Issue Date: Friday, August 27th, 2021
Issue Time: 9:35AM MDT

— A LOW flood threat has been issued for the Raton Ridge and Southeast Plains

The large-scale trough will control our weather pattern today. West and northwest flow aloft has already begun to pull in the dry air mass marked below, which can be seen in both the Denver and Grand Junction soundings this morning. This will limit the chances for precipitation over the northern and central portions of the state today, although some isolated, weak storms may still be possible over the southern Front Range. An incoming jet to our north, associated with the base of the trough, will help to tighten the surface gradient over the northwest quadrant of the state. Breezy conditions should be expected this afternoon with westerly surface winds in the 15 to 25 mph range. A Red Flag Warning has been issued for Moffat County, so use caution with any activity that could cause a spark.

Further south, better moisture will likely hold on, which will be the focal point of scattered, mountain storms today. A drier surface layer is forecast over this region, which will make strong outflow winds and lightning the main threats from the storms that develop. This should also help to temper rainfall accumulations over the San Juan and Southeast Mountains, so only light to moderate rainfall totals are anticipated. Finally, the trough axis over the Raton Ridge and Southeast Plains (shown below) should help another round training storms to develop later this afternoon/evening. It will be a battle of southerly and southeasterly surface winds, trying to keep low-level moisture in place, and the incoming dry air aloft, trying to mix out this surface moisture. If the low-level moisture can hang on, storms may produce local, heavy rainfall, which may lead to some minor flooding issues. For this reason, a LOW flood threat has been issued. Storms should begin to wind down a couple hours after the sun sets and instability drops off.

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, Southeast Mountains, Front Range, Southeast Plains & Raton Ridge:

Scattered storms should develop over the southern Front Range, Southeast Mountains and San Juan Mountains this afternoon. Better coverage of storms and slightly higher rain rates are expected south. Max 1-hour rain rates up to 0.50 inches (south) and 0.15 inches (north) will be possible. The dry surface layer will make strong outflow winds and lightning the main threats from the storms that develop. Flooding is NOT expected here.

Better surface moisture may be able to hang on over the Raton Ridge and Southeast Plains near the surface trough. If it can, training storms over the area would likely produce higher rain rates. Max 1-hour rain rates up to 1.75 inches with storm totals up to 2.75 inches would be possible over an isolated area. In addition to this, stronger storms may produce small hail and gusty outflow winds. A LOW flood threat has been issued for road, arroyo, field and small stream flooding from these storms.
Primetime: 3:30PM to 9:30PM

Palmer Ridge, Southwest Slope, Central Mountains, Northeast Plains, San Luis Valley, Urban Corridor, Grand Valley, Northwest Slope & Northern Mountains:

Dry conditions are expected over these forecast regions, especially west. A high-based storm or two may drop a few sprinkles over the Palmer Ridge, but that’s about it. Westerly surface winds are forecast to reach 15 to 25 mph over the Northwest Slope, Northern Mountains, Grand Valley and portions of the Central Mountains by this afternoon. Critical fire weather should be limited to Moffat County where a Red Flag Warning has been issued. Nonetheless, use caution with any activity that could cause a spark this afternoon.

Issue Date: Thursday, August 26th, 2021
Issue Time: 9:55AM MDT

— Flooding is NOT expected today

There’s finally a pattern shift today as the now elongated High is replaced by an approaching trough. Currently, there is still a line of thunderstorms over the Northeast Plains that has been ongoing overnight, which is producing moderate rainfall. These storms will likely continue throughout the morning, but they are expected to weaken and lift to the northeast by midday. In addition to that set of storms, lift out in front of the trough axis (orange “X”) is producing scattered, weak storms and showers across western Colorado this morning. Grand Junction’s sounding showed that PW has risen to 0.71 inches. However, most of this moisture is located around 500mb, which means the dry surface layer has helped to limit rainfall accumulation. A second round of rainfall is forecast to arrive to the area this afternoon, and storms should become more efficient rainfall producers by this evening with the moistening of the boundary layer. With faster storm motion today, due to the jet overhead, and limited surface moisture, flooding is not forecast for this area. Enjoy the widespread, beneficial rainfall and cooler temperatures as the storms arrive.

Lift is also forecast to increase over the eastern mountains and adjacent plains this afternoon with the incoming trough. This will help to return scattered storms to the area by mid-afternoon, and a couple rounds of rainfall are forecast through this evening. A couple rounds of rainfall could help to increase local accumulations for the lucky locations, but quick storm motion to the east should limit the flood threat from any individual storm today. While a quick 0.50 inches in a 15 to 30 minute span could cause some nuisance road ponding over more impervious areas, flooding is NOT forecast. Scroll down below to read more details about today’s rainfall.

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

Showers and weak storms have already begun with the first round of rainfall this morning. So far, accumulations have been on the lower-end (under 0.15 inches). Expect a second wave of scattered storms to arrive this afternoon/evening and favor the central and northern portions of these zones for more widespread accumulations. Decent rainfall is still expected over the San Juan Mountains, but is not forecast to be as widespread. The second wave of storms should produce higher rain totals over the mountains with max 1-hour rainfall accumulations up to 0.65 inches possible. Areas that receive multiple rounds of storms could reach localized totals just over an inch by morning. Stronger thunderstorms this afternoon and evening may also produce some damaging outflow winds and small hail under their cores. Due to the more gradual accumulation of rainfall with faster storm motions, flooding is NOT forecast today.
Primetime: Ongoing to Midnight

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

Scattered storms will return to the mountains and elevated ridges this afternoon. Additional develop of storms is likely over the adjacent plains. With quick steering flows from the west, storms are expected to spill into the adjacent plains by mid-afternoon. Moisture remains higher across the lower elevations, which will help to increase rain rates. Max 1-hour rain rates up to 0.70 inches (mtns) and 1 inch (plains) will be possible, but due to the quick storm motion, totals should be slightly lower. The multiple rounds of rainfall could cause some localized totals up to 1 inch by morning, and this would be most likely over the Palmer Ridge area with the increased convergence. While the quick-moving storms today may cause some nuisance road and low-lying area ponding this afternoon and evening, flooding is NOT expected. In addition to rainfall, a couple stronger storms could produce gusty outflow winds, dangerous lightning and small hail.
Primetime: 2:30PM to 2AM

Issue Date: Wednesday, August 25th, 2021
Issue Time: 10AM MDT

— A LOW flood threat has been issued for the Northeast Plains, Palmer Ridge and Urban Corridor

Shown in the visible satellite imagery below is a lot of fog and cloud cover over the northeast corner of the state behind a cold front. The passage of the front will help to keep afternoon temperatures a few degrees cooler when compared to the last couple of days. With decent moisture return behind the front, PW at Denver has risen to 0.68 inches and increases to around an inch over the plains. A surface Low over the Southeast Plains will help to hold this moisture in place on its north and east side with east and southeast surface winds, which will help set the stage for the possibility of later PM storms. Best chance to break the cap will be over the Palmer Ridge this evening/tonight, and northeast movement of the isolated storms should allow the thunderstorms that develop to spread into the Northeast Plains overnight. There may be enough mid-level energy moving through the flow to pop some additional late afternoon storms along the Southeast Plains trough axis as well. Lower-end steering flow over the area, an increase in low-level moisture and an increase in upper dynamics may cause some localized flooding issues under the stronger storm cores that develop, so a LOW flood threat has been issued.

For western Colorado, the trough to our west will continue to move eastward throughout the day. As mid-level lift and moisture arrives late tonight and into tomorrow morning expect some light showers to develop over the area. Today however, windy and dry conditions continue, and a Red Flag Warning has been re-issued for Moffat County.

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 Plains, Northeast Plains & Urban Corridor:

Biggest difference to note about storms today is their later development. It will take a bit for the cap to break, so don’t expect the first round of storms until late this afternoon and evening. There’s some uncertainty where an isolated storm or two will be able to break the cap, but the highest likelihood is over the Palmer Ridge. As storms move northeast, outflow boundaries could trigger additional convection in the moisture rich environment for scattered storm coverage. Max 1-hour rain rates up to 1.25 inches (west) and 2 inches (east) with slightly higher storm totals are possible (1.40 inches and 2.50 inches, respectively). This could cause road flooding, field ponding and flooding of local streams and creeks. A LOW flood threat has been issued, which continues into the overnight hours. Additional storms could develop over the far Southeast Plains late this afternoon, and if they develop, these storms would be capable of producing storm totals up to 1 inch.

Primetime: 4:30PM to 2:30AM

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

It will likely be too dry today for rainfall over these forecast regions today. Some late night/early morning light showers will be possible across the western border area as the trough arrives. Rainfall should pick up tomorrow as this trough moves overhead. Today, dry, hot and breezy conditions continue. A Red Flag Warning has been issued for Moffat County with the jet overhead and tightening surface gradient. Southwest surface winds are forecast to be in the 10 to 20 mph range with gusts up to 30 mph possible. Flooding is NOT forecast.

Issue Date: Tuesday, August 24th, 2021
Issue Time: 8:55AM MDT

— Flooding is NOT expected today

Southwest flow aloft will continue today as the ridge builds northward across the state, which means another day of hot temperatures. This southwest flow and westerly/southwesterly surface winds have started to and will continue to pull in a very dry air mass over the state. An eastward moving surface Low over Kansas should help to scour out any remaining moisture over the plains. With PW dropping to below 0.50 inches and as low as 0.30 inches (west), measurable rainfall chances are near zero today. That means that flooding is not expected. There will likely be a little cloud cover this afternoon over the northeast quadrant of the state and Southeast Plains with the residual moisture and some mid-level energy, but measurable rainfall is not forecast. Lastly, there is a passing trough to our north, which is expected to tighten the surface gradient and produce breezy conditions over the Northwest Slope and portions of the central/northern mountains. A Red Flag Warning has been issued for Moffat County and portions of Rio Blanco County.

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

Today’s high temperatures are forecast to be in the upper 90Fs (east) and low to mid-90Fs (Urban Corridor). Portions of the Southeast Plains could reach the century mark. For the mountain valleys, temperatures in the 80Fs are forecast. It will be breezy in the mountains this afternoon and possibly further south over the adjacent plains. Too dry for any rainfall, but some fair weather clouds could develop with residual moisture (north and east). Flooding is NOT forecast.

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

Still hot, but not as hot as it has been this summer. Upper 80Fs and up to 90F are forecast for the lower elevations, and mountain valleys should reach into the upper 70Fs to low 80Fs. Rainfall is not forecast today, so there is NO flood threat issued. A Red Flag Warning is in affect for portions of the Southwest Slope where southwest winds are forecast in the 10 to 20 mph range with gusts up to 30 mph. Be sure to use caution with any activity that could cause a spark.