Issue Date: Sunday, July 30th, 2017
Issue Time: 10:30AM MDT

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

—  LOW flood threat for Southwest Slope, San Juan Mountains, Northeast Plains

The monsoon moisture plume sticks around for another round of thunderstorms today. The Denver sounding this morning had 1.13 inches of Precipitable Water (PW), while the Grand Junction sounding had 0.93 inches with more drying in the mid-levels. Dew points over the eastern plains are as high as 65F and are also still high over the southwestern corner of the state. The high PW is marked in the water vapor image below. The mid-levels may dry out a bit over the course of the day with winds from the north, but not enough to limit heavy rainfall again this afternoon. Cloud cover continues over the southern and central mountains as well as the southern Urban Corridor, Palmer Ridge and Southeast Plains. The cloud cover will help limit temperatures again today, but has a much better chance of at least partially burning off by the afternoon allowing some instability to build unlike yesterday. With the ridge off to our north over Canada, light westerly flow will be present at the upper-levels.

Expect storms to start firing off the higher terrain just after noon to the north and a bit sooner over the south. Storms will begin to slowly move off the mountains onto the adjacent plains in the late afternoon likely favoring the higher terrain of the Palmer Divide and Raton Ridge. Storm motion will be 10-15 knots moving E/SE. Rain rates over the mountains will be as high as 1.3 inches in 1-hour with 3 to 6-hour totals up to 2 inches. There is a chance storms forming over the Cheyenne Ridge may move over the border into the Northeast Plains.

Over the San Juan Mountains, storm totals around 2 inches will warrant a Low flood threat with the antecedent rainfall. Heavy rainfall again today will create dangerous conditions over already saturated soils and burn scars. Threats include mud flows, debris slides, small stream and road flooding, so burn scars need to be watched carefully again today. Over the adjacent plains, expect storms to have max 1-hour rain rates up to 2.25 inches with 3-6 hour totals up to 4 inches. Threats include arroyo and street flooding as well as field ponding. Storms over the mountains should end a couple hours after sundown, while storms over the SE corner of the state will continue until midnight.

 

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:

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

Partly cloudy early with sunshine breaking through the clouds midday. Scattered to numerous showers and thunderstorms developing by early afternoon over the higher terrain. Max 1-hr rainfall up to 2.25 inches (adjacent plains) and 1.3 inches (mountains). Local 3-hour rainfall totals up to 4 inches over the plains. Threats include mud flows, debris slides, field ponding and arroyo and road flooding. The threat should diminish by midnight.

Primetime: 12PM to 12AM

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

Partly cloudy this morning over the southern high terrain becoming more sunny over the Central Mountains. Heavier rainfall is expected over the San Juan Mountains with max 1-hr rainfall up to 1.1 inch. 3-6 hour rainfall amounts up to 2.2 inches are possible. A Low flood threat has been posted with threats including isolated mud flows and debris slides over saturated soils.

Primetime: 11:30AM to 10PM

Issue Date: Saturday, July 29th, 2017
Issue Time: 10:35AM MDT

— MODERATE/LOW flood threat for Palmer Ridge, Northeast Plains, Urban Corridor, Front Range, Southeast Plains, Southeast Mountains, Raton Ridge, Central Mountains, San Juan Mountains and Southwest Slope

Water Vapor imagery below shows some isolated embedded showers over the mountains, with cloud cover over nearly the entire state. This cloud cover will begin to break up after strong daytime heating and should not inhibit the formation of thunderstorms today over the eastern plains. Precipitable Water (PW) values at Denver this morning were 1.21 inches and 1.17 inches at Grand Junction. Values are as high as 1.4 inches are over the Southeast Plains. This moisture is expected to stick around with the southerly and southeasterly surface winds. Some of the drier air in northern New Mexico is expected to mix into the Southeast Mountains, which will cause showers to be more isolated (but not less threatening) in nature.

Over the mountains, expect continued showers over the Central Mountains as diurnal heating will lead to an upslope flow pattern. Other storms will begin to fire early this afternoon favoring the southern mountains for the stronger convection. Storm motion will be slow once again, but eventually the storms will push off the mountains later this afternoon and move to the N/NE. Over the Southeast Plains, a boundary will set up this afternoon, which will be located in an area of high instability. Shear will be weak, so most storms should not become severe. However, slow storm motion under the ridge will allow storms to heavy precipitation along the boundary. Once again, sufficient instability will allow storms to continue well after sunset. Lingering showers could persist through about 4AM.

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:

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

Partly cloudy early with showers then scattered to numerous showers and thunderstorms developing by early afternoon. Highest coverage will be where sun is able to break through the clouds. Max 1-hr rainfall up to 2.3 inches (adjacent plains) and 1.1 inches (mountains). 3-hour rainfall up to 4 inches over the plains will support a Moderate flood threat. Threats include mud flows, debris slides, field ponding and small stream and road flooding. The threat is expected to continue over night once again.

Primetime: 1PM to 4AM

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

Mostly cloudy with scattered showers over the Central Mountains. These should increase in intensity this afternoon. Heavier rainfall is expected over the San Juan Mountains with max 1-hr rainfall up to 1.1 inch. 3-6 hour rainfall amounts up to 2.2 inches are possible. A Moderate flood threat has been posted with threats including isolated mud flows and debris slides over saturated soils.

Primetime: 12:30PM to 10PM

Issue Date: Friday, July 28th, 2017
Issue Time: 10:30AM MDT

— MODERATE/LOW flood threat for Palmer Ridge, Urban Corridor, Northeast Plains, Southeast Plains, Southeast Mountains, Raton Ridge, San Juan Mountains and Southwest Slope

This morning’s water vapor image, below shows that ample amounts of low-level water vapor are found statewide. Precipitable water (PW) values range from about 0.7 inches over the North Platte basin to 1.1 inches in the southwest corner of the state to 1.3 inches along our far eastern border. PW is expected to remain steady or increase throughout the day as southwesterly flow aloft continues to usher in moist, monsoonal air. Some stronger jet stream level winds are noted along the CO/UT border and weak upper-level divergence is supporting a mid/high cloud deck seen in the southwest part of the state. This will slightly limit instability over the western slope, though very moist low-level air will partially offset this and another round of scattered to numerous storms are expected in the San Juans and surrounding regions.

East of the Continental Divide, a tricky forecast is in store with our high resolution ensemble guidance suggesting many different possibilities today. A weak and shallow wind shift axis is noted along the I-76 axis (also accompanied by localized areas of very dense fog), possibly from last night’s outflow boundaries. This should act as a demarcation between higher heavy rainfall chances to the east and lower chances to the west. Once again, lower precipitation chances are expected north of the Denver metro due to a relative minimum in moisture content and the strongest downsloping flow. Highest storm chances today will likely be in the southeast quadrant of Colorado once again. We expect two separate areas of action. First, diurnal upslope flow combined with plenty of moisture and adequate instability will trigger slow moving storms along the foothills from Denver south through the New Mexico border. The Palmer Ridge will once again likely serve as a hot spot. Second, another separate cluster of storms is expected to fire along the aforementioned wind shift. These storms will have the potential for very heavy rainfall due to their slow motion and possibility of back-building/training of individual cells. A Moderate threat is warranted for both of these areas with a broad Low flood threat surrounding the Moderate.

Once again, with adequate instability expected to persist well after sunset, so will the chance of heavy rainfall. Activity could persist through about 2AM.

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:

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

Partly cloudy early then scattered to numerous showers and thunderstorms developing by early afternoon. Highest coverage will be along Palmer Ridge and adjacent areas to the east. Max 1-hr rainfall up to 3.0 inches (east) and 1.9 inches (west) will support a Moderate flood threat with flash flooding and small stream flooding likely. Mud flows and debris slides will be a possibility in higher elevation locations. A Low threat has been posted for broad parts of eastern Colorado. The threat is expected to persist into the early overnight hours once again.

Primetime: 1PM to 2AM

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

Mostly cloudy with scattered showers turning to thunderstorms and increasing in intensity. High rainfall coverage will be in southwest areas, especially the western portion of the San Juans. A broad Low flood threat has been posted for max 1-hr rainfall up to 1.3 inches capable of producing isolated mud flows and debris slides. A Moderate flood threat has been posted for parts of the San Juans due to an expected longer duration of heavy rainfall there.

Primetime: 12:30PM to 10PM

Issue Date: Thursday, July 27, 2017
Issue Time: 10:40AM MDT

—LOW/MODERATE flood threat for Front Range, Urban Corridor, Palmer Ridge, Central Mountains, Southeast Mountains, Raton Ridge, Southeast Plains

—LOW flood threat for San Juan Mountains, Northeast Plains

Afternoon Update (5PM): The low threat has been extended over the NE corner of the state along the NE, WY, KS border. Storms have been firing off the Cheyenne ridge this afternoon due to strong upslope flow and are moving S/SE over the state line. These storms will move into an area with PW values of 1.3 inches, high instability and 30-45 knots of shear. All of these ingredients combined are favorable for severe thunderstorm development. Threats include heavy local rain, large hail and small stream and street flooding. 1-hour rain rates will be as high as 1.9 inches and 3 hour totals up to 3.5 inches.

On the water vapor image below, the storms that persisted with the moist easterly flow overnight can be seen over the SE Plains. The High pressure has started to build back to the west and has elongated its center over NM, TX and OK. Today it will continue to build itself west and situate itself over the 4 corners region, which will cut off monsoon moisture into the region. The 500mb ridge is currently dipping into northern CO and has gained some strength since yesterday. This ridge will help produce westerly flow that will pull the drier air seen over Utah into western Colorado. Precipitable Water (PW) over the eastern portion of the state will also decrease today in the upper-levels with a more northwesterly/northerly flow. The gradient will decrease from north to south, but will still remain over 1 inch this afternoon and evening, which should be more than enough moisture for another round of heavy rainfall. Diurnal heating patterns will allow thunderstorms to fire over the higher terrain midday. Over the western slope, the limited moisture and westerly upper level flow should cause thunderstorms to be more isolated in nature and confine them to the higher terrains favoring the San Juan Mountains.

Along the Front Range and Southeast Mountains, storms will begin to organize just after noon. As they move off the mountains in the late afternoon and evening, expect a couple rounds of storms similar to yesterday. The steering winds aloft remain weak and storm motion will be S/SE at 15-20 mph. Cloud cover may limit instability over the far eastern plains, but plenty of instability from daytime heating will occur over the adjacent plains and Palmer Divide. So there is a potential for heavy, local rainfall once again today. Over the mountains, local 3 hour rainfall totals of 1.8 inches are possible. Once storms move off the mountains, stronger thunderstorms will favor the higher terrain of the Palmer Divide and could have 3 hour totals up to 3.5 inches. Outflow boundaries from storms will likely help provide low-level convergence for other storms, and an isolated storm may move into the northern portion of the state off the Cheyenne Ridge. Threats include mud flows, debris slides, gusty winds and urban and small stream flooding. Burn scars over the Southeast Mountains should be monitored closely for flash flooding, debris slides and mud flows. Fountain Creek in Colorado Springs ran into Action level yesterday evening, but should make a full recovery before the next round of storms this afternoon and evening.

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:

 Sunny this morning and drier air being entrained at the upper-levels from Utah. Limited moisture and westerly flow aloft should confine storms to the higher terrains this afternoon. Max 1-hour rain rates up to 1 inch are possible with local 24-hour totals up to 2.1 inches in the San Juan Mountains. Debris slide, mud flows and road flooding are the main threats over these saturated soils. A Low threat has been issued. Storm activity should start to subside after sundown.

Primetime: 12PM to 11PM

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

 Partly cloudy over the eastern plains this morning becoming more sunny later this morning. Front Range, Urban Corridor and Southeast Mountains should heat up rather quickly today building instability for multiple rounds of storms again today. Max 1-hour rain rates up to 1.3 inches over the higher terrain and 2.3 inches over the adjacent Plains. Burn scars will need to be monitored closely for mud flows, debris slides and flash flooding. There is a Moderate/Low flood threat issued for today.

Primetime: 12PM to 12AM