Issue Date: Wednesday, August 23, 2017
Issue Time: 10:45AM MDT

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

The state will be under light W/NW flow under the upper-level ridge today, which center has shifted a bit to the west. As seen on the water vapor image below, this will advect drier air into the mid-levels. This is expected to mix out moisture at the surface over the entire state excluding the northeast corner of the state and the Raton Ridge/western Southeast Plains. Precipitable Water (PW) is currently at 0.87 inches in Grand Junction and 0.7 inches in Denver. Even with low-level moisture mixing out in these areas throughout the day, there will still be enough residual moisture for showers over the higher terrains and adjacent plains. However, most storms today are expected to produce more wind than heavy rainfall. A lee trough is expected to set itself up over the far eastern plains and with strong southerly surface winds east of it. This will advect more moisture northwards from NE New Mexico where Tds are currently in the mid to upper 60s. Where PW is forecasted to be greater than 1 inch this afternoon/evening is marked on the map below.

The weak upper-level disturbance from yesterday will move over northern CO today, which may enhance storms that form with the diurnal flow over this area. Storms are expected to be most numerous over this area as well as the southern Southeast Mountains. A fair amount of instability with increased daytime heating and minor shear will be present over the NW corner of the state and Southeast Plains this afternoon. This is the same area where PW is expected in increase to 1.2 inches. Storms that move off the higher terrains into these areas or storms that form over these areas from outflow boundaries will be capable of producing gusty winds, hail up to 0.75 inches and heavy, local precipitation. Faster storm motion is expected over the NE corner of the state, so 1-hour rain rates are not expected to exceed 1.5 inches. Thunderstorms are expected to continue overnight in the SE plains where localized amounts are expected to exceed 2.5 inches. Since the Arkansas River base flow has been able to recede, major riverine flooding is not expected. There is a Low flood threat for 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 becoming partly cloudy this afternoon. Storms are expected to be most numerous over the northern mountains and southern SE Mountains. Threats include small stream and road flooding as well as field ponding. Gusty winds and hail up to 0.75 inches are possible with stronger thunderstorms. Burn scars need to continue to be monitored closely. Storms over the SE Plains are expected to continue into the overnight hours with localized storm totals greater than 2.5 inches. 1-hour rain rates will be up to 1.7 inches (east) and 0.7 inches (west). A Low flood threat has been issued.

Primetime: 1:30PM to 4AM

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

Cloudy over the NW corner of the state this morning. Showers expected to fire over the higher terrain around noon but will produce more wind that rain today. 1-hour rain rates up to 0.7 inches (north) and 0.5 inches (south). Flooding is not expected today.

Primetime: 11AM to 9PM

Issue Date: Tuesday, August 22, 2017
Issue Time: 10:15AM MDT

— MODERATE flood threat for Southwest Slope, San Juan Mountains and Southeast Mountains

— LOW flood threat for all of Colorado excluding eastern plains

Increased cloudiness this morning with the passage of the cold front last night, and temperatures are a bit cooler to start the day. Heavier clouds over the eastern plains is expected to cap convection this afternoon. Some light showers are still occurring across the southern border of the state. Precipitable Water (PW) values are on the rise with Denver at 0.86 inches and Grand Junction at 0.77 inches. PW over the SE Plains is currently 1 inch. A surface boundary may set up over the over the Urban Corridor this afternoon. With a fair amount of instability building throughout the day as the cloud cover breaks up, a few stronger storms may be possible. Over the western portion of the state, more widespread showers are likely. A shortwave trough, associated with the mid-level low pressure system over southern California, will move north throughout the day helping support storms that fire from the diurnal flow. With increase moisture in the atmosphere and slow steering winds under the ridge, these storms have the potential to drop heavy, local precipitation.

Storms that fire over the higher terrain will be more numerous than the previous few days. The storms east of the Continental Divide will favor the higher terrains of the Palmer and Raton Ridge as they slowly drift S/SE off the mountains. A few stronger storms may be found along the southern Urban Corridor this afternoon associated with a convergence boundary. West of the Continental Divide, very widespread showers are likely beginning around 10AM and will intensify with daytime heating. These storms will slowly move north with the shortwave. Storm totals up to 2 inches are possible. Threats include mud flows, debris slides, and road and small stream flooding, especially over burn scars. Sufficient confidence rain rates will be at least 0.5 inches over the Hayden and Junkin burn scars, so a Moderate Flood threat has been issued. Most activity should end around 11PM, but a few showers may linger with the increased mid-level energy overnight. There is a Moderate/Low flood threat for 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:

Fog and low-level clouds should burn off this morning (west) with mostly cloudy skies over the eastern plains. An increase in thunderstorm activity is expected over the SE Mountains and Front Range. Threats include brief, heavy precipitation. Gusty winds and small hail are possible with the stronger storms. Storms that form near burn scars need to be monitored closely due to high confidence storms that form will have 1-hour rain rates greater than 0.5 inches. 1-hour rain rates will be up to 1.1 inches. A Moderate/Low flood threat has been issued.

Primetime: 12PM to 10PM

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

Showers beginning this morning and increasing in intensity throughout the day. Storm totals up to 2 inches are possible over the San Juan Mountains with other storm totals near 1.5 inches. Threats include mud slides, debris flows and road and small stream flooding. A Moderate/Low flood threat has been issued.

Primetime: 11AM to 11PM

Issue Date: Monday, August 21, 2017
Issue Time: 10:45AM MDT

— LOW flood threat for portions of the Front Range, Urban Corridor, Palmer Ridge, Southeast Mountains, Southeast Plains, Raton Ridge, Central Mountains, San Juan Mountains, Southwest Slope

Visible satellite shows mostly clear skies across the state except over the southern border and SE Plains. Mid and high-level cloudiness is strongest over the SE corner of the state and is associated with the overnight, northward movement of the disturbance in NM. There seems to be a break in the cloud over northern NM now. The hope is that these clear skies will move into the heaviest clouded region this morning and that some of the clouds will be able to partially break up for the eclipse. However, ongoing convection over NM may cause high clouds to move into the state and partially or fully obstruct of the eclipse.

The monsoon plume will continue to raise Precipitable Water (PW) values in Colorado. A mid-level Low pressure center is currently located over southern California while a weak surface High will set up over Texas today. A strong southerly component of the flow from the trough/ridge gradient will continue to advect a plume of elevated moisture over the state. PW at Denver and Grand Junction this morning are 0.67 and 0.72 inches, respectfully. PW is expected to increase to 1.2 inches over the eastern plains this afternoon. Mid-level drying will be strongest over the NW corner of the state. Paired with lower PW values, thunderstorms west of the Continental Divide should be confined to south Central Mountains, San Juan Mountains and southern Southwest Slope.

Storms will begin to fire over the mountains today just after noon. East of the Continental Divide, storms should be more numerous over the higher terrain and the Palmer Ridge when compared to yesterday. With the upper-level ridge over the Pacific Northwest, there will be weak mid-level steering winds. This will cause storms that form to slowly drift west over the SW corner of the state and drift E/SE over the eastern mountains and immediate adjacent plains. The slow moving storms and increased moisture will cause local, heavy rainfall. Burn scar areas will be most at risk today for mud flows, debris slides and small stream flooding. Road flooding and field ponding is also possible over the adjacent plains. There is a low flood threat for today.

This afternoon, a convergence boundary will also help storms form over the eastern plains. With higher instability, stronger storms may produce hail up to 0.75 inches and strong winds. Although the high moisture environment will help produce heavy precipitation, should not produce 1-hour rain fall rates greater than 1.5 inches. Thus, there is no flood threat for the eastern plains. Activity is expected to end around midnight, but some lingering showers over the southern mountains is possible overnight.

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:

Most sunny this morning become partly cloudy this afternoon. An increase in thunderstorm activity is expected over the SE Mountains and Front Range. Threats include brief, heavy precipitation, gusty winds and small hail. Storms that form near burn scars need to be monitored closely. 1-hour rain rates will be up to 1.5 inches (east) and 1.2 inches (west). A Low flood threat has been issued.

Primetime: 12PM to 12AM

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

Mostly sunny with showers over the Central Mountains and SW corner of the state. Stronger storms may produce 1-hour rain rates up to 1.1 inches with storm totals up to 1.5 inches. Threats include mud flows, debris slides and road and small stream flooding. A low flood threat has been issued.

Primetime: 12PM to 11PM

Issue Date: Sunday, August 20, 2017
Issue Time: 10:00AM MDT

— Flooding is NOT expected today

Starting the day again with mostly clear skies across the state. There are a few clouds over the CO/NE/WY intersect associated with the cold front just north of the state. The cold front is more of a wind shift than a temperature reducer, but it may help keep highs a couple degrees cooler over the Northeast Plains than yesterday. A surge of monsoon moisture can be seen just south of CO over NM and AZ. This monsoonal surge will start to slowly increase moisture today, and is expected to continue to do so the next few days. Precipitable Water (PW) is forecasted to rise most over the southeastern plains and southern portion of the state today. This should produce more numerous showers over the higher terrain than we’ve seen the last couple of days.

Storms will begin to initiate with upslope flow just after noon today. They will favor the Southeast and San Juan Mountains due to the slight uptick in moisture and increase in mid-level lift, but storms are also expected to fire over the southern Front Range. As the storms move off the higher terrains, they will initially favor the Raton Ridge and Palmer Ridge, but may become more widespread across the Southeast Plains. Storm motion will be W/NW around 15mph. With the highest instability also over the Southeast Plains, a few storms may produce brief, heavy local rain, small hail, and gusty winds. Guidance is still suggesting the increased moisture will not be enough for 1-hour rain rates to exceed 1.5 inches in an hour (east) or 1 inch an hour (west), so flooding is not expected. Activity is expected to end around midnight over the eastern plains.

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:

Most sunny this morning become partly cloudy this afternoon. An increase in thunderstorms are expected over the SE Mountains and Front Range. A few of these storms may become stronger over the adjacent plains producing brief, heavy precipitation, gusty winds and small hail. 1-hour rain rates will be up to 1.2 inches (east) and 0.75 inches (west). Flooding is not expected today.

Primetime: 12PM to 12AM

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

Plentiful sunshine to start the day then it will become partly cloudy over the higher terrain this afternoon. An increase in showers is expected over the Southwest Slope and San Juan Mountains. Thunderstorms may produce 1-hour rain rates up to 0.7 inches. Flooding is not expected today.

Primetime: 12PM to 10PM