Issue Date: Tuesday, July 30th, 2019
Issue Time: 8:45AM MDT

— Flooding is NOT expected today

Warm temperatures already to start the day. Mid 60°Fs over the plains with mid-50°Fs and 60°Fs over the adjacent plains and mountain valleys. The subtropical high will once again be anchored over the Colorado/New Mexico border, which should keep the heavy rainfall threat away for another day. This morning soundings at Denver and Grand Junction show slightly higher PW values from yesterday morning, but still well below average for this time of year. Dry upper levels will likely mix out most of this surface and mid-level moisture throughout the day. This is especially true over the northern Front Range and Southeast Mountains due to downsloping winds created by a surface low over the eastern plains. This means the storms that do form will be high-based and produce more virga and wind than accumulating rainfall over the mountains and adjacent eastern plains. Only slightly better moisture holds on over the far northeast corner of the state, so storms that form over the Cheyenne Ridge and move into the state with the northwest steering flow may be capable of producing light to moderate rain rates. However, chances for this occurring are minimal.

To the west, the best moisture holds on over the southwest corner of the state. Paired with passing shortwaves around the high, expecting weak afternoon thunderstorms and showers over the western high terrains with coverage greatest to the south. The visible satellite imagery below shows some of that remaining moisture with mid and upper level cloud cover associated with the passing disturbances. A couple high-based storms may also be possible over the lower elevations of the Grand Valley and Southwest Slope that move in from Utah. The main threats today will be gusty winds and lightning with lighter rainfall rates. The first round of storms should help make the second round of storms more efficient at producing accumulating rainfall. Storms are expected to weaken a couple hours after sundown, and all activity is forecast to end by 11PM. Flooding is not expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Isolated max 1-hr rain rates up to 0.5 inches (south/central) and 0.2 inches (north) will be possible over the higher terrains. While a couple of storms may wander into the Grand Valley and Southwest Slope Valleys, max 1-hr rain rates should remain around 0.2 inches. Slow steering winds mean storms will likely sit again today, so very isolated 2-hour totals between 0.6 and 0.75 inches may be possible over the eastern San Juan Mountains and San Juan/Ouray/Hinsdale County area. Rain rates should be low enough that there is no threat for the 416 and Lake Christine burn areas, but as always, caution should be taken if moderate rain is falling over these susceptible scars. The main threats from storms today will be gusty winds and lightning.

Primetime: 1:30PM to 11PM

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

Best chance for accumulating rain today will be over the southern Front Range near the Continental Divide and south over the Raton Ridge. Max 1-hr rain rates up to 0.65 inches will be possible (Front Range/eastern Raton Ridge) with up to 0.3 inches possible over the western edge of the Raton Ridge. An isolated storm may make it into the Northeast Plains, but capping will likely cause the storm to dissipate rather quickly. A quick 0.5 inches may be possible. Storms should end west to east with all activity ending a few hours after sundown.

Primetime: 2:30PM to 10:30PM

Issue Date: Monday, July 29, 2019
Issue Time: 9:40AM MDT

–Flooding is NOT expected today 

The high pressure ridge over the southwest will continue to move its way slowly to the east and is currently situated over the CO/NM border . Flow aloft will increase today as the ridge builds overhead, with the jet streak remaining to the north of Colorado. The dry air mass that moved over the state yesterday decreased atmospheric moisture significantly, with Denver and Grand Junction measuring 0.6 and 0.41 inches of PW this morning. Counterclockwise flow around the high pressure to the south (marked H below) will slowly increase moisture throughout the state, but it will not be a major factor in today’s weather.

Surface high pressure remains over the high country and will keep most areas west of the Continental Divide dry today. Low pressure is forecast to form over central Colorado and central Wyoming midday and will be the two major drivers for precipitation this afternoon. Afternoon thunderstorms are forecast to begin over the central and southern mountain ranges early this afternoon and move to the southeast throughout the afternoon and into the early evening. Additional storms are forecast to form along a warm front over the Northeast Plains (red line below). Low levels of surface and atmospheric moisture should keep storm bases high, with the primary threat being wind gusts up to 60 mph within the storms vicinity.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Afternoon thunderstorms are forecast throughout the area this afternoon.  Over the mountainous regions and urban corridor, storms are forecast to areas south of the Denver Metro area. Storms will begin from 1 PM (west) to 3 PM (east) and end by 8 PM (north) and 12 AM (south).  Max 1 hour rainfall rates of 1.2 inches are forecast over the far eastern edge of the Northeast Plains and 0.6 inches over the Palmer Divide, and southern portions of the Front Range and Urban Corridor.  The Spring Creek burn area is not forecast to receive more than 0.25 inches in 1 hour, however storms over the area for 2-3 hours should be monitored closely.  Flooding is not forecast over the area today.

Primetime: 1PM to 12AM

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

Storms are forecast over the Central Mountains, eastern San Juan Mountains and San Luis Valley.  Dry air over the northwest quadrant of the state will limit precipitation over the area. Storms are forecast to begin by around noon and end early this evening, however weak storms may remain over the San Juan Mountains until 10PM. Max 1-hour rainfall rates of 0.75 inches are forecast over the eastern San Juan Mountains.  Storms are forecast to move over the eastern half of the San Luis Valley, but dry air underneath the storm base should limit max 1-hour rainfall rates to 0.6 inches.  Flooding is not forecast over the area today.

Primetime: 12PM to 10PM

Issue Date: Sunday, July 28, 2019
Issue Time: 9:40AM MDT

–Flooding is NOT expected today

Mostly sunny skies and seasonal temperatures are expected throughout the state today as dry air makes its way in from the west. High pressure remains centered over the desert southwest, with zonal flow over much of the western United States. The right exit region of the jet streak over northern Colorado should prevent severe weather today. Atmospheric moisture is moderate to high this morning, with Denver and Grand Junction measuring between 0.9 and 1.0 inches of PW this morning. However, most of the moisture is surface based and confined to the low-levels after yesterday’s widespread rain.  At the surface, high pressure (H below) has set in over the northwest quadrant of the state, and the low that provided rain yesterday has moved into western Nebraska. A cold front (blue line below) is forecast to move south over the eastern plains throughout the morning, which should cap most of the area to severe thunderstorms later in the day. Sunny skies and north-northwest surface flow will mix out most of the moisture statewide this morning and into the early afternoon. Dewpoints are forecast to drop 15-20 degrees statewide throughout the day. Chances for weak afternoon storms will be confined to the high country, with the highest chances for precipitation over the Continental Divide and San Juan Mountains.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts

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

Downslope flow throughout the morning and early afternoon should provide mostly sunny skies over the area today.  There is a moderate chance for afternoon thunderstorms over the high country throughout the afternoon, with the greatest chance over the Southeast Mountains.  High storm bases will limit max 1-hour rainfall rates to 0.3 inches over the mountains.  The passage of the cold front over the eastern plains this morning should cap most storms over the area.  Storms may generate off of the Raton Ridge and Chayenne Ridge mid-afternoon, providing chances for storms over the corners of the Southeast and Northeast Plains.  Max 1-hour rainfall rates of 0.6 inches are forecast over the area.

Primetime: 12PM to 8PM

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

Chances for storms today will be confined to the high country, with higher chances favoring the San Juan and Central Mountains.  Dry air advection from the northwest will confine rainfall to the highest elevations of the forecast region.  Max 1-hour rainfall rates of 0.25 inches are forecast over the Central and San Juan Mountains.  Dewpoints are forecast to drop into the teens and single digits over the northwest quadrant of the forecast area.

Primetime: 12PM to 6PM

Issue Date: 7/27/2019
Issue Time: 9:30 AM

A MODERATE FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, SOUTHEAST MOUNTAINS, CENTRAL MOUNTAINS, GRAND VALLEY, NORTHERN MOUNTAINS, AND NORTHWEST SLOPE.

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE REGIONS OUTLINED ABOVE, PLUS THE RATON RIDGE, SOUTHEAST PLAINS, PALMER RIDGE, NORTHEAST PLAINS, URBAN CORRIDOR, AND FRONT RANGE.

Another active weather day is in store for Colorado, with scattered-to-widespread showers and thunderstorms expected across much of the state. The high pressure that has been centered over the desert SW for the last couple of days remains in place, streaming elevated moisture into Colorado from the west. This moisture, combined with a mid-level disturbance expected to traverse the state today, has led to a spatially large flood threat for this forecast period. The main concerns will be mountain burn scars and other steep terrain areas, and these are the considerations behind the three separate moderate flood threat areas.

Spring Creek, Hayden Pass, and Junkins burn scars: Scattered thunderstorms expected, with maximum rain rates of 0.5-1.0 inches/hour possible under strong thunderstorms. Relatively quick storm motions from west-to-east will reduce the risk of flash flooding somewhat, but a moderate flood threat is warranted.

416, Bull Draw, and Lake Christine burn scars: Scattered-to-widespread thunderstorms are expected over the higher terrain today, and precipitable water values are running in the 90th percentile for the date. This ample moisture means efficient rainfall; maximum rain rates of 0.7-1.1 inches/hour possible. Quicker storm motions than the past couple of days from west-to-east will reduce the risk of flash flooding somewhat, but a moderate flood threat is warranted.

East of the Continental Divide, scattered thunderstorms are expected, beginning over the easternmost mountains between 11 AM and Noon, then spreading eastward over the plains as the disturbance passes through. Storm motions will mitigate the risk of flash flooding somewhat, but urban areas and other poorly drained locations will need to be watched as periods of heavy rainfall are expected under thunderstorms.

For more details on timing and rain rates, please see the zone-specific forecasts 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

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

Scattered thunderstorms expected, beginning over the higher terrain by 11 AM – Noon, then spreading eastward with time. Southeast Mountains burn scars are the main concern for flash flooding issues today, but urban areas and other poorly drained locations will also be a concern as thunderstorms will be capable of heavy rainfall in short periods of time. Maximum rain rates will be 0.5-1.25 inches/hour over the Front Range and Southeast Mountains, 1.25-1.75 inches/hour over the Urban Corridor and Raton Ridge, and 2.0-2.5 inches/hour over the Northeast Plains, Southeast Plains, and Palmer Ridge.

Timing: 11 AM – Midnight for the Front Range and Southeast Mountains, 1 PM – 11 PM for the Urban Corridor and Raton Ridge, and 2 PM – Midnight for the Northeast Plains, Southeast Plains, and Palmer Ridge

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

Scattered-to-widespread thunderstorms are expected today/tonight, beginning around 11 AM and ending from west-to-east from 8 PM – Midnight. Precipitable water values in the 90th percentile means that storms will be efficient rainfall producers, so locally heavy rainfall is a concern, especially with previous’ days rainfall saturating the soils a bit. Burn scars and steep terrain are the main concerns for flash flooding issues (including debris flows). Maximum rain rates are 0.7-1.1 inches/hour, perhaps up to 1.25 inches/hour over the San Juan Mountains. West-to-east storm motions will mitigate the flood threat somewhat, but an expansive low-to-moderate flood threat is warranted.