Issue Date: Sunday, June 14th, 2015
Issue Time: 10:20 AM

— Moderate flood threat for Urban Corridor for early evening through 3AM
— Low flood threat for the Front Range, Northeast Plains, Palmer Ridge, Southeast Plains, Southeast Mountains, Raton Ridge, San Juans and parts of Central Mountains

A potentially volatile weather situation is at hand today. The setup for today is shown by the visible satellite imagery below. During most of the day, we expect the weather to evolve in a similar fashion to yesterday. Scattered thunderstorms will develop across the higher terrain, mainly along and east of the Continental Divide and then spread east across the Plains. A few of these cells will have the potential to dump very heavy rainfall, warranting a widespread Low threat area. However, things may turn interesting later in the evening as high-resolution model guidance suggests a very moist airmass will quickly push into the Northeast Plains (see satellite image below). It appears that there will be a window of time, from around sunset through 1AM where at least scattered thunderstorm activity will be likely in the Northeast Plains and Urban Corridor region. Looking at the heavy rainfall checklist suggests one hour rain rates up to 2.5 inches will be possible. A Moderate flood threat has been issued for this area for the late evening and nighttime hours. The storms are expected to subside before sunrise 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.

Zone-Specific Forecasts

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

Isolated to scattered thunderstorms developing by early afternoon. Most storms will be weak and will not bring much rainfall. However, a few storms will produce rain rates up to 0.8 inches per hour, warranting a Low flood threat across southern portions of the region. In general, storm coverage and intensity will be higher in the south. Fire burn areas are especially vulnerable.

Prime time: 1pm through 8pm

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

Mostly sunny this morning, with high elevation thunderstorms quickly forming by noon. Coverage will be isolated to scattered during the day. Most storms will yield 0.5 inches of rainfall or less, but a few stronger storms will be capable of very heavy rainfall, up to 2.2 inches per hour. In the evening, a moist airmass will come in from the east and allow a 4-6 hour window of very heavy rainfall potential, up to 2.8 inches per hour. Street flooding will be likely, as well as stream flooding given high flows to begin with. A Moderate flood threat has been posted for the Urban Corridor, while a Low flood threat is in effect elsewhere.

Primetime: 1PM through 3AM for the Low threat, 8PM through 3AM for the Moderate threat

Southeast Plains, Southeast Mountains and Raton Ridge:

Sunny early, with isolated to scattered storms forming by early afternoon. Most cells will be light rainfall producers, but a few isolated cells will be capable of up to 2.2 inches per hour. A Low flood threat is in effect.

Primetime: 1PM through 9PM

Issue Date: June 13th, 2015
Issue Time: 10:00 AM

— Low flood threat for San Juan Mountains, Front Range, Palmer Ridge, Southeast Mountains and Raton Ridge
— Low flood threat for the South Platte River from Greeley through Fort Morgan

Several days ago, the forecast for Saturday looked mostly dry. But alas, summer weather in Colorado can quickly change on a day-to-day basis. The last piece of the disturbance that has given the state active weather since Wednesday remains positioned over the state this morning, as shown by the water vapor imagery below. Low-level moisture remains high statewide, with dewpoints in the 40s west of the Divide, and 40s/50s east of the Divide. Precipitable water has fallen to 0.6 to 0.8 inches, implying most of the drying in the past day has been in the mid and upper atmosphere.

For today, we expect the mostly clear skies this morning to quickly fill with puffy cumulus clouds. Over the higher terrain, these clouds will quickly lead to thunderstorms shortly afternoon noon. In fact, there are already several isolated thunderstorms seen on radar and satellite data this morning, a testament to the primed state of the atmosphere. We do not expect very high storm coverage today, but there will likely be a storm, or even several, that will be capable of producing very heavy short-duration rainfall. For this reason, combined with the expectation of many hikers headed to the higher elevations, a Low flood threat has been posted for the Front Range down through the Southeast Mountains, as well as the San Juans. Hikers: if you see lightning, head down to lower elevations immediately! A summertime storm can go from an innocent cumulus cloud to a flash flood producer in 30 minutes.

Otherwise, the South Platte River remains under a Low flood threat, but we have trimmed the threat area to the stretch from Greeley through Fort Morgan.

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

Mostly sunny early, with isolated to scattered thunderstorms developing by noon. Most storms will be weak and may not even yield any rainfall. However, some storms will produce rain rates up to 0.8 inches per hour, warranting a Low flood threat across southern portions of the region. In general, storm coverage and intensity will be higher in the south. Fire burn areas are especially vulnerable.

Prime time: 12pm through 8pm

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

Mostly sunny this morning, with high elevation thunderstorms quickly forming by noon. Coverage will be isolated to scattered, and most storms will be light rainfall producers. However, several isolated cells will be capable of very heavy rainfall, up to 0.7 inches in 30 minutes and 1 inch per hour. A Low flood threat has been posted over the higher terrain and adjacent foothills.

Primetime: 1pm through 9pm

The disturbance responsible for three days of active weather across Colorado has now split into two, as shown by the water vapor image below. Although as a whole the system is weakening, it will give us at least one, if not two, more days of active weather. However, the good news is that the coverage of heavy rainfall is expected to decrease noticeably today. Nonetheless, abundant moisture content, with dewpoints still in the 50s and precipitable water around 1 inch, will support heavy rainfall mainly over southeast Colorado.

For today, we expect the ongoing rainfall over the Palmer Ridge to rapidly lighten and decrease in coverage as the supporting disturbance leaves the state. However, as shown by the water vapor imagery, a low-level circulation remains intact over southeast Colorado. This disturbance will allow for the early development of thunderstorms. Adequate instability and slow, erratic storm motion will once again result in short-term very heavy rain rates. A Moderate flood threat has been posted for the Southeast Plains with a Low flood threat over the San Juans. All activity is expected to diminish shortly after sunset.

Yesterday’s heavy rainfall has once again elevated the South Platte and Arkansas Rivers into Minor flood stage. We anticipate it will take at least several days before the rivers begin to lower.

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, Urban Corridor, Northeast Plains, Northern Mountains, Northwest Slope:

Variable cloudiness and cool with showers ending by early afternoon. Additional shower activity and a weak thunderstorm cannot be ruled out, but rain rates are expected to remain below 0.8 inches per hour. No flooding is expected. Many streams and rivers are bankfull, so please monitor NWS forecasts for local hydrologic information.

Palmer Ridge, Southeast Plains, Southeast Mountains, Raton Ridge:

Partly cloudy early, with thunderstorms developing by early afternoon and lasting into the early evening. Short-term very heavy rainfall is likely, with 30 minute rain rates up to 1.7 inches, 1-hr: 2.25 inches and 3-hr: 3 inches. Flash flooding will be likely with the strongest cells, as are debris slides and mud flows. A Moderate flood threat is in place.

Primetime: 1pm through 9pm

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

Partly cloudy early, with scattered showers and thunderstorms developing by early afternoon. Coverage and intensity will highest in the south. One hour rain rates up to 0.9 inches possible, leading to isolated flash flooding. Fire burn areas are particularly vulnerable. A Low flood threat is in place for parts of the area.

Primetime: 1pm through 8pm

Issue Date: June 11th, 2015
Issue Time: 10:25 AM

— Moderate flood threat for Front Range, Urban Corridor, Palmer Ridge, parts of Northeast Plains, parts of Southeast Plains
— Low flood threat for remaining part of the state except San Luis Valley and extreme northeast

NOTE: Depending on how weather conditions progress, there may be an update to the flood threat by 3pm today. Of special interest will be the potential continuation of flood threat into the overnight hours for the Southeast Plains.

The upper-level that has been causing an active stretch of weather is finally knocking on our door. This is shown by the water vapor image, below. While the center of circulation is over Nevada and Utah, a disturbance is noted on the Colorado / Utah border. This disturbance is already sparking off shower and thunderstorm activity over the Northwest Slope. Meanwhile, conditions near the surface remain very moist for the entire state. Dewpoint temperatures are in the 50s to near 60, while precipitable water values continue to run high, at or above 1 inch for Boulder, Pueblo and Grand Junction alike. The water vapor imagery also shows the continuing presence of the very dry air aloft. However, this air is expected to scoot south and east, out of the state, and it will only minimally impact storm activity. Finally, surface observations depict an impressive cool front, by summer standards, over eastern WY and western NE.

Today, we expect thunderstorm activity to quickly ramp up statewide, with action generally beginning in the north and then progressing south and eastward. The aforementioned cool front will play a very large role in dictating the duration of the heavy rainfall threat. We expect that the cool front will enter the northeast quadrant of the state by mid-afternoon, and beginning to disrupt storm activity. Nonetheless, before the front’s entrance, there will be a 4-5 hour window of very heavy rainfall east of the Divide. A Moderate flood threat has been posted for many areas. West of the Divide, thunderstorm activity will be slightly less potent but still capable of producing short-term heavy rainfall. A Low flood threat is posted here.

While the main flood threat today will subside after sunset, lighter rainfall will continue, especially east of the Divide into the night time hours. Rain rates are expected to remain below 0.5 inches per hour, limiting the flood threat.

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

Partly cloudy skies with thunderstorms developing by early afternoon. Activity will start in the north and quickly spread southward. One hour rain rates up to 2.4 inches will be possible and 3-hour rain rates up to 3.5 inches. Storm motion is expected to be slowest along the foothills, with faster motion away from the mountains. Over and south of the Palmer Ridge, storms will also be capable of producing hail up to 1.5 inches and wind gusts up to 60 mph. A Moderate flood threat is in place for a majority of the area, with a Low flood threat elsewhere. The strongest activity will subside shortly after sunset, but moderate rainfall, up to 0.7 inches per hour, is possible through midnight.

Primetime: 1pm through 9pm for the Moderate, 12pm through midnight for the Low.

Central Mountains, Northern Mountains:

Mostly cloudy skies with showers and thunderstorms developing by early afternoon. One hour rainfall up to 1inch per hour is possible. This, combined with remaining snowmelt warrants a Low flood threat through the late evening hours. Debris slides and mud flows will be possible in the vicinity of stronger storms.

Primetime: 12pm through 8pm

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

Partly to mostly cloudy with numerous showers and thunderstorms continuing through the early evening. One hour rainfall up to 1.25 inches possible, resulting in localized flash flooding, debris flows and mud slides. A Low flood threat is in place for all except the San Luis Valley.

Prime time: 11am through 8pm