Issue Date: Friday, July 13, 2018
Issue Time: 08:40AM MDT

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

— A LOW flood threat has been issued for the Southwest Slope and San Juan Mountains

The upper level high pressure system will begin to build back to the west of Colorado today. This will pull down dry air from Wyoming due to the upper level winds having more of a northwesterly component. Over the southwest corner of the state, the upper flow will be a bit more easterly due to the location of the high. This will keep a bit more moisture over the San Juan Mountains where thunderstorms should be the most abundant this afternoon. Currently, there is some light fog over the Northeast Plains, but this is expected to burn off quickly with the entrainment of the low-level, dry air and morning heating.

Over eastern Colorado, afternoon storms should be restricted to the mountains and immediate adjacent plains. With storm motion similar to yesterday, expecting a few showers to move over northern Colorado that fire over the Cheyenne Ridge. The other area of greatest convection will be along the Front Range and where this intersects with the Palmer Ridge. Over the Southeast Mountains, storms will be more isolated when compared to yesterday. Storms that initiate near fresh burn areas (particularly Spring Creek) will need to be monitored closely. However, the threat for local, heavy rainfall is lower today. With the low-level dry air continuing to lower surface dew points, the main threats today will be gusty winds, cloud-to-ground lightning and brief rainfall.

Similar to the east, the western mountains will be entraining dry air from the north. This should limit the coverage and intensity of thunderstorms over the Northern and Central Mountains this afternoon. As mentioned above, subtropical moisture will remain over the southwest corner of the state including the San Juan Mountains. Paired with slow steering winds, there is the possibility of another afternoon of local, heavy rainfall. While intensity should decrease a bit from yesterday, the prior few days of rainfall will make runoff more likely. A Low flood threat has been issued for this area with a Moderate flood threat for the Burro and 416 burn areas. Threats include mud flows, debris slides over the higher terrains and local stream flooding over all locations in the threat area. Without much upper level forcing, thunderstorms activity should drop off quickly after sundown as instability decreases. A few showers may linger into the night, but the intensities will be below flood threat thresholds.

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:

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

Showers and thunderstorms will be most abundant over the San Juan Mountains and Southwest Slope this afternoon. Still expecting some storms over the Central and Northern Mountains, but they should be isolated. Over this area, max 1-hour rain rates up to 0.5 inches/hour are possible. Further south, max 1-hour rain rates up to 1.1 inches/hour are possible. There is high confidence thunderstorms over the south will have rain rates greater than 0.5 inches/hour, so a Moderate flood threat has been issued for the recent burn scars. If a storm tracks directly over the scars, this should be enough to trigger mud flows and debris slides. Elsewhere over the San Juans and Southwest Slope, increased runoff and 1 hour rainfall intensities will warrant a Low flood threat. The flood threat should end a couple of hours after sundown.

Primetime: 1PM to 9PM

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

Expecting thunderstorms and showers over the higher terrains again this afternoon. Dry air will continue to be pulled in from the north, so this should limit rainfall rates. To the north, max 1-hour rain rates up to 0.4 inches/hour are possible. Some rainfall may occur at the Palmer Ridge/Front Range intersect. Max 1-hour rain rates up to 0.5 inches/hour are possible here. Storms that track near the Spring Creek burn area should be monitored closely this afternoon as 0.5 inches/hour can trigger mud flows and debris slides over recent burn scars. A few showers may linger over the Southeast Mountains into the night, but flooding is not expected today.

Primetime: 2PM to 10PM

Issue Date: 7/12/2018
Issue Time: 8:37 AM

A HIGH FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS TODAY, NAMELY THE 416 FIRE AND BURRO FIRE.
A HIGH FLOOD THREAT IS FORECAST FOR THE SPRING FIRE BURN AREA.
A MODERATE FLOOD THREAT IS FORECAST FOR OTHER AREA BURN SCARS, INCLUDING THE WEST FORK COMPLEX, CHATEAU FIRE, WESTON PASS, JUNKINS, HAYDEN PASS, LAKE CHRISTINE, AND WALDO CANYON.
A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF ALL 14 REGIONS.

Moisture has increased across the state, setting the stage for scattered showers and thunderstorms capable of heavy rainfall. As you can see in the surface plot below, dewpoints are generally in the 50s across lower elevations, with upper-30s/40s readings across higher elevations. These numbers are indicative of a moist atmosphere. Additionally, there is a surface low pressure centered just south of the Palmer Ridge. This center will shift slightly throughout the day in response to upper-level forcing, but the result will remain the same – it will pull moisture from the plains into eastern Colorado, with the deepest moisture near the CO/KS border.

Due to this increased moisture statewide, a few disturbances embedded in the mid-level flow, and plenty of daytime heating, scattered showers and thunderstorms are expected across all regions. Precipitable water values are in the 90th percentile for the date in this morning’s 12Z soundings from Denver and Grand Junction, highlighting just how primed the atmosphere is for thunderstorms capable of heavy rainfall. Recent/ongoing burn scars across the Southwest Slope, San Juan Mountains, Southeast Mountains, Central Mountains, and Southern Front Range are of particular concern today, with moderate-to-high flood threats being issued. Flash flooding, mud flows, and debris slides will all be threats for those areas. More information on rain rates and timing can be found in the zone-specific 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

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

Scattered showers/thunderstorms are expected today/tonight, with coverage peaking between 3 PM and 7 PM (in concert with peak daytime heat). The best moisture, relatively speaking, will be situated across two regions: near the CO/KS border where Great Plains moisture transport will be best, and south of Highway 50, where monsoonal moisture will be deepest. Westerly flow along the Urban Corridor will keep the lower-levels somewhat drier, reducing the risk of heavy rainfall in those areas somewhat. Every region will have an area of Low Flood Threat, due to the maximum rainfall rates possible:

Urban Corridor and Palmer Ridge: 0.8-1.2 inches/hour
Northeast Plains: 1.5-2.0 inches/hour
Southeast Plains and Raton Ridge: 1.2-1.6 inches/hour

Timing: 1 PM – Midnight, with a few lingering showers/thunderstorms across the eastern plains into the early morning hours

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

Scattered-to-widespread showers and thunderstorms are expected beginning late this morning, peaking during the late afternoon/early evening hours, and diminishing after sunset, with a few lingering until around Midnight over the higher terrain of the Southwest Slope and San Juan Mountains. Due to the depth of moisture available, precipitation will reach the surface more efficiently than previous days, increasing the risk of heavy rainfall. Thus, the issuance of multiple high and moderate flood threats for area burn scars, and a widespread low flood threat. Maximum rain rates are as follows:

Northwest Slope: 0.4-0.8 inches/hour
Northern Mountains, Grand Valley, and Central Mountains: 0.8-1.2 inches/hour
Front Range: 0.6-1.2 inches/hour
Southeast Mountains, Southwest Slope, and San Juan Mountains: 1.0-1.5 inches/hour
San Luis Valley: 0.5-1.0 inches/hour

Timing: 11 AM – 9 PM, with a few lingering showers/thunderstorms over the higher terrain of the San Juan Mountains and Southwest Slope until around Midnight.

Issue Date: 7/11/2018
Issue Time: 8:25 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE AND SAN JUAN MOUNTAINS TODAY, NAMELY THE 416 FIRE AND BURRO FIRE.
A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, SOUTHEAST MOUNTAINS, RATON RIDGE, CENTRAL MOUNTAINS, GRAND VALLEY, NORTHWEST SLOPE, AND NORTHERN MOUNTAINS.

A mid-level low has continued its shift westward, finally reaching Colorado early this morning, while the mid-level high pressure that has dominated our weather pattern for the last few days has shifted north and east of the state. Both of these features have been highlighted in the water vapor image below. The presence of the low will provide support for another day of scattered showers/thunderstorms over the High Country, while also bringing the chance for isolated thunderstorms back to eastern Colorado. Due to easterly flow aloft and the presence of better moisture, the bulk of storm activity will occur along/west of the Continental Divide, with more isolated coverage over the eastern mountains (Front Range/Southeast Mountains).

Isolated storms are also expected over the Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Plains, and Raton Ridge, with the best chances along/south of I-70, in close proximity to the mid-level low. Moisture is lacking overall, so the heavy rainfall threat will be mitigated for areas away from the low-pressure center. However, a pocket of moisture has been transported alongside the low-pressure center (Southeast Mountains and Raton Ridge), so brief periods of heavy rain may occur in these areas. Thus, the issuance of the low flood threat. Otherwise, gusty winds, lightning, and periods of light rainfall will be the main threats.

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 and hot will be the main weather storm today, as much of the area remains dry and devoid of rainfall. However, a few isolated thunderstorms are expected today, thanks to the presence of the mid-level low. Moisture remains limited, though, so heavy rainfall is not expected, outside of the aforementioned areas near the mid-level low. Most rain rates will remain below 0.4 inches/hour, with maximum rain rates as follows:

Urban Corridor, Northeast Plains, and Palmer Ridge: 0.2-0.4 inches/hour
Southeast Plains and Raton Ridge: 0.6-1.0 inches/hour

Timing: Noon – 9 PM, with an isolated shower or two lingering over southern areas until midnight.

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

Scattered thunderstorms along/west of the Continental Divide, with more isolated coverage east. The bulk of the activity will once again hug the mountain ridges, where orographic lift will aid daytime heat, but expect more showers/storms to move and persist over lower valleys with the increase in mid-level support. Moisture will slowly increase throughout the day, but much of the moisture still remains bottled in the mid-levels. This will keep rain rates down somewhat, but periods of moderate rainfall are still expected. Thus, the issuance of a low/moderate flood threat. Maximum rain rates are as follows:

Northwest Slope, Northern Mountains, Grand Valley, and Central Mountains: 0.5-1.0 inches/hour
Southwest Slope and San Juan Mountains: 0.6-1.0 inches/hour
Southeast Mountains: 0.5-0.9 inches/hour
Front Range: 0.2-0.4 inches/hour
San Luis Valley: 0.2-0.5 inches/hour

Timing: 11 AM – 11 PM, with a few lingering showers/weak thunderstorms over the Southwest Slope, San Juan Mountains, Grand Valley, and Northwest Slope into the early morning hours.

Issue Date: Tuesday, July 10, 2018
Issue Time: 09:30AM MDT

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

Nearly cloudless start to the day across the state with the exception of some light clouds over the San Juan Mountains. More of the same today as the upper level high pressure system continues to sit north of Colorado. It will start its slow progression eastward today, but won’t make it too far from its current position. Also seen in the water vapor imagery below is an upper low over the panhandle of Oklahoma. This feature will slowly start to move to the west, but like the high pressure system, won’t make much progress from its current position today. Eventually as the high moves SE and settles over MO later this week, the low continues to move west then rotates clockwise around the high.

Persistent forecast for this FTB with nearly the same setup as yesterday minus a few varying details. Over eastern Colorado, dry air continues to be entrained from the east at the low levels. Precipitable Water at DIA has dropped to 0.52 inches, which is quite a bit lower than this time yesterday with the sounding showing a very dry layer near 600mb. With general subsidence and lack of moisture, precipitation for the eastern half of Colorado should be limited to the higher terrains along the Continental Divide. On the whole, rain totals are forecast to be under 0.1 inches.

More low level moisture makes its way back into the western portion of the state later this afternoon and evening, so showers and thunderstorms that initiate over the western mountains should be more widespread. Similar to yesterday, the most thunderstorm action will take place over the San Juan Mountains. With the moisture a bit higher today, the atmosphere will be able to provide multiple rounds of thunderstorms this afternoon and with greater coverage. With PW values at Grand Junction near an inch, the intensity of the storms this afternoon should also increase. There is high confidence that storms over the San Juans will have rain rates greater than 0.5 inches/hour, so a Moderate flood threat has been issued for the Burro and 416 burn areas. Threats include mud flows, debris slides and local stream flooding for storms that track over the area. Elsewhere, storm motion should be quick enough to the east that flash flooding should be avoided.

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, Southeast Plains, Northeast Plains:

Analogous forecast to yesterday as dry air continues to be pulled in from the east. PW values have really dropped off, so expecting less thunderstorm coverage this afternoon along the Divide. Max 1-hour rain rates under 0.1 inches are expected with plenty of virga and brief, windy conditions. Storms over the northern Front Range (Larimer/Weld Counties) will have higher rain rates with max 1-hour values up to 0.6 inches. High temperatures should climb a few degrees with the Front Range cities nearing or exceeding 100F. Flooding is not expected today.

Primetime: 3PM to 8PM

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

Showers and thunderstorms will initiate over the San Juan Mountains just after 1PM this afternoon. By 3PM expect coverage to increase north over the Central and Northern Mountains. With storm motion to the east, the lower valleys should see some rain later in the afternoon as the storms push off the higher terrain. Max 1-hour rain rates up to 0.85 inches are possible over the mountains with the best chance for these rates over the San Juan Mountains. Over the valleys, max 1-hour rain rates up to 0.6 inches/hour are possible. A Moderate flood threat has been issued for the 416 and Burro burn scars due to high confidence thunderstorms over the area this afternoon will produce rain rates of at least 0.5 inches/hour. Should they track over the burn areas, flash flooding may occur along with mud flows and debris slides. Elsewhere, storm motion should be fast enough that flooding should be avoided. Showers and thunderstorms may linger over the lower elevations through midnight tonight.

Primetime: 1:30PM to 12AM