FTB 08-11-2018: Isolated to Scattered Storms Across the Southwest Corner

Issue Date: Saturday, August 11th, 2018
Issue Time: 08:45AM MDT

— NO flood threat today.

Subtropical ridging continues to dominate the flow over Colorado and surrounding states as we enter the final few weeks of the summer season. While it has been a robust monsoon season across states to the south, the monsoon has yet to take a consistent hold across Colorado. This remains the case today, with the sprawling ridge across the Great Basin and Northern Rockies ushering in dry northeasterly upper-level flow across much of the state, stifling any chance at afternoon convection for many. The exception to this may be across mountainous areas of the southwestern 1/3rd or so of the state, where moisture may be just sufficient to kick off some thunderstorms capable of lightning, gusty winds, and primarily light rainfall.

As was the case yesterday, moisture is the limiting factor. Low-level moisture is near or slightly below the seasonal average (as per the Grand Junction morning sounding) but is expected to slightly increase throughout the day. Any storms that do form should be limited to higher terrain and will have high cloud bases, allowing for much of the rain to evaporate before reaching the ground. Where this evaporation occurs most rapidly, gusty winds may develop, and lightning may be a threat even if significant rain is not present in a storm. Those near active fire areas should therefore be aware of the possibility of sudden changes in wind strength and direction today, and should be prepared for the low possibility of a very isolated thunderstorm affecting recently burned areas. With the threat of substantial rain so remote today, however, no flood risk areas have been issued.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Southwest Slope, Grand Valley, Central Mountains, San Juan Mountains:

Sunny to start with today before clouds begin building over the high terrain by mid-day. Isolated showers are expected to produce gusty winds and lightning at times along with generally light rainfall. Max rainfall rates may briefly exceed 0.25” per hour in very isolated cells but will generally produce just a trace to perhaps 0.15” per hour. Storms should be moving from NE to SW at around 10-20 mph.

Primetime: 2PM to 10PM

Northwest Slope, Northern Mountains, Front Range, Urban Corridor, Northeast Plains, Palmer Ridge, San Luis Valley, Southeast Mountains, Raton Ridge, and Southeast Plains:

Generally a seasonally warm day on tap. Temperatures should max out within a few degrees either side of seasonal normals (relatively cooler to the south, warmer to the north), and cloud cover will be minimal. A very low chance for a brief shower exists in the highest terrain of the Front Range and Southeast Mountains, but rainfall will top out at just a trace to a few hundredths of an inch.

Primetime: 2PM to 9PM