Issue Date: Friday, July 24th, 2020
Issue Time: 11:00AM MDT

— A MODERATE flood threat has been issued for the Northeast Plains, Decker burn area, & 416 burn area
— A LOW flood threat has been issued for the Southwest Slope, San Juan Mountains, Grand Valley, Central Mountains, Northern Mountains, Southeast Mountains, San Luis Valley, Front Range, Urban Corridor, Palmer Ridge, Spring Creek burn area, & Lake Christine burn area

A plume of monsoon moisture can be seen draped across Colorado on the satellite water vapor image today (below) as a high pressure ridge is in place over the central plains of the US, which is continuing to pump moisture northward. This plume of moisture has boosted PW to 1.08 inches at Grand Junction and 1.06 inches at Denver in this morning’s soundings. A closer look at the Grand Junction sounding shows most of the entire depth of the troposphere is nearly saturated. The national radar image this morning shows showers over the western and northern part of the state, indicating some large-scale lift from stronger winds aloft is driving the precipitation. Surface dew points are in the 50Fs and low 60F across much of the state, with the 60Fs along the eastern plains and into the northern Urban Corridor. This low-level moisture is expected to largely remain in place today, which will provide the majority of the fuel for rainfall as clouds and early morning showers will likely cut down on strong surface heating for much of the western part of the state. This will limit the amount of instability over the mountains. Moderate southwesterly upper-level flow will cause storms and showers to track from southwest to northeast across the state today, which will limit the amount of time individual storms will be able to produce rain over an area. However, storms will track over the same locations throughout the day, increasing total 24-hour rain accumulation. As storms develop and track near the northeast corner of the state, heavy rainfall will be possible with the high low-level moisture present there.

Strong instability will not be able to build over much of the mountains today due to increased cloud cover and rain showers, especially over the northwestern corner of the state. However, over the far northeastern plains, higher instability is expected due to increased surface moisture as the lee trough supports moist south-southeasterly winds over the area. This instability, combined with some increased wind shear, could allow some severe thunderstorms to develop over the Northeast Plains. There is also the possibility of storms training in the area, so a Moderate flood threat has been issued. These severe storms could also produce gusty winds and hail.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Southwest Slope, San Juan Mountains, Grand Valley, Northwest Slope, Central Mountains, Northern Mountains, Southeast Mountains, San Luis Valley, Front Range, Urban Corridor, Palmer Ridge, & Northeast Plains:

Showers and thunderstorms will track over the area from southwest to northeast for much of the day and into the overnight hours. This will allow precipitation to train over the same areas for extended periods. Max 1-hour rain rates up to 1 inch are possible where stronger storms can fire (in the clearings), and isolated 24-hour rain totals exceeding 1 inch are likely for the San Juan Mountains, northeastern Central Mountains, western Front Range, and southeastern Northern Mountains. The Lake Christine, and Spring Creek burn areas are also under a Low flood threat due to the abundance of moisture. A moderate flood threat is expected over the Decker and 416 burn areas due to increased likelihood of heavy 24-hour rain totals over 1 inch. If a stronger storm can form over a burn area, flooding of local streams, debris slides, and mud flows would be possible.

A couple severe storms are possible over the Northeast Plains, which could also produce strong winds and small hail. A Moderate flood threat has been issued for the area. Max 1-hour rain rates up to 1.5 inches will be possible. Threats from flooding include road flooding, field ponding, and local stream flooding.

Primetime: 11AM to 6AM

Southeast Plains & Raton Ridge:

Mostly sunny and warm today with high temperatures around 5F above normal. The monsoon moisture and upper-level energy will largely stay north and west of the area, limiting the chances for storms to develop. An isolated thunderstorm along the western Raton Ridge is not out of the question, but rain rates should stay below 0.75 in/hr.

Issue Date: Thursday, July 23rd, 2020
Issue Time: 09:45AM MDT

— A LOW flood threat has been issued for the Southwest Slope, San Juan Mountains, Southeast Mountains, Central Mountains, Grand Valley, Northwest Slope, Northern Mountains, and Front Range, including the 416 burn area

Colorado is situated between a trough along the US West Coast and a high pressure ridge to the east, as seen in the image below, which is allowing continued monsoonal moisture to be pumped northward into Colorado. The shortwave that moved through yesterday has moved north of Colorado (see image below), but the moisture that it brought is lingering across the state. PW from the Grand Junction sounding this morning is sitting at 1.01 inch, which is above the 90th percentile for the date. PW is slightly lower at 0.82 inch in Denver, but still above average. Additionally, dew points are in the low to mid 50Fs in the valleys of western Colorado as well as along the plains east of the Continental Divide. This moisture will allow plenty of instability to build, especially over the mountains. Upper-level southerly flow will generally weaken today, allowing storms to drift slowly northward and increasing the possibility of extended rainfall over areas. Due to the high chance of storms over the mountains, max rain rates up to 1 in/hr, and the potential for rainfall over a prolonged period, a Low flood threat has been issued for portions of the Southwest Slope, San Juan Mountains, Southeast Mountains, Central Mountains, Grand Valley, Northwest Slope, Northern Mountains, and Front Range.

Eastern Colorado will see some scattered thunderstorms develop this afternoon, but flooding is not expected. Dew points east of the Continental Divide are in the 50Fs, but surface moisture will decrease slightly during the day. Southerly winds will prevail over much of the plains of eastern Colorado, which will not be able to transport higher moisture from the east into western parts of the plains. Some isolated thunderstorms may be able to drop some heavy rain in the Southeast and Northeast Plains, but chances for storms are 50/50 today. Temperatures will be near normal east of the Continental Divide.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Scattered thunderstorms will develop by noon over much of the high terrain, with higher chances for storms farther south. Max 1-hour rainfall up to 1 inch is possible over the Southwest Slope and San Juan Mountains, with 0.75 in/hr expected for mountain locations farther north and east. A Low flood threat is expected today over the higher terrain, including the 416 burn scar. Showers will likely linger well into the evening as continued moisture and energy is pumped into southern Colorado, which could boost 24-hour rain totals over the 1 inch mark for much of southwest Colorado.

Primetime: 12PM to Midnight

Northeast Plains, Urban Corridor, Palmer Ridge, Southeast Plains, & Raton Ridge:

Near-normal temperatures and some isolated thunderstorms are possible this afternoon and evening. Max 1-hour rain rates up to 1 inch are possible over isolated locations, but chances for storms are 50/50. The highest chances for storms are over the Palmer and Raton Ridge. Storms will move northeasterly off these ridge locations into the Northeast and Southeast Plains. Flooding is not expected today.

Primetime: 1PM to Midnight

Issue Date: Wednesday, July 22nd, 2020
Issue Time: 9:30AM MDT

— A LOW flood threat has been issued for the Northern, Central, Southeast, and San Juan Mountains as well as portions of the Northwest Slope and Grand Valley. This threat area includes the Lake Christine, Decker, and Spring Creek burn areas.

The flow around a Low, off the coast of California, and a High, over the southern border, are producing a well-defined subtropical moisture plume, which can be seen in the water vapor imagery below. Slight movement in the High has quickly elevated moisture values over western Colorado. This morning’s sounding measured PW at 0.85 inches (red star, right), which is up about 75% from last night! PW is forecast to reach close to an inch by this evening (GEFS plume forecast, right) as the High continues to be slightly displaced to the east by an incoming shortwave embedded in the southwest flow (over western Utah). This moisture and mid-level energy paired with the diurnal, upslope flow will return numerous showers and thunderstorms to western Colorado and the mountains today. Higher amount of rainfall are anticipated over the southern high terrains (including the Southeast Mountains), but the valleys, including the San Luis Valley, should also expect a little rainfall as the storms move off the mountains with the SSE steering flows.

Two factors will affect the rain rates today. The first is the heavy cloud cover over western Colorado, which may limit the area of instability for stronger thunderstorms. The other is a dry boundary layer, which may (initially) cause some extra evaporation of the rainfall. Nonetheless, trailing storms and a few stronger thunderstorms could accumulate totals capable of producing flooding. Thus, a Low flood threat has been issued. The Low flood threat includes the Lake Christine, Decker, and Spring Creek burn areas as rain rates in the area up to 0.50 inches will be possible with the stronger thunderstorms that develop.

Back to the west, surface moisture will begin to mix out over the adjacent plains and drier air will move into the eastern plains as the ridge begins to build overhead. Storm motion may push a couple storms into the immediate adjacent plains, mostly west of the I-25 corridor, but more wind than rain is anticipated with the storms.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

The heavy rainfall threat has shifted back to the west and the mountains. Over the southern mountains (San Juans & Southeast), multiple rounds of rainfall may produce some flooding issues with totals up to 1.25 inches possible by morning. Where the sun can break through and build some instability for stronger thunderstorms, max 1-hour rain rates up to 0.75 inches will be possible. Further north, there is a better chance for some stronger thunderstorms. Max 1-hour rain rates up to 0.75 inches and a quick 0.50 inches in 30-min could cause localized flash flooding issues. Storms up north could also produce small hail and strong outflow winds today. A Low flood threat has been issued for the area, which includes the Lake Christine, Decker, and Spring Creek burn area. The valleys will also likely receive some rainfall today as storms move off the high terrains. Isolated totals up to 0.25 inches are not out of the question.

Primetime: 11AM to 1AM

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

The plains should stay quiet this afternoon with SSE steering winds, general subsidence, and a drying air mass, which will allow temperatures to quickly rise throughout the day. A few storms will be possible over the Front Range near the Divide, and isolated max 1-hour rain rates up to 0.40 inches will be possible with most storms producing, at most, around 0.25 inches. As storms move into the adjacent plains, expect strong outflow winds (up to 45 mph) to develop with a large dew point depression. The elevated regions of the Palmer and Raton Ridge may see isolated totals up to 0.20 inches, but most areas will receive below 0.15 inches.

Primetime: 1:30PM to Midnight

Issue Date: Tuesday, July 21st, 2020
Issue Time: 9:05AM MDT

— A MODERATE flood threat has been issued for the Northeast Plains and Spring Creek burn area
— A LOW flood threat has been issued for the Southeast Mountains, southern Front Range, southern Urban Corridor, western Raton Ridge, Southeast Plains, and portions of the Palmer Ridge

There are some morning showers to start the day over the far Northeast Plains, which are marked in the visible satellite imagery below. A moisture boundary has been pushed back west, and can be seen along the foothills (green dashed line). This has helped increase PW values across the area. Denver’s sounding didn’t quite make it past 12km this morning, but PW was still measured at 0.95 inches with a lot deeper moisture near the surface than the last few days. This should allow for more efficient rain rates this afternoon over the foothills and adjacent plains, rather than the high-based, windy convection we’ve seen the last couple of days. With flow aloft weaker, steering flow over eastern Colorado is also forecast to decrease, which should allow for some heavy rainfall accumulations this afternoon and evening favoring the southern high terrains and Palmer Ridge.

Afternoon surface winds are expected to turn east/southeasterly by early afternoon, and that will help reinforce and increase surface moisture, as well as help produce better shear values than yesterday. Today, a shortwave (orange “X” in WY) will move through the weak northwesterly flow aloft and help spark some widespread showers and thunderstorms over eastern Colorado. This means there will be a chance for some severe thunderstorms this afternoon and evening as storms track southeast. The best chances for a severe storm looks to be along and east of Highway 71. Initially, storms look capped over the Northeast Plains this afternoon, but storms from the north should track into the area by this evening and have no trouble producing some heavy rainfall, large hail, and another round of damaging wind gusts. A Low flood threat has been issued for the southern mountains/adjacent plains, which includes the Decker burn area. The slower steering winds and higher moisture pooled along the foothills also means there is an increased threat for flash flooding, mud flows and debris slides over the Spring Creek burn area. A Moderate flood threat has been issued for the area due to higher confidence 1 to 2-hour rain totals in the area will exceed 0.50 inches.

Back to the west, the best moisture looks to be over Utah and Arizona (the other orange “X”), but some residual moisture is expected to spark another round of high-based storms over the San Juan and eastern Central Mountains. Storms will again be capable of producing brief, strong winds and dangerous lightning with only light rainfall accumulations forecast. A second wave of energy (and moisture) looks to arrive to the Southwest Slope by early tomorrow morning, so some light rainfall over the southwest corner may be possible Wednesday morning.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Looking at two areas of convection and heavy rainfall today. The first will be across the southern Front Range, Palmer Ridge, and Southeast Mountains. Sitting storms will likely produce rainfall totals just over 1 inch, and isolated totals up to 1.3 inches will be possible, which could cause flash flooding issues over urban areas as well as the steeper terrains. So, a Low flood threat has been issued, which includes the Decker burn area. Max 1-hour rain rates will likely exceed 0.50 inches over the burn area, so a Moderate flood threat has been issued. Threats include flash flooding of local streams and debris slides over the steeper terrains.

As storms move into higher moisture, instability, and upper level dynamics east, a few severe thunderstorms will be possible. The main threats will be local heavy rainfall (max 1-hour rain rates up to 2 inches), large hail, and another round of damaging wind gusts. A Low flood threat has been issued for the area. Additional storms this evening look to track across the border into an area that is expected to have very high dew points and instability (Northeast Plains). Max 1-hour rain rates up to 2.25 inches will be possible, which would cause local flash flooding issues. A Moderate flood threat has been issued for these severe thunderstorms that develop. Storms should end just before midnight.

Primetime: 5PM to 11PM

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

Rinse and repeat patter for the San Juan Mountains and eastern Central Mountains. Max 1-hour rain rates up to 0.25 inches will be possible (southern San Juans) with most totals around 0.15 inches from the isolated storms that develop. Storms will again be capable of producing very strong wind gusts. The next plume of moisture arrives to the southwest corner by early tomorrow morning, so some light rainfall may be possible. Flooding is not forecast.

Primetime: 1PM to 9PM