Issue Date: Friday, July 26th, 2019
Issue Time: 8:50AM MDT

— A MODERATE flood threat has been issued for the Spring Creek burn area
— A LOW flood threat has been issued for the Southeast Mountains, Raton Ridge, San Juan Mountains, Central Mountains and the higher terrains of the Grand Valley and Southwest Slope. This includes the Hayden Pass, Junkins, Lake Christine and 416 burn areas.

Clear start to the morning over eastern Colorado as some dry air has worked its way into the state with the northwest flow aloft. There is some morning cloudiness over western Colorado from convection yesterday and early this morning associated with the monsoon surge. This will likely limit the instability that can build this afternoon over that area, so expecting more general showers with a slight chance for a couple weak thunderstorms where clouds clear. Marked in the water vapor imagery below are two shortwaves, one that passed through the state yesterday (New Mexico) and the stronger shortwave that will affect tomorrow’s weather as it rotates around the high. The high continues to sit over the NM/AZ border before it gets displaced to the west overnight. The placement of the high is keeping PW values elevated over Grand Junction with this morning’s sounding measuring 1.14 inches, which is slight below yesterday, but still a very moist air mass and above average for this time of year. As anticipated, PW over Denver has dropped off and was measured at 0.65 inches. This should limit the flood threat over the northeast corner of the state, although slow steering winds will still allow for some moderate accumulations.

Storms are expected to initiate with upslope flow by midday; first to the west and then to the east a couple of hours later. Best coverage of afternoon thunderstorms will be over western and southern Colorado. The location of the subtropical high will have storm movement more west to east along the western Colorado border and more to the southeast elsewhere. Slower steering winds will allow for some decent 2 hour accumulations with the moderate rain rates forecast. Paired with three days of rainfall over western Colorado and the Southeast Mountains, soils are rather saturated, so increased runoff is expected this afternoon. A Low flood threat has been issued for these reasons. In addition to the Low threat, a Moderate threat has been issued for the Spring Creek Burn area due to higher confidence rain rates will exceed the 0.4 inch per hour threshold known to trigger flooding, mud flows and debris slides. The threat should end a couple of hours after sundown, although there may be some light, lingering showers over the eastern plains and high country through tomorrow morning.

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

More scattered storms are expected over the Front Range and Palmer Ridge today with the majority of the action further south were a moister air mass remains in place. A couple of storms may sneak over the Northeast Plains northern border from the Cheyenne Ridge later in the evening. Max 1-hour rain rates up to 0.7 inches will be possible with these storms. Back to the west, 1-hour rain rates between 0.15 and 0.25 inches are forecast for the aforementioned zones. Over the Southeast Mountains and Raton Ridge, max 1-hr rain rates up to 0.75 inches are possible with 2 hour totals up to 1.1 inches along the Raton Ridge. Threats today over the higher terrains include mud flows, debris slides and flash flooding of local streams and creeks. Over the Raton Ridge, field ponding, road flooding and local stream and creek flash flooding will be possible. A Low flood threat has been issued with a Moderate flood threat for the Spring Creek burn area. The Low threat over the Hayden Pass and Junkins burn areas should suffice, but please note there is a Flash Flood Watch for the Spring Creek, Junkins and Hayden Pass burn areas through this evening.

Primetime: 2PM to 11PM

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

Not much has changed from the forecast since yesterday. However, soils have become more saturated, which will cause a Low flood threat to be issued. The main threat will be increased runoff causing flash flooding of local streams and creeks. Mud flows and debris slides will also be possible over the high terrains with mild local field ponding and road flooding possible over the adjacent valleys if storms track off the mountains. Max 1-hr rain rates up to 0.9 inches (south), 0.75 inches (central) and 0.4 inches (north) will be possible. Higher rain rates look to be over the eastern San Juan Mountains, so the Low flood threat should be okay for the 416 burn area. The Low flood threat also includes the Lake Christine burn area.

Primetime: 1PM to 11PM

 

Issue Date: Thursday, July 25, 2019
Issue Time: 10:20AM MDT

–A MODERATE flood threat is issued for portions of the Palmer Ridge, Front Range and Urban Corridor.  This threat includes the Spring Creek, Junkins burn areas. 
–A LOW flood threat is issued for portions of the Southwest Slope, San Juan Mountains, Grand Valley, Northwest Slope, Northern Mountains, Central Mountains, Southeast Mountains and Raton Ridge

The strong upper level ridge remains overhead, with little to no changes in the upper level wind pattern since yesterday. Persistent flow of deep moisture on the backside of the high will provide high chances for thunderstorms throughout the state today. PW increased by approximately 0.25 inches at both Grand Junction and Denver from yesterday morning, measuring 1.28 inches and 0.98 inches respectively. Embedded within the flow is a shortwave and vorticity maximum (marked “X” below) that will make its way east throughout the day, providing strong forcing for thunderstorms. A weak surface low pressure system sits over the Southeast Plains this morning, which will delay normal upslope flow slightly and form a dryline over the eastern plains. Additionally, a cold front (blue line below) will move south over the eastern plains throughout the morning, producing thunderstorms over and south of the Palmer Ridge throughout the afternoon. Post frontal upslope flow will provide additional rainfall east of the Continental Divide later in the afternoon and into the early evening.

The primary area of concern today will be the recent burn areas within southern Front Range and Southeast Mountains.  A weak thermal low is forecast to develop over northern New Mexico and the San Luis Valley, which will pull in high levels of moisture from the eastern plains.  Moderate steering winds will allow multiple storms to slowly track over the recent burn areas and regions with near saturated soils. Over western Colorado steering flows will be much faster, reaching up to 30 mph, but deep atmospheric moisture and persistent storms will provide chances for flooding throughout the high country. Primary threats include: flash flooding of small streams and creeks, mud flows and debris slides.  Storms are forecast to begin over the high country by noon and over the plains in the early afternoon with the passing cold front.  Storms will end in a north to south fashion, between 12AM and 3AM.

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:

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

An incoming shortwave is forecast to move over the area this morning and be over central Colorado by midday. Thunderstorms are expected to form over the high country by noon and move to the southeast. Fast steering winds between 20 and 25 mph out of the northwest should prevent large accumulations over a 1 hour period, however persistent storms over a 2-3 hour period may provide chances for flooding. The heavier rain rates will favor the Central Mountains and San Juan Mountains, with max 2-3 hour rain rates of 1.75 and 1.25 inches respectively. Multiple storms tracking over the 416 burn area will provide chances of flooding, but fast winds confine the area to a Low flood threat. The Lake Christine and Weston Pass burn areas are also included with the Low flood threat area. Threats include flooding of small streams and creeks, flashing flooding, mud slides and debris flows.

Primetime: 12PM to 12AM

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

A Moderate flood threat returns today over southern Front Range, southern Urban Corridor, and the Palmer Ridge. A vorticity maximum is forecast to move over the area early this afternoon, providing lift to a moisture rich atmosphere for persistent moderate to severe thunderstorms. A cold front will make its way south over the eastern plains this morning and into the early afternoon, producing thunderstorms over and south of the Palmer Divide. Post frontal upslope flow over the eastern plains will provide additional lift over the Moderate threat area and create weak thunderstorms over the Northeast Plains. 2-3 hour rainfall rates up to 1.75 inches are forecast over the Moderate threat area. Recent precipitation has increased soil moisture over the area, which will increase the chance for flooding. Max 1 hour rainfall rates of 1.25 inches are forecast over the Southeast Plains, drier soils will reduce the chance for flooding.

A Moderate flood threat has been issued for the Spring Creek, and Junkins burn areas. Recent precipitation has created a surface environment that is primed for flooding. Persistent thunderstorms from the northwest will provide max 2-3 hour rainfall rates up to 1.8 inches over the Southeast Mountains. Threats over the burn areas include flash flooding of small creeks and streams, flooding over rural, mountain roadways, debris slides and mud flows. The threat for the Southeast Mountains extends until 3AM.

Primetime: 11AM to 3AM

Issue Date: Wednesday, July 24, 2019
Issue Time: 10:15AM MDT

— A MODERATE flood threat is issued for the 416 burn area

—A LOW flood threat is issued for portions of the San Juan Mountains, Southwest Slope, Grand Valley, Northwest Slope, Northern Mountains and Central Mountains.  This threat includes the Lake Christine burn area.

The strong mid-level ridge that has controlled our weather for the past week remains the main weather feature today.  Moisture continues to come into the area from the southwest, with PW measured at 1.04 inches at Grand Junction this morning. An incoming shortwave trough over the northern Great Plains will slowly weaken and push the ridge to the south today, transitioning upper level flow from southerly to westerly over western Colorado.  This south-southwesterly flow of moisture (yellow line below) throughout the day and into tonight will generate consistent thunderstorms over the high country. Flow around the backside of a surface high pressure system over the Missouri River Valley will keep most of the eastern plains hot and dry today.  A surface low, marked by an “L” below, is forecast to form over eastern Wyoming around noon, bringing in a cold front over the northeast plains later this afternoon.  The frontal passage will provide a chance for thunderstorms over the northeast quadrant of the state.

The primary concern for flooding today will be over the 416 burn scar, with chances for flooding over the western high country. Upper level convergence over the San Juan Mountains will cause storms to sit over the area for multiple hours. Persistent and slow moving storms over the burn scar could cause flooding this afternoon and into the evening. Surface dewpoints are forecast to remain in the upper 30°Fs to low 40°Fs to the west of the Continental Divide today, with high levels of PW present overhead.  Storms will remain confined to the higher elevations due to upslope flow, with drier air in the valleys of the western slope. Sunny skies throughout the day will mix out moisture over the eastern plains, dropping dewpoints into the 40°Fs.

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:

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

Moderate to high levels of moisture are expected over the forecast area today. Upper level forcing for severe thunderstorms is weak, however consistent moisture advection and upslope flow over the area will allow for persistent thunderstorms. A thermal low is forecast to form over the San Juan Mountains and San Luis Valley throughout the morning, allowing for strong convergence over the southwest. Persistent storms over the 416 burn area will allow for a max 2-3 hour rain rate up to 1.25 inches. Max 1-hour rain rates of 0.75 inches is forecast over the Low threat area. Thunderstorms are expected to begin around 1PM over the San Juan Mountains and Central Mountains, expanding in spatial area to encompass the entire forecast region by 3PM. Lower levels of moisture over the Southeast Mountains will limit max 3-hour rainfall rates to 0.5 inches over the recent burn areas. The threat over the 416 burn area and southern areas is expected to end by 11PM, with the threat ending in the northern areas by 3AM. Threats over the recent burn area include debris flows, mud slides and flash flooding.

Primetime: 1PM to 3AM

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

Hot temperatures and ample sunshine is forecast to mix out moisture over the eastern plains throughout the day. Surface winds out of the south-southeast will bring in hot, dry air to form a dryline over the central eastern plains. Northerly steering flows and upper level inversions will keep thunderstorms capped over the Southeast Plains. A cold front coming in out of the north-northwest will provide chances for thunderstorms over the Northeast Plains around 5PM. Moisture from the west will combine with upslope flow over the Continental Divide to form thunderstorms over the Front Range by 2PM. Max 1-hour rain rates up to 0.4 inches is forecast over the high terrain. Convergence over the Palmer Ridge with the passing cold front will provide chances for thunderstorms over the area, with max 1-hour rain rates up to 0.6 inches. Storms are forecast to end by 10PM (west) and 2AM (east).

Primetime: 2PM to 2AM

Issue Date: Tuesday, July 23rd, 2019
Issue Time: 9:40AM MDT

— A MODERATE flood threat has been issued for the 416, Hayden Pass and Spring Creek burn areas
— A LOW flood threat has been issued for the Junkins burn area  

A very strong ridge continues to reside over the area with a 596 high (mid-levels) analyzed in the RAP Mesoanalysis this morning. Marked in the water vapor imagery below are several vorticity maximums rotating around the high. These shouldn’t influence the state today, so just expecting storms to initiative with upslope flow from daytime heating. Looking at a nearly identical setup to yesterday, so storms will start firing over the mountains between 1PM and 2PM MDT. Even more dry air will works its way into the state from Wyoming. PW values are currently at 0.83 inches over Denver and 0.89 inches over Grand Junction. These values should continue to drop a little more throughout the day, which will decrease rainfall totals this afternoon. Storms are expected to more scattered over the Front Range and Southeast Mountains with increasing coverage over the San Juan and Central Mountains along with the higher elevations of the Southeast Slope and Grand Valley.

The one area of flooding concern for today are recent burn areas. Over the southwest corner of the state, some low level moisture has drifted northward due to the strengthening ridge. Over the Southeast Mountains, dry air from the north likely won’t mix out enough moisture over the area to keep the threat at bay. Slow, S and SSE drifting storms and multiple storms tracking over the same area may pose an issue for the 416, Hayden Pass, Spring Creek and Junkins burn areas. More southern storm motion should keep the Junkins burn less at risk. However, with saturated soils from yesterday, if a storm does track over the scar, high runoff will likely cause flooding issues. Moderate and Low flood threats have been issued for these reasons. The main threats are flash flooding of local streams and creeks, mud flows and debris slides. Storms should diminish a couple of hours after sundown as instability falls off, so the flood threat will decrease after the 9 to 10PM MDT window.

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

More scattered storms expected over the Southeast Mountains and Front Range today with increasing coverage over the San Juan Mountains. Activity may slightly drift into the adjacent plains favoring the Palmer and Raton Ridges, but aren’t expected to spread much further east with steering flows and upper level inversions capping the area. Max 1-hr rain rates up to 0.75 inches are possible over the eastern mountains with max rain rates increasing to 0.9 inches over the San Juan Mountains. Storms over adjacent plains and ridges may produce up to 0.75 inches. These rain rates will cause a Moderate flood threat to be issued for the 416, Hayden Pass and Spring Creek areas and a Low flood threat to be issued for the Junkins burn area. Saturated soils over the Southeast Mountains from yesterday will increase the likelihood for mud flows, debris slides and runoff.

Primetime: 2PM to 11PM

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

Increased storminess is anticipated over the Central Mountains and higher elevations of the Southwest Slope and Grand Valley. The main threats will be moderate rainfall, gusty winds (between 50-60 mph) and small hail. Max 1-hr rain rates up to 0.5 may be possible. Some isolated, lighter rain may be possible over the southern portion of the Northern Mountains, but totals are expected to remain under 0.1 inches. The San Luis Valley edges will likely see another round of rain again today. Totals up to 0.7 inches may be possible by morning with totals up to 0.25 possible over eastern Conejos County. All other areas should stay rain free today due to lack of low level moisture and southern component of the steering flow.

Primetime: 2PM to 8PM