for the severe thunderstorms that form this afternoon and evening.

High moisture remains over eastern Colorado again today. Dew points are forecast to be in the 50-60F range, which means the heavy rainfall threat returns. Expecting storms to fire off the southern Front Range, Southeast Mountains and Palmer Ridge later this afternoon. Storm motion today will be to the east/southeast, and models indicate that the discrete severe thunderstorms that fire further south this afternoon will eventually form a MCS over the far Southeast Plains by the early evening. A second wave of storms is expected to form later tonight as a boundary slides down from the north, which could also create some late night thunderstorms over the Urban Corridor. This second wave of storms will continue the flood threat over the Southeast Plains/Palmer Ridge overnight. A Low and Moderate flood threat have been issued due to the likelihood of road and small stream flooding, arroyo flooding and field ponding.

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:

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

Severe weather and heavy rainfall threat return once again to eastern Colorado. Expected severe thunderstorms today to produce large hail (up to 2.25 inch), gusty winds and possibly a tornado. High dew points will promote efficient rain rates as well. Should storms form over the northern Urban Corridor this afternoon, rain rates up to 1.25 inches/hour will be possible. If these storms track over Weld and Morgan Counties, expect some flash flooding due to saturated soils from heavy, overnight rain. Further south, over the Palmer Ridge and Southeast Plains, max 1-hr rain rates up to 2 inches/hour will be possible. Overnight rainfall over the eastern plains is expected and local totals by tomorrow morning could exceed 3 inches near the CO/KS border. For the storms that form over the Southeast Mountains, max 1-hr rain rates will be much lower (0.25 inches/hour) due to moisture being scoured east. A Moderate and Low flood threat have been issued for street flooding, field ponding and local stream flooding.

Primetime: 2PM – 5AM

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

Dry air continues to be entrained over the area from the southwest, which means there is no chance for rainfall again today. The strong winds yesterday associated with the passing trough have ended, which will drop the Red Flag Warning. Expect a few clouds over the Northern Mountains and Northwest Slope this afternoon, but should be clear elsewhere. High temperatures will continue to be on the increase, but highs today will be average for this time of year.

Issue Date: Monday, June 18, 2018
Issue Time: 09:55AM MDT

— A LOW flood threat has been issued for portions of the Northeast Plains, Urban Corridor and Front Range

The water vapor imagery below shows that most of the moisture associated with Bud has moved through the state and is replaced by dry southwest flow. The burn scars over the San Juan Mountains, along with much of western Colorado is now under the influence of the dry slot, which should put an end of the heavy rainfall chances. The sounding at Grand Junction this morning shows PW values have dropped to 0.58 inches. Today and tomorrow the upper low over Idaho will continue its slow eastward migration. Today, the jet streak will move over the northwest corner of Colorado and mix down strong winds to the surface. Wind gust this afternoon are expected to be in the 30-40mph range, which with dry air, returns critical fire weather. A Red Flag Warning has been issued through 8PM tonight for the lower elevations of this region.

In eastern Colorado, a surface cyclone is expected to develop over the eastern plains, which will help create severe weather for the Northeast Plains this afternoon. Threats include large hail, strong winds and the possibility of some isolated tornadoes. For the Southeastern Plains, the dry southwesterly flow will limit moisture for afternoon showers and thunderstorms. However, some dew points in the 30Fs near the Palmer Ridge may allow for a few scattered storms. With decent storm motion and direction in this area paired with lower dew points, heavy rainfall is not forecast.

Over the Northeast Plains, southeasterly to eastern flow will return low level moisture with dew points reaching the mid 50sF (west) and 60s (east). Storms are expected to fire over the Palmer Ridge and Front Range this afternoon. As they move east into the high dew points heavy local rainfall is likely. Later this evening a southwest to northeast band of showers sets up overnight near the I-76 corridor. With high low level moisture, local heavy rainfall is likely. A Low flood threat has been posted for this afternoon into early tomorrow morning. Threats include street and small stream flooding over the Urban Corridor and field ponding/street flooding near low roads over the eastern 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:

Palmer Ridge, Front Range, Urban Corridor, Northeast Plains:

High moisture returns to the Urban Corridor and Northeast Plains today. Initial set of thunderstorms this afternoon will have access to favorable severe weather parameters and high moisture. Threats include large hail, gusty winds, an isolated tornado and heavy rainfall. Max 1-hr rain rates up to 1.7 inches/hour are possible. Overnight a band of showers sets up near the I-76 corridor, which will allow for high rainfall accumulations. Max 1-hour rain rates up to 1.25 inches/hour are possible with local totals up to 2.25 inches by tomorrow morning. A Low flood threat has been issued for street flooding, field ponding and local stream flooding.

Primetime: 2PM – 5AM

Southeast Plains, Raton Ridge, Southeast Mountains:

Dry air will limit precipitation chances this afternoon. Expect isolated high clouds with limited rainfall over this area. An isolated storm may be possible over the Southeast Plain, but max 1-hour rain rates will be under flood thresholds. Over the Southeast Mountains, 1-hour rain rates up to 0.25 inches/hour are possible.

Primetime: 1PM –8PM

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

Southwest flow will pull in dry air to the area. Paired with increasing wind speeds over northwestern Colorado, a Red Flag Warning is in effect through this evening for the lower elevations. Clear skies are expected over the region with temperatures closer to average for this time of year. There is no flood threat today.

 

Issue Date: 6/17/2018
Issue Time: 9:30 AM

A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, NORTHEAST PLAINS, AND PALMER RIDGE.

A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR THE 416 FIRE AND BURRO FIRE AREAS.

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE NORTHERN MOUNTAINS, CENTRAL MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, AND SOUTHEAST PLAINS.

Remnants of Bud will continue to overlay the state today, with the best mid-level moisture shifted to the east as compared to the previous FTB period. Drier air is currently working its way in from eastern Utah, which will eventually eliminate the flood threat for the 416 Fire and Burro Fire during the evening hours. The main features to focus on for today’s main show, however, is the surface low and associated cool frontal boundary across eastern Colorado. I have denoted the location of these features, as of 8:16 AM MDT, in the surface map below. The surface convergence and wind shear along the frontal boundary, coinciding with the passage of the mid-/upper-level low this afternoon, will provide the trigger for scattered-to-widespread showers and thunderstorms today/tonight along, and to the north of, the frontal boundary.

The front isn’t expected to move much, perhaps sag southward a few miles, so the threat of training thunderstorms riding the boundary (northeast storm motions on a southwest-to-northeast oriented boundary) is the culprit behind today’s moderate flood threat. Plenty of moisture is in place for heavy rainfall, with precipitable water values ranging from 1.0 to 1.4 inches expected across the threat area.

Burro Fire and 416 Fire burn areas:

Flash flooding, debris, and rocks were reported across Highway 550 just north of Durango this morning. With the threat of rainfall still in the forecast through the afternoon hours, the moderate flood threat has been issued. The threat today is less than yesterday due to drier air moving in from the west, but with the rain that has already fallen, it will take even less today to produce more issues.

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

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

Along and north of the frontal boundary, scattered-to-widespread showers and thunderstorms are expected. With precipitable water values exceeding 1 inch, and ranging up to 1.4 inches near the CO/KS/NE border, rainfall production will be very efficient. The threat of training showers/thunderstorms producing periods of heavy rainfall is the culprit behind the moderate flood threat. To the south of the frontal boundary, a lack of focusing mechanism for shower/thunderstorm development will keep activity for isolated and sporadic. Maximum rain rates are as follows:

Northern Mountains, Central Mountains, and Front Range: 0.8-1.2 inches/hour
Urban Corridor and Palmer Ridge: 1.0-1.3 inches/hour
Northeast Plains: 1.5-2.0 inches/hour
Southeast Plains: 0.8-1.4 inches/hour
Raton Ridge and Southeast Mountains: 0.2-0.4 inches/hour

Threats: Flash flooding, street/field ponding (especially in poorly drained areas/intersections), low-lying area flooding along streams/creeks, mud flows/debris slides from impacted burn scars in steep terrain.

Timing: Noon – Midnight for the mountains, with a few showers/weak storms lingering into the early morning hours. Noon – 1 AM for all other areas, with a few storms over the Urban Corridor and Northeast Plains until 5 AM.

Northwest Slope, Grand Valley, San Juan Mountains, San Luis Valley, and Southwest Slope:

Isolated-to-scattered showers are expected today, with a few weak thunderstorms mixed in during the afternoon hours. Drier air is beginning to make its way in from Utah, so activity will end from west-to-east during the late afternoon and into the evening hours. Generally speaking, rainfall rates will be 0.1-0.3 inches/hour, with maximum rain rates as follows:

Northwest Slope and Grand Valley: 0.4-0.8 inches/hour
Southwest Slope and San Juan Mountains: 0.3-0.6 inches/hour
San Luis Valley: 0.2-0.4 inches/hour

Timing: Ongoing – 11 PM, with activity diminishing from west to east beginning around 5 PM.

Issue Date: 6/16/2018
Issue Time: 9:10 AM

8:15 PM UPDATE:

The event has not evolved exactly as expected, as cloud cover limited instability during the afternoon and early evening hours. This limited instability, combined with a more aggressive dry slot in the mid-level moisture has kept precipitation over the eastern Southwest Slope and San Juan Mountains to a minimum, and kept most of the precipitation to the west and north.

With that said, the High Impact Flood Threat remains in effect for the 416 Fire and the High Flood Threat remains in effect for the Burro Fire. Moisture is expected to rebound during the overnight hours, coupled with broad, mid-level support. This will set up an axis of showers and one or two thunderstorms, oriented southwest-to-northeast across western Colorado. This axis of showers/thunderstorms will be the one to watch. If it sets up to the west of the High Impact/High Flood threat areas, a bullet will have been dodged. If this sets up over the 416 Fire and Burro Fire, it will likely produce enough rain for all of the threats discussed earlier (flash flooding, mud flows, and debris slides). The areas are not out of the woods yet, so to speak. The prime time for this threat is Midnight – 6 AM, but the flood threat will remain in effect until 11 AM.

A HIGH IMPACT FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS – NAMELY FOR THE 416 FIRE AND LOCATIONS IMMEDIATELY DOWNSTREAM.

A HIGH FLOOD THREAT ENCOMPASSES THE BURRO FIRE AND LOCATIONS IMMEDIATELY DOWNSTREAM.

A LOW FLOOD THREAT SURROUNDS THESE AREAS AND INCLUDES PORTIONS OF THE NORTHERN MOUNTAINS, NORTHWEST SLOPE, GRAND VALLEY, CENTRAL MOUNTAINS, SOUTHWEST SLOPE, AND SAN JUAN MOUNTAINS.

Note: If necessary, a PM Update will be issued if the forecast deviates significantly.

Today begins the start of a wetter and cooler period for Colorado, and on most counts that is a good thing. 67% of the state, according to the United States Drought Monitor, is experiencing drought conditions. Rain is good. However, because of the dry conditions, two wildfires in particular have raged – the Burro Fire and the 416 Fire – and these burn scars (and points immediately downstream) are under the gun for flash flooding, mud flows, and debris slides through this FTB period.

A few major features, highlighted in the water vapor image below, are coming together to result in today’s flood threat. The remnants of Hurricane Bud are being pulled northward into Colorado by the upper-level low over the Pacific Northwest and a secondary, upper-level low circulation over the Californian Baja. These upper-level lows will provide ample, broad scale support for showers and thunderstorms across the state today/tonight, and the depth of the moisture being transported into the state will lead to efficient rainfall production. Pockets of precipitable water values over an inch have already begun invading southwest Colorado this morning, and those values will continue to spread northward throughout the day.

Additionally, for eastern Colorado, low-level moisture will be pulled in from the Great Plains. This will mainly impact the Northeast Plains and Urban Corridor, where a couple strong-to-severe storms will also be possible.

Burro Fire and 416 Fire burn areas:

Both fire burn areas, and locations immediately downstream, are under the High/High Impact Flood Threat today. It will only take rain rates of 0.25-0.5 inches/hour to produce flash flooding, mud flows, and debris slides, and those rates occur often when precipitable water values exceed 1 inch. Residents near these burn scars, especially those along the Highway 550 corridor including Hermosa need to be prepared. Durango, out of an abundance of caution since this is the first rainfall event over these burn scars, needs to be prepared, as well.

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

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

Scattered showers and thunderstorms are expected today/tonight. Most will be garden-variety, producing gusty winds and light-to-moderate rainfall. A few stronger thunderstorms will rumble, mainly north of I-70, producing small hail, strong winds, and brief periods of heavy rainfall. Most activity will come to an end by midnight, but a few lingering showers/weak thunderstorms will continue into the overnight/early morning hours. Relatively quick storm motions preclude the issuance of a flood threat. Maximum rain rates are as follows:

Front Range, Urban Corridor, and Palmer Ridge: 0.4-0.8 inches/hour
Northeast Plains: 1.0-1.5 inches/hour
Southeast Mountains: 0.25-0.5 inches/hour
Raton Ridge and Southeast Plains: 0.5-0.8 inches/hour

Timing: Noon – 11 PM, with a few lingering showers/weak thunderstorms into the early morning hours

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

Scattered-to-widespread showers and thunderstorms are expected. The Burro Fire and 416 Fire burn areas are under the gun today, due to their sensitivity to rainfall and the likely multiple rounds of showers/storms that will impact the area throughout this FTB period. 0.25-0.5 inches/hour rain rates are all it will take, and those rates will likely be exceeded by thunderstorm activity in the area. Flash flooding, mud flows, and debris slides are all threats in those areas.

Elsewhere across the High Country, other areas with steep terrain and burn scars will need to be monitored. The low flood threat is a result of this event being more of a 24-hour event rather than a 1-hour rainfall event. Widespread areas of 0.25-0.75 inches of rain are likely, with localized areas of 1-2 inches of rainfall possible.

Maximum rain rates are as follows:

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

Timing: 11 AM – 11 AM