Issue Date: Tuesday, July 6th, 2021
Issue Time: 9:50AM MDT

— A MODERATE flood threat has been issued for the Raton Ridge and portions of the Front Range, Urban Corridor, Southeast Mountains, Palmer Ridge and Southeast Plains
— A LOW flood threat has been issued for the Central Mountains and San Juan Mountains

It is quite moist this morning over eastern Colorado with the moisture plume still overhead. Dew points east of the green dashed line below are greater than 55F, and PW at Denver was measured at 1.09 inches despite a very dry layer around 300mb. This value is close to the maximum moving average for this point in the season (!), which means storms that develop (east) are expected to have very efficient rain rates. Northwest steering flows also remain weak, and paired with training storms over the mountains, heavy rainfall accumulations are anticipated once again. Also marked below is a shortwave (orange dashed line) that will rotate around the building Great Basin High today. In addition to providing enhanced lift over the southern portion of the eastern mountains and western San Juan Mountains for storm development this afternoon, this feature will help set up a southwest to northeast boundary over the Southeast Plains this afternoon. A handful of low-end severe storms may develop along this line, which will be capable of producing severe hail, strong outflow winds and perhaps a weak tornado.  A Moderate/Low flood threat has been issued for eastern Colorado. Flood threats for today include excessive runoff (particularly over the saturated soils west), mud flows/debris slides (mountains), road flooding and field ponding.

Over western Colorado, a drier air mass (marked above) has moved over the Northern Mountains, Northwest Slope, Grand Valley and northern Central Mountains. Better moisture remains south, so storm development this afternoon is forecast to be focused over the eastern San Juan Mountains and south Central Mountains. Storms will be capable of producing a quick 0.60 inches, which over semi-saturated soils and steep terrain may cause excessive runoff and an isolate debris flow. The Low flood threat has been extended over this region for that reason.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Front Range, Southeast Mountains, Raton Ridge & Urban Corridor:

Storms should kick off by early afternoon with upslope flow and enhance lift from the incoming shortwave over the mountains. The southern Front Range and Southeast Mountains are expected to see the bulk of the storm activity today. Max 1-hour rain rates up to 1.10 inches over the mountains and 1.50 inches over the adjacent plains are possible. Storm totals will likely be greatest near the Raton Ridge with a couple rounds of rainfall forecast, and isolated storm totals up to 2.25 inches will be possible. Rainfall this afternoon and evening could lead to road flooding, local stream/creek flooding and field ponding under the stronger storm cores. Over steeper terrains, saturate soils mean excessive runoff will be possible along with mud flows and debris slides. A Moderate/Low flood threat have been issued.

Primetime: 12:30PM to 11PM

Northeast Plains, Palmer Ridge & Southeast Plains: 

A couple severe storms are possible over the plains today along a boundary that sets up. The main threats will be severe hail, strong outflow winds and heavy rainfall. A weak tornado may also be possible. Max 1-hour rain rates up to 2.25 inches will be possible and isolated storm totals up to 2.75 inches could occur. Threats include local stream, road and arroyo flooding along with field ponding.

Primetime: 2PM to Midnight

Central Mountains, San Luis Valley & San Juan Mountains:

A quick 0.60 inches from storms over the eastern/southern San Juan and Central Mountains will be possible this afternoon and early evening. With spotty, decent rainfall accumulations over the last few days, increased runoff may be possible over the saturated areas along with mud flows and debris slides. Northwesterly steering flow may push some storms into the San Luis Valley again, and isolated totals up to 0.50 inches will be possible along the valley edges. A Low flood threat has been issued for the steeper terrains.

Primetime: 1PM to 8:30PM 

Northern Mountains, Grand Valley, Northwest Slope, & Southwest Slope:

With the drying trend beginning over these regions, not much (if any) rainfall is forecast. There may be a stray storm or two north near the Continental Divide, but only light totals are forecast. Afternoon high temperatures will reach the upper 90Fs with the warmest temperatures over the Grand Valley. Flooding is NOT forecast.

 

Issue Date: Monday, July 5th, 2021
Issue Time: 10:15AM MDT

— A MODERATE flood threat has been issued for portions of the Front Range, Palmer Ridge, Southeast Mountains and Raton Ridge
— A LOW flood threat has been posted for portions of the Northeast Plains and San Juan Mountains
— The threat will persist later than normal today, lasting into the early overnight hours

A disturbance of monsoonal origin will rotate around a weak upper-level ridge today causing widespread shower and thunderstorm activity mainly over central and western Colorado today. The disturbance was located along the UT border this morning, already causing mid to high level cloud cover and a few radar returns depicting light showers. With clear skies over the rest of Colorado, plenty of instability will develop to spark slow-moving thunderstorms that will be capable of heavy rainfall. Morning Precipitable Water from the Grand Junction sounding was 0.88 inches, up slightly from yesterday. Meanwhile, the Denver sounding showed a PW of 0.80 inches. Moisture advection into the state is weak today, so moisture levels are anticipated to stay steady or increase slightly later as rainfall moistens the atmosphere.

In terms of placement of heavy rainfall today, there are several factors at play. First, cloud cover is expected to significantly limit instability along and west of the Continental Divide. While short-term moderate to heavy rainfall is certainly possible in this area, 1-hour rainfall intensity is expected to stay below flood threat thresholds. Instead, a general wetting rainfall is expected, which is excellent news for the drought-stricken area. Further east, instability up to 1,100 J/kg is expected to develop in the higher terrain and foothills immediately east of the Continental Divide, which will support heavy rainfall in stronger storms. Furthermore, slow southward storm motion will keep storms generally moving along the higher terrain, which increases the chance for outflow boundaries interacting with the terrain and causing storm training and/or stationary cells. To account for this, a Moderate flood threat has been posted for the Front Range, Palmer Ridge, Southeast Mountains and Raton Ridge. Further east, more scattered storm coverage is expected, which warrants a Low flood threat since storms will still be capable of heavy rainfall. Severe weather will also be possible today, mainly in the form of large hail. Lastly, the timing of the disturbance is such that multiple rounds of heavy rainfall will be possible, persisting into the early overnight hours.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Multiple rounds of showers and thunderstorms this afternoon and into the late evening. Max 1-hour rainfall up to 2.3 inches. A Moderate flood threat has been posted for the higher terrain and foothills east of the Continental Divide, where max 3-hour rainfall up to 3.4 inches is possible. Threats include flash flooding, debris slides, mud flows and small creek and tributary flooding. A Low flood threat has been posted farther east where storms are expected to be more of the scattered variety. Large hail will be possible with the strongest storms, especially earlier in the afternoon before coverage increases. A Low flood threat has also been posted for the San Juan Mountains where max 1-hour rainfall up to 1.2 inches is possible.

Primetime: 12pm to midnight

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

Numerous showers and thunderstorms expected later this morning, persisting into the late evening. Max 1-hour rainfall up to 0.9 inches, especially earlier in the day before rainfall transitions to a more widespread light-to-moderate intensity type. Total (24-hour) rainfall up to 1.3 inches will be possible, which is excellent news for the drought situation. Outside of the Grizzly Creek and Pine Gulch fire burn areas, flooding is NOT expected today.

Primetime: 12PM through 10PM

Issue Date: Sunday, July 4th, 2021
Issue Time: 10:15AM MDT

— A LOW flood threat has been issued for portions of the Front Range, Palmer Ridge, Southeast Mountains, Raton Ridge and Southeast Plains

We wish everyone a Happy Independence Day!

Elevated moisture continues to hang around Colorado on this Sunday. Grand Junction’s PW has fallen slightly to 0.81 inches, still well above normal but with a notable dry layer aloft as well as drying boundary layer suggesting a continued trend of lower storm coverage west of the Continental Divide. East of the Continental Divide, PW at Denver this morning was 0.89 inches, which is well above the average value of about 0.70 inches for early July. There are two features that will support heavy rainfall today. First, a weak disturbance was noted over northwest Colorado, and as this moves slowly east/southeast, it will help trigger scattered to numerous showers and thunderstorms over the higher terrain. With weak northerly steering flow, storms are expected to have a hard time making it into the lower elevations. With elevated moisture levels and plenty of sunshine this morning, a Low flood threat is warranted for basically the entire higher terrain where stronger storms could quickly drop over 1 inch of rainfall in 45-60 minutes before dissipating. Prolific storm cores, capable of causing excessive runoff, have been noted daily for the past 3-5 days and there is nothing to suggest this pattern will end today. In short, moisture is everything in our topographically driven summer circulation. The second feature we are watching is a disturbance moving south over western Kansas, which will trigger strong to severe thunderstorms over parts of the Southeast Plains today. With copious moisture, these slow moving storms will be capable of producing isolated flash flooding, along with severe weather later this afternoon and into the early overnight hours.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Southeast Plains:

Mostly sunny early with scattered to numerous showers and storms developing later this afternoon mainly along the southern KS border. Max 1-hour rainfall up to 2.8 inches will be possible, which warrants a Low flood threat for isolated flash flooding as well as some flooding for smaller creeks and tributaries. Severe weather will also be likely with the stronger storms.

Primetime: 3PM through 2AM

Palmer Ridge, Front Range, Southeast Mountains and Raton Ridge:

Scattered showers and thunderstorms developing this afternoon and lasting into the late evening hours. Max 1-hour rainfall up to 1.3 inches warrants a Low flood threat for isolated flash flooding, debris slides and mud flows especially for higher elevations.

Primetime: 12pm to 9pm

Northeast Plains, Urban Corridor, Central Mountains and Northern Mountains:

Isolated to widely scattered showers and thunderstorms this afternoon and evening with max 1-hour rainfall up to 1.2 inches over the eastern plains to 0.7 inches elsewhere. Flooding is NOT expected today.

Primetime: 12PM through 9PM

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

Isolated to widely scattered showers and thunderstorms this afternoon and evening with max 1-hour rainfall up 0.5 inches. Flooding is NOT expected today.

Primetime: 12PM through 8PM

Issue Date: Saturday, July 3rd, 2021
Issue Time: 9:45AM MDT

— A LOW flood threat has been posted for parts of the Palmer Ridge, Northeast Plains, Southeast Mountains and Raton Ridge

This morning’s atmosphere over Colorado continues to be described as generally disorganized flow, typical of summertime over our area. However, there are a couple of features that will be key to today’s weather, as shown in the low-level water vapor image below. A ripple in the flow, a.k.a. an shortwave disturbance, was noted over southeast Wyoming stretching southwestward into western Colorado. This disturbance will trek east/southeastward around a weak upper level ridge centered over the Four Corners. Scattered to numerous showers and thunderstorms will accompany it mainly over the Northeast Plains and Southeast Plains. However, one important difference with this disturbance and those of prior days is the much stronger steering flow aloft. Storm motion is expected to increase to 20-25 mph for northeast Colorado, which will generally limit point rainfall for most of the region. Nonetheless, with elevated moisture levels in eastern Colorado, a Low flood threat has been posted for parts of eastern Colorado, where outflow boundaries interacting with the Palmer Ridge terrain could provide for a period of storm training later this afternoon. Additionally, the stronger winds aloft are expected to increase the chances of a bow-echo type convective system dominated by low level outflow, which will cause damaging winds over parts of eastern Colorado if this system materializes as guidance suggests.

An additional area of Low flood threat has been posted for parts of the Raton Ridge and Southeast Mountains, where weak upslope flow and plenty of low-level moisture will support slow-moving cells capable of localized heavy rainfall and excessive runoff.

West of the Continental Divide, this morning’s PW at Grand Junction was a rather high 0.85 inches, but the profile showed a drying boundary layer as well as a marked layer of dry layer aloft. With PW expected to drop over western Colorado, we expect lower storm coverage there today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Northeast Plains, Palmer Ridge, Southeast Plains, Southeast Mountains and Raton Ridge:

Scattered to numerous showers and thunderstorms this afternoon and into late evening. Max 1-hour rainfall up to 2.0 inches (east) and 1.2 inches (west). Up to 3.5 inches of storm total rainfall will be possible over the eastern parts of the Palmer Ridge and Northeast Plains. A Low flood threat has been posted for isolated flash flooding over the plains. Over steeper terrain of the Southeast Mountains and Raton Ridge, debris slides and mud flows will be possible under the strongest storms.

A bow echo could develop across eastern Colorado this afternoon, which could cause damaging winds exceeding 60mph. Stay tuned to local NWS offices for warnings.

Primetime (south): 12pm to 9pm
Primetime (east): 2pm to midnight

Front Range, Urban Corridor, Central Mountains and Northern Mountains:

Scattered showers and thunderstorms this afternoon and into early evening. Max 1-hour rainfall up to 0.9 inches (below 5,500 feet) and 0.7 inches (above 5,500 feet). Flooding is NOT expected today. Gusty winds could accompany the strongest storm cells especially towards the WY border.

Primetime: 12PM through 8PM

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

Widely scattered showers and storms this afternoon and evening mainly over the higher terrain. Max 1-hour rainfall up to 0.6 inches. Flooding is NOT expected today.

Primetime: 12PM through 8PM