FTB 06-18-2019: Rinse and Repeat Pattern for Heavy Rainfall and Severe Thunderstorms

Issue Date: Tuesday, June 18th, 2019
Issue Time: 9:35AM MDT

–A MODERATE flood threat is issued for the Palmer Ridge, and portions of the Urban Corridor and Southeast Plains. This includes the Arkansas River downstream of Pueblo Dam to La Junta.

–A LOW flood threat is issued for the Front Range, Urban Corridor, Southeast Plains and Northeast Plains. This includes the Junkins burn area. Additional LOW flood threats have been issued for Saguache Creek and the headwaters of the and along the Rio Grande in Mineral and west Rio Grande Counties.

Taking a look at the visible satellite imagery below, there is a lot of fog, cloud cover and some light rain over the Central Mountains to start the day. Some drier air has worked its way in from the west over the southwest corner. The moisture gradient (green lines, called isopleths) shows dew points have decreased to the low 40°Fs in this area, so clear skies over that region. The surface low, which is currently over the Oklahoma Panhandle area, continues to hold a very moist air mass in place over eastern Colorado. Westerly winds aloft will likely mix some of this moisture out and pull in lower dew points from west near the southern Southeast Mountains. This is similar to yesterday and should limit the heavy rainfall activity over the Raton Ridge area and keep the heavy rainfall threat limited to the foothills and eastern adjacent plains.

A vorticity max from the west (purple dashed line below) will help spark storm activity over the higher terrains by midday and help increase the coverage of storm activity. For western Colorado, highest accumulations will again be over the Northern and Central Mountains with lighter totals over the San Juan Mountains. Storms will likely track in from the west into the lower valleys (except the southwest corner), but flooding is not forecast for these storms. Emergency management reported flooding in the headwaters of and along the Rio Grande in Mineral and west Rio Grande Counties as well as along Saguache Creek. A Low flood threat has been issued for these Flood Warned areas.

As storms move west off the eastern high terrains, except another MCS to set up over the plains. Heavy rainfall, hail up to 1.75 inches, strong winds (greater than 60 mph) will be possible with the severe storms. Rainfall totals over the eastern border counties yesterday were quite high (see today’s SPM) and likely saturated soils; therefore, except increased runoff over these areas. Even with storm motion slightly faster than yesterday, heavy rainfall and flooding issues will still be likely with dew points over 50°F. PW values at DIA were measured at 0.91 inches (95th percentile), which is a good indication heavy rainfall will occur again this afternoon. Flood threats include street, small stream/river and arroyo flooding along with field ponding. A Moderate threat has been issued for the Palmer Ridge, southern Urban Corridor and portions of the Southeast Plains. Gages continue to run high downstream of Pueblo Dam due to snowmelt and dam releases, so the Arkansas from Pueblo to La Junta is included in the Moderate threat due to the possibility of minor lowland flooding. A Low threat has been issued for all of eastern Colorado minus the Southeast Mountains and Raton Ridge. The Junkins burn area is included in the Low threat, so use caution if a storm tracks over this area as mud flows, debris slides and flash flooding will be possible.

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.

Flood Threat Legend

 

Zone-Specific Forecasts:

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

Max 1-hr rain rates up to 1.3 inches are possible this afternoon in the Moderate threat area. Further north along the Urban Corridor, max 1-hr rain rates up to 1.1 inches are possible. Over the eastern plains, totals up to 1.5 inches are possible. While this normally wouldn’t be a threat, saturated soils from yesterday’s ran will increase runoff and the flood risk. Flooding risks today include urban flooding, street flooding, arroyo flooding and field ponding. Storms that track over the Junkins burn area should also be monitored closely as rain rates up to 0.9 inches are possible, which have been known to cause flash flooding and debris slides. A second set of storms is possible over the eastern mountains and Front Range later tonight, but flooding is not anticipated with these storms. Lastly, included in the Moderate flood threat is the area immediately downstream of Pueblo Dam (to La Junta) due to the AHPS gage remaining high throughout the day.

Primetime: 11AM to 3AM

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

Similar set up to yesterday with storms firing over the high terrains this afternoon. Once again, storms will also track into the lower valleys from the west due to increased mid-level energy in the area. Max 1-hr rain rates up to 0.7 inches (mountains) and 0.5 inches (valleys/west) are possible. Storms may linger over the Northern and Central Mountains tonight, with isolated morning totals up to 1.2 inches. Totals up to 0.15 inches is also possible over the northern portion of the San Luis Valley. The Flood Warning for central Saguache County continues as well as for the headwaters of the Rio Grande. Due to recent reports of minor flooding by emergency management, they have been given a Low flood threat. Please follow your local NWS office for the latest.

Primetime: 11AM to 3AM

FTB 06-17-2019: Severe Thunderstorms and Heavy, Overnight Rainfall Forecast for the Northeast Plains

Issue Date: Monday, June 17th, 2019
Issue Time: 10:25AM MDT

–A MODERATE flood threat is issued for the Northeast Plains and portions of the Urban Corridor, Palmer Ridge and Southeast Plains. An additional MODERATE flood threat has been issued for the Junkins burn area.

–A LOW flood threat is issued for the Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains and Southeast Plains. An additional LOW flood threat has been issued for the Hayden Pass and Spring Creek burn areas.

Riverine: A MODERATE flood threat is issued for the Arkansas River downstream of Pueblo Dam to Nepesta. A LOW flood threat continues through this afternoon for Saguache Creek just west of Saguache.

Busy water vapor imagery below to start the work week. Today, a trough will sit to our west once again with a surface low over eastern Colorado. The multiple shortwaves associated with the trough (marked in green) and surface low pulling in low level moisture over eastern Colorado has caused a cloudy, wet and foggy start to the morning. High moisture will remain intact over eastern Colorado thanks to the surface low pulling in high dew points from the south and east throughout the day. Expecting areas east of the white line below to have dew points in the low 50°Fs (west) and upper 50°Fs to 60°F (east) by this afternoon. Large PW values over the Northeast Plains and eastern Las Animas/Baca today will return the heavy rainfall threat for storms that track into this area. As storms form over the mountains early this afternoon, faster storm motion should limit the rainfall threat, thus there is only a Low flood threat to the west. Westerly winds over the south half of eastern Colorado will push the best moisture into the eastern portion of the Southeast Plains. However, enough moisture remains in place to cause issues for storms that track over recent burn areas. Thus, a Low flood threat has been issued for the Spring Creek and Hayden Pass burn areas. A Moderate threat has been issued for the Junkins burn areas as storms are expected increase their rain rates over this area.

As storms move east, slow steering winds, higher moisture and increased instability will create a favorable severe thunderstorm environment and storms will be capable of producing heavy rainfall. Initially, expect severe thunderstorms to produce large hail (up to 2 inches), strong winds and a tornado or two (northeast corner). By 6PM an MCS looks to form and hangs over the eastern plains through midnight along a convergence boundary. Therefore, high 2-3 hour rainfall totals will likely cause road and small river flooding over the Moderate threat area.

To the west, PW will also continue to increase with southwesterly flow aloft. Mixed with upper level disturbances passing through the area, rainfall should be widespread over this region as well. By early afternoon, forecasting numerous storms to form over the mountains with incoming storms from the west to bring precipitation to the lower valleys. Highest moisture remains over the north, but faster steering winds should prevent flooding. A few storms may linger through midnight over the northwest corner and Central Mountains, so isolated totals up to 1 inch are possible by tomorrow morning.

Riverine flooding continues for another day, although the flood threat is temporarily retreating. A Flood Warning continues for central Saguache County through 2PM this afternoon, so a Low flood threat has been issued for this area. With other Flood Warnings expiring over southeast corner of the state this morning and river levels dropping, increased flooding activity is not expected to be an issue. However, please continue to use caution as flows will remain elevated. A Moderate flood threat has been issued downstream of Pueblo reservoir to Nepesta where increased flows from releases and snow melt have kept the Avondale gage at Minor flooding.

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.

Flood Threat Legend

 

Zone-Specific Forecasts:

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

Increased moisture and instability this afternoon will create a heavy rainfall threat for the majority of eastern Colorado. Westerly winds over the Southeast Mountains, should push higher moisture into the eastern portion of the Southeast Plains, but the threat remains for the burn areas. A Low threat has been issued for Hayden Pass and the Spring Creek burn areas with max 1-hr rain rates up to 0.5 inches possible. A Moderate threat has been issued for the Junkins burn area due to rain rates up to 1 inch possible.

Over the northern Urban Corridor and Palmer Ridge, max 1-hr rain rates up to 1.2 inches are possible, so a Low flood threat has been issued. Increasing rain rates over the Northeast Plains and eastern portion of the Palmer Ridge are likely due to increased moisture and slow storm motion. Storms may also produce large hail, gusty winds and a possible tornado. Max 1-hr rain rates up to 1.75 inches are possible. Expecting storms to form an MCS overnight, which may produce isolated totals up to 2.5 inches by morning. Threats today include field ponding, street flooding and small river flooding. 24-hr totals up to 1.75 inches over portions of the Northeast Plains yesterday, will likely increase runoff over these regions.

Lastly, a Moderate flood threat is issued for the area immediately downstream of Pueblo Dam (to Nepesta due to the AHPS gage remaining in the Minor flooding stage throughout the day.

Primetime: 12PM to 1AM

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

Increased cloud cover this morning with some light showers thanks to a passing upper level shortwave. Moisture will continue to be on the increase over the area with southeast flow aloft. Expecting storms to form over the mountains this afternoon with showers also tracking into the lower valleys from the west. Max 1-hr rain rates up to 0.75 inches (north) and 0.5 inches (south) are possible. Storms may linger over the northwest corner and Central Mountains tonight, with isolated 24-hour totals up to 1 inch by morning.

As of 9AM: The Flood Warning for central Saguache County continues through this afternoon. With decreasing flows forecast today, not thinking anything but a Low flood threat is needed at this time. Please follow your local NWS office for the latest.

Primetime: 12PM to 9AM

FTB 06-16-2019: Slight Downtick in Overall Coverage of Storms Today

Issue Date: 6/16/2019
Issue Time: 8:15 AM

A MODERATE FLOOD THREAT IS FORECAST TODAY FOR THE FOLLOWING AREAS:

Arkansas River at Avondale due to snowmelt

A LOW FLOOD THREAT IS FORECAST TODAY FOR THE FOLLOWING AREAS:

Arkansas River at Canon City due to snowmelt
Rio Grande in the San Luis Valley due to snowmelt
Portions of the Front Range, Urban Corridor, Palmer Ridge, and Northeast Plains

NOTE: Due to snowmelt, many streams/rivers are running fast/high across the state, especially in the High Country.

In the wake of a departing upper-level disturbance, Colorado finds itself under the influence of an ever-so-slightly cooler air mass that lacks the upper-level support for thunderstorms that was present the last couple of days. That’s not to say that today will be nothing but blue skies: scattered showers/thunderstorms are expected again today thanks to remnant moisture and sunshine that will provide enough instability for their development. Due to the lack of upper-level support, slightly cooler temperatures, and marginal wind shear, nearly all of the activity will be garden variety, producing mainly gusty winds and periods of light-to-moderate rainfall.

There is one area of concern for a couple stronger storms that will be capable of heavy rainfall, and this is outlined by the low flood threat area below. The presence of a weak surface boundary in the area will provide enough wind shear and surface convergence to force the development of a couple stronger thunderstorms over portions of the Front Range, Urban Corridor, and Northeast Plains. Hail up to 1.5 inches in diameter, strong winds up to 60 mph, and periods of heavy rain will attend these stronger storms. Storm motions *should* be quick enough to avoid flash flooding issues; however, the threat of training/backbuilding storms along the boundary is enough to warrant the low flood threat.

For more details on timing and rain rates, 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.

Flood Threat Legend

Zone-Specific Forecasts

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

Scattered thunderstorms are expected over the Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains, and Northeast Plains, with more isolated-to-widely scattered coverage over the Raton Ridge and Southeast Plains. Most of the activity will be garden variety, producing periods of light-to-moderate rainfall, gusty winds, and occasional lightning. A few stronger storms are expected in the low flood threat area outlined above, with the potential for hail up to 1.5 inches in diameter, winds up to 60 mph, and periods of heavy rainfall. Maximum rainfall rates are as follows:

Front Range: 0.6-1.0 inches/hour
Urban Corridor and Palmer Ridge: 1.0-1.5 inches/hour
Northeast Plains: 1.5-2.0 inches/hour
Southeast Plains: 0.5-1.0 inches/hour
Southeast Mountains: 0.2-0.4 inches/hour
Raton Ridge: 0.3-0.7 inches/hour

Timing: 11 AM – 11 PM over the Front Range and Southeast Mountains, 1 PM – Midnight over the Urban Corridor and Raton Ridge, and 2 PM – 2 AM over the Northeast Plains and Southeast Plains

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

Scattered showers/thunderstorms are expected today, with the best coverage along/near the Continental Divide. Most valleys will likely remain dry, owing to a relative lack of moisture in the lower levels of the atmosphere. Rain rates will generally be less than 0.2 inches/hour, but a stronger thunderstorm may produce rainfall up to 0.4 inches/hour. Storm motions are expected to be quick enough to the east to avoid any flood threat.

Timing: 11 AM – 10 PM, with a few lingering showers into the early morning hours as the next upper-level disturbance approaches.

FTB 06-15-2019: Southeast Mountains Burn Scars Deserve a Watchful Eye

Issue Date: 6/15/2019
Issue Time: 9:00 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR THE FOLLOWING AREAS:

Arkansas River at Canon City due to snowmelt
Arkansas River at Avondale due to snowmelt
Rio Grande in the San Luis Valley due to snowmelt
Portions of the Southeast Mountains, Raton Ridge, and Southeast Plains, mainly for the following burn scars: Hayden Pass, Junkins, Buelah Hill, and Spring Creek.
Portions of the Front Range, Urban Corridor, and Palmer Ridge regions.

A weak disturbance aloft will shift east-northeast across the southern and Central Rockies today, providing broad upper-level support for scattered showers and thunderstorms across Colorado. All regions are expected to see some shower/storm coverage, but the greatest amount of activity will be over the Southeast Mountains, Raton Mesa, and Southeast Plains, where the best upper-level support and moisture coincide. Most activity will be garden-variety, producing periods of light-to-moderate rainfall and gusty winds. However, a few strong-to-severe storms will develop over the Southeast Mountains, Raton Ridge, and Southeast Plains, capable of periods of heavy rainfall, gusty winds up to 60 mph, and hail up to 1-1.75 inches in diameter. A special forecast discussion for the Spring Creek, Junkins, and Hayden Pass Burn Areas is below.

Spring Creek, Junkins, and Hayden Pass Burn Areas: Scattered showers and thunderstorms are expected to develop over the Southeast Mountains between 11 AM and Noon, continuing until 9-10 PM. Most rainfall will be light-to-moderate, as instability is fairly limited. However, during peak daytime heat (approx. 2 PM – 6 PM), one or two stronger thunderstorms will develop over the region. Should one of these storms move over a burn scar, flash flooding will be likely with maximum rain rates around 0.8-1.2 inches/hour. These scars should be monitored closely.

For more details on timing and rain rates, 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.

Flood Threat Legend

Zone-Specific Forecasts

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

Scattered showers/thunderstorms are expected, beginning during the late morning hours over the Front Range and Southeast Mountains, eventually spreading east over the lower elevations by 2 PM or so. Most of the activity will be garden variety, producing periods of moderate rainfall, gusty winds, and occasional lightning, but a few storms will become strong-to-severe, with attendant periods of heavy rainfall. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.8-1.2 inches/hour
Urban Corridor and Palmer Ridge: 1.0-1.5 inches/hour
Northeast Plains and Southeast Plains: 1.25-1.75 inches/hour
Raton Ridge: 0.5-0.9 inches/hour

Most showers/storms will come to an end by 9-10 PM, but a few will linger over the Southeast Plains until Midnight – 1 AM.

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

Scattered showers and garden-variety thunderstorms are expected today, with the best coverage south of I-70. Periods of light-to-moderate rainfall and gusty winds will be the main impacts, with occasional lightning and small hail attending the stronger, relatively speaking, storms. Showers/storms will begin to develop between 10 AM – Noon over the higher terrain, spreading over lower valleys with time, with most activity coming to an end by 9 PM. A couple isolated showers will continue until midnight or so. Rain rates will generally be less than 0.2 inches/hour, with maximum rates of 0.25-0.5 inches/hour possible.