Issue Date: 8/01/2015
Issue Time: 10:18 AM

A LOW FLOOD THREAT HAS BEEN ISSUED FOR THE FOLLOWING REGIONS: SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, SOUTHEAST MOUNTAINS, CENTRAL MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, AND NORTHEAST PLAINS.

Current observations show the broad, high pressure ridge continues to sit across the western US, with the mid-level circulation center over southeast NM. This overall setup will remain throughout this forecast period, allowing for the stream of subtropical moisture to continue flowing into Colorado. Precipitable water values continue to be above average statewide, with the best moisture across southern and western portions of the state. Embedded in the flow aloft is a disturbance that will work across southern and southwestern Colorado today/tonight, acting as a trigger for scattered mountain thunderstorms. Further north across the mountains, orographic effects will be responsible for the development of isolated thunderstorms.

Weak steering winds aloft will make it difficult for storms to move over the lower elevations of eastern Colorado, but a few isolated storms are expected to do just that. Western portions of the Raton Ridge, Southeast Plains, and Palmer Ridge, as well as the Urban Corridor along and south of I-70, will see a couple isolated thunderstorms this afternoon/evening. Heavy rain will be a threat with current moisture values, but a lack of organizational support aloft will mitigate the threat. In spite of this, efficient rainfall processes will occur. Maximum rain rates are discussed below in the zone-specific forecasts. Elsewhere across eastern Colorado, mostly sunny skies and hot temperatures will be the main story.

The Northeast Plains will hold a slight chance of seeing a couple of isolated thunderstorms this afternoon/evening, as a weak surface trough will lay across the area. Plenty of surface heating and moisture will be available to produce thunderstorms, the question is whether or not they can overcome the mid-level warm layer that will try and hold them down. If storms can develop, they will bring a threat of heavy rain and small hail, as well as gusty winds and lightning.

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, Raton Ridge, Palmer Ridge, and Southeast Plains:

Isolated thunderstorms are expected this afternoon for the Urban Corridor (mainly along and south of I-70), and western portions of the Raton Ridge, Southeast Plains, and Palmer Ridge. The Northeast Plains conditional chances are described above. Slow-moving storms near the higher terrain are a concern, mainly for urban areas. Maximum rain rates are as follows:

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

Timing: 1 PM – 9 PM, with a thunderstorm or two lingering until just after midnight over the Northeast Plains.

Northwest Slope, Northern Mountains, Front Range, Central Mountains, and Grand Valley:

Isolated thunderstorms are expected to develop early and continue into the evening hours before diminishing with the loss of daytime heating. Rain rates will mainly stay in the 0.2-0.4 inches/hour range, but a stronger storm over the Central Mountains and Front Range could result in maximum rain rates of 0.8-1.2 inches/hour. Slow-moving storms will be a concern over the Front Range and Central Mountains. Otherwise partly sunny skies will prevail with warm temperatures.

Timing: 11 AM – 8 PM, with a couple showers/weak thunderstorms lingering over the Central Mountains until about 11 PM.

Southeast Mountains, San Luis Valley, San Juan Mountains, and Southwest Slope:

Scattered showers and thunderstorms are expected today and tonight, with a few continuing into tomorrow morning across the San Juan Mountains and Southwest Slope. Efficient rainfall processes will occur with the amount of moisture available, so heavy rainfall from slow-moving storms will be a threat. Maximum rain rates will be 1.2-1.6 inches/hour, or 1.8-2.4 inches over 3 hours. Burn scars and saturated soils should be watched closely for issues, as they will be most susceptible to flash flooding/mud flow issues.

Timing: 11 AM – 10 PM, with a few showers and thunderstorms continuing into tomorrow morning.

Issue Date: July 31, 2015
Issue Time: 10:20AM

— Moderate flood threat for San Juans and Southeast Plains
— Low flood threat for Palmer Ridge, Southwest Slope, Southeast Mountains, San Luis Valley and Raton Ridge

This morning’s water vapor image, below, shows the continuation of a subtropical moisture feed that has elevated precipitable water (PWs) values to well above an inch in the Four Corners region. In addition to this feature, a strong jet is noted just northeast of Colorado. The presence of this jet allowed for very strong wind gusts to be transported from the upper atmosphere down to the surface yesterday as intense thunderstorms crossed the Northeast Plains. Surface dew points continue to run high, in the 50s to lower 60s across most of the state, with lower values in the northwest. PWs ranged from 0.6 (and climbing) inches in Grand Junction to near 1 inch in Boulder to 1.3 inches in Pueblo. Thus, there is ample moisture for a heavy rainfall threat.

For today’s weather evolution, we expect mostly sunny skies this morning to lead to thunderstorm activity by early afternoon. Most action today will be focused on the higher terrain, south of I-70 with some spillover onto the Palmer Ridge. High moisture content and adequate instability will support heavy rain rates capable of flash flooding. A Low flood threat has been posted for much of the higher terrain across southern Colorado. A Moderate threat is in place for the San Juans due to higher storm coverage. While most activity should subside by evening, a complex of storms may be ongoing across northeast New Mexico that could clip southeast Colorado. Very heavy rainfall, up to 2.8 inches per hour will be possible with these storms, warranting a Moderate flood threat for that region as well.

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

San Juans, Southwest Slope, Southeast Mountains, San Luis Valley, Palmer Ridge, Raton Ridge:

Mostly sunny early with scattered to widespread thunderstorms forming by early afternoon. Highest coverage will be in the southwest. Max 1-hour rain rates up to 1.3 inches will be possible, leading to isolated flash flooding, mud flows and debris slides. In addition, gusty winds up to 50 mph will be possible with the strongest storms. Activity will subside shortly after sunset. Due to higher coverage, a Moderate flood threat is in place for the San Juans, with a Low threat elsewhere.

Primetime: 1PM to 8PM

Southeast Plains:

Sunny early, then scattered thunderstorms developing by mid afternoon. Closest to the mountains, these storms will be capable of rain rates up to 1.3 inches per hour. Isolated flash flooding may be possible, warranting a Low flood threat. In the southeast corner, ongoing storm activity will likely spill over from New Mexico by early evening, and continuing through around midnight. With PW values as high as 1.6 inches, these storms could produce rain rates up to 2.8 inches per hour, and 4 inches per 3 hours. A Moderate flood threat is in place.

Primetime: 1PM to 8PM near the mountains, 3PM to 1AM in the far southeast

Northeast Plains, Front Range, Urban Corridor:

Mostly sunny early, then partly cloudy with isolated thunderstorms possible. Max 1-hour rain rates up to 0.7 inches are possible, along with gusty winds up to 45 mph. Flooding is not expected today.

Northwest Slope, Northern Mountains, Grand Valley, Central Mountains:

Mostly sunny early, then partly cloudy by mid afternoon. An isolated thunderstorm cannot be ruled out, especially farther south in the Central Mountains. However, max 1-hour rain rates will be limited to about 0.6 inches. No flooding is expected. Gusty winds up to 45 mph may accompany the strongest storms.

Issue Date: 7/30/2015
Issue Time: 10:15 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHEAST PLAINS, RATON RIDGE, SOUTHEAST MOUNTAINS, SAN JUAN MOUNTAINS, AND SOUTHWEST SLOPE.

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

The broad high-pressure ridge aloft will remain anchored to the south-central US, building slightly west and north throughout the day today. This will continue streaming subtropical moisture into Colorado, mainly south and east of a line from Logan County through Montrose County. North and west of that line, drier, westerly flow will continue and keep precipitable water values below average. This line that divides the moisture breaks the forecast into two distinct forecasts.

To the north and west of the line, mostly sunny skies and warm temperatures will rule the day, with only a few isolated showers/weak thunderstorms possible over the higher terrain of the Front Range, Central Mountains, and Northern Mountains, with one or two moving over the northern portions of the Urban Corridor and Northeast Plains. Gusty winds and lightning will be the main threats from these storms, with modest rain rates (0.4-0.8 inches/hour).

The main action today and tonight will occur to the south and east of the line mentioned above. Deeper moisture, a passing disturbance, and decent instability will combine to bring a heavy rain threat to a relatively widespread area. That is not to say there will be widespread storms, just a widespread area where the heavy rain will be possible with any thunderstorm. Coverage is expected to be isolated-to-widely scattered across the lower elevations of eastern Colorado, with more scattered coverage across the higher terrain of southern Colorado and near the CO/NM border. Storm motions will be fairly slow, especially across mountain locations. A few showers and thunderstorms will linger into the early morning hours tomorrow.

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

Northeast Plains south of I-76, Urban Corridor and Front Range south of I-70, Raton Ridge, Palmer Ridge, and Southeast Plains:

Isolated-to-widely scattered showers/thunderstorms expected, with coverage increasing from north to south. Heavy rain will be a threat, as deep moisture will be present, allowing for efficient rainfall production. Fairly slow storm motions will also be a factor, increasing the flood threat potential over locations that remain under a stationary, or near-stationary, storm. Maximum rain rates will be 2.0-3.0 inches/hour under the strongest storms, with 1.0-2.0 inches/hour being within reach for most storms.

Timing: 11 AM – Midnight, with a few showers and thunderstorms continuing into the early morning hours, mainly across southern zones.

Northwest Slope, Northern Mountains, Central Mountains, Grand Valley, Northeast Plains north of I-76, and Urban Corridor and Front Range north of I-70:

Mostly sunny and warm, with a few isolated thunderstorms possible. Drier air will be present, keeping rain rates relatively low (0.2-0.5 inches/hour over the mountains, 0.4-0.8 inches/hour over the Urban Corridor and Northeast Plains). Temperatures will be a few degrees warmer than yesterday.

Timing: 11 AM – 8 PM

Southeast Mountains, San Luis Valley, San Juan Mountains, and Southwest Slope:

Scattered showers and thunderstorms are expected, with fairly slow storm motions being a concern. The strongest storms will be capable of producing 1.2-1.8 inches/hour, or, with respect to slow-moving/stationary storms, up to 2.0-3.0 inches in 3 hours will be possible.

Timing: Primetime will be 11 AM – 10 PM, but showers and thunderstorms are expected to continue into the morning hours tomorrow.

Issue Date: 7/29/2015
Issue Time: 10:38 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHEAST MOUNTAINS, RATON RIDGE, AND SOUTHEAST PLAINS.

Today is certainly a day where the water vapor imagery is useful in the sense that it shows the locations where monsoonal moisture is present. With the mid-/upper-level high pressure system still anchored across the south-central US, southwesterly flow aloft is dragging monsoonal moisture across southern and eastern portions of Colorado. Observations show that precipitable water values are above average at Shriever AFB (~0.9 inches) and Pueblo (~1.2 inches).

This monsoonal moisture plume (denoted by the green arrow) will continue to work across southern and eastern portions of the state today, with fair amounts of moisture available along the Continental Divide and Central/Southwestern Mountains areas. The moisture, along with weak instability generated by daytime heating, will create isolated-to-scattered showers and weak thunderstorms across the Front Range, Central Mountains, and San Juan Mountains. Instability will be a bit better to the south and east, allowing for better coverage/intensity of storms across the Southeast Mountains, Raton Ridge, and portions of the Southeast Plains (both near the mountains and along the CO/NM border).

Dry air (noted on the water vapor image) will keep the Northern Mountains, Northwest Slope, Grand Valley, and Southwest Slope mostly sunny through the day. The Northeast Plains, Palmer Ridge, and areas of the Southeast Plains not mentioned above will remain dry today, as well; the atmosphere will remain stable and unsupportive of thunderstorm development. Far western portions of the Palmer Ridge and Northeast Plains could see an isolated shower/weak thunderstorm move overhead from the mountains before quickly dissipating in the stable air.

Much like yesterday, the Southeast Plains near the CO/NM border and Raton Ridge will hold the potential for thunderstorms to continue overnight, as more widespread storms are expected to develop over New Mexico and move to the northeast. For this reason, the low flood threat will continue overnight and into tomorrow.

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, and Palmer Ridge:

Mostly sunny and warm will be the main story today for the Northeast Plains and Palmer Ridge as the atmosphere remains stable overhead. The Urban Corridor, and western portions of the Northeast Plains and Palmer Ridge will likely see a couple isolated showers/thunderstorms move off the mountains overhead this afternoon and evening, before dissipating in the stable air.

Rain rates will be rather modest at 0.4-0.8 inches/hour.

Timing: 2 PM – 8 PM

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

Mostly sunny for the Grand Valley, Northern Mountains, and Northwest Slope regions, becoming partly sunny across the Southwest Slope where slightly better mid-level moisture resides. No precipitation is expected, except for a weak shower or two across the higher terrain of the Southwest Slope. Rain rates will be 0.2-0.4 inches/hour.

Timing: 11 AM – 9 PM

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

These zones will see the most thunderstorm coverage today, as well as the best rainfall intensities. Moisture values are higher to the south and east, and the rain rates below will reflect this.

Front Range: 0.5-0.8 inches/hour
Southeast Plains and Raton Ridge: 1.2-2.2 inches/hour
Southeast Mountains: 0.8-1.2 inches/hour

Timing: Noon – 10 PM for the Front Range, 11 AM – 5 AM for the Raton Ridge, 11 AM – 11 PM for the Southeast Mountains, and 1 PM – 6 AM for the Southeast Plains

Central Mountains, San Luis Valley, and San Juan Mountains:

Isolated-to-scattered showers/weak thunderstorms expected, with coverage increasing from north to south. Generally light rain will fall early, but as moisture increases during the afternoon and evening hours, rain rates will increase a bit.

Max rain rates will be 0.5-0.8 inches/hour.

Timing: 11 AM – 9 PM