Issue Date: Sunday, September 8th, 2019
Issue Time: 9:40AM MDT

— A MODERATE flood threat has been issued for the Northeast Plains and northern Urban Corridor

— A LOW flood threat has been issued for the Northern Mountains, Central Mountains, northern San Juan Mountains, Front Range and Palmer Ridge

— A LOW flood threat has been issued for the following burn areas: Lake Christine, 416/Burro, Hayden Pass, Spring Creek and Junkins

Nearly statewide rainfall is anticipated today as the trough to our west pulls to the northeast and provides moisture and largescale lift for afternoon and evening storms. The negatively tiled trough is currently over Nevada with the base of the trough marked with the orange “X”. Upper level flow will become more southwesterly this afternoon as this feature moves eastward. This pattern will also yield very high PW values (greater than 1.2 inches) over the eastern plains. The Denver sounding is currently at 0.71 inches, but expecting this to increase throughout the day with easterly and southeasterly surface flow. Trailing storms will allow accumulations to increase over the mountains, so the Low threat has been extended to areas where this will be most probable. Extremely dry soils from lack of rainfall may help increase runoff as well. The Low threat over western Colorado also includes the two new newer burn areas: 416 and Lake Christine and a NWS Flood Watch has been issued for these areas as well. Mud flows, debris slides and local stream flash flooding will be possible if storms continually track over these areas.

Over the eastern mountains, higher moisture will be in place along with slightly slower storm speeds, so a Low flood threat has been issued for this and due to the trailing storms/widespread nature of the rainfall this afternoon. Numerous flooding issues are not anticipated, but a few areas with the highest accumulations could experience mud flows, debris slides or flooding of local streams. Not thinking there is flood threat for the Southeast Mountains as drier air moves northward from New Mexico. However, there is still enough moisture and lift to cause concerns that storms will produce rain rates high enough that they could cause flash flooding issues for the Hayden Pass, Junkins, Spring Creek burn areas. Thus, the Low threat has been extended south.

Over the eastern plains, storms are likely over the Southeast Plains (far corner) as they track in from New Mexico, Texas and Oklahoma associated with the disturbance near the “X” above. Not thinking these will cause any flooding issues, but totals near 1 inch will be possible by morning. Highest moisture will be over the Northeast Plains, and as storms move off the mountains this afternoon they will also decrease in speed. Therefore, totals near 2 inches will be possible in the Moderate threat area with a couple storm cores capable of producing around 2.5 inches over the far Northeast Plains. The shortwave will eventually exit the state just after midnight with a couple lingering showers possible over the far southeast corner through early tomorrow morning. A Moderate/Low threat has been issued with Low threats for the burn areas listed above.

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, Central Mountains, Northern Mountains, San Juan Mountains, San Luis Valley:

Trailing thunderstorms and dry soils over these regions may cause flooding issues such as mud flows, debris slides and local stream flash flooding this afternoon. These threats will be exacerbated if storms track over recent burn areas. Storm totals up to 1.25 inch will be possible over the Front Range and Northern Mountains with totals up to 1 inch over the Central Mountains. Max 1-hour rain rates up to 0.75 inches will be possible over the Southeast Mountains. Over the San Juan Mountains, totals up to 0.8 inches will be possible. The San Luis Valley should see rain for the second day in a row! More widespread values of 0.5 inches will be possible with a couple isolated totals up to 0.75 inches. A Low flood threat has been issued, which includes recent burn areas.

Primetime: 12PM to 10:30PM

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

As thunderstorms exit the mountains and move to the northeast, they will encounter some very high moisture, while also decreasing in pace. Max 1-hour rain rates up to 2 inches will be possible over the Moderate threat area with isolated totals around 2.5 inches over the Northeast Plains. Field ponding, road flooding, local stream flash flooding and flooding of low-lying areas are the main flood threats. Small hail with pockets of severe hail are likely with the stronger storm cores. Flooding remains the main threat, but very strong winds may produce some damage as well with storms gaining a linear component (line of storms) as they move to the northeast. Over the Southeast Plains (southeast corner), totals up to 1 inch are possible by morning for the continuous rainfall. For the Raton Ridge and Palmer Ridge, storm totals between 0.75 and 0.9 inches will be possible. A Moderate threat has been issued with a Low threat for the Junkins, Hayden Pass and Spring Creek burn areas.

Primetime: 3PM to 1AM

Northwest Slope, Grand Valley, Southwest Slope:

Rainfall will be on the earlier end of the forecast with the trough quickly approaching. With widespread storms forecast, rainfall will be likely over the valleys as they track off the higher terrains or in from Utah. Max 1-hour rain rates up to 0.75 inches will be possible over the Northwest Slope with rates dropping to 0.5 inches over the Grand Valley. Not as much moisture is over the Southwest Slopes, but totals up to 0.25 inches (higher terrains) will be possible with 0.15 inches possible over the lower elevations. Flooding is not forecast.

Primetime: 10AM to 8PM

Issue Date: Saturday, September 7th, 2019
Issue Time: 9:50AM MDT

— A LOW flood threat has been issued for the Palmer Ridge, Raton Ridge, Southeast Plains and southern Northeast Plains

Quite the southwest to northeast disturbance in the water vapor imagery below. This is producing a lot cloud cover, scattered fog over the Northern Mountains and light showers over the San Juan Mountains. The visible satellite imagery (not shown) shows some more convective storms over the Northeast Plains, so some light showers are likely occurring with the right entrance of the jet overhead. As the trough slides west today, flow aloft will turn from southwesterly to westerly. This will pull in the disturbance from Utah (marked with an “X” below) to help spark more numerous showers and weak thunderstorms over the San Juan and Central Mountains this afternoon. This will also allow for some storms to survive over the San Luis Valley, which very much needs the rainfall. Also marked in the image below is a stationary front (red dashed line), which is yesterday’s cold front. This is helping keep moisture high over the region, but westerly flow aloft should mix the best moisture into Kansas and Nebraska (dew points over 60°F). The Northeast Plains looks to mostly remain capped this afternoon with slightly cooler temperatures forecast. There is a small potential for an isolated storm near the Kansas border tonight, and with high moisture returning and nearly stationary storms on a boundary, the Low flood threat has been extended north for this isolated incident.

Storms this afternoon will favor the southern high terrains with the highest rainfall accumulations over western Colorado occurring in the eastern San Juans and along the Divide (south). Not thinking there will be enough moisture for Southeast Mountain burn areas to reach flooding thresholds, plus swifter storm motion should also keep totals low. Of course, caution should always be used any time a storm passes over a recent scar. Over the eastern mountains, westerly flow aloft should push the storms into the adjacent plains by early afternoon where they will initially favor the higher terrains of the Palmer and Raton Ridge. As storms move eastward, outflow boundaries and slightly more southerly steering flows will likely produce storms over the Southeast Plains. Steering flows are anticipated to decrease throughout the day/eastward, and with several boundaries in the area (extra convergence) and mid-level energy moving through the flow, a Low flood threat has been issued. While widespread, heavy rainfall is not forecast, a couple storms could produce totals above flood threat thresholds if they back build/remain stationary.

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

Max 1-hour rain rates up to 0.50 inches are possible over the southern Front Range and immediate adjacent plains. Rates drop to 0.15 inches over the Southeast Mountains due to lack of low level moisture. Over the Palmer Ridge, max 1-hour rain rates up to 1 inch are possible with that increasing to 1.25 inches over the far eastern plains/eastern Raton Ridge. Should a storm linger over an area or on a boundary, storm totals up to 1.75 to 2 inches may be possible. Thus, a Low flood threat has been issued. Threats include flooding of roads, low-lying areas, field ponding, flash flooding of local streams/creeks and arroyo flooding. A couple storms may be marginally severe this afternoon with the main threat being strong winds and lightning, although marginally severe hail may also be possible, too.

Primetime: 12PM to Midnight

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

Storms should start to form fairly early today with the passing shortwave helping kick off activity. Max 1-hour rain rates up to 0.70 inches will be possible over the San Juan Mountains with isolated totals up to 1 inches possible by tomorrow morning (eastern San Juans). 1-hour rain rates decrease to 0.25 inches over the Central Mountains and to 0.15 inches over the Northern Mountains. Looks like the San Luis Valley will also get some much needed rainfall as well. Accumulations up to 0.50 inches possible over the northern and eastern regions of the valley. The shortwave moves out fairly quickly this afternoon and with westerly flow pulling in a drier air mass, storms should end by early evening. A couple morning showers are possible again over the San Juan Mountains as the next shortwave moves overhead, but flooding is not forecast.

Primetime: 12PM to 7PM

Issue Date: Friday, September 6th, 2019
Issue Time: 8:40AM MDT

— A MODERATE flood threat has been issued for the Front Range, Urban Corridor, Junkins and the Spring Creek burn areas

— A LOW flood threat has been issued for the Southeast Mountains, Central Mountains, and eastern portions of the Palmer Ridge, Raton Ridge and Southeast Plains. This threat includes the Hayden Pass burn area.

Marked in the water vapor imagery below is the aforementioned cold front from yesterday’s FTO. This feature is currently pushing south and returning lots of moisture to the atmosphere behind it. This low level moisture return is presenting itself with high dew points, heavy cloud cover and a few light showers over the Northeast Plains, Urban Corridor and Palmer Ridge. PW was a whopping 1.06 inches in the Denver sounding this morning! As the cold front pushes south it looks to stall out somewhere south of the Palmer Ridge. Post frontal upslope flow behind the front and slow storm motion will set the stage for the heavy rainfall threat this afternoon. As the next approaching trough to our west moves eastward, upper flow is forecast to turn more westerly. This will allow storms to spill into the adjacent plains this afternoon and evening with another round of lighter rainfall possible overnight with continuous upslope flow in a moisture rich environment.

As the widespread showers and weak thunderstorms kick off over the higher terrains during the early afternoon, storm movement will be to the west at 10 mph. Trailing storms may allow for higher accumulations, thus the Low flood threat for the eastern mountains. With nearly stationary/slow moving storms, a Moderate flood threat has been issued for the Spring Creek and Junkins burn areas. The Low flood threat should suffice for the Hayden Pass burn area as the better moisture will be to the west of the scar. Storms may pick up in intensity as they slide off the foothills, so a couple severe thunderstorms may be possible along the I-25 corridor this afternoon and early evening. Heavy rainfall is possible over the Urban Corridor, so a Moderate flood threat has been issued for the Denver Metro area. Storms are anticipated to weaken as the move east due to a cap and decreasing instability, so expect storms to start to disband just east of Highway 71/104°W. A Moderate/Low flood threat has been issued for Friday. For rain rates, please see the zone-specific discussions below.

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

Widespread showers and thunderstorms are forecast for this afternoon. Over the mountains, storms will be capable of producing max 1-2 hour rain totals up to 1.40 inches (over the Moderate threat area) and 1.25 inches (south). With slower storm motion, a Moderate flood threat has been issued for the Junkins and Spring Creek burn areas, with the Hayden Pass burn area under the Low threat. Threats this afternoon include flash flooding of local streams/creeks, mud flows and debris slides. Those threats are more likely over burn areas if a storm tracks overhead.

A couple severe thunderstorms may be possible as the storms move into the adjacent plains. Threats from the severe storms include severe hail (1-1.25 inch diameter), gusty winds and heavy, local rainfall. Max 1-hour rain rates up to 1.5 inches will be possible with some isolated, slightly higher storm totals. Thus, the heavy rainfall threats include field ponding, flooding of local streams/creeks, road flooding and flooding of low-lying areas. A Moderate flood threat has been issued for the Denver Metro area. Another round of light showers and weak thunderstorms is possible overnight with the continuous upslope flow.

Primetime: 1PM to 2AM

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

Unfortunately, the moisture return isn’t quite as strong west of the Continental Divide, but there should be an uptick in storm coverage this afternoon over the high terrains. Expecting another round of scattered, afternoon/evening showers and weak thunderstorms to kick off during the afternoon. Highest accumulations will again be near the Divide and over the San Juan Mountains with up to 0.75 inches possible in the stronger storm cores. A shortwave moves over the southwest corner early tomorrow morning, which may help spark another round of weak showers over the San Juan and Central Mountains. Accumulations up to 0.25 inches may be possible with these storms. Flooding is not forecast.

Primetime: 1PM to 9AM

Issue Date: Thursday, September 5th, 2019
Issue Time: 10:50AM MDT

–Flooding is NOT expected today

The high pressure ridge remains overhead once again today and has increased in strength slightly with the center of the high now measuring a height of 5,960m (5940m yesterday at this time). This means that the strength of the subsidence (sinking motion) will be stronger today, which has resulted in the mostly clear skies shown in the visible satellite imagery below. Cloud cover and storm potential will increase over western Colorado throughout the day as two weak shortwaves (marked with X below) and mid-level moisture move in from Utah. Downsloping winds this morning will mix out the surface moisture, so storms are expected to be high based once again today with the main threats being light to moderate rainfall, lightning and brief wind. Storm coverage will favor the Northern, Central and Front Range Mountains where subsidence underneath the high pressure center is less severe. Storm motion is expected to be fairly slow under the ridge and continuous storm generation over the mountains is likely. Therefore, as the rainfall continues, the atmosphere will be more conductive for higher rainfall rates later in the day. Isolated storm totals up to 0.9 inches are possible.

To the east clear skies, down sloping winds and a building ridge will allow high temperatures to increase by another 3°F to 5°F from yesterday’s values. This wind pattern will also drop dew points to the 30°Fs and low 40°F by mid-afternoon over the eastern plains. So as storms move off the high terrains into the Urban Corridors and Palmer Ridge, rain rates will be less efficient. As they move west of Highway 71 (104°W) the area looks to remain capped, so storms may produce some gusty winds as they dissipate in similar fashion to yesterday. Flooding is not expected from storms today, but rather looking at a nice wetting rainfall for the high terrains.

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

Storms are expected throughout the region this afternoon and into tonight. Coverage will favor the Front Range and Central/Northern Mountains, especially along the Continental Divide. Expecting isolated storm totals up to 0.90 inches near the Continental Divide with most of the mountains having storm totals closer to 0.50 inches.  Storms are expected to be high based once again, so brief, isolated gusts up to 40 mph may be possible with the stronger storms. Coverage will begin around noon and extend until 10 PM tonight with a few later storms forecast over the Northwest Slope and Grand Valley. Totals between 0.1 and 0.25 inches may be possible by tomorrow morning over the lower elevations with up to 0.5 inches along the Flat Tops. Flooding is not forecast today.

Primetime: 12PM to Midnight

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

Expecting high temperatures to increase by 3°F to 5°F over the area with highs reaching into the triple digits over the Northeast and Southeast Plains under the building ridge.  Thunderstorms are possible over the Urban Corridor, Palmer Ridge and Southeast Mountains, but dry air will keep the storms high-based with light accumulations once again. Isolated storm totals up to 0.6 inches are forecast over these areas favoring the Palmer Ridge once again for the highest accumulations due to extra convergence. Elsewhere over the lower elevations, max 1-hour rainfall rates will drop to 0.25 inches. Threats today include brief, wind gusts up to 40 mph and lightning. Flooding is not expected.

Primetime: 2PM to 11PM