Issue Date: 6/26/2015
Issue Time: 10:10AM

— Low flood threat for Palmer Ridge, Southeast Plains, Southeast Mountains and Raton Ridge

A new upper-level high pressure system is developing along the western North American coast and is easily seen on this morning’s water vapor imagery (see below). One the one hand, the high pressure will cause a 2-6 degrees Celsius increase in mid-level temperatures, which tends to suppress thunderstorm chances. On the other hand, this morning, as in the past two to three weeks, low-level moisture was very high with dewpoint temperatures in the 40s/50s west of the Divide and 50s/60s east of the Divide. Precipitable water values were in the 0.6 to 1.0 inch range across the state, but we expect these to lower gradually through the day. All in all, storms are expected to be confined to the higher terrain as well as the southeast portion of the state today.

We expect partly to mostly sunny skies this morning to lead to thunderstorms over the highest terrain of the Northern, Central and Southeast Mountains. Early storms will yield only light rainfall, up to 0.5 inches. As storms mature and move southeast, rainfall intensities will increase and a Low flood threat has been issued for parts of southeast Colorado. Activity may persist as late as midnight as stubborn outflow boundaries maintain convergence zones that could fuel storm activity. In the late afternoon and evening, storms may produce hail up to 1.25 inches in diameter over the Low threat area.

We have finally removed the flood threat for the Arkansas River as only very isolated stretches (notably near La Junta) remain in minor flood stage. Please check your National Weather Service products for detailed information on river stage levels.

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, jump below the map.

Zone-Specific Forecasts

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

Mostly sunny and turning warmer with high temperatures up to 100F in the lowest elevations by the Colorado River. A thunderstorm cannot be ruled out over eastern parts of the area, but rainfall will be less than 0.25 inches. No flooding is expected.

Central Mountains, Front Range, Urban Corridor, Northeast Plains:

Mostly sunny early, then turning partly cloudy with scattered thunderstorms forming over the highest terrain shortly after noon. Rainfall will be limited to about 0.7 inches, so no flooding is expected.

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

Sunny early then partly cloudy with isolated to scattered thunderstorms developing by early afternoon over the highest terrain. Storms will move southeastward over the plains by mid-afternoon. Most storms will have light rainfall, generally under 1 inch. However, some of the strongest cells will be capable of 1.8 inch per hour rainfall. A Low flood threat has been issued for parts of the area. Hail up to 1.25 inches is also possible, mainly over the plains.

Activity will diminish after sunset, but isolated storms may last through 1AM over the Raton Ridge.

Primetime: 2PM through 9PM, except through 1AM near the New Mexico border

Issue Date: 6/25/2015
Issue Time: 10:45AM

— Moderate flood threat for Northeast Plains, and parts of Palmer Ridge and Southeast Plains
— Low flood threat for San Juans
— Low flood threat for Arkansas River from below Pueblo dam through La Junta

Since yesterday, the subtropical high that has been scooting eastward with every passing day has weakened. As shown in the water vapor image, below, this has allowed the jet stream to encroach on Colorado from the north. At least three “shortwave” ripples are noted this morning. The easternmost feature is leaving the state, and taking with it some weak thunderstorms noted over the Arkansas River valley near the Kansas border. The western two features will dive into Colorado and promote scattered to widespread thunderstorm activity. Coverage will be highest the farther east one goes. However, adequate moisture will allow for thunderstorms west of the Divide also.

For today, we expect morning sunshine to lead to thunderstorms by early afternoon, starting with the highest terrain of the San Juans, Central Mountains and the Front Range. Most of these storms will be relatively light rain producers, but a few will be capable of rainfall up to 1 inch per hour west of the Divide and 1.3 inches per hour east of the Divide. A Low flood threat has been posted. Later in the afternoon, storms will move eastward over the Plains. The heavy rainfall threat will increase as storms gain access to higher moisture. Torrential short-term rainfall, with rain rates up to 0.8 inches in 30 minutes and 1.4 inches per hour will be possible. However, over the northeast portions of the state, 1-hr rainfall up to 2.5 inches and 3-hr rainfall up to 3.5 inches is possible. Additionally, the evolution of strong atmospheric wind shear will support a potential for very, very large hail, up to 3 inches in diameter towards the Nebraska and Kansas borders. A Moderate flood threat has been posted for parts of Eastern Colorado.

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, jump below the map.

Zone-Specific Forecasts

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

Partly cloudy early, then scattered thunderstorms forming by early afternoon, with higher coverage and intensity as one moves eastward. Maximum one-hour rainfall is expected to stay below 0.8 inches, and no flooding is expected. Stronger storms may produce gusty winds up to 65 mph.

San Juans, Southwest Slope, San Luis Valley:

Sunny early, then turning partly cloudy. Scattered thunderstorms are likely by early afternoon with maximum one hour rainfall up to 1.0 inch possible. This could lead to isolated flash flooding, mud slides and debris flows. Gusty winds up to 65 mph may accompany the stronger storms. A Low flood threat has been posted.

Primetime: 1pm through 8pm

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

Partly cloudy early, with scattered storms developing by early afternoon over the higher terrain. Storms will the move eastward with additional redevelopment over the Plains. Very heavy rainfall will be possible, with generally higher intensity the farther east one goes. Closest to the mountains, 1-hr rainfall up to 1.4 inches is possible. Farther east, 1-hr rainfall up to 2.5 inches is likely. Moderate and Low flood threats have been issued.

Additionally, there is the potential for very large hail, up to 3 inches in diameter, in the Moderate threat area.

Primetime: 2PM through 11PM, except through 1AM near the Kansas border

Issue Date: 6/24/2015
Issue Time: 10:10AM

— Low flood threat for Northeast Plains, Palmer Ridge and Southeast Plains
— Low flood threat for San Juans
— Low flood threat for Arkansas River from below Pueblo dam through La Junta

The upper-level high pressure system continues to retreat eastward, allowing for a return flow to develop across the Four Corners region. Today’s water vapor image, below, shows that this flow has some mid and upper-level moisture with it. As such, thunderstorm coverage is expected to increase across the state. However, one main limitation will be the surface moisture. Though surface dewpoints continue to run very high with readings over 60F in many locations, this moisture is incredibly shallow. A nice example comes from Boulder this morning: the Foothills weather station showed a dewpoint temperature of 61F, while the Mesa weather station, only 800 feet higher in elevation, had a dewpoint of 36F!

For today, we expect sunny to partly cloudy skies this morning to lead to scattered thunderstorm activity by afternoon. Coverage will be highest in the San Juans stretching northeast through the Central Mountains and eastward across the plains. Over the San Juans and parts of the Plains, a Low flood threat has been issued. Storms will also be capable of producing very gusty winds, up to 65 mph. Activity will quickly subside after sunset, except through 11pm near the Kansas border.

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, jump below the map.

Zone-Specific Forecasts

Grand Valley, Northwest Slope, Northern Mountains, Central Mountains, San Luis Valley, Front Range, Urban Corridor:

Partly cloudy early, then scattered thunderstorms forming by early afternoon. Maximum one-hour rainfall is expected to stay below 0.5 inches so no flooding is expected. Stronger storms may produce gusty winds up to 65 mph.

San Juans, Southwest Slope

Sunny early, then turning partly cloudy. Scattered thunderstorms are likely by early afternoon with maximum one hour rainfall up to 0.8 inches possible. This could lead to isolated flash flooding, mud slides and debris flows. Gusty winds up to 65 mph may accompany the stronger storms. A Low flood threat has been posted.

Primetime: 1pm through 8pm

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

Sunny early, with scattered storms forming by early afternoon. Maximum 1-hour rainfall up to 1.2 inches will be possible in the stronger storms, along with hail to 0.75 inches and gusty winds up to 65 mph.

Primetime: 2PM through 9PM, except through 11PM near the Kansas border

Issue Date: 6/23/2015
Issue Time: 10:30AM

— Low flood threat for Palmer Ridge and Northeast Plains
— Low flood threat for Arkansas River from Canon City through La Junta

Despite the presence of an upper-level high pressure ridge, storms are back in the picture east of the Continental Divide. The water vapor image, below, shows that the ridge has scooted eastward and has allowed a “return flow” to setup on its western periphery. There are several disturbances embedded in the flow over Arizona and the Four Corners that will help to fire off thunderstorms across Colorado. Acting against storm formation is the very dry air in the mid and upper-levels of the atmosphere. Precipitable water values this morning range from about 0.4 to 0.8 across the state, increasing west to east. The best chances of thunderstorm formation will be where that dry air intrusion is minimized: today we expect that to be over the Palmer Ridge and into the Northeast Plains.

For today, we expect morning sunshine to quickly boost temperatures into the 80s and 90s. Cumulus clouds will form by late morning and lead to isolated thunderstorms over the higher terrain over and east of the Continental Divide. Early storms will produce light rainfall, less than 0.25 inches. As storms mature and merge, heavier rainfall will be possible over the Palmer Ridge and Northeast Plains. A Low flood threat has been issued for these areas. In the Northeast Plains, the wind profile will also allow for large hail, up to 1.5 inches in the strongest cells. Storm activity will quickly subside after sunset closer to the mountains and by midnight towards the Kansas/Nebraska borders.

We have downgraded the Arkansas River to a Low flood threat from Canon City through La Junta. Snow melt is almost complete and very minimal additional rainfall should keep lowering the river levels.

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, jump below the map.

Zone-Specific Forecasts

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

Sunny to partly cloudy and hot with temperatures in the 90s to near 100F in the lowest elevations. A stray thunderstorm cannot be ruled out in the highest terrain, but little if any rainfall will make it to the ground. No flooding is expected.

San Juans, San Luis Valley, Raton Ridge, Southeast Plains, Southeast Mountains:

Sunny early, then turning partly cloudy. Isolated thunderstorms are possible in the afternoon and early evening. One-hour rainfall up to 0.5 inches is possible, mainly east of the Divide. No flooding is expected.

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

Sunny early, with isolated to scattered storms forming by early afternoon. Most storms will be light rainfall producers, but a few isolated cells will be capable of up to 1 inch per hour west of I-25 and 1.6 inches per hour east of I-25. A Low flood threat is in effect for parts of the area. Hail up to 1.5 inches is possible in the strongest cells of the Northeast Plains.

Primetime: 2PM through 9PM, except through 1AM over Northeast Plains