Issue Date: Monday, September 3rd, 2018
Issue Time: 09:10AM MDT

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

— A LOW flood threat has been issued for the 416/Burro and Spring Creek burn areas

Cool morning with quite a bit of cloud cover over the state to start Labor Day. There is also some moderate rainfall (and snow at higher elevations) being reported over the San Juan Mountains with dense fog over the far eastern plains that is limiting visibility to the 0.25-0.75 mile range. This is all associated with the upper low over the Southwest Slope, which is marked in the water vapor imagery below. That circulation will slowly start moving to the northeast throughout the day and into tonight, which will help keep rainfall chances fairly widespread.

Showers are expected to increase throughout the day over the western high terrains. Better moisture will be available over the San Juan Mountains, so expecting the highest 24-hour totals over this region. Ongoing cloud cover will limit the amount of instability that can build, but with slow steering winds aloft, max 1-hour rain rates up to 0.6 inches/hour are possible over the 416/Burro burn areas. Therefore, a Low flood threat has been issued for these recent burn areas. Threats including mud flows, debris slides and flash flooding of local streams.

To the east, southeasterly surface winds will help keep low-level moisture in place over the eastern plains. Precipitable Water values will also be on the rise and are forecast to exceed 1 inch this afternoon. This higher low-level moisture should remain over the adjacent plains, so flood threat criteria will not be met over Front Range and Southeast Mountains. The one exception will be the Spring Creek burn scar, where 1-hour totals will likely exceed 0.25 inches, so a Low flood threat has been issued. The big question this afternoon is how much and how quickly the cloud cover will burn off. The earlier the cloud cover burns off, the more instability will be able to build for afternoon thunderstorms. At this time, leaning towards a moderate amount of instability over the far eastern plains as we’re already starting to see clouds break up a bit. The moderate instability paired with slow steering winds aloft to the NNE, should increase rainfall totals over the eastern plains when compared to yesterday. There is a fairly good chance that minimal flood threat criteria will be reached over this area, so a Low flood threat has been issued. With drier soils and healthy crops, the nature of the flooding should be localized.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

 

Zone-Specific Forecasts:

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

Showers and thunderstorms are likely this afternoon with the heavier totals expected over the eastern plains. Over the higher terrains, storms are expected to be more widespread over the Palmer Ridge/Southern Front Range intersect and the Southeast Mountains with isolated coverage further north. Max 1-hour rain rates up to 0.75 inches (west) and 1.8 inches (east) are possible. A Low flood threat has been issued for the Spring Creek burn area as well as for the far eastern plains. Threats over the burn scar include localized stream flooding, mud flows and debris slides. Over the eastern plains, localized stream and arroyo flooding is possible along with field ponding and flooding of low-lying roads. Storms should end around midnight over the higher terrains with storms ending a couple hours later over the eastern plains.

Primetime: 12PM – 3AM

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

Showers should continue to pick up in intensity over the higher terrains throughout the day. Better moisture remains to the south, so the highest totals are expected over the San Juan Mountains though 24-hour totals close to 1 inch are possible over the Central Mountains. Instability will be minimal, so storms should be more stratiform rather than convective in nature though some isolated thunder is likely. Max 1-hour rain rates up to 0.7 inches (south) and 0.3 inches (north) are possible. A Low flood threat has been issued for the 416/Burro burn areas with localized flooding, mud flows and debris slides being a threat for storms that track directly over the recent scars. Storms are expected to end a few hour after sundown though a couple showers could linger near the Continental Divide overnight.

Primetime: 11AM – 10PM

 

Issue Date: 9/2/2018
Issue Time: 8:00 AM

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

The upper-level trough that impacted Colorado yesterday hasn’t moved much over the previous 12-18 hours, continuing to drift slowly eastward over the 4-Corners region. This will set the stage for another afternoon/evening of isolated-to-scattered showers and thunderstorms across the state. A difference between yesterday and today will be the influx of some low-level moisture across eastern Colorado, where easterly flow will bring plains moisture towards the Front Range and Southeast Mountains. Wind shear, moisture, and pockets of instability will be sufficient to produce a couple stronger storms capable of moderate-to-heavy rainfall, thus the issuance of the low flood threat for the sensitive burn scars of southeast Colorado.

Over the High Country, areas north of I-70 will remain mostly dry tomorrow, with only a couple isolated showers dotting the higher terrain. South of I-25, the influence of a mid-level stream of moisture from the south will provide the fuel for scattered showers and thunderstorms. Most of the activity will be garden-variety, with impacts being light-to-moderate rainfall, gusty winds, and lightning. Storms will move slower than yesterday, leaving the possibility for longer residence time of moderate rainfall over a sensitive burn scar; thus, the issuance of the low flood threat for portions of the Southwest Slope and San Juan Mountains regions. For more details 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, Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Plains, Southeast Mountains, and Raton Ridge:

Scattered showers and thunderstorms are expected, with the bulk of the activity occurring south of I-70. Storms will move slower than yesterday thanks to weaker mid-level flow, and this in partnership with an increase in moisture has led to the issuance of the low flood threat. Maximum rain rates are as follows:

Front Range: 0.2-0.4 inches/hour
Urban Corridor, Palmer Ridge, and Northeast Plains: 0.4-0.7 inches/hour
Southeast Plains and Raton Ridge: 1.0-1.3 inches/hour
Southeast Mountains: 0.5-0.7 inches/hour

Timing: A few showers are ongoing this morning across the Southeast Plains. Aside from those, timing will be 11 AM – 11 PM, with a couple lingering showers/weak thunderstorms into the early morning hours.

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

Isolated showers are expected north of I-70, with scattered showers and a few thunderstorms south of I-70. The best coverage will be across the higher terrain of the San Juan Mountains, Southwest Slope, and southern Central Mountains where moisture will be best. Slow-moving storms capable of moderate rainfall are behind the issuance of the low flood threat. Maximum rain rates are as follows:

Northwest Slope and Northern Mountains: 0.1-0.2 inches/hour
Grand Valley: 0.2-0.3 inches/hour
Central Mountains, Southwest Slope, San Juan Mountains, and San Luis Valley: 0.3-0.5 inches/hour.

Timing: 11 AM – 8 PM for the Northwest Slope and Northern Mountains, 11 AM – 9 PM for the Grand Valley, and 11 AM – 1 AM for the San Juan Mountains, Southwest Slope, and San Luis Valley

Issue Date: 9/1/2018
Issue Time: 8:00 AM

NO FLOOD THREAT IS FORECAST TODAY.

An upper-level trough currently situated with its axis (red dashed line) over Utah and Arizona will advance into western Colorado today, continuing the influx of mid-level moisture from the south-southwest into the state. A few weak disturbances ahead of the axis will shift across Colorado today and tonight, providing a few triggers for scattered showers and thunderstorms. Low-level moisture across much of the state remains lackluster, generally speaking, so most of the activity today will remain high-based, producing gusty winds, lightning, and brief periods of light-to-moderate rainfall.

While no flood threat has been issued, sensitive burn scars of the Southwest Slope, San Juan Mountains, and Southeast Mountains may need some attention today should multiple rounds of marginal rainfall move overhead. However, due to the scattered nature of showers/thunderstorms today, their generally high-based nature, and expected quick storm motions to the east-northeast, no flood threat is warranted.

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, Northeast Plains, Southeast Plains, and Raton Ridge:

Scattered showers and thunderstorms are expected today and tonight across the area. Most activity will be garden variety, producing more wind than rain, as low-level moisture isn’t favorable for heavy rainfall. The bets moisture, and therefore the best chance at strong thunderstorms capable of periods of moderate-to-heavy rainfall will be east of a line drawn through Raymer-Fort Morgan-Limon-Ordway-Branson. Maximum rain rates are as follows:

Urban Corridor: 0.3-0.6 inches/hour
Palmer Ridge: 0.4-0.8 inches/hour
Northeast Plains and Southeast Plains: 1.0-1.5 inches/hour
Raton Ridge: 0.4-0.6 inches/hour

Timing: 1 PM – 10 PM for the Urban Corridor, 1 PM – Midnight for the Northeast Plains and Palmer Ridge, Ongoing – 2 AM for the Raton Ridge and Southeast Plains

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

Scattered, high-based showers and thunderstorms are expected today/tonight as the upper-level trough moves into the area. Moisture is lacking, generally speaking, and storm motions are relatively quick, so no flood threat is warranted today. As mentioned above, sensitive burn scars may need a bit of monitoring should they be impacted by multiple rounds of marginal rainfall, but the probability of flash flooding is less than 10%. Rain rates will generally be below 0.1-0.2 inches/hour, with maximum rates of 0.2-0.4 inches/hour for thunderstorms south of I-70.

Timing: 11 AM – 11 PM for the Southwest Slope, San Juan Mountains, Southeast Mountains, and San Luis Valley, 11 AM – 9 PM for the Northwest Slope, Northern Mountains, Central Mountains, Front Range, and Grand Valley

Issue Date: Thursday, August 31st, 2018
Issue Time: 09:40AM MDT

— Flooding is NOT expected today

Across much of Colorado, August will come to an end with seasonably warm temperatures and a chance for afternoon thunderstorms, offering a slight break from fire weather potential. The upper-level high over the southwestern states that has continually brought dry, hot weather to the state throughout the week is finally beginning to move further east. In its wake, a shake-up in the usual late-summer pattern is expected: first, with a larger chance for shower and thunderstorm activity as a shortwave moves in to replace the withdrawing upper-level high, and then with much cooler temperatures forecast for overnight and tomorrow.

 

Above the surface, higher relative humidity values than in days previous may help aid thunderstorm development this afternoon, as shown in the mid-level water vapor imagery above. Low-level moisture, however, will still be somewhat lacking. Wind gusts, particularly in the outflow of thunderstorms, are expected but not predicted to be widespread or strong enough to warrant any critical fire weather danger for this afternoon and evening. The aforementioned thunderstorm development is not forecast to produce any flooding today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Temperatures again into the upper 80s/lower 90s during the afternoon, as morning cloud cover gives way to sunny skies into the early afternoon. By 2pm, expect towering cumulus clouds to form, first over the Front Range and Southeast Mountains, and then continue along into the eastern plains regions. Thunderstorm activity will be widespread across the eastern half of the state, where surface dew points just into the low 50s will help bring ample rainfall to the surface. Maximum hourly rainfall rates of around 0.25 inches may occur under stronger storms, particularly along the Urban Corridor and Palmer Ridge, but no flooding is anticipated today.

Primetime: 3PM – 9PM

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

Unlike areas of the state further east, thunderstorm potential will be hindered in these regions due in large part to less humid air. Mostly sunny conditions will reign today, with hot afternoon temperatures and relatively calm winds compared to earlier this week. Fire weather hazard is thus much lower today, but caution is still stressed using open flames outdoors. A stray afternoon thunderstorm cannot be ruled out completely, notably for the Northern and Central Mountains, but rainfall rates are expected to top off between 0.05 and 0.1 inches per hour. No fire weather or flood threat is forecast for today.