Issue Date: 5/1/2015
Issue Time: 10:20 AM
NO FLOOD THREAT IS FORECAST.
Welcome back to the 2015 edition of the Colorado Flood Threat Bulletin. Mother Nature decided not to allow us a few dry days to get back into the swing of things, and instead has provided Colorado with a bit of moisture to provide some early-season action. Precipitable water (IPW), shown in the image below, tells a story of increasing moisture during, and after, the cool frontal passage yesterday evening. This left-behind moisture will provide the fuel for today’s showers and thunderstorms, as sunshine and a weak mid-level disturbance provide an ignition mechanism.
A closer look at other observations reveals that most of the moisture west of the Continental Divide is confined to the mid-levels, which means that most showers and thunderstorms on that side of the state will struggle to produce moderate rainfall, resulting in mainly gusty winds and light rain at the surface. East of the Continental Divide, however, moisture is spread between the low- and mid-levels of the atmosphere, and will allow for a better chance at stronger storms and moderate-to-heavy rainfall.
The forcing mechanism for today’s showers and thunderstorms will be a combination of daytime heating and a 700-mb shortwave. These will combine to kick off isolated showers and thunderstorms over the higher terrain between 10 am and Noon. As the shortwave progresses east, and daytime heating take place, coverage and intensity will increase as storms develop over the Front Range between Noon and 2 PM. Storm motions today will take storms in a southeasterly direction at about 15-20 mph, across the plains through the afternoon and evening hours. The strongest storms will impact the Front Range, Urban Corridor, Palmer Ridge, and Northeast/Southeast Plains region (forecast zones). Stronger storms will hold the risk for 1-inch diameter hail.
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.
Zone-Specific Forecasts
Urban Corridor and Front Range:
Morning clouds will continue to thin out through this morning, resulting in mostly sunny skies by lunchtime. This will allow sunshine to heat the surface, resulting in ample instability to produce scattered thunderstorms; a few will become marginally severe with the threat of 1-inch hail and 50-55 mph wind gusts. Storm motions and insufficient moisture will preclude the issuance of any flash flood threat, but street ponding will occur underneath the stronger thunderstorms. Maximum rain rates will be in the 1.0-1.75 inch/hour range.
Timing: Scattered showers and thunderstorms will develop over the Front Range between Noon and 2 PM, moving east-southeastward with time, with storms beginning over the Urban Corridor between 2 PM and 3 PM. Activity will come to an end between 8 PM and 9 PM as the sun sets.
Palmer Ridge, Northeast Plains, and Southeast Plains:
Mostly sunny skies early, with scattered showers and thunderstorms moving across the regions in a southeasterly direction beginning around 3 PM. Storms will end, either by diminishing or exiting the state, by midnight. Gusty winds and small hail will be threats with the stronger storms, with moderate-to-heavy rainfall attending, as well. Maximum rain rates will be in the 1-2”/hour range. Some street and field ponding will occur under the strongest thunderstorms. Highest likelihood of storms will be across the Palmer Ridge and Northeast Plains, with probabilities diminishing from north to south across the Southeast Plains.
Northern Mountains, Central Mountains, Southeast Mountains, Raton Ridge, San Juan Mountains, Northwest Slope, Southwest Slope, Grand Valley, and San Luis Valley:
Mostly sunny early, becoming partly sunny this afternoon and evening as isolated, brief, showers and weak thunderstorms develop mainly over the higher terrain (11 AM-9 PM). With most of the moisture combined to the mid-levels, the result will be mainly localized gusty winds (25-35 mph) and light rain. Maximum rain rates will be around 0.25 inch/hour.
