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.

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.

Issue Date: 8/26/2017
Issue Time: 9:00 AM

NO FLOOD THREAT IS FORECAST.

The big weather story across the country is Harvey, currently a Category 1 hurricane that is expected to meander slowly across Texas. Here at home, however, a mainly dry day is on tap, with only a few isolated storms over the mountains and far eastern plains. In the water vapor imagery below, I have denoted the presence of the mid/upper high pressure centered over the Great Basin. This high pressure ridge will strengthen and expand over the region today, lowering our precipitation chances and keeping our temperatures near or just above average for this time of year. Enough moisture will be present over the high country for orographic effects to produce isolated showers/weak thunderstorms over the mountains during the afternoon and evening hours, with the preferred regions being the San Juan Mountains, Southwest Slope, Front Range, and Southeast Mountains.

Also denoted on the water vapor image is the presence of a mid-level disturbance, which will rotate around the periphery of the high pressure ridge, scraping by the far eastern plains during the afternoon and evening hours. Most of the thunderstorm activity associated with this disturbance will remain in Nebraska and Kansas, but a couple isolated thunderstorms cannot be ruled out for the Northeast and Southeast Plains, mainly east of a line from Sterling to Las Animas. For more details 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, Raton Ridge, Northeast Plains, and Southeast Plains:

Mainly dry and mostly sunny conditions will prevail for the majority of the area throughout the day today, with a slight chance for a mountain shower drifting overhead locations adjacent to the mountains and the risk for isolated strong-to-severe thunderstorms over the far eastern plains. The main threat from those thunderstorms will be strong winds and hail, with brief periods of moderate-to-heavy rainfall. Rain rates are as follows:

Urban Corridor, Palmer Ridge, and Raton Ridge: 0.05-0.15 inches/hour
Northeast Plains and Southeast Plains: 0.6-1.2 inches/hour

Timing: 1 PM – 9 PM

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

Mainly dry and mostly sunny conditions will be the name of the game for most areas today. Increasing clouds near/over the higher terrain are expected this afternoon/evening as orographic effects work on residual moisture to develop isolated mountain showers/weak thunderstorms. Preferred regions for this activity will be the San Juan Mountains, Southwest Slope, Front Range, and Southeast Mountains. Rain rates will remain well below flash flood thresholds with maximum rates of 0.15-0.35 inches/hour.

Timing: 11 AM – 9 PM

Issue Date: Friday, August 25, 2017
Issue Time: 10:40AM MDT

— Flooding is NOT expected today

The water vapor image, below, shows a weak ridge is currently positioned near the Four Corners. This ridge is expected to modestly strengthen today and support large-scale subsidence to its east. Morning Precipitable Water (PW) values at the Denver and Grand Junction radiosondes measured 0.73 and 0.61 inches, respectively. With the exception of far eastern parts of the state, PW is expected to drop into the 0.5 – 0.65 inch range by this afternoon.

With clear skies this morning and a still strong late-August sun, expect adequate instability for isolated to widely scattered showers and thunderstorms mainly east of the Continental Divide. A weak surface low pressure was noted in southeast Wyoming this morning and with the diurnal lee side trough development, we expect a weak convergence zone to setup just south of the South Platte River. This will be the focal point for the highest rainfall chances (in addition to favored higher elevation locations east of the Continental Divide). However, as already noted, coverage should be lower than Thursday. Short 15-30 minute bursts of heavy rainfall will be possible with the strongest storms especially towards the KS border. However, 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:

Sunny this morning, then partly cloudy with isolated to widely scattered showers and weak thunderstorms possible. Highest coverage will be over the higher terrain as well as parts of the Northeast Plains. Max 1-hour rain rates up to 1.1 inches (east) and 0.5 inches (west). Flooding is not expected today.

Primetime: 12PM to 9PM

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. Flooding is not expected today.

Primetime: 12PM to 8PM

Issue Date: Thursday, August 24, 2017
Issue Time: 10:25AM MDT

— LOW flood threat for Northeast Plains, Palmer Ridge, Southeast Plains, Raton Ridge

Lots of high cloud cover this morning over Colorado from convection over New Mexico and over the SW corner of the state. This will help keep high temperatures today a few degrees below normal for August. The cloud cover and ongoing showers are associated with numerous, weak shortwaves in the westerly flow. The mid-level low pressure system that has sat over southern California the last couple of days will break down and eject weak shortwaves over the state throughout the day. The first round of showers associated with these shortwaves started early this morning and a second wave is expected this afternoon. Westerly flow before the shortwave and northwesterly flow after the passage of the shortwave will continue to mix out moisture at the surface over the majority of the state. The weak upper-level ridge will move north of Colorado today and continue to be pushed east through tomorrow morning as the next weather system moves into the Pacific Northwest. Precipitable Water (PW) values at Grand Junction and Denver this morning are 0.76 and 0.64 inches. A surface Low is expected to set up again over the eastern plains, which will pull in moisture rich air on its eastern side. West of this feature, the atmosphere will remain drier. PW values are expected to increase up to 1 inch over the far eastern plains and reach 1.1 inches over the Southeast Plains.

Current showers over the western slope are expected to end mid-morning. The next set of showers will begin just after noon over the higher terrains. This afternoon, more mid-level energy will move through the state with the westerly flow and help enhance convection. The best instability will be along the Palmer Ridge and over the far eastern plains. Expect storms to move off the higher terrains later this afternoon into the adjacent plains with a SE/S storm motion. Storms to the west are expected to produce gusty winds rather than heavy, local precipitation. The outflow boundaries from these storms could help produce addition storms over the adjacent plains in the more moisture rich environment. There also seems to be a convergence boundary that sets up over the Northeast Plains this afternoon, which could produce heavy precipitation. Overall, coverage over the plains, western valleys and mountains will be more numerous than the last couple of days. Storms are expected to end over the mountains a couple hours after sundown and around midnight over the plains. There is a Low flood threat 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:

Partly cloudy this morning with the high clouds decreasing throughout the day. Coverage over the mountains is expected to be numerous, but lower moisture will produce gusty winds rather than heavy rainfall. Over the NE Plains, a convergence boundary sets up this afternoon. With higher moisture and slower storm motion, 1-hr rain rates up to 1.7 inches are possible. West, 1-hr rain rates up to 0.7 inches are possible. Threats include small stream and road flooding as well as field ponding over the plains. Gusty winds and hail up to 0.5 inches are possible with stronger thunderstorms. Storms over the plains are expected to continue until midnight with storms over the mountains ending around 10PM. A Low flood threat has been issued.

Primetime: 1PM to 12AM

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

Cloudy with ongoing showers this morning. Shower coverage will be more numerous this afternoon as a shortwave makes it way over the state. With lower moisture, storms will produce gusty winds rather than heavy, local rainfall. 1-hour rain rates up to 0.5 inches (north) and 0.7 inches (south). Flooding is not expected today.

Primetime: 11AM to 10PM