FTB 09-29-2017: Isolated Showers and Thunderstorms over the Higher Terrains and Adjacent Plains

Issue Date: Friday, September 29, 2017
Issue Time: 10:30 AM MDT

— Flooding is NOT expected today

As seen yesterday morning, showers over the eastern plains are being supported by the jet stream and mid-level energy rotating around the Low to our northwest. These showers will continue to move to the northeast and exit the state by late this morning. There is quite a bit of fog again this morning in the mountains and Urban Corridors. This should quickly burn off due to breaks in the clouds being more numerous today. Precipitable Water (PW) in Grand Junction was measured at 0.75 inches and has dropped to 0.65 inches in Denver. With more southwesterly flow today, decreases in moisture are expected today. This should make showers and thunderstorms more isolated in nature and limit accumulations.

The Low pressure is currently over the UT/WY border and will continue to move north throughout the day. Shortwave activity associated with the Low will provide enhanced lift one last time for another round of showers and thunderstorms this afternoon. Moisture will continue to retreat east throughout the day, but dew points over the southeast plains and southern mountains will be high enough for moderate rainfall further south. Breaks in cloud cover will allow some instability to build this afternoon, which will increase the possibility for thunderstorms. Isolated showers and thunderstorms are expected to form over the mountains by later this afternoon and move into the adjacent plains this evening. The storms are expected to dissipate as they move off the higher terrains, but brief heavy rain with gusty winds and thunder are possible. Overnight shower activity is not expected, but a few showers may linger over the southern mountains with weak upslope flow. Flooding is not expected 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.

Zone-Specific Forecasts:

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

Partly cloudy with some showers over the Northwest Slope. Drier air has allowed breaks in cloud cover over the region. Enough residual moisture and instability is expected for another round of showers and thunderstorms over the higher terrains this afternoon. Highest accumulations are expected over the southern San Juan Mountains; especially further east where moisture hangs on. Max 1-hr rain rates up to 0.5 inches (south) and 0.3 inches (north) are possible with 3-hr totals up to 0.8 inches (south). Flooding is not expected today.

Primetime: 1PM to 9PM

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

Cloudy and foggy this morning with rain over the eastern plains. Showers and thunderstorms likely over the higher terrains this afternoon, although they will be more isolated than the last couple of days. Highest accumulations are expected over the southern Front Range and Southeast Mountains. Max 3-hr rain rates up to 0.8 inches are possible. Showers and thunderstorms will move NE off the higher terrains this afternoon and may briefly produce heavy rain and gusty winds on the adjacent plains before dissipating. Max 1-hr rain rates up to 0.7 inches are possible.

Primetime: 2PM to 11PM