Issue Date: 5/16/2016
Issue Time: 10:25 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHEAST PLAINS AND RATON RIDGE.

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHEAST PLAINS, RATON RIDE, PALMER RIDGE, URBAN CORRIDOR, FRONT RANGE, SOUTHEAST MOUNTAINS, CENTRAL MOUNTAINS, GRAND VALLEY, NORTHWEST SLOPE, AND SOUTHWEST SLOPE.

An upper-level low will continue to work its way eastward across the western US today, spreading mid-/upper-level support for scattered-to-widespread showers overhead. Plenty of moisture will continue to be pulled into Colorado at the same time, pushing precipitable water (IPW) values well above average for this time of year (see IPW graph below). Instability will be a mitigating factor across most of Colorado due to the extensive cloud cover and cool temperatures in many places.

The best moisture/instability will be present across the far Southeast Plains/Raton Ridge, bringing about the highest expected rain rates, thus the moderate threat for those locations. A few storms will become severe, with the main threats being large hail (1-1.5 inches/diameter), damaging winds (up to 55-70 mph), and an isolated tornado or two. Heavy rain will attend the strong/severe thunderstorms; rain rates will be mentioned in the zone-specific forecast discussions below.

Overall, showers will be widespread across most of Colorado this afternoon/evening, with thunderstorms more scattered in nature. Thunderstorms will be capable of producing moderate-to-heavy rainfall, but storm motions and meager instability (in most locations) are limiting factors on the flood threat. Thunderstorm activity will peak during the afternoon and early evening hours, with scattered showers/weak thunderstorms lingering into the overnight hours. Please see the zone-specific forecast discussions below for more details.

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 (Arapahoe County and northward), and Northeast Plains:

Cloudy with scattered showers, and isolated afternoon/evening thunderstorms expected. The main threats from thunderstorms will be brief heavy rain and gusty winds. Maximum rain rates will be 0.4-0.8 inches/hour over the Northeast Plains, and 0.3-0.6 inches/hour over the Urban Corridor. High temperatures will be well below average for this time of year.

Timing: 11 AM – 8 PM, with lingering showers/weak thunderstorms through the overnight hours.

Urban Corridor (South of Arapahoe County), Southeast Plains, Palmer Ridge, and Raton Ridge:

Scattered showers and thunderstorms are expected. A few will become strong-to-severe over the Southeast Plains and Raton Ridge. Maximum rain rates vary:

Urban Corridor: 1.0-1.4 inches/hour
Palmer Ridge: 0.8-1.2 inches/hour
Southeast Plains and Raton Ridge: 1.8-2.2 inches/hour

Timing: Noon – 9 PM, with lingering showers/weak thunderstorms through the overnight hours

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

Widespread showers and thunderstorms are expected today. Thunderstorms will be capable of producing moderate-to-heavy rainfall, with stronger storms producing small hail and gusty winds up to 40-50 mph. Rain rates will vary:

Northern Mountains: 0.3-0.6 inches/hour
Front Range and Central Mountains: 0.8-1.2 inches/hour
Southeast Mountains: 1.4-1.8 inches/hour
Northwest Slope, Grand Valley, and Southwest Slope: 0.8-1.2 inches/hour
San Juan Mountains: 0.4-0.7 inches/hour
San Luis Valley: 0.2-0.5 inches/hour

Timing: Current – 8 PM, with isolated lingering showers into the early morning hours

Issue Date: Sunday May 15th, 2016
Issue Time: 10:25 AM MDT

— No Flood Threat Today

Today’s water vapor imagery, shown below, indicates that the weak upper-level high pressure system has moved slightly eastward and is no longer much of a presence. Meanwhile, a seasonably strong low-pressure center has entered the west coast and is centered just west of the Great Basin. As this system moves slowly eastward, it will support shower and some thunderstorm activity across most of Colorado.

In terms of the heavy rainfall potential,
• the atmosphere’s dynamics are certainly more conducive than yesterday
• precipitable water values range between 0.6 and 0.8 inches, which is quite a bit higher than normal for this time of year (Denver’s normal is about 0.45 for May 15th)
• morning sounding at Grand Junction (as well as Salt Lake City which is closer to the low center), most of the moisture is well above the surface. Instead, the low-level soundings favor more of a strong wind threat than a rain threat
• instability is limited, with most high-resolution probabilistic guidance such as the NCAR ensemble showing rather small chances of exceeding 500 J/kg
• storm motion will be in the 30-40 mph range, which is fast enough to limit heavy rainfall in any given location.

In all, today will see significantly more rainfall than yesterday, both in terms of coverage and intensity. However, 1-hr and 3-hr rainfall intensities are expected to stay below flood threat levels across the state. Thus, no flood threat is 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, jump below the map.

 Zone-Specific Forecasts

Urban Corridor, Front Range, Northeast Plains:

Overcast early with a few breaks in the clouds by early afternoon. Isolated to scattered showers and thunderstorms will occur from early afternoon to early evening. Max hourly rain rates up to 0.5 inches can be expected, with max 3-hourly rates up to 0.75 inches. No flood threat is expected today.

Prime-time: 1PM to 7PM

Central Mountains, Southwest Slope, Raton Ridge, Southeast Mountains, San Luis Valley, San Juan Mountains, Palmer Ridge and Southeast Plains:

Broken clouds early with scattered showers and thunderstorms developing by early afternoon and lasting into the early evening. Max hourly rain rates up to 0.7 inches are possible with max 3-hourly rain rates up to 0.9 inches. The strongest thunderstorms will be capable of producing hail up to 0.5 inches and gusty winds up to 60mph especially in the southern part of the area. No flood threat is expected today.

Prime-time: 12PM to 7PM

Grand Valley, Northern Mountains and Northwest Slope:

Broken clouds with scattered showers and a weak thunderstorm or two possible throughout the day into the late evening hours. Max hourly rain rates up to 0.5 inches will be possible. Some locations could see close to 1 inch of rainfall over the 24-hour period ending tomorrow morning. The snow level will be above 12,000 feet during the day, falling to about 9,500 feet after sunset.

Prime-time: 11AM to 9PM

Issue Date: 5/14/2016
Issue Time: 10:25 AM MDT

NO FLOOD THREAT IS FORECAST.

Colorado remains downstream of a weak upper-level ridge. Though the ridge may be weak, it is still a ridge, and will cause overall downward motion in the mid-levels of the atmosphere today. Meanwhile, as shown nicely in the visible satellite image below, a low cloud deck has setup shop below about 8,000 feet east of the Continental Divide. This is courtesy of the shallow, moist cool front passage yesterday. The low cloud deck will slowly erode, but will limit how much heating will occur under its footprint. This will leave most of eastern Colorado with below normal temperatures.

The best chances for rainfall today will be in the southern part of the state. As the Southeast Mountains, Raton Ridge break out of the cloud deck, there will be enough moisture and instability to kick up at least an isolated shower and even a weak thunderstorm. However, rain rates will be far below levels required for flooding. Thus, no flood threat is expected today.

Looking ahead, active weather will return to our state late Sunday, and continue into Monday.

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.

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

Overcast early with clouds slowly eroding by mid-afternoon. Areas with sunshine will quickly jump into the low 70s. However, areas that hold on to clouds the longest may struggle to get to 60F. No flood threat today.

Central Mountains, Southwest Slope, Northwest Slope, Grand Valley, and Northern Mountains:

Sunny and mild today with near average temperatures. A few clouds will develop especially towards the south, with a possible shower or two. Maximum hourly rain rates will be below 0.1 inch. No flood threat today.

San Juan Mountains, San Luis Valley, Southeast Mountains and Raton Ridge:

Sunny early with cumulus clouds popping up by early afternoon. Isolated to scattered showers and even a weak thunderstorm will be seen from early afternoon to the early evening hours. Maximum hourly rain rates of 0.3 inches are possible, especially over the Raton Ridge. No flood threat today.

 

Issue Date: 5/13/2016
Issue Time: 9:15 AM

NO FLOOD THREAT IS FORECAST.

High pressure yesterday helped to squeeze moisture out of the state, easily seen in the IPW chart below. As of this morning, all of the four usual reporting stations were below 0.3 inches. This dip in moisture combined with high pressure has kept Colorado dry through this morning, and will into the early afternoon hours. With that said, a quick-moving cool front, with shallow moisture, will race across eastern Colorado today; it has already entered northeast Colorado this morning. The cool front will mainly bring a wind shift through the early afternoon hours. However, as low-level flow becomes increasingly easterly with time, moisture will deepen across eastern Colorado from north-to-south. This will bring isolated showers, and a thunderstorm or two, back into the forecast.

Rain rates will remain light from any activity, owing to the dry nature of the airmass overall and lack of upper-level support. The Front Range, Northeast Plains, and Urban Corridor will see the isolated activity begin first, between 4 and 7 PM. Over time, as the upslope flow develops southward, the Palmer Ridge, Southeast Plains, Southeast Mountains, and Raton Ridge will get involved during the evening and overnight hours. Otherwise, over the rest of the High Country, today and tonight will be marked by mostly sunny/clear skies with only some high-based clouds/virga over the higher terrain.

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, Northeast Plains, Raton Ridge and Southeast Plains:

Mostly sunny and dry for most, with only a few isolated showers/storms creeping back into the forecast later this afternoon and through the overnight hours. Rain rates will remain low at 0.05-0.1 inches/hour.

Timing for Urban Corridor, Northeast Plains: 4 PM – 6 AM
Timing for Palmer Ridge, Southeast Plains, and Raton Ridge: 11 PM – 6 AM

Front Range, Northern Mountains, Central Mountains, and Southeast Mountains:

Mostly sunny and dry for most, especially in the lower valleys. Isolated showers/storms are expected over the higher terrain, with the Front Range and Southeast Mountains holding the best relative chance of the four regions. For the Central Mountains, only the easternmost peaks will have a shot at an isolated shower or two. Rain rates will remain low at 0.05-0.1 inches/hour.

Timing for Front Range: 4 PM – 6 AM
Timing for Northern Mountains: 6 PM – 10 PM
Timing for Central Mountains and Southeast Mountains: 10 PM – 5 AM

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

Mostly sunny and dry, with only a few high-based clouds hanging around the higher terrain. Some virga and gusty winds may result from those clouds, but no precipitation is expected.