FTB 07-11-2018: Mid-Level Low Makes an Appearance

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.

Flood Threat Legend

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.