Issue Date: 6/30/2015
Issue Time: 9:45AM

Flooding is NOT expected today.

The active month of June will end with a twist as generally dry, and very hot weather is expected today. This is all courtesy of an impressive, though temporary, ridge of high pressure parked just west of Colorado, as shown by the water vapor image below. The ridge will promote very warm mid and upper-level temperatures: for example, the freezing level today will be around 20,000 feet. Because surface moisture still exists, with morning dewpoints in the 40s to low 50s, there will be some isolated to widely scattered thunderstorms. However, with precipitable water falling from 0.6-0.8 inches this morning to about 0.5 inches by late afternoon, we expect rainfall to stay below 0.5 inches. Hikers: do not forget that thunderstorms can produce lightning even without rainfall!

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

Grand Valley, Northwest Slope, Southwest Slope, San Luis Valley:

Mostly sunny and very hot today with high temperatures up to 105F in the lowest elevations. An isolated thunderstorms coming from the higher terrain is not impossible, but will produce more of a gusty wind and lightning threat that any rainfall.

Central Mountains, Northern Mountains, Front Range, Southeast Mountains, San Juans:

Mostly sunny early, then partly cloudy and warm with isolated to widely scattered thunderstorms forming by mid afternoon. Hourly rain rates are expected to stay below 0.5 inches, and no flooding is expected.

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

Mostly sunny early with a few clouds forming by early afternoon. An isolated thunderstorm cannot be ruled out, especially by the Wyoming border. However, rainfall will stay below 0.25 inches and no flooding is expected.

Issue Date: 6/29/2015
Issue Time: 10:22 AM

A LOW FLOOD THREAT HAS BEEN ISSUED FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, CENTRAL MOUNTAINS AND SAN JUAN MOUNTAINS.

The forecast has been fairly consistent over the last few days as the upper-level ridge continues to be anchored across the Western US, centered over Utah. This is has left Colorado under the influence of northerly flow aloft, creating mean storm motions from north to south, and leaving the bulk of shower/thunderstorm activity over the High Country. Moisture has not only remained, but maintained, near-average to above-average, and today is no different; precipitable water is above average for this date, running between 0.75 and 1.0 inches at the normal four reporting stations shown in the graph below (Boulder – blue, Grand Junction – green, Pueblo – pink, and Shriever AFB – red).

Scattered showers and thunderstorms are expected across the High Country, following the diurnal pattern of beginning around lunchtime, maximizing coverage during the late afternoon and early evening, before diminishing just after sunset as daytime heating ends and radiational cooling begins. Just as yesterday, a few isolated thunderstorms are expected over the adjacent lower elevations of the Urban Corridor, Palmer Ridge, Northeast Plains, and Southeast Plains, with the relative best chances occurring near the preferred terrain of the Front Range, Palmer Ridge, and Southeast Mountains. Adding an additional complexity to today’s forecast is a weak surface boundary that will scrape across the far Northeast and Southeast Plains, providing support for isolated afternoon/evening thunderstorms. Primary concerns with most thunderstorm activity will be gusty outflow winds, lightning, small hail, and brief moderate-to-heavy rain. For more specifics regarding rain rates, check out 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

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

Mostly sunny and hot will be the main story today, as high temperatures remain in the mid-80s to low-90s across the regions. Isolated thunderstorms are expected this afternoon and evening, thanks to the conditions outlined above. The main threats will be lightning, strong outflow winds, hail (up to 1.5 inches in diameter), and brief moderate-to-heavy rain. Rain rates will typically be 0.4-0.8 inches/hour, but a couple strong/marginally severe storms could produce rain up to 0.9-1.3 inches/hour.

Timing: Noon – 10 PM

Front Range and Northern Mountains:

Isolated showers and thunderstorms expected, with the main threats being gusty outflow winds, small hail, and lightning. The Front Range south of I-70 will hold the best chance for bouts with brief heavy rain, with rain rates in the 0.5-0.8 inches/hour range. With most of the moisture confined to the mid-levels, and relatively shallow low-level moisture, dry air beneath the cloud base will eat away at precipitation before reaching the surface. However, an outflow boundary from another storm interacting with a thunderstorm over the southern Front Range could push maximum rain rates to 0.8-1.2 inches/hour. This is a relatively low probability, but cannot be ruled out, thus the inclusion in the outlined Low Flood Threat area.

Timing: Noon – 8 PM

Northwest Slope and Grand Valley:

Mostly sunny and hot will be the main story of the day, with an isolated thunderstorm or two possible over the higher terrain near the Central Mountain and Southwest Slope regions. The main threats from any isolated thunderstorms will be lightning and gusty outflow winds, as rain rates will stay below 0.25 inches/hour.

Timing: Noon – 6 PM

Central Mountains, Southeast Mountains, San Luis Valley, Southwest Slope, and San Juan Mountains:

Scattered showers and thunderstorms expected, mainly over the higher terrain. With mean storm motions from north to south, activity will move over lower elevations and valleys with time. Rain rates will typically be in the 0.3-0.6 inches/hour range, but brief heavy rain over the San Juan Mountains (0.9-1.3 inches/hour) and Central Mountains (0.8-1.2 inches/hour) is possible. The main threats from thunderstorms will be gusty outflow winds, lightning, and small hail. There have been numerous reported injuries in the mountains from lightning over the last few weeks, so please be aware of changing weather conditions and seek shelter, if necessary.

Timing: 11 AM – 9 PM

Issue Date: 6/28/2015
Issue Time: 9:57 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, CENTRAL MOUNTAINS, SOUTHEAST MOUNTAINS, SAN JUAN MOUNTAINS, AND SOUTHWEST SLOPE.

The upper-level ridge centered over western Utah continues its dominance over the western US today. One main difference over yesterday is that a bit more subtropical moisture has rotated into Colorado under the ridge, pushing precipitable water values slightly above average. This will lead to a slight uptick in thunderstorm coverage today, but, due to mean storm motions from north to south, most will still remain confined to the High Country. An isolated thunderstorm or two will develop during the late afternoon/early evening over the Urban Corridor thanks to outflow boundaries from storms over the higher terrain.

A feature of note in today’s forecast is a weak shortwave that will move overhead during the early-to-mid afternoon hours. In addition to helping initiate storms over the higher terrain, this will also allow one or two isolated thunderstorms to develop over the Palmer Ridge and southern portions of the Urban Corridor, moving southward with time. With surface high pressure and upper-level high pressure in place, these storms will not last very long as they move away from the preferred terrain of the Palmer Ridge. Additionally, most of the precipitation that falls from these storms will likely not reach the ground due to high cloud bases. Maximum rain rates will be 0.2-0.5 inches/hour.

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 and Palmer Ridge:

Mostly sunny, with a couple of isolated thunderstorms possible this afternoon and evening. The main threat from storms will be gusty outflow winds, small hail, and lightning. With high cloud bases, though, much of the precipitation will evaporate before reaching the surface, resulting in maximum rain rates of 0.2-0.5 inches/hour. An outflow boundary moving off of the mountains and over the Urban Corridor will provide the best opportunity for a storm to produce locally heavy rain, though the chances are low. This is accounted for in the low flood threat area. If this situation occurs, maximum rain rates will push to 0.8-1.2 inches/hour.

Timing: 1 PM – 9 PM

Southeast Plains, Northeast Plains and Raton Ridge:

Mostly sunny and hot will be the main story today across these regions. Plains regions near the preferred terrain of the Palmer Ridge, and Raton Ridge near the Southeast Mountains, will hold a chance for an isolated thunderstorm to drift overhead, although chances are slim. Maximum rain rates will be 0.3-0.6 inches/hour.

Timing: 3 PM – 9 PM

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

Mostly sunny early, becoming partly sunny this afternoon as scattered thunderstorms begin to develop over the higher terrain. The main threats from thunderstorms will be gusty outflow winds, small hail, and lightning, but brief heavy rain cannot be ruled out. Most rain rates will be light (0.2-0.4 inches/hour), but a stronger storm or two could produce rain at 0.6-1.0 inches/hour. The San Juan Mountains will be the main region to watch today as the best moisture resides there. Maximum rain rates will be 1.0-1.4 inches/hour for the San Juan Mountains.

Timing: Noon – 8 PM, with a few showers/weak thunderstorms lingering until midnight over southern regions.

Issue Date: 6/27/2015
Issue Time: 9:47 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, SOUTHEAST MOUNTAINS, AND RATON RIDGE.

An upper-level ridge has set down roots across the Western US, centered over western Utah. The location of the high pressure center is important, as it will place Colorado under north-northwesterly flow aloft. This will keep storms mainly confined to the high country, with a slight chance of an isolated shower/thunderstorm to stray over adjacent lower elevations of the Urban Corridor (Pikes Peak region and south) and Southeast Plains.

With upper-level ridging in place, isolated-to-scattered showers and thunderstorms will rely on daytime heating to initiate activity over the mountains. The favored terrain for scattered storms will be the San Juan Mountains and Southeast Mountains, with more isolated coverage over the mountains of the Front Range, Northern Mountains, Southwest Slope, and Central Mountains. Gusty outflow winds and lightning will be the main impacts of storm activity, along with brief moderate-to-heavy rain. Precipitable water is near average, and while some drying is expected today, there will still be enough available for maximum rain rates around 0.8-1.2 inches/hour over the San Juan Mountains and Southeast Mountains. Elsewhere over the high country, maximum rain rates will be 0.4-0.7 inches/hour.

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, Southeast Plains, Northeast Plains and Raton Ridge:

Partly sunny near the interface with the higher terrain, mostly sunny further east. A stray, isolated thunderstorm or two will move off of the higher terrain and over adjacent portions of the Urban Corridor (Pikes Peak region and south), Southeast Plains, and Raton Ridge. Otherwise, the rest of the area will stay dry and warm a few degrees over yesterday’s high temperatures.

Any thunderstorm activity will result in mainly gusty winds, lightning, and brief light-to-moderate rainfall. Maximum rain rates will be in the 0.25-0.5 inches/hour.

Timing: 1 PM – 8 PM

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

Isolated-to-scattered showers and thunderstorms will develop around lunchtime over the higher terrain of the Front Range, Northern Mountains, Central Mountains, San Juan Mountains, Southeast Mountains, and Southwest Slope. The best coverage will be across the San Juan Mountains and Southeast Mountains, as discussed above in the main discussion. A few weak thunderstorms will stray over lower elevations, with gusty outflow winds, lightning, and light-to-moderate rainfall being the main threats.

Maximum rain rates around 0.8-1.2 inches/hour over the San Juan Mountains and Southeast Mountains, and elsewhere over the high country will be 0.4-0.7 inches/hour.

Timing: Noon – 9 PM