FTB 09-11-2017: Uptick in Low-Level Moisture and Slow Steering Winds Increase Flood Risk

Issue Date: Monday, September 11, 2017
Issue Time: 10:05 AM MDT

LOW flood threat for portions of the Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains, Central Mountains

The persistent weather pattern continues over the state again today. Colorado will continue to sit under the ridge with light westerly flow aloft. To the east and west are two low pressure systems creating a bit of an omega block. The low pressure system over the coast of California continues to slowly usher in moisture and mid-level energy over the state creating daily rounds of precipitation. Precipitable Water (PW) continues to rise across the state. This morning’s sounding at Denver recorded 0.87 inches and Grand Junction was measured at 0.99 inches. Moderate mid-level drying and increasing dew points mean more rain will reach the surface than the last couple of days, although gusty winds are still likely. There also seems to be some added mid-level energy and surface instability this afternoon, which will help intensify the coverage and strength of the storms that initiate over the higher terrains.

Scattered storms over the high country are expected again today and will begin early this afternoon. The most numerous coverage is expected to be over the Central Mountains and Front Range. Slow steering winds aloft will increase rain totals as storms slowly track east. This may present problems for fresh burn scars, and confidence is sufficient enough that storms that do form in this area will have rain rates greater than 0.5 inches. Elsewhere in the higher terrains, max 1-hr rain rates up to 1.1 inches are possible, so a Low flood threat has been issued. Threats include debris slides, mud flows and small stream and road flooding. As storms move off the higher terrains, they are expected to favor the Palmer Ridge where dew points are forecasted to increase throughout the day. Gusty winds are likely with the stronger storms as well as max 1-hr rain rates up to 1.2 inches. Storms are also likely to drift off the higher terrain along the Urban Corridor and subsequent outflow boundaries may continue storm development. These storms should have max 1-hr rain rates under flood threat criteria. Most storms will end around midnight with some lingering showers overnight. There is a Low flood threat today.

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.

Flood Threat Legend

Zone-Specific Forecasts:

Front Range, Urban Corridor, Northeast Plains, Palmer Ridge, Southeast Mountains, Raton Ridge, Southeast Plains, Central Mountains:

Partly cloudy this morning this morning with partial clearing. Becoming partly cloudy again this afternoon with thunderstorm development over the mountains. Slow storm movement with increased moisture and upper-level energy has created a Low flood threat. Threats include mud flows, debris slides and small stream and road flooding. Burn scars should be monitored closely. Max 1-hr rain rates up to 1.2 inches (east) and 1.1 inches (west).  A Low flood threat has been issued.

Primetime: 1:30PM to 12AM

Northwest Slope, Grand Valley, Southwest Slope, Northern Mountains, San Luis Valley, San Juan Mountains:

Mostly sunny this morning becoming partly cloudy this afternoon over the higher terrains. Slow storm movement and increased moisture will increase totals from the prior two days. Max 1-hr rain rates up to 0.6 inches (south) and 0.8 inches (north) are possible. Flooding is not expected today.

Primetime: 12PM to 11PM