Issue Date: 5/2/2018
Issue Time: 9:05 AM

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

The water vapor imagery below tells a large part of this period’s weather story. The upper-level low, highlighted by the red “L”, and associated trough will swing across the region today, bringing broad support for showers and thunderstorms nearly statewide. An attendant surface low-pressure center will also develop over the Southeast Plains, which will force upslope flow across the Northeast Plains, Urban Corridor, and into the Front Range – this is the one of the driving mechanisms behind today’s low flood threat.

Overall, it is going to be a day of widespread precipitation across Colorado, with higher elevation snow (above 9000-10,000 feet) combining with lower elevation showers and thunderstorms. A couple severe storms are expected to rumble across the Northeast Plains, where better instability and moisture will be in place. The low flood threat is of the long-duration, moderate rainfall variety, with a few stronger thunderstorms sprinkled in. Upslope flow, good moisture, and multiple rounds of rainfall are the driving force, and more specifics regarding timing and rain rates will be laid out in the zone-specific forecast discussions below.

For the far Southeast Plains, specifically Baca County and eastern portions of Las Animas County, rainfall will be hard to come by as the low-levels will remain too dry. In fact, Red Flag Warnings are in place for these areas this afternoon and evening due to the expected dry and windy conditions.

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, and Northeast Plains:

Scattered-to-widespread showers and thunderstorms are expected throughout the period, producing periods of moderate rainfall, gusty winds, and small hail. A few strong-to-severe thunderstorms are expected east of I-25, and mainly over the Northeast Plains region. The main threat from these stronger storms will be hail up to 1.25 inches in diameter, brief periods of heavy rain, and strong winds up to 40-50 mph. The snow-level will spend much of the day between above 11,000 feet, dropping to around 9,000-10,000 feet overnight. While it won’t rain/snow constantly during the entire period, expect several rounds of precipitation, especially over/near the mountains, with more scattered thunderstorms over the plains. Maximum rain rates are as follows:

Front Range: 0.25-0.5 inches/hour
Urban Corridor: 0.5-0.8 inches/hour
Palmer Ridge: 0.5-1.0 inches/hour
Northeast Plains: 1.0-1.25 inches/hour

Timing: 11 AM – 11 AM

Raton Ridge and Southeast Plains:

While there is fire danger across Baca County and eastern Las Animas County, these regions will otherwise see scattered showers/thunderstorms during the period. Most rainfall will be of the light-to-moderate variety, as low-level moisture will still lack in these areas. The only area of concern is the recent MM 117 fire burn in El Paso County; this will be its first real rainfall test, so out of caution is should be monitored for any issues that may arise. Rainfall rates will generally be in the 0.05-0.15 inches/hour range, with a few thunderstorms over the better moisture in the northwest portions of the Southeast Plains region being able to produce 0.4-0.6 inches/hour.

Timing: 11 AM – 2 AM, with a few lingering showers into tomorrow morning

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

Scattered-to-widespread showers and a few thunderstorms are expected today, with snowfall above roughly 10,000 feet and rainfall below. Most of the activity will occur over the higher elevations, where upslope flow will drive more persistent activity in an otherwise transient storm regime. Locations below 10,000 feet will generally pick up on anywhere from a trace-to-0.25 inches of rainfall, with higher totals up to 1.0 inches or so expected where rainfall is most persistent. Above 10,000 feet, snowfall will result in liquid equivalence of anywhere from 0.5-2.5 inches, with the highest peaks generally receiving the most. As usual, the San Luis Valley will receive the least amount of rainfall, picking up on maybe 0.1 inches total. Overall, maximum rainfall rates will be in the 0.2-0.5 inches/hour range.

Timing: 11 AM – 11 AM

Issue Date: 5/1/2018
Issue Time: 9:20 AM

Welcome back to the 2018 FTB season. We look forward to another successful season serving you.

NO FLOOD THREAT IS FORECAST.

It is only fitting that Mother Nature would welcome the FTB back with a day of weather that ranges from fire weather conditions to showers/thunderstorms, and even a severe storm or two. In the infrared imagery below, we can gather a bit of information on why unsettled weather is in the forecast. The upper-level trough axis, denoted by the red-dashed line, will swing towards the east/northeast today, with a jet streak (denoted by the yellow-dashed region) that will nose into Colorado, providing upper-level support for showers/thunderstorms across the high country and northeast Colorado.

Generally speaking, the activity over the much of the high country will be in the form of garden variety showers, producing mainly gusty winds and periods of light rainfall. The exception to this will be over the Front Range, where an isolated thunderstorm or two will produce lightning, gusty winds, and a brief period of moderate rainfall. Out over the Urban Corridor and Northeast Plains, scattered showers and thunderstorms are expected, with a couple reaching severe thresholds (strong winds, hail up to 1.25 inches, isolated tornado). More details on the timing and rain rates can be found in the zone-specific forecast discussions below.

For Southeast Colorado, namely the Southeast Plains and Raton Ridge regions, dry and windy conditions will exist, resulting in increased fire danger through today and into the evening hours tonight, before slightly better moisture returns as a cold front moves in from the north and reduces the fire danger risk.

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, and Northeast Plains:

Scattered showers/thunderstorms are expected today/tonight, kicking off just before lunch time (10-11 AM) over the Front Range and then spreading over the Urban Corridor around Noon and then into the Northeast Plains by 1-2 PM. Brief periods of moderate rainfall will occur underneath the strongest storms, but fairly quick storm motions will keep rainfall below flash flood thresholds. Some street/field ponding in poorly drained areas can be expected under the strongest thunderstorms. The peak of thunderstorm coverage will occur during the late afternoon/early evening hours, winding down by the late evening hours, with only isolated activity persisting until midnight. A stray shower or two cannot be ruled out for the morning hours tomorrow. Maximum rain rates are as follows:

Front Range: 0.25-0.5 inches/hour
Urban Corridor: 0.3-0.6 inches/hour
Northeast Plains: 0.75-1.25 inches/hour

Timing: 10 AM – 10 PM for the Front Range, Noon – Midnight for the Urban Corridor, and 1 PM – Midnight for the Northeast Plains

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

Dry conditions are on tap for today, especially for the Raton Ridge and Southeast Plains regions where critical fire danger conditions are expected. A stray shower/weak thunderstorm may impact the Palmer Divide during the evening hours as the cold front pushes southward, but little rain is expected.

Timing: 8 PM – 3 AM for the Palmer Ridge

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

Scattered showers and a few thunderstorms are expected today across the area, with the bulk of afternoon/evening activity expected over the higher terrain of the Northern Mountains, Northwest Slope, Southwest Slope, and Grand Valley regions, with more isolated activity expected over the Central Mountains and San Juan Mountains regions. The Southeast Mountains are expected to stay dry during the afternoon/evening hours.

Overnight, showers will continue, but the regions impacted the most will shift, as scattered showers will exist over the Southwest Slope, San Juan Mountains, and Grand Valley regions, with isolated showers elsewhere as the Southeast Mountains finally get in on the isolated shower activity.

Rain rates will be generally be in the 0.0.5-0.15 inches/hour range, with some pockets of heavier rain pushing the 0.2-0.3 inches/hour range.

Issue Date: Saturday, September 30, 2017
Issue Time: 10:30AM MDT

— Flooding is NOT expected today

NOTE: This is the last scheduled Flood Threat Bulletin of the 2017 season. However, additional Bulletins may be necessary next week to cover the heavy rainfall threat anticipated in southern/eastern Colorado.

A broad upper-level trough continues to be positioned over the western half of the United States, as shown in this morning’s water vapor image, below. Despite the many, rather disorganized smaller-scale features, it is apparent that plenty of upward motion is currently occurring east of the trough’s axis in UT, western CO and northern New Mexico. In fact, showers and isolated weak thunderstorms are already occurring in the San Juan Mountains, showing that the system is bringing plenty of dynamical support. From the standpoint of heavy rainfall, the main limiting threat will once again be moisture, along with fast steering winds. This morning’s Precipitable Water (PW) measurements at Grand Junction and Denver are a rather subdued 0.54 and 0.48 inches, respectively. Higher values approaching 1 inch are found just east of the Colorado border into KS and NE. However, with only a weak easterly component of low-level flow, PW is expected to remain generally steady across the state.

With plenty of dynamical support, we expect a round of numerous to widespread shower and storm activity coinciding with peak heating this afternoon. Highest coverage will be over the higher terrain, mainly west of the Continental Divide. Rain rates are expected to remain well below flood threat thresholds over most of the state. Isolated higher rain rates are possible with storms that come off the Palmer and Cheyenne ridges. However, we expect that even these will stay just below flood threat intensity. Thus, flooding is not expected today. Nonetheless, widespread precipitation totals above 0.25 inches are expected over the central and western part of the state.

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, scroll below the map.

Zone-Specific Forecasts:

Northeast Plains, Southeast Plains:

Mostly sunny this morning then becoming partly cloudy and breezy with isolated to scattered showers and thunderstorms this afternoon and evening. Highest coverage will be over western areas, towards the foothills. Max 1-hour rain rates up to 1.2 inches possible with the strongest storm cells, along with gusty winds up to 55 mph. Flooding is not expected today.

Primetime: 2PM to 9PM

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

Mostly cloudy and cool with numerous shower and weak thunderstorms increasing in coverage this afternoon. Max 1-hour rainfall up to 0.4 inches (north) and 0.7 inches (far south, along NM border). Snow levels 10,000 feet (north) and 11,500 (south). Gusty winds and small hail could accompany the strongest storms. Flooding is not expected today.

Primetime: 11AM to 10PM, with light rain and snow showers continuing overnight

Southeast Mountains, Raton Ridge, Front Range, Urban Corridor, Palmer Ridge:

Mostly sunny this morning, then increasing clouds with scattered to numerous showers and weak thunderstorms developing by early afternoon. Highest coverage will be over the foothills and higher terrain. Max 1-hour rain rates up to 0.75 inches (below 6,000 feet) and 0.6 inches (above 6,000 feet). Snow level will fluctuate around 11,000 feet, lowering later tonight. Gusty winds up to 50 mph and small hail could accompany the strongest cells. Flooding is not expected today.

Primetime: 2PM to 9PM, with light rain and snow showers continuing overnight

Issue Date: Friday, September 29, 2017
Issue Time: 10:30 AM MDT

— Flooding is NOT expected today

As seen yesterday morning, showers over the eastern plains are being supported by the jet stream and mid-level energy rotating around the Low to our northwest. These showers will continue to move to the northeast and exit the state by late this morning. There is quite a bit of fog again this morning in the mountains and Urban Corridors. This should quickly burn off due to breaks in the clouds being more numerous today. Precipitable Water (PW) in Grand Junction was measured at 0.75 inches and has dropped to 0.65 inches in Denver. With more southwesterly flow today, decreases in moisture are expected today. This should make showers and thunderstorms more isolated in nature and limit accumulations.

The Low pressure is currently over the UT/WY border and will continue to move north throughout the day. Shortwave activity associated with the Low will provide enhanced lift one last time for another round of showers and thunderstorms this afternoon. Moisture will continue to retreat east throughout the day, but dew points over the southeast plains and southern mountains will be high enough for moderate rainfall further south. Breaks in cloud cover will allow some instability to build this afternoon, which will increase the possibility for thunderstorms. Isolated showers and thunderstorms are expected to form over the mountains by later this afternoon and move into the adjacent plains this evening. The storms are expected to dissipate as they move off the higher terrains, but brief heavy rain with gusty winds and thunder are possible. Overnight shower activity is not expected, but a few showers may linger over the southern mountains with weak upslope flow. Flooding is not 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, scroll below the map.

Zone-Specific Forecasts:

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

Partly cloudy with some showers over the Northwest Slope. Drier air has allowed breaks in cloud cover over the region. Enough residual moisture and instability is expected for another round of showers and thunderstorms over the higher terrains this afternoon. Highest accumulations are expected over the southern San Juan Mountains; especially further east where moisture hangs on. Max 1-hr rain rates up to 0.5 inches (south) and 0.3 inches (north) are possible with 3-hr totals up to 0.8 inches (south). Flooding is not expected today.

Primetime: 1PM to 9PM

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

Cloudy and foggy this morning with rain over the eastern plains. Showers and thunderstorms likely over the higher terrains this afternoon, although they will be more isolated than the last couple of days. Highest accumulations are expected over the southern Front Range and Southeast Mountains. Max 3-hr rain rates up to 0.8 inches are possible. Showers and thunderstorms will move NE off the higher terrains this afternoon and may briefly produce heavy rain and gusty winds on the adjacent plains before dissipating. Max 1-hr rain rates up to 0.7 inches are possible.

Primetime: 2PM to 11PM