Issue Date: Tuesday, June 4th, 2019
Issue Time: 8:30AM MDT

–Flooding is NOT expected today

Minus a few high clouds over the San Juan Mountains, which are dispersing quickly, it’s a clear start to the day. Still quite a bit of snowpack over the mountains in the visible image below. This will continue to melt with above average temperatures forecast again today. Expect high temperatures to be on par with high temperatures from yesterday. The upper level low is currently over the Baja CA Peninsula and will move east today, which will center it over south, central Arizona and the Mexico border by this evening. This means upper flow will remain westerly except over the southwest corner where flow will have more of a southwesterly component.

A drier air mass remains over the state, which should limit the heavy rainfall threat once again. PW was measured at 0.43 inches at Denver this morning. There is a slight increase in mid-level energy, so expecting storm coverage to be more widespread over the mountains this afternoon. The weak thunderstorms may produce some small hail, but high-bases will make the main threats today gusty outflow winds and lightning. As storms move into the eastern plains this afternoon, better moisture will reside near Colorado’s eastern border, so expecting storms to become more efficient at producing rainfall in this area. Decent storm motion should only allow for moderate rainfall totals. Overall, similar setup to yesterday, but expecting storms to be more widespread over the southern half of Colorado. Flooding is not forecast.

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:

Southeast Mountains, San Juan Mountains, Southeast Plains, Raton Ridge, Northeast Plains, Palmer Ridge:

Increased storm activity is forecast across southern Colorado and the eastern Colorado border. Max 1-hr rain rates over the San Juans will be 0.4 inches with more general rain rates in the 0.1 to 0.25 inch/hour range. Thus, stronger thunderstorms that track near the 416 burn area should be monitored closely. Over the Southeast Mountains max 1-hr rain rates will remain below 0.25 inches, so not too worried for recent burn areas here. Over the eastern plains, isolated 1-hr totals up to 1.3 inches are possible though most storms will produce 1-hr rain rates between 0.8 and 1 inch.

Primetime: 11:30AM to 10PM

Front Range, Urban Corridor, Northern Mountains, Central Mountains, Northwest Slope, Grand Valley, Southwest Slope, San Luis Valley:

Similar to yesterday, storms will form over the mountains by early afternoon. A bit drier air is in place over these regions, so storms will be high-based once again. This will translate to the main threats today being lightning and gusty winds. Not totally out of the question for a couple of weak thunderstorms to produce 0.25 inch hail. Max 1-hr rain rates over the mountains are expected to be 0.3 inches (Front Range) and 0.15 inches (west of the Divide). Not expecting totals above trace amounts for the lower elevations in western CO with most storms will only producing cloud cover. A storm might wander into the Urban Corridor again this afternoon, but totals are expected to remain under 0.3 inches. The Conejos and San Antonio Rivers are still under a Flood Warning for high flows and minor flooding of low-lying areas. This is expected to continue for the next few days, but flood stage remains only at Action level today.

Primetime: 12PM to 9PM

Issue Date: Monday, June 3rd, 2019
Issue Time: 8:45AM MDT

The low begins to move south towards the Baja Peninsula this afternoon, which will allow for a thermal ridge to build back to the northwest over the state. This will change upper level flow to more southwest over western Colorado with more westerly winds this afternoon over eastern Colorado. Models are also showing a surface low forming by mid-afternoon over eastern Colorado. This will pull in better low level moisture over the Northeast Plains on its north side and help scour our moisture over the Southeast Mountains and the adjacent Southeast Plains. Thus, thunderstorm activity will be more widespread over the Northeast Plains with more limited coverage over the southeast corner of the state as the storms move west.

Diurnal flow will kick off thunderstorms over the mountains and Raton Ridge by early afternoon with storm motion to the west at 15 to 20 knots. With more mid-level moisture present than low level moisture, storms will continue to be high-based, which should limit the heavy rainfall potential. Higher moisture along the Kansas/Nebraska/Colorado border over the Northeast Plains will allow some decent CAPE values to build, so an isolated severe thunderstorms may be possible. Hail up to 2 inches, gusts up to 60mph and moderate rainfall will be the main threats with the severe thunderstorms. To the west, less low level moisture will be available, so lightning, gusty winds and small hail will be the main threats over the Northern, Central and San Juan Mountains. Flooding is not forecast 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:

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

Storms will form over the mountains and Raton Ridge this afternoon with the aid of diurnal flow and a surface low just north of the Palmer Ridge. This will pull in better moisture on its north side, so storms will be more abundant as the move west into the Northeast Plains. Max 1-hr rain rates up to 0.4 inches (west) and 1.15 inches (east) are possible. Further south, storm activity will be limited to the far southeast corner of the state. Max 1-hr rain rates over the Raton Ridge up to 0.15 inches are possible with totals up to 1 inch over the southeast corner. High bases and decent storm movement should limit the flood threat, thus there is no flood threat issued. Without any upper dynamics to support overnight thunderstorms, storms will come to an end a couple hours after sundown.

Primetime: 1PM to 10PM

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

Not quite as much moisture over this area with southwest and westerly flow scouring out low-level moisture. Some weak afternoon storms will be possible over the higher terrains, but the heavier accumulations will be along and near the Continental Divide over the Central and Northern Mountains. Isolated totals up to 0.3 inches will be possible with more general totals in the 0.1 to 0.2 inch range. Small hail and gusty winds will likely accompany the stronger storms. Expect high temperatures to reach the 80°Fs in the valleys and upper 50°Fs to mid-60°Fs in the mountains. With the warm temperatures, snow melt has been occurring rapidly since Saturday. There is currently a flood advisory for the San Antonio River for minor flooding in Manassa, Sanford and Antonito possible. No flooding has been reported yet, but gages in the area remain high.

Primetime: 1PM to 9PM

Issue Date: 6/2/2019
Issue Time: 8:30 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE URBAN CORRIDOR, NORTHEAST PLAINS, PALMER RIDGE, SOUTHEAST PLAINS, AND RATON RIDGE.

There isn’t much change in the large-scale weather pattern as compared to yesterday, with an upper-level low still spinning over SoCal/southern NV, an upper-ridge building over the central US, and southwest flow between the two features continuing to bring some mid-level moisture to Colorado. This will lead to a very similar day as yesterday, albeit with a few more thunderstorms thanks to a weak shortwave disturbance that will pass overhead this afternoon/evening. West of the Divide, low-level moisture remains a bit lackluster, so expect activity to be high-based and produce mainly gusty winds and light rain, with a few episodes of pea-sized hail under one or two stronger storms.

East of the Divide, the weather story is much the same as yesterday, except the threat of heavy rainfall has increased somewhat thanks to a slight uptick in low-level moisture as compared to yesterday. Scattered thunderstorms will first develop over the Front Range/Southeast Mountains around lunchtime, then spread eastward through the afternoon/evening across the plains. Large hail up to 2 inches in diameter and strong winds up to 65 mph will be the main severe threats, and an isolated tornado or two cannot be ruled out. Heavy rain will also attend stronger storms east of the mountains, so a low flash flood threat has been issued. For more details on timing and rain rates, 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. 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 are expected today/tonight, developing first over the Front Range/Southeast Mountains around lunchtime, spreading eastward over the plains with time. A few of the storms will be severe, capable of producing hail up to 2 inches in diameter, strong winds up to 65 mph, and an isolated tornado or two. Heavy rainfall will also be a concern with moisture slightly increased since yesterday; however, storm motions will lessen the risk of flash flooding, so only a low flood threat is warranted. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.25-0.5 inches/hour
Urban Corridor: 1.0-1.2 inches/hour
Palmer Ridge: 1.5-2.5 inches/hour
Northeast Plains and Southeast Plains: 2.0-2.75 inches/hour
Raton Ridge: 1.0-1.3 inches/hour

Timing: Noon – 10 PM for the Front Range/Southeast Mountains, 1 PM – 10 PM for the Urban Corridor, 2 PM – Midnight for the Palmer Ridge, Northeast Plains and Southeast Plains, 2 PM – 9 PM for the Raton Ridge

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

Scattered high-based showers/thunderstorms are expected, beginning around 11 AM, maximizing coverage & intensity between 3 PM and 6 PM, then gradually diminishing and ending by 10 PM. Gusty winds, light rainfall, and occasional lightning will be the main impacts, with one or two stronger storms capable of producing up to 50 mph wind gusts in valley locations and pea-sized hail. Most rain rates will be less than 0.1 inches/hour, but maximum rain rates will be 0.2-0.5 inches/hour under the strongest storms. Storm motions will be quick enough to the northeast to avoid any flood threat concerns.

Issue Date: 6/1/2019
Issue Time: 8:55 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, AND SOUTHEAST PLAINS.

On the first day of Meteorological Summer, the large-scale weather pattern features an upper-level low sinking southward along the West Coast, allowing for a building ridge of high pressure over the southern/central Rockies. Embedded in the southwest flow aloft between these two pressure centers is a ribbon of decent mid-level moisture that will continue to overspread Colorado. This moisture will be the fuel behind a few scattered showers/weak thunderstorms along/west of the Continental Divide today, all of which will be high-based owing to a lack of low-level moisture. Light precipitation and gusty winds will be the main impacts associated with this activity.

East of the Continental Divide, and mainly along/east of the Front Range/Southeast Mountains, easterly upslope flow will usher in the return of surface dewpoints in the 40s/low 50s. This increase in moisture, coupled with good daytime heating, will allow for the development of scattered thunderstorms across the area. There will be enough instability for a few of the storms to become strong/severe, with the highest relative risk over the far Southeast Plains where the combination of instability/wind shear will be most favorable. The main threats will be strong winds and hail up to 2 inches in diameter; an isolated tornado or two cannot be ruled out.

For more details on timing and rain rates, 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. 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 are expected today, beginning around lunchtime over the Front Range and Southeast Mountains, spreading eastward with time over eastern Colorado. A secondary focus for initiation besides the higher terrain will be a weak surface boundary over the far Southeast Plains; this boundary is the reason for the higher, relatively speaking, severe threat today as mentioned above. The main threats will be strong winds and hail up to 2 inches in diameter; an isolated tornado or two cannot be ruled out. Maximum rain rates are as follows:

Front Range: 0.6-1.0 inches/hour
Southeast Mountains: 0.4-0.6 inches/hour
Urban Corridor: 0.8-1.2 inches/hour
Northeast Plains, Southeast Plains, and Palmer Ridge: 1.5-2.0 inches/hour
Raton Ridge: 0.5-0.8 inches/hour

Timing: Noon – 9 PM for the Front Range and Southeast Mountains, 1 PM – 10 PM for the Urban Corridor, 1 PM – 11 for the Palmer Ridge, and 1 PM – Midnight for the Northeast Plains and Southeast Plains

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

Scattered showers/weak thunderstorms are expected today as daytime heating and orographic effects work on good mid-level moisture. Due to a lack of low-level moisture, activity will be high-based, with the main impacts being gusty winds, light rainfall, and occasional lightning. Rain rates will generally be less than 0.1 inches/hour everywhere, with maximum rates of 0.15-0.30 inches/hour over the San Juan Mountains and Southwest Slope.

Timing: 11 AM – 9 PM, with an isolated, lingering shower or two until 11 PM over the higher terrain