Issue Date: 5/03/2015
Issue Time: 10:43 AM
THERE IS A LOW FLOOD THREAT FOR PORTIONS OF THE FRONT RANGE AND URBAN CORRIDOR, INCLUDING THE WALDO CANYON, HAYMAN-TELLER, FOURMILE CANYON, AND HIGH PARK BURN SCARS.
Moisture continues to be stuck underneath the flattened, upper-level ridge that has been over the region for a few days now. Precipitable water values are just above average for this date, and isolated-to-scattered showers and thunderstorms are expected again this afternoon/evening across the state, with a few lingering into the overnight hours. Just like yesterday, though, most of the moisture this afternoon and early evening will be confined to the mid-levels, meaning that most shower and thunderstorm activity will produce rain on the light-to-moderate end of the scale. The earliest round of thunderstorms that develop will remain high-based, providing more gusty winds and lightning than rain. West of the Divide, this is how most of the day will play out, as thunderstorms will follow the typical diurnal cycle, developing around noon and ending just after sunset; a few showers will linger overnight, as the mid-levels remain moist.
The bulk of this forecast will sound the same as the previous two days, except for a very important distinction – a weak cool front (shown in the image above) will drop south across eastern Colorado today. This cool front will provide a focal point for convection this afternoon, as well as provide upslope flow to bring a slight uptick in moisture later this afternoon and through the overnight. This will bring a greater risk for heavier rain to develop mainly along and east of I-25, in the 1.0-1.5 inch/hour range. There is potential for storm development over the Front Range and Urban Corridor after cool frontal passage as moisture increases into the mountains, leading to the low flood threat over portions of the Front Range and Urban Corridor, including the Waldo Canyon, Hayman-Teller, Fourmile Canyon, and High Park burn scars.
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, Front Range, and Palmer Ridge:
The bulk of thunderstorm activity will occur this afternoon ahead of, and in concert with, cool frontal passage. Rain rates will generally be in the 0.25-0.65 inches/hour range. After cool frontal passage, however, moisture will increase into the mountains as easterly, upslope flow develops. This is the reason for the low flood threat from this afternoon and into the overnight hours. Rain rates will be maximized in the 1-1.5 inches/hour range, which can cause flooding issues on burn scars and in urban areas.
Timing: Noon – 6 AM
Northeast Plains, and Southeast Plains:
Isolated-to-scattered showers and thunderstorms will develop/enter the region around 2 PM, and diminish nearly entirely by midnight. Main threats will be gusty winds and lightning, but moderate-to-heavy rain under the strongest storms will be maximized in the 0.8-1.3 inches/hour range. Small hail will be attendant to the strongest few storms.
Northern Mountains, Central Mountains, Southeast Mountains, Raton Ridge, San Juan Mountains, Northwest Slope, Southwest Slope, Grand Valley, and San Luis Valley:
Isolated-to-scattered showers and thunderstorms will follow the typical diurnal cycle today, beginning just before noon, and diminishing after sunset. Most storms will remain over the higher terrain, but a few will drift over adjacent valleys. Maximum rain rates will be in the 0.5-0.7 inches/hour range.
A few showers and thunderstorms will continue overnight over the higher terrain, as the next round of mid-level disturbances rounds into Colorado from the southwest.
Timing: 11 AM – 6 AM.
