Issue Date: 8/31/2019
Issue Time: 6:55 AM

NO FLOOD THREAT IS FORECAST TODAY.

An upper-level ridge over the southwestern US will continue to build over Colorado today, resulting in a warmer and overall drier day across the state. Thus, the main weather story today will be the above-average temperatures and plenty of sunshine. With that said, residual moisture from previous days’ activity, combined with orographic influences, will allow for a few isolated thunderstorms over/near the higher terrain. Not much rainfall is expected due to a lack of near-surface moisture; much of the rainfall will evaporate before reaching the ground. Gusty winds, cloud-to-ground lightning, and brief periods of light-to-moderate rainfall will be all that storms can muster today.

For more details on timing and rain rates, please see the zone-specific forecasts below.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, jump below the map.

Zone-Specific Forecasts

Urban Corridor, Northeast Plains, Southeast Plains, Palmer Ridge, and Raton Ridge:

Mostly sunny and warm temperatures will be the main weather story today as the upper-level high pressure builds over the state. A couple isolated, high-based thunderstorms will rumble over areas adjacent to the higher terrain, as well as along the Palmer Ridge and Raton Ridge, but nothing more than brief periods of light-to-moderate rainfall (less than 0.25 inches/hour), gusty winds, and perhaps some small hail are expected. Further east over the plains, nothing but sunshine expected.

Timing: 2 PM – 10 PM

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

Mostly sunny skies will rule the start of the day, with fair weather cumulus building through the afternoon and early evening hours. A few isolated thunderstorms will develop thanks to daytime heating and orographic effects, mainly south of I-70. Gusty winds, brief periods of light rainfall (less than 0.15 inches/hour), and cloud-to-ground lightning will be the main impacts from any thunderstorm development. As dusk approaches and the day turns to night, clouds will clear out quickly, leaving mostly clear skies for the overnight hours.

Timing: Noon – 9 PM

Issue Date: Friday, August 30th, 2019
Issue Time: 9:35AM MDT

— A LOW flood threat has been issued for the southern Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Plains, Raton Ridge, Southeast Mountains, Junkins burn area and the Spring Creek burn area

Taking a look at the visible satellite imagery below, there are a couple of noteworthy features. First, the next shortwave can be seen along the dashed orange line. As upper level flow changes from westerly to northwesterly, expect this feature to arrive to the Northeast Plains this afternoon, which will help aid in shower and thunderstorm development. The second noteworthy feature is the cloud cover over the eastern plains, which indicates higher values of moisture have returned to the area. In fact, dew points over the Southeast Plains are already greater than 50°F, which is marked by the green solid line below. PW this morning at Denver was measured at 0.81 inches, which is quite the increase from the last couple of days. Throughout the day, southeasterly and easterly surface flow will reinforce and strengthen the low level moisture over the eastern plains. This will combat westerly flow aloft that will mix out moisture from west to east off the eastern high terrains. Thus, the heavy rainfall threat will mostly be east of I-25. The one exception is near the Wet and southern Southeast Mountains where stronger easterly surface flow will advect in higher moisture. Rain rates will be high enough to cause flash flooding issues over the Spring Creek and Junkins burn areas if a storm tracks overhead, so these scars are included in the Low flood threat.

With decent shear and CAPE in place, some isolated severe thunderstorms will be possible over the eastern plains where the cap can break. Storms this afternoon are forecast to be more scattered in nature due to the stability, but severe hail and damaging winds will be possible with a couple of the storms that are able to develop. Storm motion is forecast to the southeast at 10 to 15 mph, so local heavy rainfall is forecast, too, with the pulse-like storms. Note, there is a second wave of storms possible over the far northeast corner between 8 and 11PM that move in from the Nebraska panhandle, and if the cap can break, these storms will also be heavy rainfall producers. Thus, the low threat has been extended to the northeast corner.

Back to the west, dry thunderstorms are forecast again with the best chances for storms over the high terrains near and along the Continental Divide. PW at Grand Junction was measured at 0.72 inches with a lot of moisture above 600mb. So, there is enough moisture that critical fire weather should not be realized, but surface accumulations will remain light with the best chance for measurable rainfall over the Northern Mountains. Storms should end statewide around midnight.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

 

Zone-Specific Forecasts:

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

Plenty of action today thanks the approaching shortwave helping break the cap. Severe thunderstorms over the eastern plains will be capable of producing up to 1.25 inch hail and strong gusts (the main threat). In the Low flood threat area, max 1-hour rain rates up to 1.25 inches (west) and 1.8 inches (east) will be possible. Flash flooding is also possible over the Spring Creek and Junkins burn areas as there is moderate confidence all storms in the area will be capable of producing 1-hour rain rates greater than 0.50 inches and up to 0.75 inches. Flood threats over the burn areas include flash flooding of local streams, debris slides and mud flows. Flood threats over the eastern plains include field ponding, road flooding, local stream flash flooding and arroyo flooding (Southeast Plains). Lower rain rates (up to 0.6 inches) will be possible for storms that form over the Front Range and Southeast Mountains with the post frontal upslope flow. A Low flood threat has been issued due to the more isolated nature of the heavy rainfall producing storms this afternoon.

Primetime: 1:30PM to Midnight

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

A little bit of cloud cover where the shortwave is overhead this morning. An increase in moisture should limit the critical fire weather this afternoon, but dry thunderstorms will still be possible as well as gusty outflow winds. Best chances for measurable rainfall this afternoon will be over the Northern Mountains where isolated storm totals up to 0.2 inches will be possible. Flooding is not forecast.

Primetime: 1PM to 9PM

Issue Date: Thursday, August 29th, 2019
Issue Time: 9:25AM MDT

Relatively busy water vapor imagery below compared to the last couple of days. The subtropical high will move to the east throughout the day as a couple shortwaves move through the state with westerly (western CO) and northwesterly (eastern CO) upper level flow. Higher PW values continue to stay to our south and east in this setup, although moisture slightly recovers with the passing disturbances. PW was measured at 0.42 inches and 0.52 inches at Denver and Grand Junction, respectively. For western Colorado, this means some weak showers and dry thunderstorms may be possible over the higher terrains as the shortwave over Utah (marked below) shifts west and enhances upslope flow. Most storms are expected to produce gusty outflow winds rather than measurable rainfall. The main threat will be dangerous cloud-to-ground lightning in a low relative humidity environment with 10 to 15 mph sustained southwest surface winds. A Red Flag Warning has been issued for the Northwest Slope through 9PM this evening with enhanced fire weather anticipated over the mountains.

To the east, a cold front will start to drop south this morning associated with the passing trough. Moisture is forecast to increase to some extent behind this feature, which will allow for some high-based, weak thunderstorms over the Front Range this afternoon and evening driven by the diurnal flow. Again, gusts from storms and cloud-to-ground lightning will be the main threats rather than accumulating rainfall, so enhanced fire weather is forecast for the eastern mountains as well. Not looking like there will be a lot of storms associated with this feature over the eastern plains, but a couple weak thunderstorms may fire along this boundary over the far Southeast Plains this afternoon. Flooding is not forecast.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Hot temperatures and low relative humidity continues with an increase in chances for high-based storms this afternoon. The threat of dry thunderstorms returns the Red Flag Warning to the Northwest Slope with enhanced fire weather forecast for the higher terrains. Best chance for measurable rainfall will be over the San Juan Mountains/Dolores County and along the Continental Divide. Highest totals could reach 0.15 inches, but gusty winds and virga are more the more likely scenario with storms this afternoon and evening. High temperatures are forecast to reach the mid 90°Fs over the lower valleys.

Primetime: Noon to 10PM

Urban Corridor, Palmer Ridge, Raton Ridge, Southeast Plains, Northeast Plains:

The Southeast Plains will come close to the 100°F mark, so the cool down earlier this week will feel like a distance memory. A couple storms could fire along the cold front this afternoon over the Southeast Plains. Small hail, gusty winds and light rainfall will be the main threats. Max 1-hour rain rates up to 0.25 inches will be possible. Guidance hinting at some weak post frontal upslope storms over the Raton Ridge and southern Front Range around midnight, but totals should remain under 0.1 inches.

Primetime: 2PM to 9PM

Issue Date: Wednesday, August 28th, 2019
Issue Time: 10:15AM MDT

–Flooding is NOT expected today

Hot, dry weather is expected statewide today as the upper level high continues to build over the desert southwest.  Shown in the mid-level water vapor imagery below is the dry air mass that has been over the state throughout this week (yellow shading).  Just how dry is it? PW continues to near (daily) record minimums both at Grand Junction and Denver. As a result, measurable rainfall is very unlikely statewide. An isolated thunderstorm may pop over Baca County along a dryline, but chances of this happening are low.

Surface winds are anticipated to increase, and with relative humility forecast to be in the teens to single digits, a Red Flag Warning has been issued for Moffat County and the upper elevations of the Front Range, Northern Mountains and Central Mountains through 8PM this evening.  Elevated fire danger is forecast for the entire state with the low relative humidity values this afternoon.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

A Red Flag Warning has been issued for northwest Moffat County and the high elevations of Front Range, Northern Mountains and Central Mountains. Over Moffat County, sustained southwest winds between 10 and 15 mph are forecast with gusts up to 30 mph. Over the mountains, sustained, westerly winds are forecast to be between 10 and 20 mph with most wind gusts in the 30 to 35 mph range. Please use caution with open flames as critical fire weather allows fire to spread rapidly. The heat begins to return as well with high temperatures increasing by ~5-7°F. The Grand Valley and Southwest Slope are expected to reach the mid 90°Fs once again. Expect an increase in cloud cover from west to east overnight as the next system moves into the state.

Urban Corridor, Northeast Plains, Palmer Ridge, Southeast Plains, Southeast Mountains, Raton Ridge:

High temperatures are forecast to increase significantly over the region today (greater than 10°F over the Northeast Plains). Sunny skies and southerly surface flow will be the culprit of the rapid rise in temperatures. Highs are expected to reach into the low to mid 90°Fs over the eastern plains and the 80°Fs over the higher terrain to the west. Upslope flow of residual moisture over the Raton Ridge could produce a raindrop or two, but virga is the more likely scenario. The best chance for rainfall today, which is still an outside shot, will be over Baca County. There may be a thunderstorm that pops along the dryline with lift provided from a passing shortwave. Max 1-hour rain rates up to 0.5 inches will be possible if this storm can break the cap.

Primetime: 2:30PM to 6PM