FTB 09-28-2015: Changes on the Way, Rain Re-Appears in the Forecast

Issue Date: 9/28/2015
Issue Time: 8:35 AM

NO FLOOD THREAT IS FORECAST.

The upper-level ridge has been/will continue to be flattened today by an upper-level disturbance working across the northern US, placing Colorado under west-northwest flow aloft. Embedded in the flow aloft is a fairly moist plume of mid-level moisture; this will increase precipitable water values slightly over those seen below in the IPW graph. The increase in moisture, combined with marginal instability, will provide more cloud cover today, as well as increase the chances for showers/weak thunderstorms over the higher terrain (especially the Northwest Slope, Northern Mountains, Front Range, and Central Mountains).

IPW_09282015

Associated with the disturbance is a cool front that will slowly work its way southward across eastern Colorado today/tonight. The front, combine with sufficient moisture at the surface and aloft, will allow for spotty showers and weak thunderstorms to develop from the Front Range/Southeast mountains eastward this afternoon through the evening, continuing into the overnight hours. Rain heavy enough to cause flash flooding is not expected. Instead, most showers/weak thunderstorms will produce light-to-moderate rainfall. For more details on rain rates and timing, please see the zone-specific forecasts below.

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.

Flood Threat Legend

Zone-Specific Forecasts

Northwest Slope, Northern Mountains, Front Range, Southeast Mountains, Central Mountains, and San Juan Mountains:

Isolated-to-scattered showers and weak thunderstorms are expected, with the best coverage across the Northwest Slope, Northern Mountains, Front Range, and Central Mountains, and lesser coverage across the San Juan Mountains and Southeast Mountains. Maximum rain rates will be 0.5-0.8 inches/hour, with the heaviest rainfall (relatively speaking) falling across the Front Range/Continental Divide.

Timing: Noon – 10 PM, with a few isolated showers continuing into the overnight/early morning hours.

Urban Corridor, Northeast Plains, Southeast Plains, Palmer Ridge, and Raton Ridge:

Partly-to-mostly sunny early, with clouds increasing through the afternoon and evening as the cool front works its way through the area. Isolated-to-scattered showers/weak thunderstorms are expected, developing from north-to-south in the wake of the cool front. Maximum rain rates will be 0.6-0.9 inches/hour. Extended periods of rainfall will potentially result in 1.2-1.6 inches/3-hour rain rates across the Palmer Ridge, southern Urban Corridor, Raton Ridge, and Southeast Plains.

Timing will break down as follows:

Northeast Plains: 2 PM – 1 AM, with lingering isolated showers into the morning hours tomorrow
Urban Corridor: 2 PM – 1 AM, with lingering isolated showers until 4 AM
Palmer Ridge: 4 PM – 1 AM, with lingering isolated showers into the morning hours tomorrow
Raton Ridge: 5 PM – Midnight, with a few isolated showers lingering until 4 AM
Southeast Plains: 5 PM – 1 AM, with lingering isolated showers into the morning hours tomorrow

Grand Valley, San Luis Valley, and Southwest Slope:

Mostly sunny and warm, with high temperatures similar to yesterday’s readings. A bit more mid- and high-level clouds will encroach on the area today, more so for the Grand Valley and Southwest Slope than the San Luis Valley, providing a little natural shade during the afternoon and evening hours.