SPM 08-28-2017: Isolated Storms East, Heat Cranks Out West

Issue Date: Monday, August 28, 2017
Issue Time: 10:50AM MDT

Summary:

An upper-level ridge was established to the west of Colorado on Sunday, causing very warm temperatures west of the Continental Divide. Out east, plenty of sunshine made up for the marginal boundary layer moisture, supporting isolated thunderstorms across the climatologically favored parts of the western Palmer Ridge, Southeast Mountains, San Juans and San Luis Valley. The winners for highest rainfall amounts were (according to CoCoRaHS) Teller and Fremont counties with 0.78 and 0.54 inches, respectively. Other isolated locations received up to 0.5 inches. Even the normally dry San Luis Valley received some rainfall. A Flood Advisory was posted for the sensitive Hayden Pass burn scar during the afternoon. The Hayden Pass SNOTEL site received 0.2 inches as of this morning. Fortunately, no flooding was reported in the area, as of today.

Out west, high temperatures soared well into the 90s F for lower elevation locations below 5,000 feet. For example, Grand Junction got up to 97F, which is well above normal for this time of year.

For rainfall estimates in your area, check out our State Precipitation Map below.

Click Here For Map Overview

The map below shows radar-estimated, rainfall gage-adjusted Quantitative Precipitation Estimates (QPE) across Colorado. The map is updated daily during the operational season (May 1 – Sep 30) by 11AM. The following six layers are currently available: 24-hour, 48-hour and 72-hour total precipitation, as well as maximum 1-hour, 2-hour and 6-hour precipitation over the past 24 hour period (to estimate where flash flooding may have occurred). The accumulation ending time is 6AM of the date shown in the bottom right corner. Also shown optionally are fire burn areas since 2012. The home button in the top left corner resets the map to the original zoom.

Note: We have identified a possible underestimation in QPE over the southwest part of the state. We are working to on this issue, and will provide an update as soon as possible.

FTB 08-28-2017: Strong Ridge To Continue Supporting Generally Dry Weather

Issue Date: Monday, August 28, 2017
Issue Time: 9:55AM MDT

— Flooding is NOT expected today

This morning’s water vapor image, below, continues to show the remnants of Hurricane Harvey as the dominant feature across the central United States. However, closer to home, Colorado will continue to be under the firm control of a seasonably strong upper-level ridge centered over the Great Basin. Subsidence will support mainly clear skies with a few afternoon clouds and isolated storms possible over the higher elevations of southern Colorado. Morning Precipitable Water (PW) values were 0.70 and 0.50 inches at Denver and Grand Junction, respectively. PW is expected to decrease slowly through the day as drier northerly flow is advected into the state. A weak frontal boundary, a residual from yesterday’s cool front, was noted in southeast Colorado. This is expected to “wash out” by early afternoon, replaced by the climatologically favored lee side trough across eastern Colorado. The end result will be downsloping flow that will suppress storm activity anywhere outside of the high country (mainly Palmer Ridge, Southeast Mountains and San Juans). Storms that do develop will cause brief moderate rainfall, along with gusty winds. 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:

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

Mostly sunny this morning, then partly cloudy with isolated showers and weak thunderstorms possible. Highest coverage will be over the higher terrain of the Southeast Mountains and Palmer Ridge. Max 1-hour rain rates up to 0.5 inches (north) and 0.7 inches (far south). Gusty winds will accompany the strongest storms. Flooding is not expected today.

Primetime: 12PM to 8PM

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

Sunny early with isolated showers and a weak thunderstorm possible this afternoon. Highest coverage will be over the San Juans. Max 1-hour rainfall up to 0.5 inches is possible. Gusty winds will accompany the strongest cells. Flooding is not expected today.

Primetime: 12PM to 8PM

SPM 08-27-2017: Isolated Showers and Weak Thunderstorms Dotted the High Country

Issue Date: Sunday, August 27, 2017
Issue Time: 10:55 AM MDT

Summary:

Daytime heating and orographic effects battled a strengthening high pressure ridge over the Great Basin in a fight for Colorado weather supremacy yesterday. The high pressure ridge won the overall battle, keeping the vast majority of Colorado dry and warm yesterday. The August sun managed a few wins, however, as isolated showers/weak thunderstorms dotted the high country, resulting in mainly light rain and gusty outflow winds.

Flash flooding was not reported on Friday. For a look at precipitation estimates in your area, please see our State Precipitation Map below.

Click Here For Map Overview

The map below shows radar-estimated, rainfall gage-adjusted Quantitative Precipitation Estimates (QPE) across Colorado. The map is updated daily during the operational season (May 1 – Sep 30) by 11AM. The following six layers are currently available: 24-hour, 48-hour and 72-hour total precipitation, as well as maximum 1-hour, 2-hour and 6-hour precipitation over the past 24 hour period (to estimate where flash flooding may have occurred). The accumulation ending time is 6AM of the date shown in the bottom right corner. Also shown optionally are fire burn areas since 2012. The home button in the top left corner resets the map to the original zoom.

Note: We have identified a possible underestimation in QPE over the southwest part of the state. We are working to on this issue, and will provide an update as soon as possible.

FTB 08-27-2017: Weak Cool Front Bringing a Few Changes

Issue Date: 8/27/2017
Issue Time: 8:35 AM

NO FLOOD THREAT IS FORECAST.

Minimal changes to the forecast can be attributed to a weak cool front passing through eastern Colorado this morning. First, the cool front will help knock afternoon high temperatures down to seasonal levels across the plains. Second, behind the front, weak upslope flow will help back enough moisture into the foothills/mountains and provide enough lift to produce scattered mountain storms over the Front Range and Southeast Mountains. One or two of these storms may drift over areas along/west of I-25, bringing mainly gusty winds and brief rainfall to those areas. Finally, the cool front will *attempt* to spark a few isolated thunderstorms over the Southeast Plains this afternoon/evening, mainly along and south of Highway 50.

For western Colorado, the mountains and adjacent valleys will once again see isolated-to-scattered showers/storms, especially over the Central Mountains, Southwest Slope, San Juan Mountains, and San Luis Valley. The main impacts from this activity will be gusty winds up to 40 mph and brief light-to-moderate rainfall. Most activity will wind down by 9-10 PM tonight, with a few lingering showers/storms over southern areas until Midnight or so.

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.

Flood Threat Legend

Zone-Specific Forecasts

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

Conditions will be dry for the majority of the region today. Areas along/west of I-25 may see one or two mountain showers/thunderstorms drift overhead, bringing mainly gusty winds and brief periods of rainfall. Also, the cool front is expected to produce an isolated thunderstorm or two over areas south of Highway 50 in the Southeast Plains region. Maximum rain rates are as follows:

Northeast Plains: N/A
Urban Corridor and Palmer Ridge: 0.25-0.5 inches/hour
Raton Ridge and Southeast Plains: 0.6-1.2 inches/hour

Timing: 2 PM – 10 PM

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

For the Front Range and Southeast Mountains, upslope flow and a bit more moisture will help kick off isolated-to-scattered showers/thunderstorms throughout the day and into the nighttime hours. Gusty outflow winds (up to 40 mph) and brief periods of light-to-moderate rainfall are the main threats from this activity.

To the west, mountains and adjacent valleys will once again see isolated-to-scattered showers/storms as ororgraphic effects and daytime heating play on residual moisture. The main impacts will be gusty outflow winds to 40 mph and periods of light-to-moderate rainfall. Maximum rain rates are as follows:

Northwest Slope, Grand Valley, and Northern Mountains: 0.1-0.25 inches/hour
Central Mountains, Southwest Slope, Southeast Mountains, and Front Range: 0.4-0.8 inches/hour
San Juan Mountains and San Luis Valley: 0.5-0.9 inches/hour

Timing: Noon – 10 PM, with a few lingering showers/storms over southern areas until Midnight/1 AM.