Issue Date: Tuesday, July 18, 2017
Issue Time: 10:35AM MDT

—MODERATE flood threat for Northeast Plains, Southeast Mountain burn scars

 —LOW flood threat for portions of the Front Range, Urban Corridor, Palmer Ridge, Northeast Plains

The ridge starts to build a bit north today but Westerlies will remain in place over the northern portion of the state. The showers over northwest CO will begin to move to the northeast and dissipate later this morning. Partly cloudy skies will be left in its wake and cooler high temperatures for this portion of the state.  As temperatures being to heat up for the day, upslope flow will set up and trigger thunderstorms in the high country and a few isolated storms over the Palmer Divide. Storms in the central mountains and San Juan Mountains will have max 1-hr rain rates up to 0.75 inches. Precipitable Water values will increase over the Northeast Plains to over 1 inch this afternoon. Over Front Range and Southeast Mountains, there will be better access to this moisture for the slow moving storms. A Moderate flood threat has again been placed over burn scars over in the Southeast Mountains due to sufficient confidence storms that form will produce over 0.5 inches per hour. There is also a Low threat over the Front Range and Palmer Ridge intersect that will provide ample lift for storms in a moisture friendly environment. Storms that form will produce flash flooding, gusty winds and small hail. Threats include mud slides, debris flows, urban and small stream flash flooding.

Over the Northeast Plains, a Moderate flood threat has been issued due to the high moisture and stronger dynamics this afternoon. Some isolated thunderstorms will form along a surface boundary near the NE and KS borders. Storm motion will be to the south/southeast. There will be moderate instability that will build throughout the day with the boundary triggering the storms early this evening. Some shear will exist helping sustain the thunderstorms. Max 1-hr rain rates up to 2.2 inches are forecasted accompanied by strong winds, heavy rain and hail up to 1 inch in diameter. 3-hour totals up to 3.3 inches will be possible. Threats include field ponding, small stream flooding and localized street flooding.

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, Northern Mountains, Central Mountains, Southwest Slope, San Juan Mountains, San Luis Valley, Raton Ridge:

Partly cloudy today over the NW portion of the state as the disturbance moves to the northeast. Isolated showers will form over the higher terrain this afternoon. Higher rain rates will be confined to the Central and Southern Mountains with rain rates up to 0.75 inches per hour. Storms will have gusty winds and small hail. There is no flood threat for today.

Primetime: 12PM to 1AM

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

Sunny this morning becoming partly cloudy this afternoon as storms begin to form over the higher terrain and Palmer Divide. Storms will have rain rates up to 1.2 inches per hour in the mountains and adjacent plains. Due to saturated soils, flash flooding, small stream flooding, mudslides and debris flows are possible today over burn scars. A Moderate threat has been issued over the burn scars on the SE Mountains due to sufficient confidence storms that form will have rain rates greater than 0.5 inches. A Moderate threat is also in place over the Northeast Plains where a surface boundary will trigger storms early this evening. Max 1-hr rain rates up to 2.2 inches can be expected with these storms with 3-hr totals of 3.3 inches.

Primetime: 12PM to 1AM

Issue Date: Monday, July 17, 2017
Issue Time: 10:25AM MDT

—MODERATE flood threat for Hayden Pass burn scar

—LOW flood threat for portions of Northern Mountains, Central Mountains, Front Range, Southeast Mountains, San Juan Mountains and Southeast Slope

A high pressure ridge continues to hold over Colorado, Nebraska and Wyoming today. With the ridge north of Colorado, limited SE and SW flow at the surface will cap the amount of moisture pulled into the state. There is strong drying over northeastern CO today and the circulation over the SE portion of the state will move into KS limiting storm potential on the Southeast Plains. Precipitable Water (PW) at Denver this morning was 0.84 inches and 0.79 inches in Grand Junction. These are not forecasted to rise much throughout the day. Enough moisture remains in the mountains for thunderstorms to fire again with upslope flow this afternoon. Storms will form more numerously in the northern portion of the mountains compared to yesterday.

As storms begin to move SE off the higher terrain this afternoon, they are expected to weaken. The better moisture remains off to the east over KS and NE. Due to saturated soils in the mountains, expect some extra runoff with storms that form. Moisture will favor the southern mountains and be more widespread in coverage. Recent burn scars in the Southeast Mountains need to be monitored closely as there is sufficient confidence storms that form will have rain rates greater than 0.5 inches. Heavy rainfall could cause local flooding, debris slides and mud flows over the already saturated soils. Storms over the high terrain will begin to dissipate around 10PM.

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, Northeast Plains, Palmer Ridge, San Luis Valley, Southeast Plains

Mostly sunny today. Isolated showers will form over the higher terrain this afternoon. When they move off the higher terrain, they are expected to weaken quickly. Max 1-hr rain rates of 0.7 inches and storms will begin to dissipate around 10PM. There is no flood threat for today.

Primetime: 12AM to 11PM

Northern Mountains, Central Mountains, Front Range, Urban Corridor, San Juan Mountains, Southeast Mountains, Raton Ridge, Southwest Slope:

Sunny this morning becoming partly cloudy this afternoon as storms begin to form over the higher terrain. Max 1-hr rain rates are expected to be as high as 1.2 inches. Storms will quickly weaken as they move off the higher terrain. Due to saturated soils, flash flooding, small stream flooding, mudslides and debris flows are possible today. A Low threat has been issued. Burn scars need to be monitored closely again today as there is sufficient confidence storms will produce rain rates greater than 0.5 inches per hour. A Moderate flood threat has been posted for the Hayden burn scar due to moist soils from antecedent rainfall the last three days.

Primetime: 12PM to 12AM

Issue Date: 7/16/2017
Issue Time: 8:05 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHEAST PLAINS, SOUTHEAST PLAINS, RATON RIDGE, PALMER RIDGE, URBAN CORRIDOR, FRONT RANGE, SOUTHEAST MOUNTAINS, CENTRAL MOUNTAINS, AND SAN JUAN MOUNTAINS.

The flood threat will continue today, but the good news is the threat is lower with a downtick in the number of showers/thunderstorms expected. This morning’s visible satellite image paints the picture that shows clearer skies overall to start the day, with the most activity occurring across eastern Colorado nearest the slow-moving mid-level disturbance. As the disturbance slowly continues eastward, drier air will filter in from the north, helping to limit (not completely eliminate, though) showers/thunderstorms across the Northern Mountains, northern Front Range/Urban Corridor, and Northeast Plains. Further to the south, moisture will hang on, leaving the opportunity for heavy rainfall in the forecast.

Across the western slope, isolated showers/thunderstorms will fire up over the higher terrain due to orographic effects and daytime heating, but with much less intensity and coverage than previous days. The threat of heavy rainfall still exists across the San Juan Mountains, due to the availability of better moisture from the south, so the low flood threat is extended to cover this region. For more specific details, please see the zone-specific forecast discussions below.

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

Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains, and Southeast Plains:

Isolated-to-scattered showers/thunderstorms expected, with the best coverage across the Southeast Plains and Raton Ridge. Drier air filtering in from the north will help limit coverage to “isolated” across the Northeast Plains, Palmer Ridge, and Urban Corridor. At any rate, moisture and storm motions will still be favorable for periods of heavy rain, so the low flood threat is warranted. Maximum rain rates are as follows:

Urban Corridor and Palmer Ridge: 1.0-1.5 inches/hour
Northeast Plains: 1.0-2.0 inches/hour
Southeast Plains: 1.5-2.5 inches/hour
Raton Ridge: 1.0-1.8 inches/hour

Timing: 2 PM – 11 PM

Front Range, Southeast Mountains, Central Mountains, San Luis Valley, and San Juan Mountains:

Isolated-to-scattered showers and thunderstorms expected, with the best coverage south of I-70. Periods of locally heavy rainfall are possible, and may exceed flash flood thresholds for areas covered by the low flood threat. Burn scars, poorly drained areas, and locations that have received heavy rain over the past several days are the main concerns. Maximum rain rates are as follows:

Front Range: 0.8-1.4 inches/hour
Southeast Mountains: 1.0-1.5 inches/hour
Central Mountains and San Juan Mountains: 0.8-1.2 inches/hour
San Luis Valley: 1.0-1.4 inches/hour

Timing: Noon – 11 PM

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

A few isolated/widely scattered showers/thunderstorms are expected across these regions, but it will otherwise be mostly sunny and hot, especially for lower elevations. The Southwest Slope will experience the best coverage of showers/storms due to its proximity to better moisture. Maximum rain rates are as follows:

Northern Mountains, Grand Valley, and Southwest Slope: 0.4-0.8 inches/hour
Northwest Slope: 0.3-0.7 inches/hour

Timing: Noon – 11 PM

Issue Date: 7/15/2017
Issue Time: 8:00 AM

A MODERATE FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE URBAN CORRIDOR, FRONT RANGE, SOUTHEAST MOUNTAINS, PALMER RIDGE, SOUTHEAST PLAINS, AND NORTHEAST PLAINS. A LOW FLOOD THREAT ENCOMPASSES THOSE AREAS, AND INCLUDES PORTIONS OF THE RATON RIDGE, CENTRAL MOUNTAINS, AND SAN JUAN MOUNTAINS.

Underneath the upper-level ridge sits a mid-level disturbance and ample moisture, which will be the main culprits behind another active forecast for today’s period. Comparable to yesterday, storm motions will be fairly slow as steering winds are weak, so expect another day where the main threat from thunderstorms is heavy rainfall. These slow storm motions are evidenced by the ongoing convection over eastern Colorado.

Every region across the state should see at least one shower/storm, with the most activity occurring along and south of I-70. A few showers/storms will persist overnight, mainly across the eastern plains/Palmer Ridge as the disturbance continues to slowly drift towards the CO/KS border. For more information on timing and rain/rates, please see the zone-specific forecast discussions below.

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

Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains, and Southeast Plains:

Scattered showers/thunderstorms are expected today/tonight, with slow-storm motions keeping heavy rainfall the main threat. Localized ponding issues will occur in poorly drained areas (urban and rural) under most thunderstorms, with a moderate flash flood threat due to stronger thunderstorms. Maximum rain rates are as follows:

Urban Corridor, Raton Ridge, and Palmer Ridge: 1.5-2.0 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.5 inches/hour

Timing: Ongoing – Midnight, with scattered showers/thunderstorms persisting mainly over the Northeast Plains and Southeast Plains into the morning hours tomorrow.

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

Scattered showers/thunderstorms are expected, with the bulk of activity occurring along and south of I-70. Burn scars are the primary concern for the flash flood threat today, as well as areas that have received recent heavy rainfall. Activity will ramp up around 11 AM this morning, increasing in coverage through the afternoon/early evening hours, and then diminishing through the later evening/nighttime hours. Most (if not all) activity should come to an end by midnight. Maximum rain rates are as follows:

Northern Mountains, Northwest Slope, Southwest Slope, and Grand Valley: 0.4-0.8 inches/hour
Front Range, Southeast Mountains, and Central Mountains: 0.9-1.4 inches/hour
San Juan Mountains and San Luis Valley: 0.7-1.1 inches/hour