Issue Date: Saturday, August 1st, 2020
Issue Time: 09:30AM MDT

— Flooding is NOT expected today

Today’s weather setup looks very similar to yesterday as we remain under north-northwesterly flow aloft due to being crammed between a high amplitude upper-level ridge to the west and a trough to the east (see satellite image below). The satellite water vapor imagery below indicates Colorado is not in extremely dry air (light blue rather than orange/yellow), but this morning’s soundings only show 0.6 inches of PW at Denver and Grand Junction, a slight decrease since yesterday for Denver and a slight increase for Grand Junction. However, the moderate north-northwest flow is not transporting high amounts of moisture into Colorado as conditions look similar along the eastern Rockies up into Montana. Surface dew points this morning show a gradient from west to east, with western Colorado showing drier 30Fs and eastern Colorado upper 40Fs to mid 50Fs. This means higher chances for rain-producing thunderstorms exists over the eastern half of Colorado today. Little cloud clover is evident over Colorado this morning, which will allow plenty of diurnal heating and mixing in the boundary layer. This mixing will lower surface dew points into the 40Fs for the eastern plains of Colorado. However, there should be plenty of moisture and instability for high-based thunderstorms to develop over the mountains this afternoon, especially over the Front Range, Southeast Mountains, and southern San Juan Mountains. But, due to the higher cloud bases and plenty of sub-cloud evaporation, heavy rainfall capable of causing flooding is not expected today.

Overnight and early morning showers and thunderstorms may be possible along the Northeast Plains as a cold front sags its way south. This current cold front is located across South Dakota and has been labeled on the image below. This front will push in cooler and more moist air from the north and act as a convergence boundary where showers and storms could develop, but due to its overnight and early morning arrival, instability will be limited. This should keep rain rates below 0.6 in/hr. No flooding is expected from these showers and 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:

Northern Mountains, Central Mountains, San Juan Mountains, Front Range, Southeast Mountains, San Luis Valley, Raton Ridge, Urban Corridor, Palmer Ridge, Northeast Plains, & Southeast Plains:

Scattered thunderstorms will develop this afternoon over the mountains and track south-southeast into the adjacent plains. Storms could produce max rain rates up to 0.2 in/hr west of the Continental Divide and up to 0.7 in/hr east of the Divide. The highest chances and coverage of storms will be over the Front Range, Southeast Mountains, and southern San Juan Mountains. Due to moderate storm motions and dry sub-cloud air, flooding is not expected over the mountains and adjacent plains. Some small hail and gusty winds up to 50 mph are possible with the stronger storms.

Overnight and early morning showers and possible in the Northeast Plains as a cold front moves into the area. Rain rates up to 0.6 in/hr are possible, but flooding is not expected.

Primetime: 1PM to ongoing

Northwest Slope, Grand Valley, & Southwest Slope:

Partly cloudy and warm today with high temperatures near 100F for lower elevations of the Grand Valley. Some weak storms may fire over the high terrain, but rain rates should stay below 0.2 in/hr. No flooding is expected today.

Issue Date: Friday, July 31st, 2020
Issue Time: 10:15AM MDT

— Flooding is NOT expected today

Strong northerly flow continues over Colorado today due to the state being stuck between a high amplitude ridge to the west and a departing low pressure system/trough to the east (see satellite image below). This strong flow aloft will cause diurnally-driven storms to move quickly to the south-southeast. Some moisture is present along the plains of eastern Colorado this morning where dew points are near or just above the 50F mark, but the moisture looks shallow. The morning Denver sounding shows abundant dry air aloft with PW similar to yesterday at 0.75 inches. Even more dry air is evident in the Grand Junction sounding (PW = 0.51 inches), indicating storms will favor the eastern portion of the state. The dry air will help mix out surface moisture, and drop dew points into the 30Fs and 40Fs, which will limit the amount of instability that can build and cause storms to have higher bases and produce more gusty winds than rainfall. There will still be enough moisture to fire isolated to scattered storms over the mountain terrains with ample sunshine, and storms should favor the eastern mountains and southern San Juan Mountains for development. Better moisture will remain further south over the Southeast Mountains today, so higher rain rates will be expected here. Storms will have difficulty producing heavy rain due to fast storm motions and the limited low-level moisture, so flooding is not expected today.

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:

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

Isolated to scattered diurnal thunderstorms will fire over the higher terrain and track south-southeast this afternoon. The highest chances for storm coverage will be over the Sangre de Cristo Mountains, and max 1-hour rain rates up to 0.4 inches will be possible. Slightly higher totals might be possible over the western Raton Ridge further south. Flooding is not expected today, but as always, if a storm tracks directly over a recent burn area, there is a chance for flash flooding issues, so use caution if near one. Further north and west, max 1-hour rain rates up to 0.25 inches will be possible. Storms could also produce gusty outflow winds (up to 45mph).

An isolated thunderstorm or two will likely track into the Urban Corridor and plains regions as they move off the mountains, but these storms should dissipate quickly and may produce some strong outflow winds as this occurs. Additionally, some storms may track into the Northeast Plains, but quick storm motion to the south should keep totals around 0.5 inches. No flooding is expected.

Primetime: 1PM to 11PM

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

Mostly sunny and warm today with high temperatures possibly reaching 100F for the Grand Valley. Small, isolated diurnal storms are possible over the southern Central and San Juan Mountains, but rain rates should stay under 0.1 in/hr. Storms could produce brief gusts up to 40 mph. Flooding is not forecasted.

Issue Date: Thursday, July 30th, 2020
Issue Time: 9:50AM MDT

— A LOW flood threat has been issued for the Northeast Plains, Southeast Plains, Front Range, Urban Corridor, and portions of the Palmer Ridge

Back to issuing flood threats after a quick, one-day break. The satellite image below shows two strong and distinct air masses at play over the state. The much drier air to our west/southwest from the High (clear conditions) and the more unsettled, wetter air mass to the northeast from the passing trough (generating showers and cloud cover). This upper trough, that has been affecting the weather the last couple of days, will finally push south and brush Colorado’s eastern border producing unsettled weather over the eastern plains. Mid-level energy and ample moisture with the feature is expected to generate non-severe thunderstorms and multiple rounds of rainfall over the Northeast Plains. With these storms starting by late morning, increasing in intensity by this afternoon, and lingering through the evening, a Low flood threat has been issued. While precipitation totals could be on the higher end, hopefully the expected lower 1-hour rain rates can temper the flood threat somewhat. Threats include field ponding, road flooding, and flooding of low-lying areas.

A second, weaker shortwave will slide south in to the northern high terrains later this afternoon with the NNW flow aloft, and help spark some isolated thunderstorms in tandem with upslope flow over the Front Range. It’s likely that the storms that form over the Northeast Plains will push a moisture boundary back to the west, so decent rainfall accumulations will be possible under the stronger storms as dew points in the plains are in the upper 50Fs to low 60Fs. Again, storm motion will be relatively fast, so the flood threat will be limited to only the stronger storms that develop. Additionally, a quick 0.5 in 30-min could cause some nuisance road flooding or ponding as storms track south along the I-25 corridor. A Low flood threat has been issued for these regions.

Over western Colorado, it has quickly dried out from the monsoon moisture early this week with PW measured at 0.50 inches this morning. Capping aloft and a dry atmosphere will drop-off the rainfall chances to nearly nil today. Outsides of some cloud cover over the mountains near the Continental Divide, it should be a bluebird day.

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:

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

Multiple rounds of rain with some non-severe thunderstorms will be possible over the Northeast Plains by late this morning into the evening with the passing trough. Isolated storm totals up to 2.2 inches will be possible by Friday morning with the training rainfall. A stronger storm could also push into the area that forms over the Cheyenne Ridge. A Low flood threat has been issued for field ponding and flooding of roads/low-lying areas.

Over the Front Range in to the Urban Corridor, isolated max 1-hour rain rates up to 1 inches will be possible if the moisture can push westward into the foothills and I-25 corridor. A quick 0.5 inches in 30 minutes could also produce some nuisance flooding in roads and low-lying areas. A Low flood threat has been issued. Unsure how far south across the I-25 corridor storms will be able to track before decreasing instability puts a cap on the convection.

Primetime: 11AM to 9PM

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

High temperatures will be on the rise today with the bluebird conditions. Highs are expected to reach into 90Fs over the lower elevations with 70Fs in the mountains. A few clouds are forecast by this afternoon over the peaks near the Continental Divide, but rainfall is not forecast.

Issue Date: Wednesday, July 29th, 2020
Issue Time: 10:10AM MDT

— Flooding is NOT expected today

Today, Colorado continues to be situated between a shortwave trough to the north and an amplifying dry, high pressure ridge to the southwest. The water vapor satellite imagery below shows the clouds and moisture over Wyoming associated with the Low that moved in from California a couple days ago. This setup has produced drying northwesterly winds over the majority of the state, which has and will continue to scour out low-level moisture in a more stable atmosphere. PW values have dropped off significantly, since the monsoon plume has been pushed south and east, to just over 0.7 inch at Denver and Grand Junction. Some isolated mountain showers are still expected to develop over the higher terrain today due to abundant heating and leftover moisture. However the drier air, faster steering flows, and low rainfall rates will give the soils a chance to dry out. No flooding is expected over the mountains today.

As the Low pressure system tracks southeast into southwest Nebraska, the far Northeast Plains will likely see some stronger storms. However, the position of the Low farther east will mainly support drier northwesterly winds and a possible cool front or outflow boundary dropping into the Northeast Plains of Colorado later this afternoon and evening. If surface moisture can hang on, rather than being scoured out to the east, a couple stronger storms could produce isolated totals up to 1.5 inches where outflow boundaries increase convergence. However, moderate storm motions of 20-25 mph should keep the threat area small enough that flooding is not expected. If overnight storms look to track into the area later this afternoon, a PM update will be issued. At this time, there is a better probability that the heavy PM rainfall will be over Nebraska.

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, Southeast Plains, Urban Corridor, & Palmer Ridge:

Scattered thunderstorms may track through the Northeast Plains this afternoon and evening, and isolated max rain rates up to 1.5 inch are possible. Showers could linger into the morning along the northeast corner of the state as the low pressure system drifts southward along the eastern border of Colorado. Chances for rain quickly decrease further west with the drier air and more stable air mass in place, so accumulations over the mountains should stay under 0.1 inches. Flooding is not expected today.

Primetime: 12PM to ongoing

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

Mostly sunny with isolated mountain showers developing after noon. With dry air continuing to move into the area, the weak storms could produce some brief, gusty outflow winds. Any showers that develop should quickly move southeast, and totals are expected to stay below 0.1 inches. Flooding is not forecasted.