Issue Date: June 10th, 2015
Issue Time: 10:55 AM (Updated 3PM)

— Moderate flood threat for Palmer Divide and parts of Northeast Plains
— Low flood threat for Northeast Plains, Urban Corridor, Front Range, parts of Palmer Ridge and parts of Southeast Plains
— Low flood threat for Central Mountains, Northern Mountains, parts of Grand Valley and parts of San Juans
— Low flood threat for parts of Arkansas and South Platte River

Afternoon update: Active period from 3PM-8PM across the Urban Corridor and most of Eastern Colorado as disturbance moves eastward off the higher terrain. All Flood threats maintained, plus Low flood threat added for Southeast Plains. Activity expected to subside after sunset.

An active weather day is on tap for many across Colorado. Surface dew points this morning are in the 50s across many lower elevation locations. Precipitable water values are at or above 1 inch at Pueblo, Grand Junction and Boulder. Moist upslope flow is present for many east of the Divide. The water vapor image, below, shows additional critical information. First is the presence of an upper-level low to the west. Though this feature is still far away, it will send off several disturbances that will promote periods of upward motion throughout the day. On the other hand, one important negative factor is a large swath of extremely dry upper-level air noted across Arizona and western parts of Mexico. This airmass will try to impede northeastward into Colorado, but will have to compete with thunderstorms sending large amounts of moisture upward. We expect the upper-level drying to provide a cap on the heavy rainfall threat across a large portion of southeast Colorado.

For today, we expect ongoing shower and thunderstorm activity to continue both west and east of the Divide. Over the higher terrain, rainfall on top of the snowmelt will continue to support a Low flood threat. Meanwhile, farther east, thunderstorm activity will have access to more moisture, allowing for a heavier rainfall threat. Of particular concern today is the northern parts of the Palmer Ridge, where rainfall up to 2 inches per hour will be possible. A Moderate flood threat has been issued here.

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 and Palmer Divide

Mostly cloudy skies this morning with intermittent sunshine through the early afternoon. Showers and weak thunderstorms are ongoing this morning, but rain rates will be at or below 0.5 inches per hour. By early afternoon, expect stronger thunderstorms to arrive from the west. The strongest storms will produce 1-hour rain rates up to 2 inches, and 3-hr rain rates up to 3 inches. A Moderate flood threat has been posted for parts of the area, surrounded by a Low flood threat. Isolated hail, up to 1.25 inches will be possible with the strongest cells.

Primetime: 2pm through 10pm for the Moderate threat, 2pm through 2am for the Low threat

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

Partly cloudy skies with isolated to scattered showers and thunderstorms developing by early afternoon. Drying aloft will translate to the surface and limit rain rates to about 0.6 inches per hour.

Primetime: 2pm through 8pm

Central Mountains, Northern Mountains:

Mostly cloudy skies with scattered to widespread showers and thunderstorms continuing throughout the day. Hourly rain rates up to 1.0 inch will be possible, which combined with the remaining snowmelt, warrants a Low flood threat.

Primetime: 1pm through 9pm

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

Mostly cloudy with numerous showers and thunderstorms continuing through the early evening before moving off to the east. Hourly rain rates up to 0.9 inches will be possible. Snowmelt is also ongoing across the higher terrain. The combination of the two warrants a Low flood threat mainly for the central and southern areas.

 

Primetime: 11am through 8pm

Issue Date: 6/9/2015
Issue Time: 10:00 AM

VARIOUS LOW FLOOD THREATS HAVE BEEN ISSUED ACROSS WESTERN COLORADO FOR SNOWMELT AND RUNOFF. CHECK THE FLOOD THREAT MAP BELOW FOR DETAILS.

A LOW FLOOD THREAT CONTINUES FOR PORTIONS OF THE CACHE LA POUDRE, SOUTH PLATTE, AND ARKANSAS RIVERS.

Mid- and Upper-Level high pressure ridging will continue to be in place over Colorado today, leading to another day of limited showers and thunderstorms. There will be a bit more activity than yesterday, thanks to the return of *some* moisture and weaker subsidence aloft, but overall it should be another pleasant day. The higher terrain of the Front Range, Central Mountains, and Northern Mountains will be the main focus for isolated showers and thunderstorms this afternoon/evening, but a couple of storms will also be possible across the Urban Corridor, Northeast Plains, Palmer Ridge, and Raton Ridge. With very little instability and a lack of upper-level support, showers and thunderstorms will be of the garden variety, producing mainly gusty winds and brief light-to-moderate rainfall.

Changes are on the way, though, as the high pressure ridging slides east of the state tonight and an increase in moisture will move in from the southwest. The increased moisture (remnants of former-Hurricane Blanca) will be fed into Colorado thanks to an approaching low pressure system from the west (red “L” on the water vapor image below). The low pressure system is slow-moving because it hasn’t become entrenched with the approaching upper-level trough over the Pacific, so there aren’t big changes coming tonight. It will take a bit longer for the direct effects of the system to be felt. Instead, the increase in moisture will feed an increase in clouds/showers during the late afternoon and evening hours tonight across the Southwest Slope, San Juan Mountains, and Grand Valley. Heavy rainfall is not expected from any showers, but rather this is the precursor to the main event coming over the next few days.

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:

Mostly sunny and warm, with temperatures climbing higher than yesterday. A few isolated, afternoon/evening showers and thunderstorms cannot be ruled out, but will most likely occur near enhanced terrain, such as the Palmer Ridge, Raton Ridge, and Cheyenne Ridge.

Rain rates will generally be 0.2-0.4 inches/hour, but a stronger storm or two will be able to produce rain at 0.5-0.7 inches/hour.

Timing: 2 PM – 9 PM

Front Range, Northern Mountains, Northwest Slope, Central Mountains:

Mostly sunny early, becoming partly sunny during the afternoon as isolated showers and weak thunderstorms develop over the ridge tops. Heavy rainfall is not expected from any activity, as rain rates will be in the 0.2-0.4 inches/hour range. Expect activity to diminish quickly around sunset.

Timing: Noon – 9 PM

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

Mostly sunny and warm, with a few isolated showers and weak thunderstorms possible over the San Juan Mountains and Southeast Mountains this afternoon/evening thanks to favorable southwest flow. Moisture will begin to increase from the southwest during the late afternoon/evening and continue through the overnight, leading to increasing clouds and a few showers over the higher terrain.

Timing: 2 PM – 9 PM, with a few showers overnight as moisture encroaches further into the state from the southwest.

Issue Date: 6/8/2015
Issue Time: 10:11 AM

VARIOUS LOW FLOOD THREATS HAVE BEEN ISSUED ACROSS WESTERN COLORADO FOR SNOWMELT, RUNOFF, AND THE WEST SALT CREEK LANDSLIDE AREA. CHECK THE FLOOD THREAT MAP BELOW FOR DETAILS.

A LOW FLOOD THREAT CONTINUES FOR PORTIONS OF THE CACHE LA POUDRE, SOUTH PLATTE, AND ARKANSAS RIVERS.

A much drier day is in store for today, and just typing those words feels like a sigh of relief. The moisture remnants of former Hurricane Andres have moved on to the east as high pressure ridging has built in over the west. Two separate high-pressure ridges are noted in the water vapor image below; one centered over the Pacific NW, the other over SW Texas/Mexico. These two high pressure regions will phase together as the day progresses, placing Colorado under broad-scale subsidence and a much drier air mass. Additionally, surface high pressure continues to build across the state, and this is good news if you are looking for a pleasant day.

As is the case nearly every day in Colorado, the whole story cannot be explained by the large-scale conditions. Instead, the forecast must account for the impacts of terrain and residual moisture left behind by previous day’s storms. Due to this, isolated showers and weak thunderstorms are expected over the higher terrain, with a few moving over adjacent low elevations thanks to westerly flow aloft. The further away from the mountains and their orographic influences, the less the chances become for any activity.

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:

Mostly sunny skies and warm temperatures will make for a pleasant Monday. High clouds will increase over the Urban Corridor this afternoon and evening as remnants of higher terrain activity is blown over the area. A couple of showers and weak thunderstorms will attempt to move off of the higher terrain and over adjacent lower elevations, mainly across the Urban Corridor and western portions of the Palmer Ridge. The Northeast Plains will stay dry overall, but the portions of the Southeast Plains that are adjacent to the Southeast Mountains and Raton Ridge will hold a chance for an isolated shower/thunderstorms moving overhead off of the higher terrain this afternoon/evening.

Rain rates will generally be 0.2-0.4 inches/hour, with a potentially stronger storm producing maximum rain rates of 0.6-0.8 inches/hour.

Timing: 3 PM – 10 PM

Front Range, Northern Mountains, Northwest Slope, Central Mountains, San Juan Mountains, Raton Ridge, and Southeast Mountains:

Isolated showers and weak thunderstorms are expected over the ridge tops to break up the otherwise mostly sunny skies. A few showers/weak thunderstorms will move overhead of the adjacent lower valleys, but they will diminish quickly with the loss of orographic support.

The Raton Ridge may see a strong-to-severe thunderstorm or two this afternoon/evening, but otherwise thunderstorms will be garden variety.

Rain rates will generally be 0.2-0.4 inches/hour, but stronger storms over the Raton Ridge will potentially produce 0.6-0.8 inches/hour.

Timing: 11 AM – 10 PM

Grand Valley, San Luis Valley, and Southwest Slope:

Mostly sunny and warm will be the name of the game today, as the lower elevations across these region will not support any shower or thunderstorm activity. The only location with a chance of an isolated shower or two will be over the higher terrain in eastern portions of the Grand Valley Region.

Issue Date: 6/7/2015
Issue Time: 10:24 AM

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

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

A LOW FLOOD THREAT CONTINUES DUE TO ACTION-TO-MINOR STAGE FLOODNG FOR PORTIONS OF THE ARKANSAS RIVER, SOUTH PLATTE RIVER, AND CACHE LA POUDRE RIVER.

The upper-level pattern has remained relatively unchanged as the blocking high pressure ridge continues across the central US, keeping southwest flow over Colorado. Making a difference in the pattern is the high pressure ridging building in over the Pacific Northwest, which is helping to elongate/shear the upper-level low that has been responsible for the active period the last few days. This trough will migrate eastward and exit the region soon, but in the meantime, Colorado is left with another day of active weather. With that said, however, the introduction of drier air from the southwest today will help to limit storm coverage slightly.

At the surface, a weak front has pushed southward across eastern Colorado, and is now oriented along an East-West line from near Pueblo through Lamar. This has reinforced low-level moisture north of the front, and will provide for another day of strong-to-severe storms east of the mountains, capable of producing heavy rainfall.

The dry air from the southwest will make a bigger impact west of the Continental Divide, leading to slightly higher based storms that will produce rain less efficiently than yesterday. Residual moisture and orographic lift will still be favorable for a few stronger thunderstorms to develop, mainly over the San Juan Mountains where shear and upper-level support will be best. For more details, jump to the Zone-Specific forecasts below the map.

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

Scattered showers and thunderstorms expected this afternoon and evening, a few will become severe. Even though deep moisture has been lessened overall, the passing cool front has reinforced low-level moisture across the area. This will allow a few stronger storms to produce heavy rainfall, with maximum rain rates of 1.2-2.0 inches/hour. Storm motions will mitigate some of the flooding concern, but locations have received heavy rain over the last few days. Main concerns for flooding issues will be street flooding in urban areas, rising streams in low-lying areas, and burn scars. Field ponding will also be an issue under heavy rain due to saturated conditions.

Timing: 11 AM – 9 PM will be primetime, with showers and thunderstorms diminishing overnight from north to south.

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

Scattered showers and thunderstorms are expected this afternoon and evening, diminishing quickly just after sunset. With moisture less than yesterday, storms will be less efficient at producing heavy rainfall, though brief heavy rain will still be a threat with stronger thunderstorms. The main concern for flash flooding issues will be the San Juan Mountains and Southwest Slope regions for reasons described above. Additionally, with rising temperatures causing snowmelt, streams are already running a bit high and will likely respond quicker to any rainfall.

Maximum rain rates will not be particularly high at 0.4-0.8 inches/hour. Flash flooding concerns stem mainly from antecedent conditions.

Timing: 11 AM – 8 PM, quickly diminishing thereafter.