Issue Date: Wednesday, July 26, 2017
Issue Time: 10:50AM MDT

—HIGH flood threat for portions of the Southeast Plains. There will be an ongoing threat for the Southeast Plains overnight.

—MODERATE flood threat for portions of the Northeast Plains, Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains, Raton Ridge, Southeast Plains

—LOW flood threat for nearly the entire state

Afternoon Update (5pm): The efficiency of storms thus far has been very impressive. The High flood threat will remain, but the western portion of the high threat has been been dropped. Storms currently firing over the Palmer Divide are expected to move southeast later this evening, thus the high threat has been extended north. These heavy rainfall producing storms will last into the night, and showers may linger into the early morning hours. More drying has occurred over the Western portion of the state, so the Low threat has been pulled back to areas that have the better moisture and lift.

Moisture is abundant this morning across the entire state with both Denver and Grand Junction soundings showing very juicy low and mid-levels.  Precipitable Water (PW) at Denver was 1.21 inches and Grand Junction was measured at 1.41 inches. Dew points readings on the plains are as high as 64F in the northeast corner of the state with at least 60F over most of the eastern plains. A stationary front was draped across the Northeast Plains early this morning, which is responsible for the stratus deck over the Northeast Plains and northern portion of the Urban Corridor. Monsoon flow remains in place today with southwest winds in the upper levels due to the High pressure centered over Oklahoma. Early this morning, there were also lingering light showers over the Central and Northern Mountains.

Today, the moisture will remain in tack in both the lower and mid-levels, but cloud cover may limit where instability can build. Along the Front Range, storms will favor the higher terrains for initiation around noon. As they move off the mountains in the late afternoon, storms should survive along the Urban Corridor. Cloud cover may limit how far east these storms are able to survive, but some isolated storms could survive further east along the southern portion of the Front Range within the higher-elevated Palmer Ridge. Rain rates up to 1.75 inches per hour are possible with 3-hour totals up to 2.6 inches.

The Southeast Plains are able to build a decent amount of instability this afternoon. There also appears to be some weak shear, so this environment should be primed for heavy rainfall and possibly a few severe storms. After storms begin moving off the higher terrain, models show a Mesoscale Convective System (MCS) forming that will persist well into the night and early morning hours. Storm motion will be the east/southeast at 15 knots, so very widespread, heavy rainfall is likely. Localized 3-6 hour totals exceeding 4.5 inches are likely. Threats include small hail, gusty winds, field ponding and small stream and road flooding. Over the Southeast Mountains, burn scars should be monitored closely today with the high moisture and widespread, heavy rainfall. Threats over the steeper terrain include small stream and road flooding, debris slides and mud flows.

Over the western portion of the state, moisture mixes out a bit compared to the last couple of days. However, PW still remains high enough that localized, heavy rainfall will occur over the higher terrain with upslope flow beginning midday. The more easterly movement of the storms should keep storms confined to the higher terrain. Over already saturated soils, there is still a threat for debris slides, mud flows and road flooding. Small streams have already been reported as running high, so these need to be monitored closely for road flooding. 1-hour rain rates will be just under 1 inch, but localized 24-hour totals could be as high as 2.1 inches.

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, scroll below the map.

Zone-Specific Forecasts:

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

Cloudy this morning over the northwest with skies partially clearing before upslope flow begins around 11AM. Max 1-hour rain rates just under 1 inch are possible with local 24-hour totals up to 2.1 inches. Debris slide, mud flows and road flooding are the main threats. A Low threat has been issued for the higher terrain portions of the region. Storm activity should start to subside after sundown, but some storms may linger until midnight.

Primetime: 11AM to 12AM

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

Partly cloudy over the Northeast Plains and northern Urban Corridor. Clouds will begin to break up along the Urban Corridor, but not as much over the Northeast Plains, which will limit instability. Max 1-hour rain rates up to 1.75 inches will be possible which could cause urban and small stream flooding. Burn scars will need to be monitored closely for mud flows, debris slides and flash flooding. Over the adjacent plains, localized 3-6 hour totals will likely exceed 4.5 inches. There is a High/Moderate flood threat for the storms over the Southeast Plains that continues overnight.

Primetime: 12PM to 4AM

Issue Date: Tuesday, July 25, 2017
Issue Time: 10:20AM MDT

 —LOW/MODERATE flood threat for portions of the Northwest Slope, Northern Mountains, Grand Valley, Central Mountains, Southwest Slope, San Juan Mountains, Front Range, Urban Corridor, Northeast Plains

The surge of monsoon moisture yesterday brought nearly continuous thunderstorms and showers to the western portion of the state yesterday. After sundown, showers continued over the Southwest Slope and moved northward throughout the morning hours. Light precipitation is still occurring under some of the deeper plumes. Cloud cover from this complex of storms can be seen in the visible satellite image below. This satellite image reflects how much moisture has returned with this surge and will play a role in the heavy rainfall 24-hour totals today. Precipitable Water (PW) was measured at 1.31 inches in Grand Junction this morning, which is near record levels! In Denver, PW was at 0.69 inches but is forecasted to rise throughout the day to over 1 inch.

 

A High pressure center is currently positioned over the Texas Panhandle, with a trough off the coast of northern California. These features, along with the weak upper-level ridge to our southeast, is helping transport the monsoon moisture northward. PW is forecasted to rise over 1 inch nearly statewide by early this afternoon, with the western slope still slightly increasing. This moisture has and will continue to reach the higher terrain west of the Continental Divide. With steering flow aloft being 10-15 knots, heavy and widespread rainfall is expected. Current storms will continue to move north/northwest with the vorticity maximum and the next set of storms will begin to fire over the higher terrain just after noon. Although 1-hour rain rates will won’t likely be higher than 1-inch per hour, 3-hr totals up to 1.8 inches are possible and 24-hour totals up to 2 inches. This additional precipitation will be enough to trigger mud flows, land slides, small stream and road flooding especially over burn scars and locations that have accumulated a lot of rainfall the last few days.

Further east, cloud cover should begin to burn off in the late morning hours. Where the sun is able to shine through, more instability will be able to build during the early afternoon. The more easterly movement of the storms will allow them to drift into the adjacent plains in the late afternoon. Higher terrain areas along the Palmer Divide in the southern Urban Corridor will be favored for the heavier rain-producing thunderstorms initially. Rain rates up to 1.1 inches per hour are conceivable with 3-hr rates up to 1.8 inches. Over the Northeast Plains, there is a possibility for some severe storms as long as cloud cover doesn’t become an issue and outflow boundaries help trigger surface convergence. With higher PW, thunderstorms could produce heavy rainfall. Rain rates up to 1.75 inches per hour are possible with 3-hr rates up to 2 inches. Gusty winds, 1-inch hail, field ponding and road flooding are possible with the more severe thunderstorms.

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, scroll below the map.

Zone-Specific Forecasts:

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

Cloudy this morning with some lingering showers moving to the north. Max 1-hour rain rates up to 1 inch are possible with 24-hour totals up to 2.3 inches. Debris slide, mud flows and isolated flash flooding will be possible. A Moderate threat has been issued for western portions of the region with a Low covering all areas that have had lots of rain the last few days. Storm activity should start to subside after sundown, but some storms may linger until midnight.

Primetime: 11AM to 12AM

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

Partly cloudy becoming sunny with cooler temperatures where cloud cover persists. Over the high terrain, more isolated showers over the Southeast Mountains and more widespread up north. Max 1-hour rain rates up to 0.8 inches will be possible. Over the adjacent plains, max 1-hr rain rates up 1.1 inches possible with 3-hr totals near 1.8 inches. Gusty winds and small hail will likely accompany the bigger storms that form. There is a Low flood threat.

Primetime: 12PM to 12AM

Issue Date: Monday, July 24, 2017
Issue Time: 10:45AM MDT

— MODERATE/LOW flood threat for Northwest Slope, Grand Valley, Central Mountains, Southwest Slope, San Juan Mountains

This morning’s GOES-16 low-level water vapor image, below, shows a classic monsoon flow pattern across the Four Corners region. A weak upper-level high is centered over central Colorado, with drier air to its east and moist air on its west side. Ongoing showers and storm activity can be easily seen in Arizona and New Mexico. Despite some suggestion even a few days ago that drier air will impinge on western Colorado, this has not occurred. In fact, this morning, surface dew point temperatures are approaching near 60F on the southwest side of the San Juans – a very high reading for this region. Precipitable water (PW) values are over 1 inch along the southwest CO border with NM and UT. PW is expected to gradually increase through the day as clockwise flow around the ridge, combined with outflow boundaries will increase boundary layer moisture. Weak steering winds this morning will turn northeast at 10-15 mph, which is slow enough to allow for heavy rainfall to accumulate at any given locale. A Moderate flood threat has been posted for climatologically favored foothills in the San Juans Mountains as well as the Uncompahgre and Roan plateaus. Mud flows and debris slides will be the primary risk today, though isolated flash flooding will also be possible.

Farther east, lower boundary layer moisture today suggests lower rainfall intensities compared to the past few days. Although the Palmer Ridge has witnessed rainfall rates on the high side of ensemble guidance over the last 48-72 hours, today’s guidance shows a large enough drop compared to yesterday that even “worst-case scenario” type intensities should remain below flood threat levels.

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, scroll below the map.

Zone-Specific Forecasts:

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

Partly cloudy early then scattered to numerous showers and thunderstorms developing by late morning. Max 1-hour rain rates up to 1.3 inches, with max 24-hour rates up to 2.3 inches. Mud flows and debris slides will be the primary threat, though isolated flash flooding will also be possible. A Moderate flood threat has been issued for western parts of the region, with a Low threat surrounding that. Storm activity will be possible through the late evening hours, as a steady supply of monsoon moisture gets advected northward.

Primetime: 11:30AM to 1AM

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

Sunny early then becoming partly cloudy with isolated showers and a weak thunderstorm possible this afternoon. Max 1-hour rainfall up to 1 inch will be possible. Gusty winds could accompany the strongest cells. Flooding is not expected today.

Primetime: 1PM to 8PM

Issue Date: Sunday, July 23, 2017
Issue Time: 09:40AM MDT

—LOW flood threat for portions of the Front Range, Urban Corridor, Central Mountains, San Juan Mountains, Southwest Slope, Southeast Mountains, Southeast Plains, Raton Ridge

With the upper-level ridge off to the northwest of Colorado and the High pressure over Utah, drier air has moved into the state which can be seen in the water vapor imagery below. Throughout the day, the ridge will move slightly to the east, but the large-scale wind pattern will not allow ample monsoon moisture to return to Colorado. Precipitable Water (PW) this morning at Denver was 0.81 inches and 0.62 inches in Grand Junction with large amounts of drying in the upper-levels. This should limit the widespread potential for heavy rainfall as compared with the last few days.

 

Daytime heating will help build some instability over the mountains just as upslope flow begins around noon. There should still be enough moisture in the atmosphere for thunderstorms to fire over the southern mountains, but they will be more isolated in nature when compared to the last few days. Most storms will be confined to the high country and quickly evaporate as they move off the mountains, but one or two storms over the immediate and adjacent plains cannot be ruled out further south. Local, heavy rain is still possible for the stronger isolated thunderstorms. The main threats today will be debris slides over saturated soils, small stream and road flooding, gusty winds and small hail with the more severe storms.

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, scroll below the map.

Zone-Specific Forecasts:

 

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

Sunny this morning with storms beginning to form over the higher terrain around noon. Storms should be mostly confined to the higher terrain with an isolated storm over the adjacent plains possible. Overall, the rainfall will be more isolated in nature with 1-hour rain rates up to 1.3 inches in the mountains and 1.6 inches over the adjacent plains. 3-hr totals up to 2 inches are possible. Storms will start to dissipate after sundown and quickly come to an end. There is a Low flood threat for today.

Primetime: 12PM to 10PM

Northwest Slope, Northern Mountains, Central Mountains, Grand Valley, Northeast Plains, Front Range, Palmer Ridge:

Sunny today with temperatures slightly cooler than yesterday. Rain rates over the higher terrain will be as high as 0.8 inches per hour with 3-hr totals near 1.3 inches. Gusty winds will likely accompany the bigger storms that form. There is no flood threat.

Primetime: 12PM to 10PM