Issue Date: Tuesday, August 15, 2017
Issue Time: 10:55AM MDT
—LOW flood threat for Urban Corridor, Palmer Ridge, Northeast Plains
—Threat will continue into the overnight hours
—Afternoon forecast update is possible today
Despite general drying, especially across central and western Colorado, above normal low-level moisture continues to hang on in the northeast quadrant of our state. As shown in the water vapor image, below, a large-scale trough is positioned over the west coast. It is currently too far west to have a direct influence on our weather. However, it is supporting a surface low pressure system over southeast Colorado. This will maintain its intensity through this afternoon, promoting the influx of moist air into northeast Colorado. Although morning Precipitable Water (PW) values at the two main sounding sites, Grand Junction and Denver, are a relatively unimpressive 0.69 and 0.67 inches, respectively, much higher moisture exists just to the east. For example, the North Platte sounding’s PW was 1.28 inches, which is in the 90+ percentile for this time of year. This moist air will be readily available for import into Colorado this afternoon and evening.
For today, we expect several rounds of showers and thunderstorms across mainly the northern half of Colorado as well as the far southern areas over the Raton Ridge. The highest rain coverage and intensity will be in the Northeast Plains. Afternoon and evening thunderstorms will have the potential to cause isolated flash flooding. In addition, large-scale outflow boundaries are expected to arrive into northeast Colorado from convection farther north in the late evening hours. Thus, a secondary round of isolated heavy rainfall will be possible south and east of the South Platte River into the early overnight hours. A Low flood threat has been posted for today/tonight for isolated flash flooding, street flooding and small stream flooding. Heavy rainfall coverage is not expected to be wide enough for major rivering flooding. Large hail, up to 1.75 inches, will be possible with the strongest cells this afternoon in the Northeast Plains.
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, scroll below the map.
Zone-Specific Forecasts:
Front Range, Urban Corridor, Palmer Ridge, Northeast Plains, Southeast Mountains, Raton Ridge, Southeast Plains:
Scattered showers and thunderstorms developing by early afternoon. Highest coverage will be over the Palmer Ridge and Northeast Plains. Max 1-hour rainfall up to 2.9 inches (east) and 1.0 inches (west). Max 3-hour rainfall up to 3.8 inches across eastern areas. A Low flood threat has been posted for isolated flash flooding, street flooding small stream flooding (for higher elevations). A secondary round of storms is possible after sunset and the Low flood threat persists into the early overnight hours.
Primetime: 1PM to 3AM
Northwest Slope, Grand Valley, Southwest Slope, Northern Mountains, Central Mountains, San Juan Mountains, San Luis Valley:
Partly cloudy early with isolated to scattered showers and weak thunderstorms developing by afternoon. Highest coverage will be over northern areas (especially north of I-70). Max 1-hour rainfall up to 0.6 inches is possible. Gusty winds up to 50 mph and small hail could accompany the strongest cells. Activity will quickly subside after sunset.
Primetime: 12PM to 9PM
