FTB 07-10-2018: Afternoon Thunderstorms Continue to Rumble for Western Colorado

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.

Flood Threat Legend

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