Issue Date: 7/21/2018
Issue Time: 7:30 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE FRONT RANGE, CENTRAL MOUNTAINS, SOUTHEAST MOUNTAINS, URBAN CORRIDOR, PALMER RIDGE, RATON RIDGE, NORTHEAST PLAINS, AND SOUTHEAST PLAINS.

The upper-level high will shift back towards the west-northwest today, in response to a deepening upper-level low over the eastern United States. This will reduce the impact of monsoonal moisture over Colorado, keeping the deepest moisture over Utah, and reducing the threat of heavy rainfall over the mountains. Another day of scattered showers/thunderstorms is on tap for the High Country west of the Front Range/Southeast Mountains, thanks to orographic forcing and residual moisture underneath the ridge, but expect them to produce more gusty winds than rain as low-level moisture is lacking. For these reasons, no flood threats are warranted for the High Country west of the Continental Divide. However, due to the sensitive nature of recent/ongoing burn scars, it would be a good idea to monitor them, just in case.

For areas east of the Continental Divide, an influx of low-level moisture from the Great Plains will provide fuel for scattered showers/thunderstorms. Initially, storms will mainly produce gusty winds and periods of light rainfall as precipitation has to overcome meager relative humidity in the low-levels caused by the hot temperatures. However, as storms mature, and produce enough precipitation to sufficiently saturate the low-levels, periods of moderate-to-heavy rainfall will be a concern. Decent enough storm motions will mitigate the flood threat somewhat, so recent/ongoing burn scars over the Front Range/Southeast Mountains, low-lying intersections, poorly drained locations, and field ponding will be the main concerns for the low flood threat area. For more details on rain rates and timing, please see the zone-specific forecast discussions below.

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

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

Scattered showers/thunderstorms are expected today, in response to the influx of low-level moisture from the Great Plains. Eventually, storms will be capable of producing periods of moderate-to-heavy rainfall, for reasons outlined in the main discussion above. Storm motions will mitigate the flood threat somewhat, so the main concerns will be for recent/ongoing burn scars in the mountains, poorly drained intersections and low-lying urban areas, as well as low-lying fields/roads where ponding can occur. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.8-1.2 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 1.0-1.4 inches/hour3
Northeast Plains and Southeast Plains: 1.25-1.75 inches/hour

Timing: Noon – 10 PM for the Front Range/Southeast Mountains, 1 PM – 11 PM for the Urban Corridor, Palmer Ridge, and Raton Ridge, and 2 PM – 2 AM for the Northeast Plains and Southeast Plains

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

Garden-variety scattered showers/thunderstorms are expected today, with relatively dry air in the low-levels reducing precipitation efficiency at the surface. The main threat from any activity will be gusty winds, light rainfall, and lightning. Storm motions and rain rates preclude the issuance of any flood threat, but as mentioned above, it will be a good idea to monitor sensitive burn scars, just in case. Generally speaking, rain rates will be below 0.1 inches/hour, with maximum rain rates around 0.2-0.4 inches/hour. The best chance at moderate rainfall (0.3-0.6 inches/hour) will be eastern sections of the Central Mountains region.

Timing: 11 AM – 9 PM. During the overnight hours, monsoonal moisture will begin to work back into far western Colorado, so a couple showers will linger near the CO/UT border into tomorrow morning.

Issue Date: Friday, July 20th, 2018
Issue Time: 08:30AM MDT

— A LOW flood threat has been issued for the 416 and Burro burn areas

The shift in the weather pattern begins today. The upper level high will start to move into NM and the Texas panhandle as seen in the water vapor imagery below. This will shift the subtropical moisture axis on its west side into western Colorado and start pulling higher low and mid-level moisture. The position of the high will limit how far north the larger Precipitable Water (PW) values will get, but there will be an uptick in shower activity across all the western higher terrain this afternoon. The storms to the north will likely produce gusty winds and plentiful virga as surface moisture is not as abundant as further south. With low level moisture returning to the San Juan Mountains, the 416 and Burro burn scars will need to be monitored closely for storms that track over those areas this afternoon. The max 1-hour rain rates are expected to exceed 0.25 inches/hour over San Juans, so a Low flood threat has been issued for the two burn scars.

Similar to the west, over eastern Colorado, the higher PW values will be located over the southern half of the state and far eastern plains. This means increased shower activity over the Southeast Mountains, Raton Ridge and Southeast Plains this afternoon and evening. There will be a fairly large spread between the dew points and temperature over southern mountains and adjacent plains, so gusty winds are expected with the storms that form this afternoon. Better moisture is able to hold on over the Southeast Plains, so as the storms make their way east, they will increase their rain rate efficiencies. However, max 1-hour rain rates will remain below 1 inch, so flooding is not expected.

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

Subtropical moisture begins to return to western CO this afternoon. Increased shower and thunderstorm activity is expected for the southern half of these regions. To the north, expecting more cloud cover and virga. There is a Low threat for the 416 and Burro burn scars as storms in the area are expected to have max 1-hour rain rates up to 0.4 inches/hour. If one of these storms tracks over a recent burn scar, this could trigger mud flows and debris slides. Max 1-hour rain rates will be closer to 0.2 inches/hour over the Central Mountains. Thunderstorms will transition into lighter showers after sundown, and all shower activity will end by 10PM.

Primetime: 1:30PM to 8PM

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

Similar to western Colorado, the southern high terrains will have the bulk of the afternoon thunderstorm activity. With a higher spread between dew point and temperature, rain rates will be under 0.25 inches/hour. As the storms track east, they will encounter better moisture over the eastern plains. The best chances for thunderstorms this afternoon will be over the Southeast Plains, though a stray thunderstorm could form over the Northeast Plains. Max 1-hour rain rates up to 0.8 inches are possible with gusty winds and dangerous cloud-to-ground lightning.

Primetime: 2PM to 10:30PM

 

Issue Date: 7/19/2018
Issue Time: 6:30 AM

NO FLOOD THREAT IS FORECAST TODAY.

A near repeat of yesterday is on tap for today, with plenty of sunshine and hot temperatures being the main weather story. Just as yesterday, high pressure aloft sits just to the west/southwest of Colorado, keeping the flow of drier air coming, while also acting to suppress most attempts at precipitation. Even so, a few isolated showers/thunderstorms are expected to overcome the relatively unfavorable conditions over the higher terrain along/south of I-70. Periods of light-to-moderate rainfall will be about all the atmosphere can muster, as drier air in the low-levels limit intensity of storms and rain rates at the surface.

East of the mountains, hot and dry conditions will dominate, with high temperatures pushing into the upper 90s across most areas, with more than a couple locations reaching into the low-100s. An isolated high-based storm or two will be possible over the Raton Ridge and far Southeast Plains near the CO/KS border, where dewpoints will hang on in the low-to-mid 40s, providing just enough fuel for development. Heavy rainfall resulting in flooding is not a concern, as dry air below cloud bases will limit rain rates at the surface.

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

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

Hot and dry is the weather headline today, with abundant sunshine blanketing the area. A few cumulus clouds will bubble during the afternoon hours, with a few streaks of virga dotting the sky. A couple isolated, high-based storms during the afternoon/evening over the Raton Ridge and the far Southeast Plains near the CO/KS border cannot be ruled out, with the main impacts being gusty winds, lightning, and brief periods of moderate rainfall. Maximum rain rates will be 0.25-0.5 inches/hour.

Timing: 1 PM – 10 PM

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

Mostly sunny skies and hot temperatures are on tap today, with a few isolated storms over the higher terrain along/south of I-70 to break up the monotony. The majority of any shower/thunderstorm activity will occur over the higher terrain of the San Juan Mountains and Southwest Slope regions where moisture is best (relatively speaking). Drier air below cloud bases will limit precipitation efficiency, so heavy rainfall is not expected. Like yesterday, it would be a good idea to keep an eye on sensitive burn scars that have received rainfall over the past few days, just in case. Generally, rain rates will be less than 0.15 inches/hour, with maximum rain rates of 0.2-0.4 inches/hour.

Timing: 1 PM – 9 PM, with a couple lingering showers until Midnight or so over southern mountains.

Issue Date: 7/18/2018
Issue Time: 8:05 AM

NO FLOOD THREAT IS FORECAST TODAY.

Upper-level high pressure will become centered over southern UT/northern AZ later today, ushering in drier air from the northwest across the northern half of Colorado. Across southern Colorado, moisture trapped under the ridge will provide the fuel for a few weak, isolated thunderstorms, mainly over the higher terrain of the Southwest Slope, San Juan Mountains, Grand Valley, Southeast Mountains, and southern portions of the Central Mountains and Front Range regions. The main story today, though, will be the increase in high temperatures and sunshine compared to previous days.

One or two isolated storms are also possible over the lower elevations of eastern Colorado, south of I-70, near the higher terrain. Over the Southeast Plains, near the CO/KS border, an isolated strong-to-marginally severe thunderstorm cannot be ruled out. In general, though, the day will be marked by temperatures 5-10 degrees warmer than yesterday with plenty of sunshine.

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

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

Mostly sunny skies and dry conditions will be the name of the weather game for the vast majority of the area as drier air and high pressure moves in. A couple isolated storms during the afternoon/evening hours are possible near the higher terrain south of I-70, as well as along the CO/KS border. Brief periods of moderate rainfall will attend stronger storms, but flooding issues are not expected. Maximum rain rates will be 0.25-0.5 inches/hour.

Timing: 4 PM – 10 PM

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

Much of the area will remain dry today, with high temperatures warming 5-10 degrees or so over yesterday’s reading. A few isolated showers/weak thunderstorms are expected over the higher terrain south of I-70. Brief periods of moderate rainfall will attend thunderstorms, but owing to their widely isolated nature, no flood threat will be issued. It is recommended to keep an eye on the 416 Fire, Burro Fire, and West Fork complex scars due to the amount of rainfall they have received over the past few days, just in case. Maximum rain rates will be 0.25-0.5 inches/hour, with rain rates generally below 0.2 inches/hour.

Timing: 1 PM – 9 PM, with a couple lingering showers over southern mountains until 11 PM – Midnight