Issue Date: Saturday, August 3rd, 2019
Issue Time: 10:10AM MDT

-A MODERATE threat has been issued for the 416 burn area

-A LOW flood threat has been issued for portions of the Southwest Slope, San Juan Mountains, Central Mountains, Front Range, Urban Corridor and Southeast Mountains. This threat includes the Junkins, Hayden Pass, and Spring Creek burn areas

Overall the upper level pattern is similar to yesterday, with the subtropical high now positioned over the Four Corners. As a result, storms are forecast to be confined to the mountains once again today. Clockwise flow, shown in the midlevel water vapor imagery below, will confine moisture to the southern mountain ranges, while northerly flow over the eastern plains should cap most storms over the area. Atmospheric moisture levels are moderate, with PW measuring around 0.75 inches at Denver and Grand Junction this morning. Surface high pressure centered over the Central Mountains will produce downsloping winds this morning and combine with sunny skies to mix out surface moisture throughout the state. A surface dryline over the northwest should prevent storm activity over the area.

There are currently no shortwaves forecast to move over Colorado today, meaning storms will be upslope driven systems over the mountains. Convection is forecast to begin early this afternoon, primarily over the mountain ranges to the south of I-70. Upper level steering flows will be slow to moderate, allowing storms to linger over areas for 1.5-2 hours. Multiple storms passing over the burn areas and steep terrains will create the greatest threat today, so a Moderate flood threat has been issued over the 416 burn area.

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

Storms are forecast to begin early this afternoon, primarily over the regions within the Low flood threat area. Steering flows out of the north-northwest will cause storms to favor the southern facing slopes. Max 3-hour rainfall rates up to 1.25 inches are forecast over the Central Mountains, San Juan Mountains, and Southwest Slope, with isolated max 1-hour rainfall rates up to 0.75 inches. Dry air incoming from the northwest will limit rain over the Grand Valley, Northwest Slope and Northern Mountains to max 1-hour rainfall rates of 0.3 inches. Storms may drift over the San Luis Valley, but accumulations are forecast to be minimal. Threats over and near the 416 burn area include flash flooding, flooding of small streams and rivers, debris slides and mud flows. Storms over most areas will end in the late afternoon to early evening, however the threat over the southwest corner extends into tomorrow morning.

Primetime: 1PM to 5AM

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

Storms today are likely to be confined to the mountains, with chances over the southern Urban Corridor and western Palmer Ridge as well. Steering flows between 15 and 20 mph out of the north-northwest should prevent storms over the eastern plains. Moderate chances for persistent storms over a 2-3 hour period over the Southern Front Range, southern Urban Corridor, and Southeast Mountains has issued a Low Flood Threat over the area. This threat includes the Hayden Pass, Junkins and Spring Creek burn areas. Max 2-3 hour rainfall rates up to 1.25 inches are forecast over the area, with isolated pockets of up to 1.5 inches. Max 1-hour rainfall rates of 0.6 inches are also possible over these areas. The primary threat is over steep terrain and burn areas, with threats of flash flooding, debris flows, and mud slides. Storms are forecast throughout the afternoon and into the early evening, with the threat over the Southeast Mountains ending by 11PM. Storms may move off of the mountains and over the adjacent plains, however max 1-hour rain rates will be limited to 0.3 inches.

Primetime: 1PM to 11PM

Issue Date: Friday, August 2nd, 2019
Issue Time: 9:00AM MDT

— A MODERATE flood threat has been issued for the Spring Creek, Junkins and Hayden Pass burn areas
— A LOW flood threat has been issued for the Raton Ridge, Southeast Mountains and portions of the Urban Corridor, Front Range and Central Mountains

The weak cold front from yesterday has moved completely through the Southeast Plains leaving behind cooler morning temperatures and some fog. Dew points over the eastern plains are well into the 60°Fs, so not surprised by the widespread nature of the fog. It should continue to burn off as the sun heats up the surface. The subtropical high is currently over New Mexico. It is forecast to start to move to the west today, which will pull in a drier air mass into western Colorado. PW has already dropped to by about 0.2 inches in this morning’s sounding. This should limit storms to the higher terrains with scattered, weak thunderstorms and light showers possible with the residual moisture. Storms will be high-based, so not expecting much accumulation.

With steering flows having a more of a northerly component today and most of the adjacent plains capped, storms over eastern Colorado are expected to be confined to the mountains. There is a high likelihood for some spillover thunderstorms onto the Raton Ridge as well. No shortwaves or boundaries are spotted in the water vapor imagery, so the diurnally driven storms should only be weak thunderstorms with small hail and some brief, gusty winds also possible. Behind the front, low level moisture should be high (as seen with the dew points below), so heavy rainfall is anticipated over the Southern Front Range and Southeast Mountains. Trailing storms may produce just over an inch of rain in a 1.5-2 hour period or a quick 0.5 inches in 30 minutes, so a Low flood threat has been issued. With high moisture and trialing storms, the recent burn areas in the Southeast Mountains have an elevated threat. So a Moderate flood threat has been issued for these areas.

 

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

Most of the eastern plains and adjacent plains should remain rain free this afternoon. However, there is a 50/50 chance for some thunderstorms along the southern border from the Southeast Mountains to the KS/OK border. As far as rainfall, trailing storms make the threat today more of a 1.5-2 hour threat. Isolated storm totals up to 1.25 inches may be possible (more likely values will be closer to 1 inch) over the Southeast Mountains and western Raton Ridge. With burn area flooding thresholds likely being met this afternoon by storms in the area, a Moderate flood threat has been issued. One inch totals over the Park/Teller County are also possible by tomorrow morning. Note the flood threat is slightly less over this area due to more gradual rain rates. Flood threats today include mud flows, debris slides, local stream/creek flash flooding and flooding of low-lying intersections. A couple storms may linger through the night over the Southeast Mountains, but the threat should a couple hours after the sun sets.

Primetime: 1:30PM to 11PM

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

Best chance for thunderstorms today will be over the eastern portion of the Central and San Juan Mountains. Higher moisture to the south should increase max 1-hour rain rates up to 0.75 inches. Storm totals over the 416 burn area should remain below flood threat criteria, though this should be monitored closely if multiple storms track over the scar. Elsewhere, storms are forecast be more isolated over the higher elevations. With drier air moving in from the west, max 1-hour rain rates drop off to 0.2 inches over the north. With the current environment, a couple of storms may linger over the highest terrains of the eastern Central and San Juan through the night, but most storms are expected to dissipate a couple hours after sundown.

Primetime: 12:30PM to 11PM

Issue Date: Thursday, August 1, 2019
Issue Time: 10:20AM MDT

-A MODERATE flood threat has been issued for portions of the Northeast Plains, Palmer Ridge, and Southeast Plains.  A MODERATE flood threat has also been issued for the 416 and Lake Christine burn areas

-A LOW flood threat has been issued for portions of the Southwest Slope, San Juan Mountains, Grand Valley, Central Mountains, Northwest Slope, Northern Mountains, Front Range and Urban Corridor 

The atmosphere is saturated across the state today as monsoonal levels of moisture have come in from the southwest. The high pressure ridge has moved slightly to the east, putting Colorado right on the path of high moisture advection. PW this morning was measured in the 95th percentile at Grand Junction, with 1.23 inches. Model derived PW over Denver is 1.12 inches. Moisture is also high at the surface, with dewpoints (green contours below) in the 60°Fs over the far eastern plains and 50°Fs over the western slope. Cloud cover this morning will prevent surface moisture from mixing out, keeping instability moderate to high over the Northeast Plains. Continual flow of moist air over the mountains will produce thunderstorms over the high country throughout the day and into the night.

A shortwave and vorticity maximum (X below) is forecast to move across the northern border throughout the day, providing lift for severe thunderstorms this afternoon and into the night. At the surface there is currently a low pressure system (“L” below) over the Southeast Plains. Upslope flow to the north of the low will provide continuous moisture advection to the northeast quadrant of the state, while downsloping flow over the southeast quadrant should prevent severe storms over the area. Slow upper level steering flows of 12-17 mph (east) and 17-22 mph (west) will create a threat that is 2-3 hours in nature. A low level jet is forecast to form over the eastern plains by sundown tonight, which will provide dynamic forcing for severe storms until 2AM. The National Weather Service has issued a Flash Flood Watch for: northeast Weld County, Morgan County, central and east Adams and Arapahoe Counties, north and northeast Elbert County, north Lincoln County, Logan County and Washington County.

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, Northeast Plains, Palmer Ridge, Southeast Plains, Southeast Mountains, Raton Ridge

Passage of the shortwave over the northern border will produce severe thunderstorms over the northern half of the forecast region this afternoon and into the early morning.  Storms will begin over the high country around noon and move over the adjacent plains by 2PM.  A quasi-linear convective system (QLCS) or line of storms capable of producing strong winds is forecast to form over the Northeast Plains mid-afternoon, producing widespread rain over the area.  Slow steering winds will create a 2-3 hour threat over most areas, but isolated 1-hour heavy rain is still possible.  Over the northern half of the Front Range and Urban Corridor, max 2-3 hour rainfall rates up to 1.5 inches and isolated max 1-hour rain rate up to 0.75 inches are possible.  Hail up to 0.5 inch diameter is forecast for these areas.  Over the Northeast Plains max 2-3 hour rainfall rates of 2.5 inches and max 1-hour rainfall rates of 1.75 to 2 inches are forecast within the Moderate Flood Threat region.  Hail up to 1.75 inches diameter is forecast over the area as well.  Threats include flooding of small streams and rivers, flooding of roadways and low laying intersections, and field ponding.

Downsloping flow over the southern half of the Front Range and Urban Corridor, as well as the Southeast Mountains will keep rainfall rates low.  Max 1-hour rainfall rates of 0.5 inches are forecast, with the higher rates more likely to the north.  Areas of the Southeast Plains outside of the threat area are forecast to have max 1-hour rainfall rates of 0.3 inches, with isolated pockets up to 0.5 inches.

Primetime: 12PM to 2AM

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

A Moderate Flood Threat is Issued for the 416 and Lake Christine burn areas, with max 2-3 hour rainfall rates up to 1.25 and 0.75 inches respectively.  Multiple storms passing over the burn areas may cause flash flooding, with threats of mud slides, debris flows and flooding of small rivers and streams.  Over the high country, max 1 hour rainfall rates are forecast to be between 0.5 and 0.75 inches, with isolated storms capable of producing 1 inch.  Multiple rounds of storms over the area will provide max 2-3 hour rainfall rates up to 1.5 inches.  Threats include flash flooding and flooding of roadways and low laying intersections.

Primetime: 12PM to 12AM

Issue Date: Wednesday, July 31, 2019
Issue Time: 10:35AM MDT

— Flooding is NOT expected today

The subtropical high pressure that has been controlling our weather this past week will continue to build and move it’s way east throughout the day today. The mid-level water vapor imagery below shows high levels of moisture to the west of Colorado, which will move it’s way slowly over the area the next few days. This morning’s sounding over Grand Junction shows an increase in moisture from yesterday, measuring 0.98 inches of PW. Dewpoints over the western slope are also high this morning, measuring in the 40°Fs and 50°Fs over the lower terrain.  Midlevel winds will increase throughout the day, with a weak low level jet developing overnight over the northwest corner of the state. Persistent thunderstorms over the area provide the highest chances for isolated moderate rainfall over 2-3 hours. Storms are forecast to the west of the Continental Divide throughout the afternoon and into the early evening, with storms over the northwest quadrant extending into the early morning.

To the west of the Continental Divide the setup will be similar to yesterday, but moisture levels will increase throughout the day. PW was measured at 0.69 inches over Denver this morning, but is forecast to increase up to 1.7 inches over the Northeast Plains. Low pressure over the eastern plains will aid downslope flow to create a dryline (orange line below) over the eastern plains this morning. The low is forecast to remain and deepen, which will pull surface moisture back to the west throughout the forecast period. Upslope flow over the foothills and the dryline will provide forcing for thunderstorms this afternoon. Storms are forecast to begin over the Raton Ridge and Southeast Plains by 12PM, with storms over the Palmer Ridge and Northeast plains this afternoon and into the night.

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:

Isolated max 3-hour rainfall rates up to 0.75 inches will be possible over the northern regions, with max 24-hour totals up to 1.5 inches.  Expect the highest daily totals over the Northwest Slope and Northern Mountains, with persistent storms throughout the duration of the forecast period. Continual moisture advection and steering winds between 10 and 15 mph will bring multiple rounds of storms over the area.  Rain will favor the high terrain over the Southwest Slope and San Juan Mountains, with isolated max 3-hour rainfall rates up to 0.5 inches.  Storms will begin by noon over the southern regions, extending through the central and northern regions by 2PM.  Rainfall is forecast over all elevations over the central and northern regions due to high levels of surface moisture.  The San Luis Valley is forecast to receive little to no precipitation.  Wind gusts up to 50 mph are expected over the lower elevations once again today.

Primetime: 12PM to 5AM

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

Storms today are most likely along the Continental Divide and areas over and near the Cheyenne Ridge, Palmer Ridge and Raton Ridge.  Most storms are forecast to remain capped over the eastern plains, but chances for isolated severe weather are still possible.  Max 1-hour rainfall rates of 1.25 inches are possible, although unlikely, over the Northeast Plains, southern Urban Corridor and Palmer Ridge. Over the high terrain, max 1-hour rainfall rates up to 0.3 inches are possible.  Storms are forecast to begin over the Raton Ridge and Southeast Mountains by noon, with storms over the Front Range by 2PM.  Late afternoon thunderstorms may form off of the Palmer Ridge and move over the Northeast Plains early tonight.  Flooding is not forecast over the area.

Primetime: 12PM to 2AM