FTB 05-28-2015: Disturbance To Aid Thunderstorms, But Limited Flood Threat

Issue Date: May 28th, 2015
Issue Time: 10:10AM MDT

— LOW flood threat for parts of Northeast Plains, Palmer Ridge and Southeast Plains
— LOW flood threat for South Platte River from Greeley through Fort Morgan
— LOW flood threat for Arkansas River from Pueblo through La Junta

A disturbance is moving into Colorado from the northwest, shown by the water vapor image below. The disturbance’s passage will coincide with the maximum heating of the day, which will increase thunderstorm activity compared to yesterday. However, despite favorable upper-level dynamics, one important missing piece to heavy rainfall today is low-level moisture. Although morning dewpoints are in the 40s and 50s, precipitable water values are only around 0.6 inches. More importantly, since the disturbance is arriving from the northwest, this will allow dry air to mix down the eastern side of the Divide. The end result is that only eastern Colorado will have enough low-level moisture to warrant a low flood threat. There, in addition to heavy rainfall, large hail up to 1.75 inches and wind gusts up to 60 mph are all possible with stronger storms. Away from the threat area, expect scattered thunderstorms with one hour rain rates in the 0.2 to 0.5 inch range, along with small hail up to 0.5 inches.

watervapor_20150528

In addition to the flash flood threat today, the Arkansas and South Platte Rivers continue to run in minor flood stage. Today’s activity is very unlikely to significantly impact either river. Nonetheless, we expect both rivers to stay elevated due to the abundant upstream runoff.

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.

05282015_LFT
Flood Threat Legend

 

Zone Specific Forecasts

Southwest Slope, Northwest Slope, Grand Valley, and San Luis Valley:

Partly to mostly cloudy with scattered showers and thunderstorms. Hourly rainfall up to 0.4 inches will be possible, along with small hail up to 0.5 inches and gusty winds up to 60 mph. No flooding is expected today.

Northern Mountains, Central Mountains and San Juan Mountains:

Scattered showers and thunderstorms developing by early afternoon. Hourly rainfall up to 0.6 inches will be possible, along with small hail and gusty winds. No flooding is expected today.

Front Range, Urban Corridor, Northeast Plains, Southeast Plains and Palmer Ridge:

Becoming partly cloudy with thunderstorms developing by early afternoon. Closer to the mountains, hourly rain rates up to 0.7 inches will be possible. Farther east, stronger storms will be capable of up to 1.8 inches per hour of rainfall. A Low flood threat has been posted for the eastern part of the Palmer Ridge and the entire Kansas border. The strongest storms will be capable of 1.75 inch hail, and winds up to 60 mph.

Prime Time: 2pm through 9pm

Southeast Mountains, Raton Ridge:

Mostly sunny early, then becoming partly cloudy. An isolated high based thunderstorm cannot be ruled out. However, the passage of a dryline will lower dewpoints into the 20s and 30s preventing heavy rainfall. Gusty winds up to 35 mph will be likely in the afternoon, but the fire danger is not of concern due to wet soils. No flooding is expected today.