FTB 08-30-2016: More Heavy Rainfall Possible Today

Issue Date: Tuesday, August 30th, 2016
Issue Time: 10:45AM MDT

MODERATE flood threat for Northeast Plains, Palmer Ridge, Urban Corridor
LOW flood threat for Front Range, Southeast Plains, Southeast Mountains, Raton Ridge

The morning water vapor image, shown below, shows the key factors in a somewhat challenging forecast today. While most of the western US is under the influence of a weak upper-level ridge, the disturbance that has affected Colorado for the past 48 hours remains centered over the western part of the state. Despite slowly losing strength today, it will continue to be a factor by favoring weak upward motion east of the Continental Divide. Low-level moisture has increased over the eastern part of the state with precipitable water values running in the 0.9 – 1.2 inch range. High surface dewpoints, up to 63F, can be found this morning along the KS border. Sunshine is in abundance this morning for almost all. Collectively, it will not be a problem to generate scattered to widespread thunderstorms capable of heavy rainfall for many areas east of the Divide, especially in the Northeast Plains. A Low flood threat has been posted to account for this. The more uncertain aspect is centered around a plume of very moist low-level air that is forecasted to move westward into CO a few hours before sunset. With a relatively deep easterly flow, about 10,000 feet high, this could spark off an additional round of slow-moving storms capable of very heavy rainfall rates. Although this is not guaranteed, the severity of the rainfall rates warrants a Moderate flood threat for parts of northeast CO. High antecedent rainfall will also be a contributing factor for western areas of the Moderate threat region.

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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, scroll below the map.
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Flood Threat Legend

Zone-Specific Forecasts:

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

Sunny early then scattered to widespread thunderstorms developing by early afternoon. Coverage will be highest in the foothills as well as the Northeast Plains. Max 30-minute rainfall up to 1.1 inches is possible, with max 1-hr rates up to 2.1 inches. Isolated flash flooding, debris slides and mud flows are possible, especially in areas that have received previous rainfall. Hail up to 0.75 inches is possible under the strongest cells. A secondary flare up of storms is possible in the late evening hours, warranted a Moderate flood threat for parts of the region. Otherwise, a Low flood threat is in place.

Primetime: 2PM to 2AM

San Juan Mountains, Southwest Slope:

Mostly sunny this morning then isolated to scattered to showers and thunderstorms developing by early afternoon. Coverage will be highest in the San Juans. Max 1-hr rain rates up to 0.6 inches possible. Hail up to 0.5 inches could accompany the strongest cells. Graupel is possible above 12,500 feet. Flooding is not expected today.

Primetime: 12PM to 7:30PM

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

Mostly sunny early then isolated showers and a weak storm possible through the early evening hours. Max 1-hour rain rates up to 0.3 inches. Flooding is not expected today.