Issue Date: Friday, July 14, 2017
Issue Time: 10:30AM MDT

—HIGH flood threat for burn scars over the Southeast Mountains

—MODERATE flood threat for Palmer Ridge, Southeast Mountains, Southeast Plains, Raton Ridge and San Juan Mountains

—LOW flood threat for Front Range, Central Mountains, Grand Valley, Southwest Slope, Urban Corridor, Palmer Ridge

Only subtle changes are expected to today’s weather pattern, compared to what was observed on Thursday. As shown in the water vapor image, below, we continue to see a duel between the upper-level ridge just west of our state with copious amounts of low-level moisture available in southeast Colorado. Despite the fact the the ridge will strengthen today, once again, the moisture will win out today (at least for the roughly the southern half of the state). To the north, the water vapor imagery also shows a strong moisture gradient with a marked drop-off in relative humidity roughly between the 500-600 mb level: this is clearly seen on the 12Z Denver sounding this morning. This feature handily squashed convection convection forming north of the Palmer Ridge on Thursday and will continue to do so today.

For southeast Colorado, storms will develop before noon, capable of producing rainfall up to 2.4 inches per hour. A broad Moderate flood threat has been posted, further warranted since wide parts of the area have received over 1 inch of rainfall in the past 48 hours (see Storm Total Precipitation map for more).

For southwest Colorado, efficient rainfall producing storms will once again form today. Guidance indicates the potential for slightly higher rain rates – warranting a small Moderate threat area surrounded by a Low threat.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Sunny early then storms developing by early afternoon. Max 1-hour rainfall up to 2.4 inches with max 3-hour rainfall up to 3.3 inches. Isolated flash flooding will be likely in the Moderate threat area, with mud flows and debris slides possible in the foothills. The 2016 fire burn areas have once again been placed under a High flood threat due to high confidence that over 0.5 inches of rainfall per hour is possible there.

Primetime: 11:30AM to 2AM (though highest rain rates will subside after 11PM)

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

Sunny early then thunderstorms and showers quickly developing by noon. Max 1-hour rain rates up to 1.2 inches with max 3-hour up to 1.9 inches. Parts of the San Juans have been placed under a Moderate flood threat with a Low flood threat surrounding that region. Debris slides and mud flows will be the main risks, though isolated flash flooding will also be possible.

Primetime: 11:30AM to 8:30PM

Northwest Slope, Northern Mountains, Front Range, Urban Corridor, Northeast Plains:

Sunny early then turning partly cloudy and warmer with an isolated to scattered showers and thunderstorms possible during the afternoon and evening. Max 1-hour rainfall up to 1.5 inches (far east) to 1.0 inches (central) and 0.5 inches (west). Flooding is not expected today.

Primetime: 11:30AM to 8:30PM

Issue Date: Thursday, July 13, 2017
Issue Time: 11:00AM MDT

—HIGH flood threat for burn scars over the Southeast Mountains

—MODERATE flood threat for Front Range, Palmer Ridge, Southeast Mountains, Southeast Plains and Raton Ridge

—LOW flood threat for Northwest Slope, Northern Mountains, Front Range, Central Mountains, Grand Valley, Southwest Slope, San Juan Mountains, Southeast Mountains, Southeast Plains, Urban Corridor, Palmer Ridge and Raton Ridge

The upper level ridge off to the north and west of Colorado will begin to build and move east today, but will stay far enough north for moisture to return to the state with southerly and southeasterly surface winds. Precipitable Water values currently are 0.91 inches this morning for Denver and 0.97 inches for Grand Junction. PW values over the Southeast Plains are 1.4 inches now and are expected to increase to 1.5 inches again today. Lamar’s current dew point is 66F, which is very high. As the upslope flow sets up, easterly surface winds will help pull even more moisture in from southern KS. There is a lot of mixing out of the moisture in the mid-levels over the Northeast Plains, so storm formation should be confined to the southern high country and Palmer Divide.

Another focal point of heavy rains is over the Southeast Plains where the moisture gradient is marked below. A fair amount of energy is expected to build up over the Southeast Plains during the afternoon, so storms that form off the higher terrain should be able to sustain themselves. Steering winds remain weak, so storms will once again will have access to high PW and be moving slow (to the S/SW) making them heavy rainfall producers. Wet soils will increase runoff as well as field ponding. The main threats today are heavy rain, flash flooding, gusty winds, urban and small stream flooding, mud flows and debris slides. A High threat has again been placed of the recent burn scars in the Southeast Mountains as there is sufficient confidence storms that form will have rain rates greater than 0.5 inches. Heavy rainfall could cause local flooding and debris flows over the already saturated soils. Storms over the high terrain will begin to dissipate around 10PM while thunderstorms in the eastern plains will continue through 2AM.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Northwest Slope, Northern Mountains, Grand Valley, Central Mountains, San Luis Valley, Northeast Plains:

Partly cloudy this morning becoming sunny. Higher precipitation amounts will be over higher terrain in central and southern CO with max 1-hr rain rates of 1 inch. Storms over the higher terrain will end around 10PM. There is a Low flood threat for the Flat Top Mountains, which experienced over an inch of measureable precipitation yesterday. With 1-hour max rain rates of 1.1 inches forecasted here, this could easily trigger mudslides, debris flows and local flash flooding.

Primetime: 11AM to 10PM

Front Range, Southeast Mountains, Urban Corridor, Raton Ridge, Palmer Ridge, Southeast Plains, San Juan Mountains, Southwest Slope:

Partly cloudy this morning becoming sunny. Temperatures should be near normal or a few degrees below. Over the mountains, 1-hr rain rates are expected to be as high as 1.2 inches with 1-hr rain rates as high as 2.5 inches over the eastern plains. Over the eastern plains, 3 hour rainfall totals of 3.25 inches are possible, which is why a Moderate threat has been issued. Flash flooding, urban and small stream flooding, field ponding, mudslides and debris flows are possible today. Some storms over the plains may become severe with winds up to 60 mph and small hail. Burn scars need to be monitored closely again today as there is sufficient confidence storms will produce rain rates greater than 0.5 inches per hour. This paired with moist soil from measurable rainfall the last three days warrants a High threat.

Primetime: 11AM to 2AM

Issue Date: Wednesday, July 12, 2017
Issue Time: 11:00AM MDT

—HIGH flood threat for parts of Southeast Plains

—MODERATE flood threat for Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Plains, and burn scars over the Southeast Mountains

—LOW flood threat for Southwest Slope, San Juan Mountains, Southeast Mountains, Raton Ridge, Front Range, Urban Corridor, Southeast Plains, Northeast Plains, Palmer Ridge

PM Update: Near record Precipitable Water exceeding 1.5 inches is noted in eastern Colorado, along with a mesoscale surface low pressure circulation over the southeast part of the state. Numerous rounds of showers and storms are expected, capable of producing very heavy rainfall. Isolated flash flooding is likely over the higher threat area. Farther north, a lack of instability has reduced heavy rainfall chances though showers are still expected well into the evening.

There still seems to be a disturbance over the central and southern portions of Colorado this morning as seen in the visible satellite below. This should move through the state this morning and clouds will begin to burn off early afternoon with daytime heating. The cloud deck will help keep temperatures closer to normal today. Over the plains, a cold front is currently positioned along the WY/NE border and will push southward into the eastern plains early this afternoon. This could help organize a few isolated thunderstorms that form along the high terrain and Palmer Divide. The main threats include heavy rain, flooding, hail and gusty winds. Storms will become widespread on the eastern plains in the early evening hours to midnight.

The upper level ridge will begin to rebuild itself this afternoon over Idaho and Montana. Although this will mix out some of the moisture west of the Continental Divide, residual moisture from yesterday will be enough to fire storms off the higher terrain again early this afternoon. Expect rainfall totals to be a bit lower than yesterday as you move north. Current Precipitable Water (PW) readings are 1.2 inches for Grand Junction and 1 inch for Denver. Moisture over Denver is expected to increase to 1.2 inches today with the portions of the eastern plains reaching 1.5 inches. Once the storms begin to move off the higher terrain in the afternoon, expect slow moving storms again today. Threats include heavy local rainfall, urban and small stream flash flooding, debris slides, mud flows and field ponding. Fresh fire scars will need to be monitored throughout the afternoon. The burn scars in the Southeast Mountains have had rain the last couple of days, so another day of rain rates greater than 0.5 inches warrant a High threat. Storms over the high terrain will begin to dissipate around 10PM while thunderstorms in the eastern plains will continue through 1AM.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Partly cloudy this morning with storms beginning to end late morning. Cloud cover will begin to burn off just before storms begin to fire off the high terrain again. Higher precipitation amounts will be in central and southern CO with max 1-hr rain rates of 1.2 inches. Local flash flooding, mudslides and debris flows are possible today which is why a Low Threat is warranted.

Primetime: 11AM to 10PM

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

Partly cloudy this morning in the mountains and Northeast Plains. Expect clouds to burn off midday, but they will help keep temperatures near normal. 1-hr rain rates are expect to be as high as 2.5 inches, which is why a Moderate threat has been issued. Flash flooding, urban and small stream flooding, field ponding, mudslides and debris flows are possible today. Some storms over the plains may become severe with winds up to 60 mph and small hail. Burn scars need to be monitored closely again today as there is sufficient confidence storms will produce rain rates greater than 0.5 inches per hour. This paired with moist soil from measurable rainfall the last two days warrants a High threat.

Primetime: 12AM to 1AM

Issue Date: Tuesday, July 11, 2017
Issue Time: 10:45AM MDT

—LOW flood threat for Northwest Slope, Northern Mountains, Front Range, Urban Corridor, Grand Valley, Central Mountains, Palmer Ridge, Southwest Slope, San Juan Mountains, Southeast Mountains

More zonal flow aloft over Colorado will help moisture return to the state today. At the surface, the breakdown of the persistent ridge pattern will allow southwesterly and westerly flow at the surface. This will provide the influx of moisture, especially to the western portion of the Continental Divide. Morning soundings have precipitable water at Denver and Grand Junction higher than this time yesterday, and they are both expected to rise over an inch throughout the day. Strong daytime heating will once again create upslope flow and storms will begin to form over the higher terrain midday. Storm coverage will be more widespread than yesterday.

The storms will move off the mountains mid-afternoon into the southern Urban Corridor, Palmer Ridge and Southeast Mountains, but will not dissipate like yesterday. Weaker winds aloft will limit steering and speed of storms. This combination of slow storms with high moisture will warrant a low threat today. Any storms that form near burn scars need to be closely monitored as they could trigger flash flooding, mudslides or debris flows. Another Low threat was placed over the Junkins and Hayden Pass burn scar due to sufficient confidence any storms that form will produce over 0.5 inches per hour. Additionally, many outflow boundaries from yesterday, and new outflow boundaries that form from storms today, will aid in surface convergence for supplementary storm formation this afternoon and evening. A portion of the jet will dip into northern CO this evening, which will provide extra lift for storms in this area and help trigger a second round of showers into the night. Storms are expected to dissipate over the mountains around midnight and linger into the early morning over the eastern plains.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Partly cloudy for the western slope and portions of the mountains. It will become sunny today just before storms begin to form over the high country midday. Storms will be more widespread than yesterday with more moisture, so the main threats are heavy local rains, gusty winds and small hail. An upper level jet will drop close to northern CO this evening helping provide additional lift in this area for a second round of storms this evening. Max 1-hour rainfall rates of 1.5 inches are expected over the mountains. 30-min rain rates could be as 0.8 inches. Local flash flooding, mudslides and debris flows are possible today.

Primetime: 11AM to 1AM

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

Clouds will burn off this morning allowing the sun to shine through. Storms will begin to form over the high country midday. They will move off the mountains mid-afternoon and have max 1-hour rainfall rates of 1.5 inches. 30-min rain rates could be as high as 0.9 inches. The low threat is limited to the southern Urban Corridor over the higher terrain. There was an additional Low threat placed over the Hayden Pass and Junkins burn scar due to sufficient confidence rainfall rates of 0.5 inches per hour are likely. Local flash flooding, mudslides and debris flows are possible today, especially over burn scars.

Primetime: 1PM to 4AM