Issue Date: 5/04/2015
Issue Time: 11:08 AM
LOW FLOOD THREAT IS FORECAST FOR TODAY FOR PORTIONS OF THE URBAN CORRIDOR, FRONT RANGE, PALMER RIDGE, NORTHEAST PLAINS, RATON RIDGE, SOUTHEAST MOUNTAINS, SAN JUAN MUONTAINS, CENTRAL MOUNTAINS AND NORTHERN MOUNTAINS. BE SURE TO CHECK THE MAP BELOW FOR SPECIFIC LOCATIONS.
Moisture has been on the increase since yesterday, with IPW values (shown below) climbing to between 0.6-0.85 inches at the normal reporting stations (Boulder – DSRC, Grand Junction – MC01, Pueblo – PUB5, and Shriever AFB – AMC2). This is due to the moisture plume being pulled across the Desert SW and into Colorado by an upper-level low currently centered over southern CA. This places Colorado under a moist, southwesterly flow, which will contribute to the increased coverage of showers/thunderstorms today and tonight. Precipitable Water values, as measured by atmospheric soundings from Grand Junction and Denver at 6 AM, are in the 90th percentile for this date, showing just how “juicy” the atmosphere is today. With that said, though, we still haven’t reached the 1 inch IPW mark this season, which is the benchmark for a typical, summertime heavy rain/flood potential day.
Limiting today’s potential for heavy rain to cause flash flooding is relatively insufficient instability for the most flood prone areas along the Front Range and Urban Corridor. Cloud cover from this morning’s showers is still stuffed into much of northeast Colorado, though it is starting to thin out across the Palmer Ridge and southern Front Range/Urban Corridor regions. This cloud cover will minimize the work that the sun can do to warm up the surface, lessening the amount of instability that it can create in those areas. On the flip side of that same coin, the upper-level low will provide vertical motion to compensate for that lack of instability, and so moderate-to-heavy rain cannot be ruled out.
West of the Divide, much of the cloud cover from last night has thinned, leaving mostly sunny skies to heat the surface and increase instability. Additionally, support from the upper-level low will aid in thunderstorm development. Widespread heavy rain is not likely, but a few isolated thunderstorms producing rain in the 0.8-1.4 inches/hour range is not out of the question.
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 Northeast Plains:
Scattered showers and thunderstorms capable of producing periods of moderate-to-heavy rain are likely. Rain rates will generally be in the 0.5-0.8 inches/hour range, but the strongest storms could produce rain in the 1.0-1.6 inches/hour range. Limiting the flood potential is the cloud cover still in place over much of the region, though it is thinning out over southern reaches of the area.
Primetime: Noon – Midnight
Palmer Ridge:
Cloud cover is thinning quickly, which will allow the sun to warm the surface. This will create an environment capable of producing moderate-to-heavy rain in the 1.0-1.6 inches/hour range.
Primetime: Noon – 11 PM.
Southeast Plains and Raton Ridge:
Sufficient moisture and instability this afternoon will combine to produce scattered strong thunderstorms, with maximum rain rates in the 1.5-2.25 inches/hour range. The strongest storms will produce small hail (1.0 inch) and gusty winds (45-60 mph).
Primetime: 1 PM – 6 AM for the Southeast Plains, Noon – Midnight for the Raton Ridge
Northern Mountains, Central Mountains, Southeast Mountains, and San Juan Mountains:
Scattered showers and thunderstorms are expected this afternoon and evening, before diminishing after sunset. A few will continue through the overnight hours as the upper-level low continues to track eastward towards the state. Rain rates this afternoon and evening will generally be in the 0.4-0.7 inches/hour range, but the strongest storms could produce rain at 0.7-1.25 inches/hour.
Primetime: 11 AM – 8 PM
Northwest Slope, Southwest Slope, Grand Valley, and San Luis Valley:
Scattered showers and thunderstorms are expected to develop over the adjacent higher terrain, and a few will move overhead throughout today and tonight. Rain rates will generally be in the 0.4-0.8 inches/hour range, but the strongest storms will be capable of 0.7-1.25 inches/hour.
Primetime: 11 AM – 4 AM
