Issue Date: Monday, July 10, 2017
Issue Time: 09:45AM MDT

—Flooding is NOT expected today

The upper level ridge shifts more to the east today while also becoming more zonal this afternoon. This westerly flow will allow a bit more mid-level moisture to build up over the high country west of the Continental Divide. Some embedded vorticitiy maximums in the zonal flow aloft will help produce a little extra lift over the northern portion of the state. Storms will develop with upslope flow early this afternoon over the higher terrain and should be more widespread in coverage than yesterday. Precipitable water values at Denver and Grand Junction this morning were 0.69 inches and 0.84 inches, respectively. Moisture is only expected to increase a little throughout the day, so all storms that form will have hourly precipitation rates under flood threat criteria with the main threat being small hail and gusty winds. Over the NE corner of the state, a weak cold front will set up this afternoon. This could help support some isolated severe weather in the Northeast Plains. These isolated storms could produce hail up to 1 inch diameter, wind gusts up to 60 mph and 1-hour rain rates up to 1 inch.

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, Urban Corridor, Palmer Ridge Northeast Plains, Grand Valley, San Juan Mountains, Southwest Slope, San Luis Valley, Southeast Mountains:

Sunny and then becoming partly cloudy with storms forming over the high country early this afternoon. Storms should be more widespread than yesterday with the main threat being gusty winds, small hail and lightning. A weak front will be positioned over the Northeast Plains near the NE border that may support some isolated severe storms later this afternoon. Max 1-hour rainfall rates of 0.75 inches are expected over the mountains. 1-hour rain rates over the Northeast Plains will be up to 1 inch. Flooding is not expected today.

Primetime: 11AM to 1AM

Southeast Plains, Raton Ridge:

Sunny throughout the day with high temperatures 5-10F above normal. Storms that develop over the higher terrain will not affect the Southeast Plains.

Issue Date: Sunday, July 9, 2017
Issue Time: 10AM MDT

— Flooding is NOT expected today

In the wake of yesterday’s weak disturbance, a significantly drier atmosphere is seen across most of Colorado this morning as seen in the low-level water vapor image below. Precipitable water (PW) values have dropped from 0.8 – 1 inch yesterday into the 0.4 – 0.7 inch range today. As the weak disturbance continues to move southward within the clockwise flow around the Great Basin ridge, weak subsidence will follow in its wake. Expect a significant reduction in storm coverage today, with most activity limited to the CO/NM border. Brief heavy rainfall will once again be likely today, but the intensity will not be enough to warrant a flood threat. With increased sunshine expected, very hot temperatures will be back in the forecast unless you are lucky enough to get a rain-cooled outflow boundary later this afternoon.

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:

San Luis Valley, San Juan Mountains, Southeast Mountains:

Sunny early then partly cloudy with scattered showers and storms developing by early afternoon. Max 30-minute rainfall up to 0.5 inches, with max 1-hour rainfall up to 0.75 inches. Flooding is NOT expected today.

Primetime: 12PM to 8PM

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

Mostly sunny early then partly cloudy with isolated showers and a weak thunderstorm possible over the higher terrain this afternoon. Max 30-minute rainfall up to 0.4 inches, Flooding is NOT expected today.

Primetime: 12PM to 8PM

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

Sunny early, then partly cloudy and continued warm today with high temperatures 5 – 15F above normal. Isolated to widely scattered thunderstorms and showers are possible this afternoon, with highest coverage across southern areas. Max 30-minute rainfall up to 0.2 inches. Gusty winds and dry lightning with the strongest storms will continue to pose a wildfire threat. Flooding is not expected today.

Primetime: 12PM to 7PM

Issue Date: Saturday, July 8, 2017
Issue Time: 9:35AM MDT

— MODERATE flood threat for Junkins, Beulah Hill and Hayden Pass fire burns
— LOW flood threat for Front Range, Urban Corridor, Palmer Ridge, Southeast Plains, Raton Ridge and Southeast Mountains

As the water vapor image shows, below, the main player in driving today’s weather across Colorado will continue to be the upper-level ridge located over the southwest US. Although this ridge will promote weak subsidence and above normal temperatures statewide, it is not the full story. Low-level moisture has continued to steadily increase, with Precipitable Water (PW) values exceeding 0.5 inches statewide as of this morning. West of the Continental Divide, this moisture is mainly at mid-levels, thus, though storms will again be seen, heavy rainfall will be lacking. In areas to the east, with PW values exceeding 0.75 inches even for locations above 6,000 feet, isolated heavy rainfall will once again be a good bet today. Compared to yesterday, two other notable features are seen this morning. First, a weak vorticity maximum identified over southern Wyoming will help create lift as it moves southeast across the Colorado. Second, storm steering winds will have a weak easterly component today, implying the potential for training storms near the foothills. A Low flood threat has been issued for parts of east/southeast Colorado today. However, a Moderate flood threat has been posted for the fresh 2016 fire burn areas in the Sangre de Cristo and Wet Mountains.

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:

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

Mostly sunny early then partly cloudy with scattered to widespread showers and thunderstorms developing by early afternoon. Highest coverage will be closer to the mountains and southern areas. The initial storms will likely produce outflow boundaries for additional activity into the late afternoon and early evening. Max 30-minute rainfall up to 1.5 inches, with max 1 hour rainfall up to 2.2 inches. A Low flood threat has been posted for parts of the region. A Moderate flood threat has been posted for the Hayden Pass, Junkins and Beulah Hill fire scars due to greater than 50% chance of seeing 0.5 inch per hour rainfall intensity.

Primetime: 12PM to 10PM

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

Sunny early, then partly cloudy and continued warm today with high temperatures 5 – 10F above normal. Isolated to widely scattered thunderstorms and showers are expected this afternoon, with highest coverage across southern areas. Max 30-minute rainfall up to 0.3 inches, except up to 0.6 inches in the San Juans near the NM border. Gusty winds and dry lightning with the strongest storms will continue to pose a wildfire threat. Flooding is not expected today.

Primetime: 1PM to 8PM

Issue Date: Friday, July 7, 2017
Issue Time: 11:00AM MDT

—Low Threat for Northern Mountains, Urban Corridor, Front Range, Northeast Plains, Palmer Ridge, Southeast Plains and Southeast Mountains

Update:
The Low Threat has been extended south to include all of the Southeast Plains and Raton Ridge. An outflow boundary is moving southeast from Pueblo and El Paso County. With high temperatures, dew points near 50F and the slow moving nature of the storms, local flooding can be expected. Rain rates up to 2.3 inches per hour are expected with 3-hour totals up to 3.6 inches. NWS issued a flood advisory over the Junkins burn scar.

—————————- Previous Discussion —————————-

The high pressure continues to be parked over the four corners region once again today. There is a noticeable uptick in Precipitable Water (PW) this morning across the state, but especially over the eastern plains. Denver’s sounding this morning showed the PW at 0.76 inches and is expected to approach or exceed 1 inch this afternoon. This indicates the potential of thunderstorms capable of heavy rainfall this afternoon. Expect upslope flow again with storms forming over the higher terrain and Palmer Divide. The increase in moisture, will cause thunderstorm formation to be more plentiful across the higher terrain. Dew points are expected to reach 55F-60F on the eastern plains.

A cold front will drop into the Northeast Plains and stall out over the Palmer Divide this afternoon. This forcing will provide low-level convergence that will generate scattered to numerous thunderstorm development. Severe weather (large hail, strong wind) is possible if it moves through when peak heating and instability are occurring. Outflow boundaries from all storms are likely to provide an additional lifting mechanism for storm formation as they have during the last couple of days. The main threats will be small hail, gusty winds and heavy rain. The main threats will be small hail, gusty winds and heavy rain. Rain rates up to 2.3 inches per hour are forecasted with the increased moisture and slow storm motion. Three hour rain totals could be up to 3.6 inches. A Low Threat has been issued.

Over the Wet Mountains, a separate Low Threat has been issued. There is sufficient confidence that storms that form will have rain rates greater than 0.5 inches per hour. Over the fresh burn scars from last year, these rain rates could trigger flash flooding, mud slides and debris flows.

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:

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

Sunny early with thunderstorms forming over the higher terrain this afternoon. Storms over the eastern plains could become severe with the main threats being small hail and gusty winds. Max 1-hour rainfall for 2.3 inches is possible with the slow moving storms. A Low flood threat has been posted for isolated flash flooding, debris slides and mud flows. A separate Low flood threat has been issued for the Wet Mountains due to sufficient confidence in rainfall rates greater than 0.5 inches occurring over 2016’s burn scars.

Primetime: 1PM to 12AM

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

Sunny early becoming partly cloudy in the afternoon. An isolated shower or weak storm will be possible over higher terrain and close to the mountains. Max 1-hour rainfall up to 0.4 inches under storm cores. Flooding is not expected today.

Primetime: 12AM to 11PM