FTB 08-31-2016: Heavy Rainfall Threat Still Present, Shifts South

Issue Date: Wednesday, August 31st, 2016
Issue Time: 10:45AM MDT

MODERATE flood threat for Palmer Ridge, Southeast Mountains
LOW flood threat for Front Range, Southeast Plains, Raton Ridge

The morning weather map, see water vapor image below, shows many similar features as yesterday. Despite the presence of a large-scale ridge over the Rocky Mountain states, a disturbance remains across Colorado, seemingly lost from the main steering winds. This disturbance has been slowly weakening, as measured by 500 mb temperatures rising by several degrees every day including today. However, as we saw yesterday, it is still causing generally favorable conditions for scattered to widespread thunderstorm activity mainly east of the Continental Divide. We expect much more of the same today, though with an overall southward shift in the region of stronger storms. Early storms will form across the higher terrain as well as parts of the Northeast and Southeast Plains. These will be garden variety cells, likely incapable of flood-worthy rainfall. However, later in the afternoon, more organized storms are expected across mainly southeast CO. Isolated flash flooding will be possible with these cells, warranted a Low flood threat. A small area of the western Palmer Ridge and Wet Mountains is under a Moderate flood threat due to favorable upslope winds during the late afternoon and early evening hours. Hail up to 1.25 inches will be possible with the earlier storms especially farther north as dry air aloft slowly works its way into the area.

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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.
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Flood Threat Legend

Zone-Specific Forecasts:

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

Sunny early then scattered thunderstorms developing by early afternoon. Coverage will be highest in the foothills as well as the Northeast and Southeast Plains. Max 30-minute rainfall up to 1.2 inches is possible, with max 1-hr rates up to 2.2 inches especially later in the day in the southern parts of the area. A Low flood threat has been posted for southern parts of the area for isolated flash flooding. A localized Moderate threat is posted for higher terrain where late afternoon/early evening storms could pose a threat of mud flows and debris slides. Hail up to 1.25 inches is possible under the strongest cells especially earlier in the afternoon.

Primetime: 2PM to midnight, especially for southern areas

San Juan Mountains, Southwest Slope:

Mostly sunny this morning then scattered to showers and thunderstorms developing by early afternoon. Coverage will be highest in the San Juans. Max 1-hr rain rates up to 0.6 inches possible. Hail up to 0.5 inches could accompany the strongest cells. Graupel is possible above 12,500 feet. Flooding is not expected today.

Primetime: 1PM to 7:30PM

San Luis Valley, Northwest Slope, Northern Mountains, Central Mountains, Grand Valley:

Mostly sunny early then isolated showers and a weak storm possible through the early evening hours. Max 1-hour rain rates up to 0.3 inches. Flooding is not expected today.