Issue Date: Saturday, August 29th, 2020
Issue Time: 10:40AM MDT

— A LOW flood threat has been issued for the Raton Ridge and southern Southeast Plains regions, as well as the Cameron Peak, Williams Fork, Grizzly Creek, and Spring Creek burn areas

— A MODERATE flood threat has been issued for the Decker burn area

Abundant rainfall yesterday has added moisture to low-levels today, as surface dew points are in the 40Fs and 50Fs across the state, with 60Fs in southeast Colorado. The shortwave associate with the heavy rain over southeast Colorado yesterday can be seen moving through eastern Kansas this morning on the satellite image below (labelled with an “X”). Mid-level moisture also remains over Colorado today with a brief monsoonal flow setup. This has boosted PW values to 0.9 inches at Denver and Grand Junction when compared to this time yesterday. The bubble of moisture over the southwestern US is evident in the visible + IR “sandwich” satellite image this morning as the white, blue, and green colors (see image below). This moisture will allow widespread coverage of afternoon storms today.

A batch of clouds and showers is moving through western Colorado this morning, which is associated with a piece of shortwave energy traveling through the flow. This shortwave will continue to move east during the day today, and it will be the focus of the heavier rainfall today. Mid-level winds are weak this morning over Colorado (10-15 mph), but winds will increase behind this shortwave later this afternoon (25-30 mph). This means storms that form earlier in the day will move slower, whereas storms later this afternoon should move east at a decent pace, which helps lower the chances for flooding. The clouds and showers over western Colorado will also act to keep temperatures cool and limit instability, so chances for heavy rainfall over the western slope are low today. The highest chances for heavy rainfall will be along the eastern mountains and plains where some daytime heating can increase instability before the shortwave moves overhead.

Due to plenty of moisture and some added lift from the shortwave, a Low flood threat has been issued for the Raton Ridge and southern Southeast Plains regions. Additionally, a Low flood threat has been issued for the more susceptible burn areas, including the Cameron Peak, Williams Fork, Grizzly Creek, and Spring Creek burn scars. A moderate flood threat has been issued for the Decker burn scar due to higher rain rates and increased coverage of storms.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Showers and clouds will move into the Front Range area by 11AM, which should limit storms early. A round of storms later in the day could move through, but rain rates should stay below 0.4 in/hr over the Front Range and Urban Corridor. A corridor of southerly flow adjacent to the high terrain will allow moisture to remain high along the plains adjacent to the mountains, but drier air along the northeast border of Colorado will cause storms to dissipate as they move farther east in the Northeast Plains. There is a chance a stronger storm may move southeast off the Cheyenne Ridge into the Northeast Plains, which could boost rain rates up to 0.9 in/hr, but these storms should move east fairly quickly due to increasing mid-level winds. No flooding is expected over these northern regions.

Storms will develop slightly later (by 1PM) over the Southeast Mountains as the shortwave moves east. Due to slightly higher surface moisture available over the Southeast Plains and some extra time for instability to build, the highest rain rates are expected there as storms move east off the mountains with the passing shortwave. Storms will likely grow upscale, further increasing coverage and rain rates. Max rain rates up to 1 in/hr are possible with the stronger storms that develop over the Palmer Ridge, Southeast Plains, and Raton Ridge. A cap should cause storms to struggle as they approach the eastern border. Due to the large amount of rain received over the Southeast Plains yesterday and the chance for some heavy downpours today, a Low flood threat has been issued for the Raton Ridge and southern portions of the Southeast Plains. Additionally, a Low flood threat has been issued for the Spring Creek burn area due to moist soils from yesterday’s rainfall and the high likelihood of storms moving across the area today with rain rates up to 0.5 in/hr possible.

Primetime: 11AM to 12AM

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

Showers are moving through the Grand Valley, Central Mountains, and northern San Juan Mountains this morning, which will limit diurnal heating today for much of the area. However, once this batch of clouds and showers moves east, some afternoon storms will fire over the higher terrains. By then, some stronger mid-level winds will develop, so storms should not linger too long over areas. But, due to moderate surface and mid-level moisture, rain rates up to 0.7 in/hr are possible over the southern San Juan Mountains, where the highest surface dew points exists this morning (50Fs). Rain rates decrease further north and west, with up to 0.4 in/hr possible for the high elevations of the Central and Northern Mountains and the Flat Tops in the Northwest Slope. Due to the high likelihood of storms and moderate chances for rain rates over 0.25 in/hr, a Low flood threat has been issued for the new Cameron Peak, Williams Fork, and Grizzly Creek burn scars. A moderate flood threat has been issued for the Decker burn area, where slightly higher chances of receiving over 0.25 inches in an hour are expected. The Pine Gulch burn area should be far enough west that flooding rainfall is not expected, with rain rates under 0.2 in/hr. Flash flooding, mud flows, and debris slides are possible in these vulnerable burn scars.

Primetime: 10AM to 8PM

Issue Date: Friday, August 28th, 2020
Issue Time: 9:15AM MDT

— A HIGH flood threat has been issued for the Spring Creek burn area

— A MODERATE flood threat has been issued for the Raton Ridge, Southeast Plains, and Decker burn area

— A LOW flood threat has been issued for the Front Range, Southeast Mountains, San Juan Mountains, Palmer Ridge, southern Northeast Plain, Urban Corridor, & Cameron Peak burn area

Quite a bit of cloud cover over the state to start this morning and perhaps some weak showers over the southwest corner of the state. The High is being pushed south by a passing trough, which is also dropping a cold front through eastern Colorado this morning. Along the front, gusts around 35 mph are being reported, and it should bring cooler high temperatures to eastern CO this afternoon. Moisture is also increasing behind the northerly flow over eastern Colorado, but it looks fairly shallow in the Denver sounding this morning. Therefore, as the day goes on, expecting the surface moisture further north to mix out with more westerly flow aloft (drying), which will limit the flood threat over this area. For the most part, the majority of the rainfall is expected to occur south of I-70. Due to rain rates up to 0.25 inches/hour still possible over the northern Front Range, a Low flood threat has been issued for the Cameron Peak burn area due to high probability of storms forming near the area with extra upper level lift.

The shortwave energy producing the lift for the cloud cover/weak showers over the southwest corner will start to move to the northeast, and with a little daytime heating and increased moisture, expecting an uptick in intensity and coverage of storms. This is especially true over the southern mountains and immediate adjacent plains where higher moisture will help increase rainfall coverage and rain rates. While rain totals won’t be quite as high over the San Juan Mountains (less surface moisture), training storm could produce some higher totals over the southern and eastern San Juan Mountains, so it has been included in the Low threat.

Recent burn areas over the Southeast Mountains will also be more susceptible to flash flood today, especially the Spring Creek burn area since it has received a couple round of rain the last couple of days. With rain totals up between 0.75 inches (north) and 1 inch (south) possible, a High flood threat has been issued for the Spring Creek burn area, and a Moderate flood threat has been issued for the Decker burn area. Over the Raton Ridge, extra convergence from the elevation and front will produce widespread, heavy rainfall, thus the Moderate flood threat for this area. Overnight rainfall is expected for the Southeast Plains. Should moisture be able to hang on a bit further north, some heavy rainfall will also be possible over the Palmer Ridge and east, so the Low threat extends to the north.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Southeast Mountains, Front Range, & San Juan Mountains:

Multiple rounds of rainfall are expected over the mountains this afternoon. Isolated totals up to 1 inch will be possible over the southern/eastern San Juan Mountains, while over the southern Front Range and Southeast Mountains, more widespread totals of 1 inch will be possible. In addition to heavy rainfall, storms could produce small hail and strong outflow winds. The heavy rainfall potential will put burn areas under an elevated flood threat this afternoon, so a High flood threat has been issued for the Spring Creek burn area and a Moderate flood threat for the Decker burn area. Further north, rain rates should decrease, but max 1-hour rain rates up to 0.25 inches will still be possible. So, if storms form over the fresh Cameron Creek burn area, flash flooding could be an issue. Thus, the Low flood threat.  If storms form over-top of a burn area, flash flooding, mud flows, and debris slides are all possible.

Primetime: 12PM to 10PM

Palmer Ridge, Raton Ridge, Urban Corridor, Southeast Plains, San Luis Valley, & Northeast Plains:

Heavy rainfall will be likely south of I-70 this afternoon, so a Low and Moderate flood threat have been issued. The best chance for widespread rainfall will be south over the Raton Ridge and Southeast Plains. Max 1-hour rain rates up to 2 inches are expected over the area with widespread totals over 1 inch. Further north, totals up to 1.5 inches (east) and 1.25 inches (west) will be possible, thus the Low flood threat. A couple severe storms may be possible as well (south) with the threats being large hail and then wind as upscale growth occurs. The main flood threats from the heavy downpours this evening will be arroyo flooding, local creek flooding, road flooding, and field ponding. The SLV is also expected to get some rain with isolated totals up to 0.30 inches possible in the interior of the valley.

Primetime: 3:30PM to 4AM

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

Increased storm chances today when compared to yesterday, but the scattered storms should mostly stick to the high terrains. With less moisture at the surface (Continental Divide acting as a barrier), rain rates should be lower with some gusty outflow winds possible. Further north, max 1-hour rain rates should stay under 0.15 inches for the most part, but over the Central Mountains near the Divide, totals up to 0.40 inches will be possible. Prolonged rainfall is not expected over any area, so no flood threats have been issued for recent burn areas. As always, use caution if a storm tracks overhead. A second wave of rain is expected to arrive at midnight, which may bring some light rain to the lower elevations of the Grand Valley and Southwest Slope.

Primetime: 11AM to ongoing

Issue Date: Thursday, August 27th, 2020
Issue Time: 8:45AM MDT 

— Flooding is NOT expected today

A lot going on in the water vapor imagery below. To our north, there’s a bit of a dirty ridge pattern with some ongoing convection over the northern Rockies and Dakotas associated with an incoming trough. To our southeast, Hurricane Laura made landfall overnight (1AM) and produced 150 mph winds! Those winds have died down to about 120 mph this morning and are forecast to drop to about 75 mph by midday, so life threatening storm surge is occurring along with heavy rainfall. There’s also a really nice dry slot over the Midwest between the two systems. Over Colorado, the elongated High is expected to continue to influence our weather today. Therefore, expecting another round of showers over the mountains and elevated terrains in western Colorado.

The morning soundings at Denver and Grand Junction show most of the moisture below (blue shades) in the mid-levels with it being quite dry at the surface and upper levels. This should reduce rain rates, intensity, and coverage of storms today when compared to yesterday. Not seeing any well-defined shortwave either, so convection should be more pop-like over the high terrains meaning shorter duration and small rainfall cores. As storms move off the eastern mountains with the northwest steering flows, convection is expected to weaken. So, outside of some scattered, weak storms over the elevated ridges, it should remain mostly dry over the lower elevations. Flooding is not expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Another round of diurnally driven scattered storms are forecast over the mountains and elevated western terrains this afternoon. Decreasing intensity, coverage, and small, short-lived storm cores should put the fresh burn areas at less risk for flash flooding. As always, if a storm tracks overhead, use caution and follow NWS for all of the latest flash flood warnings. The Spring Creek burn area has received quite a bit of beneficial rain the last couple of days (just over a half inch). If a storm tracks over the southern end of the burn area, please use extra caution as this area has proven to be the most susceptible to mud/debris flows. Confidence is not very high that a storm will form over the scar or last long enough/produce enough rain to hit our thresholds for flooding, so no flood threat has been issued. Just wanted to mention the antecedent soil conditions for awareness.

As far as rain totals go, over the eastern mountains, isolated rain totals up to 0.50 inches will be possible with most storms producing between 0.10 and 0.25 inches. The higher totals will be more likely further south. Over western Colorado, isolated totals up to 0.50 inches (south) and 0.25 inches (north) will be possible. Highest totals are expected over the southern/eastern San Juan Mountains again, and all storms today will be capable of producing brief windy conditions (~35 mph gusts). Flooding is not forecast, and a couple weak showers could linger over the high terrains overnight.

Primetime: 12:30PM to 11PM

Palmer Ridge, Raton Ridge, Urban Corridor, Southeast Plains, San Luis Valley, & Northeast Plains:

These regions should remain mostly dry today with little to no rainfall expected for the SLV. Expect storms to weak as they move off the eastern mountains later this afternoon, but some light rainfall will be possible along the I-25 corridor before they dissipate. As the storms weaken, expect some brief windy conditions. Over the elevated ridges, isolated totals up to 0.20 inches will be possible with most storms producing lower to trace amounts of rainfall. As far as high temperatures, expect another day with upper 90Fs along the I-25 corridor and slightly higher temperatures east. The heat wave continues, but there’s a change coming early next week.

Primetime: 3PM to 10PM

Issue Date: Wednesday, August 26th, 2020
Issue Time: 11:00AM MDT

— A LOW flood threat has been issued for the Northern Mountains, Front Range, Central Mountains, San Juan Mountains, Southeast Mountains, and Palmer Ridge.
— This threat includes recent burn areas: Spring Creek, 416, Decker, Lake Christine, Cameron Peak, and Williams Fork

Moisture continues to increase under an elongated High pressure system that is sitting over Colorado today, which will further increase chances for thunderstorms and wetting rainfall over the high terrains. This plume of moisture is best visualized in this morning’s water vapor imagery by the increased blue colors (see image below). Soundings this morning for Denver and Grand Junction show that moisture continues mainly in the mid- and upper-levels with significant dew point depressions near the surface. However, surface moisture looks a little higher today due to the added moisture from precipitation yesterday, so this will mean an increase in rain totals. Increased instability from the extra moisture will allow for some more widespread thunderstorm development. Storms should form over most high terrains by noon, and will continue to have slow storm movements under the high, so this increases the chances for wetting rainfall as storms linger over the peaks for extended periods. Due to the possibility of 1-inch rain totals over a couple hours with increased moisture, a Low flood threat has been issued for most mountain regions. Additional storms may fire along the Palmer Divide with outflow boundaries providing lift to break the weaker cap. With slow storm motion and increased convergence, these storms may also produce some localized flooding issues. Gusty winds are also a possibility with storms today due to the inverted-V profiles.

A couple storms may also be possible over the Northeast Plains and near the Cheyenne Ridge, but with rain rates up to 1 in/hr, flooding is not expected.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Storms will fire again over the high terrains this afternoon, which will likely produce some local, heavy downpours (max rain rates up to 0.8 in/hr), gusty winds, and lightning. Due to slow storm motions, several storms could remain over the same area for a couple hours. Although storm cores should remain small, they could lead to rain accumulations up to 1 inch, so a Low flood threat has been issued for the higher elevations of all mountain regions with a couple lingering light showers possible overnight. Of particular concern is flash flooding over steep terrain and burn areas, including the Spring Creek, 416, Decker, and Lake Christine burn areas. Additionally, flash flooding and mud flows over the current Cameron Peak and Williams Fork wildfires are possible with 24-hour rain totals up to 1.5 inches possible near the area. Gusty outflow winds and lightning could worsen the fire danger where little to no rain is able to fall, mainly over the Northwest Slope and Grand Valley.

Dry air moving into the northwest corner of the state should lower rainfall chances there. The lower elevations of the San Luis Valley will likely see more sub-cloud evaporation, but still some significant accumulations are possible (up to 0.8 inch in 2 hours).

Primetime: 12PM to 12AM

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

It will be above average temperatures again today, with a moderate chance for storms over the Palmer Ridge, Urban Corridor, Front Range, and Northeast Plains. Storms will form over the Front Range by noon and could produce 1 inch of rain over a couple hours, so a Low threat has been issued. Most storms moving off the Front Range into the northern Urban Corridor will dissipate, but storms could drop heavier rain along the southern Urban Corridor. A couple stronger storms could develop over the Palmer Ridge and Northeast Plains with rain rates up to 1 in/hr, so the Low threat has been extended to the western Palmer Ridge. Gusty outflow winds are also possible from storms today due to the lower surface moisture.

Primetime: 12PM to 12AM