Issue Date: Sunday, August 21st, 2022
Issue Time: 11:00AM MDT

— A MODERATE flood threat has been issued for the Central Mountains, Northern Mountains, & Front Range
— A LOW flood threat has been issued for the Urban Corridor, Northwest Slope, Grand Valley, San Juan Mountains, Southwest Slope, & Southeast Mountains
— Fire-Burn Forecast Summary: 3 burn areas under HIGH threat, 4 burn areas under MODERATE threat, 3 burn areas under LOW threat; click HERE for more info 

A few widely scattered rain showers are ongoing this morning across portions of northwestern Colorado in association with the upper trough centered over far northeast Utah. As the low moves southeast through Colorado today, moisture advection and mid-level lift will accompany it. This morning, Grand Junction measured a PW value of 1.03 inches, and Platteville measured a similar PW value of 1 inch, indicating plentiful column moisture. Surface dewpoints ranging from the mid-40s to mid-50s°F indicate sufficient moisture through the boundary layer for storms to utilize this afternoon.

That said, cloud cover and the early rain showers are expected to keep instability fairly limited across the northern portions of the state. Greater clearing further south should allow instability to reach forecast values between 1000-1500 across central Colorado this afternoon. Additionally, the midlevel energy from the deepening Low is forecast to reach central Colorado by early afternoon, by which point numerous rain showers are anticipated to overspread much of the higher elevations west of the Continental Divide. A few of these storms may spill onto the adjacent foothills and Urban Corridor. Upper-level steering flow is anticipated to be quite slow, perhaps only 5 to 10mph, so storms that form are expected to be slow-moving and thus produce a couple to several hours of rainfall.

The greatest concern for heavy rainfall and flooding potential exists over the higher elevations of central and western Colorado where storms are more likely to anchor to the higher terrain given the slow steering speeds. As mentioned, a few storms may drift onto the adjacent foothills and produce isolated, locally heavy rainfall as well. A MODERATE flood threat has been issued for portions of central and northern Colorado, and a LOW flood threat for mainly mountainous areas south and west.

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:

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

Widely scattered rain showers across parts of western Colorado this morning are forecast to increase in coverage this afternoon across mainly the higher elevations, with some spillover into the adjacent lower elevations. Max 1-hour rain rates up to 1.75 inches and 3-hour rain rates up to 2.75 inches over the Front Range, Central Mountains, and Northern Mountains could cause urban and small stream flooding and field ponding in lower elevations with poor drainage, as well as excessive runoff, debris slides, and mud flows over steep terrain. A MODERATE flood threat has been issued for these forecast zones. Several hours of rainfall can be expected, although the greatest threat should be with the initial, more convective rainfall. Afterwards, lighter rain rates associated with more stratiform precipitation is anticipated.

Meanwhile for portions of southern and western Colorado, max 1-hour rain rates up to 1.25 inches and 3-hour rain rates up to 2.5 inches could cause minor urban and small stream flooding, along with excessive runoff, debris slides, and mud flows over steep terrain. A LOW flood threat has been issued for portions of the Southeast Mountains, San Juan Mountains, Southwest Slope, Grand Valley, and Northwest Slope, as well as extending into parts of the Urban Corridor.

Primetime: Ongoing to Midnight

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

Mainly clear skies are noted across eastern Colorado this morning, while slightly below average temperatures are forecast. Most storms and associated heavy rainfall are expected to remain confined to the higher elevations and adjacent foothills west. A stray storm or two may drift into the eastern plains this afternoon and produce brief, isolated 30-minute rain rates up to 0.4 inches, along with gusty winds. NO flooding is expected for the Palmer Ridge or eastern Plains today. Over the western Raton Ridge, max 1-hour rain rates up to 1.25 inches and 3-hour rain rates up to 2.5 inches are possible, and a LOW flood threat has been extended into the western portion of this zone.

Primetime: 3PM to Midnight

Issue Date: Saturday, August 20th, 2022
Issue Time: 9:55AM MDT

— A MODERATE flood threat has been issued for the Front Range
— A LOW flood threat has been issued for the Northwest Slope, Grand Valley, Southwest Slope, San Juan Mountains, Central Mountains, Southeast Mountains, Raton Ridge, Southeast Plains and Urban Corridor
— Fire-Burn Forecast Summary: 6 burn areas under MODERATE threat; 2 burn areas under LOW threat; click HERE for more info

Monsoon moisture and mid-level energy are over the state this morning helping to create lots of cloud cover and some light to moderate rainfall. The Low over Utah and High over northeast Colorado are combining to create southerly flow, which will continue to pull in more moisture and mid-level energy across the southern border today. A new batch of storms are expected to arrive to the southern border by late morning, and some intensification over the Southeast Plains is anticipated this afternoon. Additional storms are forecast to develop over the northern and central mountain areas. Steering flows look to gain more of a westerly component by late this afternoon as the ridge builds northwards, which should help push some of the storms into the immediate adjacent plains. Not much change is anticipated in the speed of the storms, so some longer duration rainfall will be likely again with coverage expanding to areas along and near the Continental Divide.

As expected, moisture throughout the atmosphere has increased both east and west with PW at Grand Junction and Platteville measured at 1.03 inches and 0.93 inches, respectively. So, there should be plenty for scattered to numerous storms to develop with increasing upslope flow and some additional lift from mid-level energy. With the ongoing cloud cover, showers and cooler temperatures, instability may be limited today, especially south, which would promote more stratiform instead of convective rainfall. However, pockets of 600-1000 J/kg are still likely to materialize over central and northern Colorado, which will keep the flood threat going today. Similar to yesterday, the initial convective rainfall is expected to pose a flood threat along with longer duration rainfall over a 2-to-3-hour period. A MODERATE and LOW flood threat has been issued.

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:

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

Initial scattered convection and then more numerous storms with moderate rain rates are anticipated today for the mountains. Max 1-hour rain rates up to 1.5 inches and 3-hour rain rates up to 2.75 inches will be possible. A MODERATE flood threat has been issued. The flood threat should primarily be in the first 1 to 2 hours of storm develop with temperatures expected to drop quickly and produce more stratiform rainfall thereafter. Some spillover into the immediate adjacent plains is forecast this evening with the LOW flood threat extending slightly east into the elevated ridges where max 1-hour rain rates up to 1.75 inches will be possible. Flood threats today include ponding in low-lying areas, road flooding and debris slides/mud flows over steeper terrain. The flood threat should end later this evening with some storms lingering into the overnight hours for the mountains.

Primetime: 12:30PM to 2AM

Southeast Mountains, Raton Ridge, Southeast Plains, San Juan Mountains, Southwest Slope, San Luis Valley, Northwest Slope, Northern Mountains & Grand Valley:

Scattered storms are forecast north today with more numerous storms forecast south. Max 30-minute rain rates up to 1 inch (north) and 1-hour rain rates up to 1.5 inches (south) are forecast. Some longer duration rainfall is again anticipated for the San Juan Mountains and nearby elevated regions with storm totals up to 2.25 inches possible. A LOW flood threat has been issued, and if more intense storms track over the same areas as yesterday, an increase in runoff is expected. Rainfall will likely linger over the mountains tonight with the flood threat ending this evening.

Primetime: 12PM to 4AM

Issue Date: Friday, August 19th, 2022
Issue Time: 10:40AM MDT

— A MODERATE flood threat has been issued for the Grand Valley, Southwest Slope and portions of the western San Juan Mountains
— A LOW flood threat has been issued for the Northwest Slope, Central Mountains, Northern Mountains, Front Range, Urban Corridor, Palmer Ridge
— Fire-Burn Forecast Summary: 2 burn area under MODERATE threat; 5 burn areas under LOW threat; click HERE for more info

There will be another shift in the synoptic pattern today as the elongated High begins to break up as a Low and associated shortwaves move over the state from the west. In addition to the Low from the west, a Low northeast of Colorado is expected to drop a shortwave and jet into the far eastern plains later this evening, which may allow rainfall to linger over the eastern plains tonight. Both features will help to increase rainfall chances east and west today with storms forecast to become scattered to numerous by late this afternoon.

Over western Colorado, an increase in moisture can be seen by the shades of blue and white in the water vapor imagery above. Lift out in front of the shortwaves (orange “X’s”) has already started to produce moderate showers over the Grand Valley and Southwest Slope. PW at Grand Junction was measured at 0.85 inches with a dew point around 40°F. As the day goes on, rainfall and increasing moisture will likely help to moisten the boundary layer and produce higher rainfall efficiency both over the valleys and high terrain. Slow steering flows should also contribute to higher rainfall accumulations over the high terrain. So, initial convection is expected to pose a flood threat along with longer duration rainfall over a 2-to-3-hour period. A Moderate flood threat has been issued with the potential for road flooding, ponding in low-lying areas and mud flows/debris slides over steeper terrain.

Surface moisture is also on the rise over portions of the eastern mountains, and PW at Platteville was measured at 0.67 inches, showing an increasing trend from yesterday. Upslope flow and moisture advection should take over by this afternoon favoring the northern and central high terrain for scattered storm development. Northwest steering flow is expected to push the storms into the adjacent plains with storms most likely to survive over the elevated ridges. Generally, the lack of surface moisture should limit the flood threat, but isolated heavy rainfall may be possible over the Front Range near the Continental Divide and along the elevated Palmer Ridge where extra convergence my occur.  A LOW flood threat has been issued.

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:

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

Scattered to numerous storms are forecast this afternoon through this evening. Max 1-hour rain rates up to 1.5 inches and 2-to-3-hour storm totals up to 2.25 inches will be possible. With the drier surface layer north/central and higher-end DCAPE values, the more intense thunderstorms that develop could produce some strong outflow winds as well. A MODERATE flood threat has been issued. Flood threats include road flooding, ponding of low-lying areas, rises on local streams/creeks and mud flows/debris slides over steeper terrain. Lighter rainfall will likely linger overnight with a second round of scattered showers beginning tomorrow morning.

Primetime: 11AM to Ongoing

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

Scattered storms return to the eastern mountains today with best coverage forecast along the Front Range. An isolated storm may produce 30-minute rain rates up to 1 inch, which could cause road flooding, mud flows or debris slides under its core. Over the Southeast Mountains, 30-minute rain rates up to 0.4 inches will be possible. As storms move off into the adjacent plains, strong outflow winds are anticipated with rainfall totals generally under 0.5 inches. Slower steering flow, extra convergence over the Palmer Ridge, and moisture advection this afternoon may allow a storm or two to produce 1-hour rain rates up to 1.5 inches this evening. For these reasons, a LOW flood threat has been issued. Some lighter rainfall may linger overnight with a second wave of precipitation possible before tomorrow’s FTB is produced.

Primetime: 12:30PM to Ongoing

Issue Date: Thursday, August 18th, 2022
Issue Time: 10:15 AM MDT

— Flooding is NOT expected today

This morning, an upper ridge positioned over southeast Idaho continues to push dry air into the region, as shown in the water vapor image below. As the high-pressure center continues to build in from the northwest, the dry, sinking air should suppress the return flow of moisture and provide a break in rainfall for most of the state today. That said, some lingering monsoonal moisture is in place across the Four Corners region of southwest Colorado. Grand Junction measured a PW value of 0.80 inches, which reveals a decrease from yesterday but with somewhat higher values near 1 inch south. And while instability is somewhat modest in the area with values forecast to reach between 500-1000 J/kg this afternoon, the residual moisture in tandem with added uplift from elevated terrain should be sufficient to allow for isolated storm development over the southwest portions of the state this afternoon. These storms may produce briefly heavy rainfall particularly where they may briefly anchor to the steeper terrain, but rain rates are expected to remain below flood thresholds. Additionally, storm cores are expected to be small and produce only localized impacts, so NO flooding is expected for western Colorado today.

Further east, Platteville measured a PW of only 0.57 inches this morning, which is a significant decrease from prior days as the moisture continues to be scoured out from the southward surge of dry air. An upper-level disturbance is forecast to move from the Nebraska/South Dakota border southward across the eastern plains of Colorado this afternoon and evening. This feature could trigger a few afternoon storms along the boundary. Instability is forecast to reach between 1500-2000 J/kg of CAPE for portions of the eastern plains this afternoon and early evening, and there may be enough moisture recovery in the boundary layer to allow for some isolated briefly heavy downpours. However, the dry air intrusion and subsidence should keep rain rates below flood thresholds. Therefore, there is NO flooding expected for eastern Colorado 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: 

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

Fog across the San Luis Valley from early this morning continues to dissipate this morning, otherwise, skies are mostly clear and temperatures are a few degrees warmer than yesterday. This afternoon, a couple rounds of isolated are possible over the Southwest Slope and western San Juan Mountains where the residual monsoonal moisture is in place. These storms could produce max 30-minute rain rates up to 0.6 inches, with isolated 1-hour rain rates up to 0.75 inches possible if a storm is able to anchor to the higher terrain. Some light runoff and gusty winds will be possible with these storms; however, given the smaller storm cores likely, NO flooding is expected today.

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

Some patchy fog over the far eastern plains is dissipating this morning. Otherwise, skies are clear and drier, warmer conditions are expected for these forecast zones today. This afternoon, a few isolated storms may be possible in association with a southward-moving upper-level impulse. Given significant drying over the last 24 hours along with somewhat faster steering flow, rain rates up to 0.4 inches in 30 minutes are anticipated over portions of the eastern Palmer Ridge, and Northeast and Southeast Plains. If moisture recovery is sufficient this evening across the Southeast Plains, isolated 1-hour rain rates up to 0.75 inches are possible if a stronger storm or two develops. Additionally, small hail and gusty winds would be possible with these storms. However, NO flooding is expected today.