FTB 05-27-2016: A Low Flood Threat Remains In Place For Eastern Colorado

Issue Date: Friday, May 27th, 2016
Issue Time: 10:30 AM

— LOW flood threat today for parts of the Northeast Plains, Palmer Ridge and Southeast Plains
— LOW flood threat today for parts of Grand Valley (landslide possible)

In today’s water vapor imagery, shown below, we see the remains of yesterday’s low pressure system that generated all kinds of active weather across Colorado (check out our Storm Total Precipitation discussion). As is often the case with the day after the storm, a downtick in rainfall activity is expected today. However, some active will still remain across parts of the state.

Let’s discuss the details:
• the atmosphere’s dynamics are weakening with the departing and weakening low pressure; mid-level height rises of 30 – 60 meters are expected throughout the days favoring weak subsidence
• atmospheric instability will be limited for most of the state with less than 750 J/kg of instability for most; the only exception is the far eastern part of the state where instabilities up to 1,500 J/kg will be possible
• precipitable water values are in line with their seasonal averages, though overall drying is expected for the majority of the state (again with the exception of the far east)
• storm motions will be in the 30+ mph range which will limit the amount of time a location experiences heavy rainfall; again, the exception is the far east where southeasterly boundary layer winds will lower storm motions
• Yesterday’s rainfall in the South Platte basin will slowly drain into the river, but is not expected to raise river levels above the flood stage
• With the cool temperatures, snow continues to melt in an orderly fashion and is not expected to induce flooding at high-elevation streams.

The details above warrant a low flood threat for the far eastern part of the state where hourly rainfalls could exceed 1.5 inches per hour, with 3-hour totals approaching 2.4 inches. The rest of the state is not expected to experience flooding.

We also want to point out that a Flash Flood Watch has been issued by the Grand Junction NWS for the Salt Creek landslide area (Mesa County). We urge everyone in that area to keep up to date with local officials or the NWS.

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.
FTB_20160527Zone-Specific Forecasts

Northeast Plains, Southeast Plains, Palmer Divide:

Partly sunny with scattered rain showers early with scattered thunderstorms developing by early afternoon. One hour rainfall up to 1.6 inches is possible with 3-hour rainfall up to 2.4 inches. A Low flood threat is in place for the far eastern parts of the region for localized road and field flooding.

Prime-time: 12PM to 8PM

Central Mountains, Northern Mountains, Southeast Mountains, San Juan Mountains, San Luis Valley, Front Range, Urban Corridor, Raton Ridge:

Mostly cloudy with scattered rain showers through the day, gradually decreasing in coverage later. A few weak thunderstorms are possible during the afternoon in the lower elevations below 7,000 feet. One hour rain rates up to 0.6 inches possible in the strongest storms. Up to 1.2 inches of total precipitation possible by tomorrow morning. The snow line will be 10,000 feet early, moving up to about 11,500 feet by later in the afternoon.

Prime-time: 12PM to 7PM

Grand Valley, Northwest Slope, Southwest Slope:

Scattered clouds with gradually clearing skies. A stray shower or even weak thunderstorm cannot be ruled out, but max 1-hr rain rates will stay below 0.4 inches. Flooding is not expected. However, folks should pay attention to local officials in the Mesa County area regarding the condition of the Salt Creek landslide.