Issue Date: 7/29/2018
Issue Time: 7:45 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHEAST PLAINS, SOUTHEAST PLAINS, AND PALMER RIDGE.

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

Colorado continues to sit underneath west/northwesterly flow aloft thanks to the upper-level high to our southwest that has refused budge. This means, yes, another day of scattered showers/thunderstorms, with most of the concerns for heavy rain/flash flooding east of the Continental Divide thanks to low-level easterly flow reinforcing good moisture for those areas. Relatively quick storm motions will be our friend and keep today from being a higher threat day than low-to-moderate; thunderstorms are expected to dump heavy rainfall as they quickly race to the southeast and east. Heavy rainfall has impacted much of far eastern Colorado the last few days, and that antecedent soil moisture combined with today/tonight’s heavy rainfall potential has prompted the moderate flood threat for those areas.

West of the Continental Divide, drier low-level air is expected to lead to a downtick in thunderstorm coverage and intensity. Orographic lift (and the close proximity of the mid-level disturbance) will generate isolated showers/thunderstorms, mainly south of I-70. In fact, north of I-70, dry low-levels combined with gusty winds have led to the issuance of Red Flag Warnings for some of those areas – please check with your local NWS office for more details. The low flood threat over the Southwest Slope and San Juan Mountains is largely due to the sensitive burn scars and the potential for brief moderate-to-heavy rainfall. In general, the main impacts from any activity will be gusty winds, light rain, and lightning. For more information on rain rates and timing, 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

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

Scattered showers and thunderstorms are expected again today/tonight. A few strong-to-severe thunderstorms will impact the area, mainly east of I-25, with the main threats being heavy rainfall, damaging straight-line winds, and large hail (up to 2.0 inches in diameter). An isolated tornado or two cannot be ruled out. While daytime heating/instability will drive the afternoon/evening thunderstorms, scattered storms are expected to continue into the early morning hours as the mid-level disturbance generates lift over the region. Plenty of moisture is available, and thunderstorms are expected to dump heavy amounts of rainfall in short periods of time. However, storm motions will be quick, helping to mitigate the flood threat. Maximum rainfall rates are as follows:

Front Range and Southeast Mountains: 0.6-1.0 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 1.0-1.75 inches/hour
Northeast Plains and Southeast Plains: 1.75-2.50 inches/30 minutes

Timing: Noon – Midnight for the Front Range and Southeast Mountains, 1 PM – 2 AM for the Urban Corridor and Palmer Ridge,1 PM – 3 AM for the Northeast Plains, 2 PM – 5 AM for the Southeast Plains and Raton Ridge

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

Isolated showers/thunderstorms, mainly south of I-70. Low-level moisture has been reduced, so the main threats will be gusty winds and brief periods of light-to-moderate rainfall from the strongest storms. Sensitive burn scars over the San Juan Mountains and Southwest Slope have been issued a low-end, low flood threat. To the north of I-70, breezy and dry conditions have led to the issuance of a Red Flag Warning for the Northwest Slope – please check with your local NWS office for more details. East of the Continental Divide in the Northern Mountains and Central Mountains regions, brief heavy rainfall remains a threat, albeit a low one, so a low flood threat has been issued. Maximum rainfall rates are as follows.

San Juan Mountains and Southwest Slope: 0.3-0.7 inches/hour
Northern Mountains and Central Mountains: 0.4-0.8 inches/hour
Northwest Slope: N/A
Grand Valley and San Luis Valley: 0.2-0.4 inches/hour

Timing: Noon – 9 PM, with a few showers/thunderstorms continuing along/east of the Continental Divide until midnight

Issue Date: 7/28/2018
Issue Time: 8:25 AM

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

The upper-level high pressure system situated to the southwest of Colorado has moved little since yesterday, leaving large-scale conditions similar to yesterday. This will lead to another period of scattered showers/thunderstorms across the state, with severe weather possible along/east of the Front Range to the CO/KS border. Moisture continues to run above normal, so heavy rainfall remains likely from all stronger thunderstorms. Working against the flood threat, however, is that storms are expected to move a bit quicker than yesterday, with storm motions generally to the east-southeast at 20-30 mph. The main areas to watch for flash flooding will be sensitive burn scars, steep terrain, and poorly drained urban areas, and this is reflected in the flood threat areas outlined in the map below.

Showers/thunderstorms will first develop over the mountains and foothills around lunchtime, spreading east-southeastward with time, exiting the state around midnight or so. East of the mountains, a few storms will reach severe thresholds, producing large hail (1.0-2.5 inches in diameter possible), strong winds (up to 70 mph), and an isolated tornado or two. For more information on rain rates and timing, 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

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

Scattered showers and thunderstorms expected again today/tonight, with a few reaching severe thresholds, especially east of I-25 and north of Highway 50. Heavy rain, strong winds, large hail, and a couple isolated tornadoes are possible. Storm motions will be quick enough to mitigate most of the flood risk, but urban areas, vulnerable terrain, sensitive burn scars, and areas that have received heavy rain over the last few days should be monitored. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.6-1.0 inches/hour
Urban Corridor and Palmer Ridge: 1.0-1.2 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.5 inches/hour
Raton Ridge: 0.3-0.6 inches/hour

Timing: 11 AM – 11 PM for the Front Range and Southeast Mountains, Noon – Midnight elsewhere

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

Another day of scattered showers/thunderstorms are expected, beginning around lunchtime, peaking in coverage/intensity during the late afternoon/early evening, and diminishing quickly after sunset. The main impacts will be gusty winds and periods of light-to-moderate rainfall, as drier air below cloud bases zaps the atmosphere’s ability to efficiently produce heavy precipitation. The best low-level moisture remains over the Southwest Slope and San Juan Mountains, thus the low flood threat continues for those regions. Maximum rain rates are as follows:

Northwest Slope, Grand Valley, and San Luis Valley: 0.2-0.5 inches/hour
Northern Mountains: 0.4-0.7 inches/hour
Central Mountains: 0.5-0.8 inches/hour
Southwest Slope and San Juan Mountains: 0.6-1.0 inches/hour

Timing: 11 AM – 9 PM, with a few lingering showers/weak thunderstorms until midnight

Issue Date: 7/27/2018
Issue Time: 9:52 AM

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

The upper-level high still sits to the southwest of Colorado, continuing to send a stream of mid-level moisture across our area. This will set the stage for another period of scattered showers/thunderstorms across the state. Precipitable water values continue to run above seasonal average, so heavy rainfall will be a threat once again. The strongest storms of the day will occur east of the Divide, where conditions are favorable for the development of a few severe storms today, especially east of I-25. Large hail, damaging winds, and periods of heavy rainfall will be the main threats, with an isolated tornado or two also possible. The good news on the heavy rainfall threat is that storm motions will be quick enough to help mitigate the flood threat, but it will not eliminate it completely. A broad low flood threat is once again in place.

To the west of the Divide, an uptick in showers/thunderstorms as compared to yesterday is expected. Just as for storms east of the Divide, storm motions will help mitigate the flood threat, but not eliminate it completely. In fact, a moderate flood threat is in place for burn scars of the Southwest Slope and San Juan Mountains regions, due to the combination of antecedent soil moisture, sensitivity of burn scars, and the threat of additional heavy rainfall. For additional information on rain rates and timing, 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

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

Scattered showers/thunderstorms expected today/tonight, capable of heavy rainfall. A few storms will become severe, producing large hail, damaging winds, and an isolated tornado or two. Relatively quick storm motions will limit the flood threat, but not eliminate it completely. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.6-1.2 inches/hour
Urban Corridor, Raton Ridge, and Palmer Ridge: 1.2-1.8 inches/hour
Northeast Plains and Southeast Plains: 2.0-2.5 inches/hour

Timing: Noon – 11 PM for the Front Range and Southeast Mountains, 1 PM – 1 AM for the Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains, and Southeast Plains

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

Scattered showers and thunderstorms are on tap today/tonight. Most will be garden-variety, but enough moisture exists for a few storms to produce periods of moderate-to-heavy rainfall, especially over southern mountains. Maximum rain rates are as follows:

Southwest Slope, San Juan Mountains, and Central Mountains: 0.8-1.2 inches/hour
Northwest Slope and Grand Valley: 0.25-0.5 inches/hour
Northern Mountains: 0.6-1.0 inches/hour
San Luis Valley: 0.5-1.0 inches/hour

Timing: 11 AM – 9 PM, with a few lingering showers/weak thunderstorms until midnight.

Issue Date: 7/26/2018
Issue Time: 8:42 AM

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

The upper-level high that has kept moisture streaming across Colorado the past few days isn’t budging much today. This means another day/night of scattered showers and thunderstorms across the state. Over the High Country west of the Continental Divide, precipitable water values will be less than yesterday as drier air works in from the west/northwest, and a downtick in storm coverage is expected for those areas. Even so, there will be enough moisture available for moderate rainfall rates, especially over southern mountains. This moisture, combined with antecedent soil moisture and burn scar concerns, are the culprits behind the low flood threat over the Southwest Slope and San Juan Mountains.

East of the Continental Divide, low-level easterly flow will reinforce moisture values, keeping precipitable water values near/above 1 inch across much of the area, but especially east of I-25. This will provide the fuel for scattered showers and thunderstorms capable of heavy rainfall. Storm motions will be a bit faster today, so that will mitigate the flood threat somewhat, reducing storm residence time over one location. With that said, however, the last few days of heavy rain will exacerbate runoff in areas that have received it, especially in areas of steep and vulnerable terrain. Thus, the issuance of the Moderate Flood Threat for portions of of the Southeast Mountains, Front Range, Urban Corridor, Raton Ridge, and Southeast Plains regions. Eastern plains areas that have received excessive rainfall will also deserve a close eye inside the low flood threat zone. 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

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

Another unsettled period of scattered showers/thunderstorms are expected, capable of heavy rainfall. Storm motions will be quicker than previous days, so the flooding threat will be mitigated somewhat. As mentioned above, areas that have received heavy rainfall over the last few days are at the highest relative risk of flash flooding issues. The wind/instability profile will be conducive to a few strong-to-severe thunderstorms, capable of producing large hail up to 1.75 inches in diameter, strong winds (gusts up to 70 mph), and an isolated tornado or two. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 1.0-1.2 inches/hour
Urban Corridor: 1.0-1.4 inches/hour
Northeast Plains, Southeast Plains, Palmer Ridge, and Raton Ridge: 1.75-2.5 inches/hour

Timing: Noon – 9 PM over the Front Range and Southeast Mountains, with a lingering shower/thunderstorm or two over the Southeast Mountains until 11 PM. 1 PM – 10 PM for the Urban Corridor and Palmer Ridge, and 1 PM – Midnight for the Northeast Plains, Southeast Plains, and Raton Ridge. A few showers/thunderstorms will linger near the CO/KS border into the early morning hours.

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

Scattered showers and thunderstorms are expected again today/tonight, though a slight downtick in coverage and intensity is expected compared to previous days. As usual, activity will get its start around 11 AM – Noon, increase in coverage through the late afternoon/early evening, and diminish as sunset rolls around. Storm motions will be quicker than previous days, to the south-southeast at 15-25 mph, so the flood threat will be mitigated somewhat. Maximum rain rates are as follows:

Northwest Slope and Grand Valley: 0.1-0.3 inches/hour
Northern Mountains and Central Mountains: 0.4-0.8 inches/hour
Southwest Slope, San Juan Mountains, and San Luis Valley: 0.5-0.9 inches/hour

Timing: 11 AM – 9 PM