Issue Date: 8/12/2016
Issue Time: 9:48 AM

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE URBAN CORRIDOR, PALMER RIDGE, SOUTHEAST PLAINS, RATON RIDGE, SOUTHEAST MOUNTAINS, AND FRONT RANGE.

The Continental Divide defines a clear line in the sand for today’s forecast, so to speak. For areas west of the Divide, mostly sunny skies and dry conditions will rule the forecast, with only an isolated brief shower or two possible over the higher terrain near the Continental Divide. Moisture, as evident in the IPW graph below, is lower over western Colorado, with Grand Junction measuring about 0.4 inches IPW this morning. Afternoon high temperatures will be a few degrees cooler than yesterday behind the weak cool front that passed through overnight.

Along the Divide and to the east, slightly better moisture is in place, albeit not a significant amount. IPW values in the graph below show Schriever AFB and Boulder at approximately 0.6 inches, well below the 1 inch threshold that we often discuss. With some lingering moisture (mainly in the low-levels), northwest flow aloft, and light easterly surface flow, the potential exists for a few strong/severe storms to develop along the I-25 corridor south of Douglas County, including the eastern slopes of the mountains and extending east over the Palmer Ridge and south across the Southeast Plains. Any strong/severe storms in this area will have the potential to produce locally heavy rainfall; thus, the issuance of the low flood threat. For the rest of the area, isolated-to-widely scattered showers/thunderstorms will be possible, but a more subsident airmass overhead will limit their intensity and coverage. For more details 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, Northeast Plains, Palmer Ridge, Southeast Plains and Raton Ridge:

Isolated-to-scattered showers/storms expected. A few will be strong/severe, mainly across the low flood threat area. Most showers and storms will be garden variety, producing gusty winds, lightning, and light-to-moderate rainfall. Over the low flood threat area, better moisture pooling has taken place and stronger storms will be capable of producing locally heavy rainfall. Maximum rain rates are as follows:

Urban Corridor: 0.6-1.0 inches/hour
Palmer Ridge: 0.9-1.4 inches/hour
Northeast Plains: 0.4-0.8 inches/hour
Southeast Plains and Raton Ridge: 1.2-2.0 inches/hour

Timing: 1 PM – Midnight, with a few showers/storms ongoing across the Southeast Plains and Raton Ridge into the morning hours

Front Range and Southeast Mountains:

Isolated-to-scattered showers/storms expected. The best coverage will occur south of I-70. With lesser moisture than lower elevations, most storms will be garden variety, producing more gusty winds and lightning than rain. Still, brief periods of moderate-to-heavy rainfall will be possible for eastern slopes, mainly south of Highway 24. Maximum rain rates will be 0.6-1.0 inches/hour.

Timing: 1 PM – Midnight

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

A couple isolated showers/weak storms are expected across the higher terrain near the Continental Divide. Otherwise, today will be mostly sunny and dry, with high temperatures a few degrees cooler than yesterday. Maximum rain rates from any activity will be less than 0.2 inches/hour.

Timing: Noon – 8 PM

Issue Date: 8/11/2016
Issue Time: 9:58 AM

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE NORTHEAST PLAINS, PALMER RIDGE, AND SOUTHEAST PLAINS.

Current water vapor analysis shows the upper-level trough swinging across western states, with the base of the trough over the Great Basin. At the surface, a cool front is draped across the far northeast plains and back across southern Wyoming. This front will swing through eastern Colorado today, providing a focus for the development of scattered showers and thunderstorms. Out west, drier air will be transported in from the west-southwest, keeping IPW values subdued (green line = Grand Junction) and limiting shower/thunderstorm activity. A few isolated showers/storms are still expected over the higher terrain, but will mainly result in gusty winds, lightning, and periods of light-to-moderate rainfall.

Along the I-25 corridor and into the foothills, the atmospheric profile shows the same inverted-V characteristics as yesterday. This will lead any showers/storms in those areas to produce gusty winds, lightning, and light-to-moderate rainfall. Brief heavy downpours will be possible if any storms interact with others outflow boundaries, but this chance is small enough to not warrant any flood threat outlines.

Further east, moisture content is better, with IPW values between 0.9-1.3 inches for much of the eastern Plains per the latest analysis. This amount of moisture will help storms produce efficient rainfall, with storms capable of producing rain at 1.5-2.5 inches/hour. Relatively quick storm motions will help reduce the flood threat. With these considerations in mind, only a low flood threat is warranted. See discussions below for more details on timing and rain rates.

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

Scattered showers/storms are expected, with the heaviest rain/strongest storms occurring east of the I-25 corridor. Stronger storms will be capable of producing hail (up to 1.5 inches in diameter), strong winds (gusts up to 60 mph), and locally heavy rainfall. Main flooding concerns will be small streams and normally dry creeks, as well as street/field ponding. Maximum rain rates will be 1.5-2.5 inches/hour for the Palmer Ridge, Northeast Plains, and Southeast Plains, and 0.6-0.8 inches/hour for the Urban Corridor and Raton Ridge.

Timing: Noon – Midnight, with a few storms continuing into the morning hours

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

Isolated-to-widely scattered showers/storms expected, mainly over the higher terrain. The best coverage will occur over the Northern Mountains, Front Range, and Southeast Mountains, with slightly lesser coverage elsewhere. Rain rates will remain below flood threat thresholds, with maximum rates of 0.2-0.4 inches/hour.

Timing: 11 AM – 10 PM, with a few showers/storms continuing over the Front Range and Southeast Mountains until 3 AM.

Issue Date: 8/10/2016
Issue Time: 9:37 AM

NO FLOOD THREAT IS FORECAST.

Current water vapor analysis shows that the upper-level low has not moved much from yesterday’s position, sliding northeast ever so slightly. This has kept Colorado under generally southwest flow aloft, and precipitable water has remained nearly steady from yesterday’s values. More specifically, this morning’s soundings from both Grand Junction (0.76”) and Denver (0.65”) show precipitable water values hovering near average for the date. Additionally, the soundings show an inverted-V profile, indicating that the main threat from most of today’s storms will be gusty winds and lightning, with light-to-moderate rainfall.

The eastern plains (east of I-25) and portions of southwest Colorado will be exceptions to the rule today, for two different reasons:

– The plains have better low-level moisture than areas to the west, thanks to being on the eastern side of a lee trough. Dewpoints range in the 50s to low 60s, which will be enough fuel for brief periods of heavy rainfall.

– For Southwest Colorado, a better moisture influx from the south will keep IPW values near the 1 inch mark, signalling fuel for efficient rainfall.

For both areas, storm motions and a lack of strong forcing will keep rain rates below flood threat levels, thus not flood threat is warranted. Areas of southwest Colorado that have received heavy rain over the past week or so will still need to be monitored for potential mud/debris/rock slide issues should a stronger thunderstorm, relatively speaking, move overhead.

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

Isolated-to-widely scattered showers/thunderstorms expected this afternoon and evening. Most will be run-of-the-mill, producing light-to-moderate rainfall, gusty winds, and lightning. One or two storms over the plains, east of I-25, will become stronger, producing brief periods of locally heavy rainfall and small hail. No flash flooding is expected, but street/field ponding is possible underneath any strong thunderstorms. Maximum rain rates will be as follows:

Urban Corridor and Palmer Ridge: 0.4-0.6 inches/hour
Raton Ridge: 0.4-0.8 inches/hour
Northeast Plains and Southeast Plains: 0.8-1.2 inches/hour

Timing: 1 PM – Midnight

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

Widely scattered-to-scattered showers/storms expected. The best coverage, relatively speaking, will be over the Central Mountains, Southwest Slope, and San Juan Mountains. Most rain rates will be between 0.1-0.3 inches/hour, but a stronger storm or two will be possible, producing rain rates of 0.4-0.6 inches/hour. Otherwise, gusty winds and lightning will be the main threats.

Timing: 10 AM – 10 PM, with a few isolated showers lingering into the morning hours

Issue Date: 8/9/2016
Issue Time: 9:28 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE NORTHEAST PLAINS AND PALMER RIDGE.

Shower/thunderstorm activity will take a downswing today as drier air invades from the west/southwest. As shown in the water vapor image below, the low pressure trough digging along the west coast is acting to pull drier air (red colors) into the region. The moist plume across New Mexico and western Texas has been shunted to the south and east by this dry air, and IPW values have fallen in concert. With all of that said, there will be enough residual moisture to fuel isolated-to-widely scattered showers/thunderstorms; first developing over the higher terrain, and then moving northeastward over the lower elevations. Outflow boundaries from the mountain convection, as well as surface dewpoints in the 40s and 50s, will provide enough moisture for periods of heavy rain from any stronger thunderstorms that develop. The low flood threat area takes this into account. 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, Northeast Plains, Palmer Ridge, Southeast Plains and Raton Ridge:

Isolated-to-widely scattered showers/storms are expected this afternoon and evening, moving to the northeast with the steering flow. Most storms will be garden variety, producing gusty winds and lightning, with periods of light-to-moderate rainfall. A couple storms may become strong/severe over the Palmer Ridge and Northeast Plains, producing bouts with heavy rainfall. For this reason, the low flood threat has been issued. Maximum rain rates will be 0.4-0.8 inches/hour for the Urban Corridor and Raton Ridge, 0.8-1.2 inches/hour for the Southeast Plains, and 1.0-2.0 inches/hour for the Palmer Ridge and Northeast Plains.

Timing: 1 PM – 9 PM for the Urban Corridor and Raton Ridge, 3 PM – 11 PM for the Palmer Ridge, 1 PM – 11 PM for the Southeast Plains, and 3 PM – 1 AM for the Northeast Plains

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

Widely scattered showers/thunderstorms are expected this afternoon/evening. Most will be garden variety, with gusty winds and lightning being the main threats. The best chances for storms will be over the higher terrain of the Southwest Slope, San Juan Mountains, Central Mountains, Northern Mountains, and Front Range. Most rain rates will be 0.2-0.4 inches/hour, with maximum rain rates around 0.4-0.8 inches/hour.

Timing: 11 AM – 9 PM, with a few showers redeveloping over southwestern mountains during the early morning hours tomorrow in association with the next moisture surge