Issue Date: Sunday, September 25th, 2016
Issue Time: 9:00AM MDT

— Flooding is NOT expected today

As the water vapor image, below, shows the trough that has been in our weather discussion for about a week has moved east of Colorado. Interestingly and somewhat unexpectedly, a part of the disturbance broke off and is now spinning by itself near Baja California. This may increase subtropical moisture across the Southwest US in the coming days, but is not a factor today. Instead, Colorado will begin to be influenced by the rather strong ridge centered just west of California. This will promote downward motion and aside from a few boundary layer clouds today, it will be sunny across the state. In the low-levels, cool northerly flow will ensure at least one more day of slightly below normal temperatures. Neither precipitation nor flooding is 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.

 

Issue Date: Saturday, September 24th, 2016
Issue Time: 8:50AM MDT

— Flooding is NOT expected today

The strong upper-level trough finally entered Colorado overnight, bringing a slew of changes for many and unofficially signaling the start of fall. In terms of the today’s flood threat, this morning’s precipitable water (PW) chart, below, shows all one needs to know. Moisture, both mid and low-level, has plummeted statewide with PWs at all five stations that we typically use reading below 0.5 inches. Despite the presence of some dynamics overhead, without moisture there will be no threat of heavy rainfall today. Otherwise, expect windy conditions to slowly subside by late afternoon. Ongoing rain and high-elevation snow showers are expected to continue across the Northern Mountains, Central Mountains and Northwest Slope making it feel like winter. For every else, enjoy the first true taste of fall!

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.

Issue Date: Friday, September 23rd, 2016
Issue Time: 9:45AM MDT

— Flooding is NOT expected today

The large-scale trough continues its eastward movement across the Great Basin. As of this morning, it was centered over western Utah. However, without the support of subtropical moisture, dry air has begun to get entrained into the trough. For example, the precipitable water (PW) values over Colorado have dropped from near 1 inch on Thursday to the 0.55 – 0.8 inch range this morning. PW will likely continue to slowly decline, except for far eastern areas where south-southeasterly flow will bring in Gulf of Mexico moisture. Although widespread showers and perhaps a weak thunderstorm are expected over the western slope, rainfall intensities will be lower than Thursday with declining moisture. Instead, the highest rainfall rates today are expected across far eastern Colorado where the “warm sector” will be found. A dryline will develop across eastern Colorado late this morning and will likely serve as the focal point for a broken line of thunderstorms. With an excessive amount of unidirectional shear in place today, these storms will have a hard time keeping their updrafts intact. Thus, the heavy rainfall threat will be limited, and flooding is not expected. The more impactful weather today will be the gusty winds especially east of the Continental Divide. A Red Flag warning is in place for parts of southeast Colorado for this afternoon.

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.

Issue Date: 9/22/2016
Issue Time: 9:40 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHWEST SLOPE, GRAND VALLEY, SOUTHWEST SLOPE, AND SAN JUAN MOUNTAINS.

A fairly active day is in store for the High Country and Western Slope, with isolated-to-scattered showers/storms filtering across eastern Colorado. The “Chance of Precipitation” from our internal tool highlights this well (image below). The upper-level low will continue its shift into the Great Basin, bringing two major factors that are leading to the active day:

1. Increasing moisture, mainly in the low- and mid-levels, will result in greater fuel for showers/storms
2. Providing broad-scale, dynamic support for numerous showers/thunderstorms

Those two factors, paired with better instability than previous days, will lead to better shower/thunderstorm coverage, with an isolated strong/severe thunderstorm mixed in. Stronger storms will be capable of brief periods of heavy rainfall, but quick storm motions will reduce the risk of flash flooding. With all factors considered, a low flood threat is warranted for the regions mentioned in the italicized line above. East of the mountains, much of the moisture will reside between 3 km and 5 km above ground level, helping to reduce the risk of heavy rainfall. For more information on rain rates and timing, please see the zone-specific forecast discussions below.

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, jump below the map.

Zone-Specific Forecasts

Urban Corridor, Palmer Ridge, Northeast Plains, Raton Ridge and Southeast Plains:

Isolated-to-scattered showers/storms are expected, with the best coverage along/near the mountains and the preferred terrain of the Palmer Ridge and Raton Ridge. Primary threats from stronger thunderstorms will be strong, gusty winds (up to 45 mph), small hail, and lightning. Maximum rain rates will be as follows:

Urban Corridor and Raton Ridge: 0.4-0.7 inches/hour
Southeast Plains: 0.6-1.0 inches/hour
Palmer Ridge: 0.3-0.6 inches/hour
Northeast Plains: 0.6-0.9 inches/hour

Timing: 1 PM – 11 PM

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

Numerous showers/thunderstorms are expected throughout today and tonight, with the best coverage over the San Juan Mountains, Southwest Slope, Grand Valley, and Northwest Slope. Isolated severe storms will mix in along/near the Utah border, with the main threats being damaging wind gusts and lightning. In addition to the showers/thunderstorms, tightening pressure gradients will result in strong/gusty winds throughout the day, with many High Wind Warnings issued. Please visit your local NWS office website for more details. As for maximum rain rates, they are as follows:

Northwest Slope, Grand Valley, Southwest Slope, and San Juan Mountains: 0.6-0.8 inches/hour
Front Range, Southeast Mountains, San Luis Valley, and Northern Mountains: 0.4-0.6 inches/hour
Central Mountains: 0.3-0.5 inches/hour

While rain rates will be marginal for flash flooding, multiple rounds of rainfall will be the main cause for concern, especially in steeper terrain areas where mudflows/landslides/etc. are common, relatively speaking.

Timing: 11 AM – 11 AM