Issue Date: 6/03/2015
Issue Time: 10:20 AM (Updated: 1:26 PM)

UPDATE: EXTENDING THE LOW FLOOD THREAT UNTIL 8 AM TOMORROW MORNING.

Moist, upslope flow will likely continue tonight over the low flood threat area as the surface low remains over SW KS/SE CO. This will maintain moisture convergence into NE Colorado into the overnight hours. Uncertainties exist regarding placement of the low level jet and associated convergence axis, but it is likely that a few thunderstorms capable of heavy rain will be ongoing after midnight across the Northeast Plains and Palmer Ridge. These storms will be capable of producing rain rates of 1-2 inches/hour, large hail, and strong winds. Be sure and stay up-to-date on the evolving weather scenario with your local NWS office for all watches and warnings. Updates have been added to the Zone-Specific forecast, as well.

A LOW FLOOD THREAT IS FORECAST FOR THE URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, AND PORTIONS OF THE FRONT RANGE AND SOUTHEAST PLAINS. A LOW FLOOD THREAT CONTINUES FOR PORTIONS OF THE CACHE LA POUDRE AND SOUTH PLATTE RIVERS.

Today’s forecast is a tale of two different environments, thanks to a few factors: a surface “low,” moist, upslope flow, and dry mid- and upper-level air. All of these factors are easy to pick out in the visible imagery below. The moisture being brought in by the easterly, upslope flow is confined to the lower levels, with westerly winds and dry air existing above ~ 750 mb. Due to this, the moisture is confined east of the mountains and north of the surface low, which really sets up a defined boundary for thunderstorm development during this forecast period. For locations without the low-level moisture (west of the Continental Divide and south of Highway 50), the weather will be dry and warm, underneath mostly sunny skies.

The area of interest today is for locations along and east of the Front Range and north of Highway 50; this is where the low-level moisture, instability, and shear will reside. Even with the best moisture located in this region, precipitable water values are ~average due to the drier mid- and upper-levels. This means that storms will not be the most efficient at producing heavy rain, and thus, the flood threat will remain low. However, with storm motions not expected to be quick, a slow-moving cell will be capable of producing a heavy amount of rain.

Strong instability and sufficient deep-layer shear will be favorable for supercells producing large hail (1-2 inches in diameter) and damaging winds (gusts up to 60-70 mph) in the aforementioned area. Low-level flow and strong updrafts will support a tornado threat, as well. Be sure to stay up-to-date on all watches and warning from your local NWS office.

For a look into maximum rain rates and timing of storms, check out 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, Southeast Plains (along and North of Highway 50), and Northeast Plains:

Isolated-to-scattered strong-to-severe thunderstorms are expected, beginning between 1-2 PM over the Front Range, 1-3 PM over the Urban Corridor and Palmer Ridge, 3-5 PM for the Northeast Plains, and 2-5 PM for the Southeast Plains. The regions that will receive the greatest relative coverage of storms will be the Urban Corridor, Palmer Ridge, and Northeast Plains. Maximum rain rates will be in the 1.75-2.25 inches/hour range for the Urban Corridor, Palmer Ridge, and Northeast Plains; 0.6-1.0 inches/hour for the Front Range; and 0.6-1.2 inches/hour for the Southeast Plains.

Traffic in the Urban Corridor will likely be impacted by any strong-to-severe storm with the threat of heavy rain and large hail, especially between the hours of 3 PM and 8 PM. This will be important to monitor for the afternoon/evening commute.

Thunderstorms will end from west to east as they continue to push eastward into NE and KS.

The latest observations and trends warrant an update to the forecast. Moisture continues to stream in northeastern Colorado, and it is likely that this will continue through the overnight as the surface low stalls over SW KS/SE CO. This means that a few thunderstorms capable of heavy rain will be ongoing after midnight across the Northeast Plains and Palmer Ridge. These storms will be capable of producing 1-2 inches/hour rain rates, large hail (1-1.5 inches in diameter), and strong winds.

Northern Mountains, Northwest Slope, Central Mountains, San Juan Mountains, Grand Valley, San Luis Valley, Southwest Slope, Southeast Mountains, Raton Ridge, and Southeast Plains (south of Highway 50):

It will be a warm and sunny day across these regions as dry air rules the forecast. High temperatures will be a few degrees above normal; very pleasant for any outdoor activities you may have planned. As the surface low moves east this evening, an isolated shower/weak thunderstorm cannot be ruled out near the CO/KS border for the Southeast Plains, but chances look slim. Otherwise, a clear night is on tap.

Issue Date: 6/03/2015
Issue Time: 10:20 AM

A LOW FLOOD THREAT IS FORECAST FOR THE URBAN CORRIDOR, PALMER RIDGE, NORTHEAST PLAINS, AND PORTIONS OF THE FRONT RANGE AND SOUTHEAST PLAINS. A LOW FLOOD THREAT CONTINUES FOR PORTIONS OF THE CACHE LA POUDRE AND SOUTH PLATTE RIVERS.

Today’s forecast is a tale of two different environments, thanks to a few factors: a surface “low,” moist, upslope flow, and dry mid- and upper-level air. All of these factors are easy to pick out in the visible imagery below. The moisture being brought in by the easterly, upslope flow is confined to the lower levels, with westerly winds and dry air existing above ~ 750 mb. Due to this, the moisture is confined east of the mountains and north of the surface low, which really sets up a defined boundary for thunderstorm development during this forecast period. For locations without the low-level moisture (west of the Continental Divide and south of Highway 50), the weather will be dry and warm, underneath mostly sunny skies.

The area of interest today is for locations along and east of the Front Range and north of Highway 50; this is where the low-level moisture, instability, and shear will reside. Even with the best moisture located in this region, precipitable water values are ~average due to the drier mid- and upper-levels. This means that storms will not be the most efficient at producing heavy rain, and thus, the flood threat will remain low. However, with storm motions not expected to be quick, a slow-moving cell will be capable of producing a heavy amount of rain.

Strong instability and sufficient deep-layer shear will be favorable for supercells producing large hail (1-2 inches in diameter) and damaging winds (gusts up to 60-70 mph) in the aforementioned area. Low-level flow and strong updrafts will support a tornado threat, as well. Be sure to stay up-to-date on all watches and warning from your local NWS office.

For a look into maximum rain rates and timing of storms, check out 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, Southeast Plains (along and North of Highway 50), and Northeast Plains:

Isolated-to-scattered strong-to-severe thunderstorms are expected, beginning between 1-2 PM over the Front Range, 1-3 PM over the Urban Corridor and Palmer Ridge, 3-5 PM for the Northeast Plains, and 2-5 PM for the Southeast Plains. The regions that will receive the greatest relative coverage of storms will be the Urban Corridor, Palmer Ridge, and Northeast Plains. Maximum rain rates will be in the 1.75-2.25 inches/hour range for the Urban Corridor, Palmer Ridge, and Northeast Plains; 0.6-1.0 inches/hour for the Front Range; and 0.6-1.2 inches/hour for the Southeast Plains.

Traffic in the Urban Corridor will likely be impacted by any strong-to-severe storm with the threat of heavy rain and large hail, especially between the hours of 3 PM and 8 PM. This will be important to monitor for the afternoon/evening commute.

Thunderstorms will end from west to east this evening as they continue to push eastward into NE and KS.

Northern Mountains, Northwest Slope, Central Mountains, San Juan Mountains, Grand Valley, San Luis Valley, Southwest Slope, Southeast Mountains, Raton Ridge, and Southeast Plains (south of Highway 50):

It will be a warm and sunny day across these regions as dry air rules the forecast. High temperatures will be a few degrees above normal; very pleasant for any outdoor activities you may have planned. As the surface low moves east this evening, an isolated shower/weak thunderstorm cannot be ruled out near the CO/KS border for the Southeast Plains, but chances look slim. Otherwise, a clear night is on tap.

Issue Date: 6/02/2015
Issue Time: 10:45AM MDT

—Low flood threat for parts of Northeast Plains

It is no secret that most of the state had a very wet May. Part of this rainfall percolated deep into the soils and is now being called back up through evaporation. Partly as a result of this, dewpoints east of the Continental Divide are very high this morning: in the 50s to low 60s. Typically, this may be the first sign of an impending heavy rainfall threat. However, this morning there is a clash between very dry middle and upper-level air to the west and a moist low-level air to the east, as shown by the water vapor image. In addition, the image shows that the ridge of the past few days has scooted east, and is being replaced by an approaching upper-level low.

Today will mark a transition day. The moist air is expected to be eroded by drier air by early afternoon. This is confirmed by this morning’s soundings at Denver and Grand Junction as well as low precipitable water values of 0.2 to 0.4 inches. However, a weak overhead disturbance is expected to fuel isolated to scattered thunderstorms for the very far northeast corner of the state. Those storms will have access to very large instability and moisture, and will be capable of producing rain rates up to 2.5 inches per hour. A Low flood threat has been posted for parts of the Northeast Plains for localized flash flooding.

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

Northeast Plains:

Sunny early, then turning partly cloudy. Isolated to scattered thunderstorms forming in the far northeast corner. Hourly rain rates up to 2.5 inches possible, along with hail up to 1.5 inches and wind gusts to 60 mph. A Low flood threat has been posted.

Primetime: 3pm through 8pm

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

Mostly sunny, warm and dry with temperatures rising into the 80s to near 90F. No flood threat is expected today.

Northern Mountains, Central Mountains, San Juan Mountains, Front Range, Urban Corridor, Northeast Plains, Palmer Divide, Southeast Plains, Southeast Mountains, Raton Ridge:

Mostly sunny with a few afternoon clouds possible. Much drier todays with dewpoints falling into the 10s and 20s, and perhaps even lower for some high elevation areas. No flooding is expected today.

Issue Date: 6/01/2015
Issue Time: 10:15 AM

NO FLOOD THREAT IS FORECAST.

The first day of Meteorological Summer will feature an early summer-like day, and the water vapor image below tells that story well. The upper-level high pressure ridge (marked by the blue “H”) is currently situated over the Central/Southern Rockies and will shift eastward today as the upper-level low (red “L”) continues to push in over the Pacific Northwest. As the ridge slides east, flow aloft will become more west/southwesterly, bringing in warmer, drier air from the west/southwest.

Aside from the usual orographic culprit producing isolated showers/thunderstorms over the higher terrain, the main feature of the day that will interrupt the sunshine is the embedded weak disturbance (black line). This disturbance will rotate around the ridge, helping to organize isolated-to-scattered thunderstorms over eastern Colorado this afternoon and evening. While most showers/thunderstorms will remain high-based across the state, it is over the Northeast Plains, Southeast Plains, and Palmer Ridge that storms will tap into more moisture, shear, and instability, giving storms the necessary ingredients to become strong-to-severe. The main threats will be lightning, gusty winds, hail, and brief heavy rain.

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 and Urban Corridor:

Mostly sunny and warm, with isolated-to-scattered showers and thunderstorms expected this afternoon and evening, diminishing quickly after sunset with the loss of daytime heating. Expect storms to be high-based, producing mainly gusty winds and lightning. Rain rates will generally be in the 0.2-0.5 inches/hour range, with storm motions limiting the amount of rainfall potential in any one location.

Timing: Noon – 8 PM

Palmer Ridge, Southeast Plains and Northeast Plains:

Isolated-to-scattered showers and thunderstorms are expected this afternoon and evening, with a few becoming strong-to-severe. Brief, heavy rain will fall from the stronger storms, with maximum rain rates of 2.0-2.5 inches/hour under the strongest storms. However, easterly storm motions will be relatively quick, limiting rainfall potential in any one location, and thus no flood threat will be issued. Gusty winds (greater than 50 mph), hail (greater than 1 inch in diameter), and lightning will be threats with the strongest storms, so be sure and monitor local NWS offices for any warnings associated with these storms.

Timing: 1 PM – Midnight

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

High-based, isolated, weak showers and thunderstorms are expected to develop by 11 AM, continuing through the afternoon, before diminishing quickly after sunset with the loss of daytime heating. The relative “bulk” of the isolated activity will be confined to the higher terrain of the San Juan Mountains, Central Mountains, and Northern Mountains. Showers and thunderstorms will attempt to drift over the lower valleys, but storms that do will diminish quickly without the continued orographic support. Maximum rain rates will be 0.2-0.4 inches/hour, but with dry air expected below cloud bases, the effective rain rates will likely be closer to 0.1-0.3 inches/hour.

Timing: 11 AM – 8 PM