FTB 07-29-2020: Dry Air Moves into Western Colorado, but Storms over Northeast Colorado Could Bring Brief Downpours

Issue Date: Wednesday, July 29th, 2020
Issue Time: 10:10AM MDT

— Flooding is NOT expected today

Today, Colorado continues to be situated between a shortwave trough to the north and an amplifying dry, high pressure ridge to the southwest. The water vapor satellite imagery below shows the clouds and moisture over Wyoming associated with the Low that moved in from California a couple days ago. This setup has produced drying northwesterly winds over the majority of the state, which has and will continue to scour out low-level moisture in a more stable atmosphere. PW values have dropped off significantly, since the monsoon plume has been pushed south and east, to just over 0.7 inch at Denver and Grand Junction. Some isolated mountain showers are still expected to develop over the higher terrain today due to abundant heating and leftover moisture. However the drier air, faster steering flows, and low rainfall rates will give the soils a chance to dry out. No flooding is expected over the mountains today.

As the Low pressure system tracks southeast into southwest Nebraska, the far Northeast Plains will likely see some stronger storms. However, the position of the Low farther east will mainly support drier northwesterly winds and a possible cool front or outflow boundary dropping into the Northeast Plains of Colorado later this afternoon and evening. If surface moisture can hang on, rather than being scoured out to the east, a couple stronger storms could produce isolated totals up to 1.5 inches where outflow boundaries increase convergence. However, moderate storm motions of 20-25 mph should keep the threat area small enough that flooding is not expected. If overnight storms look to track into the area later this afternoon, a PM update will be issued. At this time, there is a better probability that the heavy PM rainfall will be over Nebraska.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Northeast Plains, Southeast Plains, Urban Corridor, & Palmer Ridge:

Scattered thunderstorms may track through the Northeast Plains this afternoon and evening, and isolated max rain rates up to 1.5 inch are possible. Showers could linger into the morning along the northeast corner of the state as the low pressure system drifts southward along the eastern border of Colorado. Chances for rain quickly decrease further west with the drier air and more stable air mass in place, so accumulations over the mountains should stay under 0.1 inches. Flooding is not expected today.

Primetime: 12PM to ongoing

Northwest Slope, Northern Mountains, Grand Valley, Southwest Slope, Central Mountains, San Juan Mountains, San Luis Valley, Southeast Mountains, Front Range & Raton Ridge:

Mostly sunny with isolated mountain showers developing after noon. With dry air continuing to move into the area, the weak storms could produce some brief, gusty outflow winds. Any showers that develop should quickly move southeast, and totals are expected to stay below 0.1 inches. Flooding is not forecasted.