FTB 07-26-2017: Abundant Moisture Will Produce Heavy Rainfall

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.

Flood Threat Legend

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

STP 07-26-2017: Continuous Rain Causes Flooding Problems for Western Colorado

Issue Date: Wednesday, July 26, 2017
Issue Time: 10:05AM MDT

Summary:

Yesterday morning started with clouds over most of the state and lingering showers over the west, central portion of the state. Cloud cover helped both keep temperatures down as well as limited instability over the northern portion of the state. Higher moisture also began to pour into the eastern portion of the state throughout the day. Daytime heating helped burn off some cloud cover, and around noon, the next set of storms started firing over the higher terrain starting in the south. Over the Western portion of the state, estimated 1-hour rain rates were under an inch. However, ongoing showers and thunderstorms throughout the day made a problematic situation for 3- and 24-hour totals on already saturated soils. Several Areal Flood Advisories were issued. Storm total estimates were as high as 2 inches in the mountains with the highest reported 1-hour rainfall of 1.82 inches in Saguache County at a CoCoRaHS station. In Montrose, 0.5 inches of rain fall in 25 minutes. Another location in Montrose reported 0.85 inches in 30 minutes. Trimble, CO reported 1.1 inches in the 24-hour period. Water was flowing across Highway 141 at mile marker 3 north of Dove Creek in Dolores County. All creeks north of Dove Creek were reported to be running full and spilling into the washes west of Dove Creek that cross Highway 491.

In the Front Range, cloud cover helped limit instability along the Urban Corridor. Storms over the higher terrain had storm totals up to 1.6 inches, but most quickly dissipated or weakened as they moved into the plains except over the Palmer Divide. An isolated storm managed to hold together out over the Southeastern Plains. The winds were strong enough to blow over several trees near Lamar at 4:30PM. Storm totals were as high as 3 inches with 1-hour rain rates up to 1.5 inches. Lastly, heavy rain producing thunderstorms were able to initiate over the NE corner of the state in the higher instability during the late afternoon and evening. Storm totals were 1.5 inches. There was no flooding reported with these storms.

To see how much precipitation fell in your neighborhood the last 24-hours, check out the Precipitation Map below:

Storm Total Precip Legend

STP 07-25-2017: Plume of Monsoon Moisture

Issue Date: Tuesday, July 25, 2017
Issue Time: 10:50AM MDT

Summary:

A surge of monsoon flow yesterday brought extremely high amounts of moisture into the state. Precipitable Water was at near record levels over the western portion of the state. This allowed numerous storms began firing over the higher terrain with the upslope flow around 11am. There was nearly continuous rain in the western portion of the state yesterday that continued through this morning. Isolated light showers are ongoing over the Southwest Slope and are moving northward/northwestward. These storms should begin to dissipate just as the next round begins to fire over the higher terrain. The continuous rainfall on saturated soils again today will exacerbate the danger of debris slides, mud flows and small stream flooding.

Yesterday, the 1-hour maximum rain rates were estimated by radar to be just over 0.5 inches over the western portion of the state. The more meaningful 24-hour accumulations, on top of already saturated soils, were estimated to be as high as 1.6 inches.  Heavy rainfall was reported in Durango with 0.75 inches falling in a short period of time. Over La Plata County, heavy rain of 0.94 inches was reported. The CoCoRaHS stations in La Plata County had widespread reports of 0.75-0.85 inches. A SNOTEL site in the San Juan Mountains reported 1.30 inches falling in the 24-hour period. Gusty winds accompanied these storms with a gust of 51 mph recorded at the Grand Junction Airport. Over the Front Range, an isolated cell in Teller County dropped an estimated 1.5 inches of rain. Large rivers continue to run under Action Stage in the higher terrain and Western Slope, but small streams are likely running high and should be monitored closely throughout the day with this next round of precipitation.

As of this morning, there were no flood reports for Monday. For rainfall estimates in your area, take a look at the Precipitation Map below.

Storm Total Precip Legend

FTB 07-25-2017: Continuing Heavy Rain with Moisture Surge for the Western Slope

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.

Flood Threat Legend

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