Issue Date: Monday, August 17th, 2020
Issue Time: 09:50AM MDT

— Flooding is NOT expected today

Colorado is still positioned on the eastern side of a highly amplified high pressure ridge, which is centered over southeast Nevada/southwest Utah (see image below). This ridge is keeping moisture well west of Colorado, over northern California and eastern Oregon, and will continue to circulate drier air over eastern Colorado (see image below). This drier air will mix out some leftover low-level moisture over the plains, where dew points are in the 50Fs this morning, which will lower the dew points and decrease the chances for storms today over the plains. Some mid-level moisture has pushed into the central and southern mountains, which will keep rainfall in the forecast today. Weak mid- and upper-level winds, as well as the absence of any significant shortwaves, will favor slow-moving, isolated thunderstorms over the mountains. These storms will drift south during the day due to the northerly upper-level winds, but high bases mean less rainfall and more wind, so no flooding is expected today.

Wildfire smoke is expected to continue to impact much of the state again today as smoke is transported south by the northerly winds. An air quality alert has been re-issued by the National Weather Service for much of the Grand Valley, Central & Northern Mountains, and Front Range/Urban Corridor. Hot and dry conditions are expected once again over the west/northwest part of the state today, which will not help with mitigating the fire danger.

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:

Today will be another day with above average temperatures, with highs in the low to mid 90Fs for much of the plains. Some leftover moisture will allow some isolated storms to form over the higher terrains first this afternoon, which should dissipate if they move into lower-elevation regions as they move south. Max rain rates from these isolated storms should stay below 0.5 in/hr. Although convection should remain limited farther east over the plains, some storms may be able to track through the northeast corner of the state after firing over the Cheyenne Ridge to the north. Max rain rates from these discrete storms should stay below 0.7 in/hr if they are able to fire, so no flooding is expected.

Primetime: 1PM to 10PM

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

Smokey skies and hot today for the Northwest Slope, Grand Valley, and Southwest Slope. Moderate chances exist for high-elevations storms to fire over the Central & San Juan Mountains. Max rain rates from these storms should stay below 0.3 in/hr as moisture is limited to the mid and upper levels. No flooding is expected today. Air quality will be an issue for many locations as wildfire smoke continues to stream south over the area.

Primetime: 1PM to 10PM

Issue Date: Sunday, August 16th, 2020
Issue Time: 9:20AM MDT

— A LOW flood threat has been issued for the Northeast Plains, Southeast Plains, eastern Palmer Ridge, and eastern Raton Ridge. This threat also includes the Spring Creek burn area.

Lots of smoke is still trapped under the ridge, and it’s very widespread and thick over the eastern plains (marked below). The High will continue to strengthen over the Great Basin today, which will keep high temperatures on the rise over the western half of the state and hot temperatures in the forecast statewide. It’s still pretty dry over the western slope and Northern/Central Mountains, as seen by the cloud free conditions, so precipitation chances will continue to be near zero. A little moisture looks like it will combine with some mid-level energy over the San Juan Mountains, so expect another round of high-based showers over the eastern/southern San Juan Mountains this afternoon with slightly higher totals when compared to yesterday.

Over the Southeast Mountains, chances for precipitation also increase today. The slow-moving storms will be capable of producing isolated totals around 0.75 inches, which could be problematic if one forms over the Spring Creek burn area, so a Low flood threat has been issued. About a quarter of an inch fell yesterday on the southern portion of the burn area (gauge observation), which caused flash flooding and a debris flow onto Highway 12. This seems to be the most sensitive area of the scar.

A convergence boundary (weak cold front) will set up over the eastern plains and Raton Ridge this afternoon, which could spark some isolated storms. Less shear and a lack of a noticeable shortwave moving through the flow today means that storm coverage will be less and storms should be weaker when compared to yesterday. However, the slow steering winds will still allow the smaller storm cores to drop some heavy rainfall if they can break through the cap. Thus, the Low flood threat has been re-issued with dew points forecast in the 60Fs and PW just over 1 inch. Rainfall should start to end a couple hours after sundown.

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

Upslope flow will cause more widespread storms to form over the Southeast Mountains today, and southerly steering flow could push a few storms into the San Luis Valley where morning totals up to 0.25 inches will be possible. Isolated totals over the Southeast Mountains could reach 0.75 inches, so a Low flood threat has been issued for the Spring Creek burn area. More isolated storms are forecast over the Palmer Ridge and southern Front Range with totals up to 0.90 inches possible. Storms that move south, just off the foothills, could produce some severe hail again as well. Further north, a storm or two could form over the northern Front Range, but rain rates should remain around 0.50 inches with no rainfall again for the Denver Metro area.

Over the eastern plains, expect some more intense storms as parameters are more favorable with the stronger southeasterly surface winds. Still a chance a few storms could become severe that form along the convergence boundary, but the threat is lower than yesterday. The main threats from the severe storms that develop include heavy rainfall, large hail, and damaging outflow winds. A weak tornado could also be possible with extra spin along the front. With max 1-hour rain rates up to 1.75 inches possible, a Low flood threat has been issued.

Primetime: 1:30PM to 11PM

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

Looking like there’s still some mid-level moisture over the eastern/southern San Juan Mountains. This will spark another round of storms and some mid-level energy could help slightly increase totals and coverage when compared to yesterday. Isolated, totals up to 0.40 inches will be possible. Dry everywhere else with hot temperatures forecast again. Warmer temperatures near surface in today’s Grand Junction sounding and the HRRR Smoke indicate the smoke will take longer to mix out, so expect less near surface visibility with poor air quality.

Primetime: 1:30PM to 8PM

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

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

The High has shifted west and will start to build northward later today and into tonight, which will start to give the upper flow more of a northerly component over the state. This is especially true over eastern Colorado. Dry air will continue to dominate the majority of the state with PW measured at 0.39 inches in Grand Junction this morning, so this will keep precipitation chances low to nil over western Colorado and most of the high terrains. At the surface, more southeasterly and easterly surface winds are expected over the eastern plains and southern border due to a surface High over the High Plains, which will pull in some higher low-level moisture. Over the Front Range and Urban Corridor, expecting more of a drying, northwesterly surface wind. Paired with more westerly upper flow (also drying), the Front Range and Urban Corridor should stay dry today.

The combination of the surface winds will help set up a convergence boundary further east, which could initiate some severe thunderstorms this afternoon and evening over the plains. With more northerly steering winds and a shortwave moving around the ridge helping to spark and maintain convection, the storms could drop some heavy rainfall as they move south. It also looks like a moderately strong low-level jet could aid in keeping the convection going into the late hours of the night. Additionally, stronger upslope flow over the Southeast Mountains, Raton and Palmer Ridge should generate some additional storms, and as the storms move off the mountains, they will be capable of producing some heavier rainfall. A Low flood threat has been issued for the plains as well as over the Raton Ridge where extra convergence will give a better chance for some higher rainfall totals.

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:

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

These areas will have the higher moisture this afternoon and evening, giving them the best chance for some rainfall. Isolated, heavier rain will be possible over the Raton Ridge/Southeast Mountain intersect and slightly east with extra convergence along the ridge. Max 1-hour rain rates up to 1.2 inches will be possible, so a Low flood threat has been issued. Over the Southeast Mountains, rain rates up to 0.25 inches will be possible.

Severe thunderstorms over the eastern plains today and tonight could produce max 1-hour rain rates up to 2.75 inches. Some of the guidance is showing convection staying more isolated, but if the convection can become upscale tonight (MCS), that’s when the higher rain rates should be expected. Slightly better chances for these higher rain totals over the Southeast Plains, but if storms can break the cap over the Northeast Plains, early this evening, rain rates up to 1.9 inches will be possible. There is also a threat for very large hail and damaging outflow winds with the severe storms that develop. A Low flood threat has been issued.

Primetime: 1PM to 3AM

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

It should stay mostly dry in the regions today with temperatures rising a couple degrees. There’s still some upper-level moisture over the San Juan Mountains (blue in the water vapor imagery), so some high-based storms will be possible further east and south. The main threat will be gusty outflow winds with only isolated measurable rain possible (under 0.10 inch totals). Air quality will stay low, especially with another fire starting in Grand County yesterday. The more northerly flow aloft will help push some of the smoke further south. With the dry and hot conditions, fire growth is still expected today.

Primetime: 1PM to 8PM

Issue Date: Friday, August 14th, 2020
Issue Time: 8:05AM MDT

— Flooding is NOT expected today

There’s quite a bit of smoke across the state this morning, along with a new fire near Fort Collins highlighted in the visible satellite imagery below. Daytime heating will once again help mix out some of the smoke, so expect visibility to improve slightly from late morning into the afternoon. The eastward moving tough, to our north, will drop a cold front through eastern Colorado this morning, but it will be more of a wind shift than cooling feature. Not much moisture accompanying it either, so the weak upslope flow that occurs behind it this afternoon won’t produce much, if any, precipitation. The best chance for a thunderstorm or two will be over the far Southeast Plains where a convergence boundary sets up with a surface low. If storms form in the area, they will quickly move into Kansas where better storm parameters will exist for severe thunderstorm development. There is also a chance for some light rainfall over the eastern San Juan and Southeast Mountains. Some mid-level moisture, marked by the cloud cover below (purple), has worked its way in across the southern border. Isolated showers that do form will be high-based and produce more wind than rainfall, so flooding is not forecast 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:

San Juan Mountains, San Luis Valley, Southeast Mountains, Southeast Plains, & Raton Ridge:

Some upper level moisture has moved northwards across the southern border. This will help spark some isolated showers and cloud cover over the high terrains today. Isolated storm totals up to 0.15 inches will be possible, but most storms will produce only gusty outflow winds and sprinkles. A stronger storm or two could form over the Southeast Plains along a surface convergence boundary before quickly crossing into Kansas. Max 1-hour rain rates up to 1.20 inch will be possible. Flooding is not forecast today.

Primetime: 1PM to 10PM

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

As the High to our south begins to move westward today and tonight, the plume of smoke is expected to shift with it. Upper level winds gain more of a northerly component tonight, so areas to the south should expect a little more smoke in the overnight hours and by Saturday morning. With the new fire in Fort Collins, not sure the wind shift will bring relief from the smoke to the Urban Corridor. It’ll be too dry for any rainfall this afternoon, but some broken cloud cover should still be able to form. Winds might slightly increase from the north as the front drops south, but the stronger winds should stay over the far eastern plains.

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

It will remain dry again this afternoon. Some mid-level energy should mix with the slight increase in upper level moisture bringing more cloud cover and possibly a weak shower to the inner mountains. Stronger wind speeds will likely mix down to the surface again. However, with the trough to east, the pressure gradient (and associated wind) should decrease on the large-scale. While fire danger is still high with the dry fuels and low relative humidity values, a general decrease in surface winds means that no Red Flag Warning has been issued.