Issue Date: Wednesday, August 7, 2019
Issue Time: 10:30AM MDT

–A MODERATE flood threat has been issued for the 416 burn area

–A LOW flood threat has been issued for the Northeast Plains and portions of the Palmer Ridge, Southeast Plains, Southwest Slope, San Juan Mountains, Grand Valley and Central Mountains.  This includes the Spring Creek burn area.

A monsoonal moisture surge will occur over western Colorado today as the subtropical high moves east throughout the day, allowing advection of high PW values northward. This increase in moisture can be seen by the cloud cover over southwest Colorado in the visible satellite imagery below.  Embedded within the flow is a shortwave marked by an “X”, which will make its way eastward throughout the day. The high levels of moisture coupled with this upper level dynamic forcing is forecast to cause widespread precipitation over the high country. Upper level steering flows between 10 and 15 mph over western Colorado will allow storms to sit over the Low threat area. Cloud cover associated with the approaching shortwave will likely limit instability for stronger thunderstorms. However, persistent, pulse-like storms over the area will cause some moderate 2-3 hour rainfall totals. The widespread nature of the moderate rainfall totals will cause a Low flood threat to be issued. If multiple storms track over the 416 burn scar, there is a chance for flooding due to totals in the area reaching up to 1 inch over a 2-3 hour period.

Thunderstorms are also forecast over the eastern plains, which will be generated by a surface dry line (orange dashed line below).  The passage of the shortwave overhead will generate and deepen a new surface low over the area by mid-afternoon. This will help to scour out moisture along the Front Range and Southeast Mountains, so more scattered storms are anticipated over the eastern mountains with rain rates under flood threat criteria. The one exception is the Spring Creek burn area. The chances of flooding over the burn area are on the lower end of the Low threat spectrum, but storms early in the day may prime the atmosphere for 1 to 1.5 hour rainfall rates up to 0.5 inches.  Higher moisture over the Northeast Plains will cause some heavy rainfall with the shortwave passing at peak heating. Storms moving between 15 and 20 mph to the southeast should be fast enough that the threat should only last for 1 to 2 hours. A couple stronger thunderstorms are possible before an MCS forms, which may cause isolated storms to produce wind gusts up to 60 mph and up to 1.25 inch diameter hail. There is a Low flood threat issued for this area.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Storms are expected over the high country throughout the afternoon and some may linger overnight over the high terrains. Heavier rainfall rates are forecast to favor the higher elevations of the Southwest Slope, San Juan Mountains, Grand Valley and southern Central Mountains. Moisture is plentiful over the western San Juan Mountains, so isolated totals up to 1.25 inches will be possible by tomorrow morning. Max 1-hour rainfall rates up to 0.8 inches are possible near the 416 burn area, so a Moderate threat has been issued. Threats over the burn area and steeper mountain slopes include mud slides, debris flows and flash flooding of small creeks and streams. Drier air to the north will limit max 1-hour rainfall rates to 0.25 inches.

Primetime: 11AM to Midnight

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

A line of storms are forecast over the Northeast Plains early this afternoon forming along the boundary. Expect these storms to turn into a MCS later this evening. The primary flood threat will be over a 1.5 to 2 hour period, with 1-hour max rainfall rates just under 2 inches possible. Isolated storm totals up to 2.25 inches may be possible by morning. A couple storms may form over the southeast plains off of outflow boundaries from the north and max 1-hour rainfall rates of 0.3 inches are forecast over the area. Back to the west over the mountains and adjacent northern Urban Corridor, weak thunderstorms may produce max 1-hour rainfall rates up to 0.5 inches. While there is limited moisture over the Southeast Mountains, storms will still be capable of producing rain rates up to 0.5 inches, so a Low threat has been issued for the Spring Creek burn area. Threats over the burn area (if a storm tracks directly over it) include flash flooding, debris slides and mud flows.

Primetime: 1PM to 1:30AM

Issue Date: Tuesday, August 6th, 2019
Issue Time: 8:45AM MDT

— Flooding is NOT expected today

A drier air mass has worked its way into the majority of the state with the subtropical high over the New Mexico and Arizona border. This can be witnessed below (visible satellite imagery) by the lack of cloud cover over our area. Other than a few clouds over the southeast corner, which are exiting to the south as we speak, it’s a clear start to the morning. Dry air should continue to be advected in from Wyoming, which will limit afternoon showers to the southern high terrains where a bit better residual moisture can hold on and mix with some more mid-level energy for greater coverage. The scattered to isolated storms that are able to form over the northern high terrains today will be high-based, so not expecting much accumulation. Storms today will also likely produce some brief, gusty winds. Additional storms are likely over the eastern Northeast Plains/Palmer Ridge area due to convergence near the surface trough. Quick steering flows to the southeast should keep rain rates under flood threat criteria. Therefore, flooding is not forecast.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Temperatures are on the rise. Highs today over the lower valleys are expected to crawl back into the upper 90°Fs with 80°Fs in the lower mountain valleys. Increased cloud cover is anticipated this afternoon triggered by the elevation and residual moisture. Weak storms over the Northern and Central Mountains will likely produce only trace amounts of precipitation with numerous clouds only producing a couple raindrops and occasional lightning. To the south, more continuous, pulse-like precipitation will help rain rates become more efficient throughout the day. Isolated totals up to 0.5 inches will be possible by tomorrow morning over the eastern and southern slopes of the San Juan Mountains. Rainfall rates will be rather low, so not issuing a threat for the 416 burn area. However, any storm that lingers over the burn scar should be monitored closely.

Primetime: 2PM to Midnight

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

The building ridge and dry air will also produce a 5-7°F rise in high temperatures today over these regions. Heaviest rainfall is anticipated over the southern Southeast Mountains and eastern plains along the Kansas and Colorado border. Isolated max 1-hour rain rates up to 0.4 inches will be possible over the Southeast Mountains/eastern Raton Ridge. With higher dew points over the eastern plains, thanks to the low level flow, max 1-hour rain rates up to 0.9 inches will be possible. The isolated storms that are able to form over the Front Range and Urban Corridor should produce only trace amounts of rain, if any at all. Mostly they’ll provide a cooling effect from the afternoon sun. Flooding is not anticipated.

Primetime: 2:30PM to 11PM

Issue Date: Monday, August 5, 2019
Issue Time: 10:35AM MDT

-A LOW flood threat has been issued for portions of the Southeast Mountains and Southeast Plains, including the Spring Creek and Junkins burn areas

The state will dry out a bit today after widespread precipitation over the high country and Northeast Plains yesterday. Shown in the low-level water vapor imagery below, the subtropical high pressure system (marked “H”) has moved back to the west. This will cut off monsoonal moisture flow slightly and limit precipitation over western Colorado. Isolated showers are still possible over most areas, but will be light in nature. The shortwave and vorticity maximum that effected the state yesterday is now positioned over the Southeast Plains. The surface low pressure system underneath the shortwave will pull moist air down from the north, but limit upslope flow over the eastern mountain ranges this afternoon.

The highest chance for precipitation during the day will be over the Continental Divide and Northeast Plains. Weak upslope flow over the high terrain will generate light storms this afternoon. A cold front (dashed blue line) is forecast to move in from the north late this afternoon, providing chances for thunderstorms to generate off of the Cheyenne Ridge and Palmer Ridge. Fast upper level steering flows up to 30 mph will decrease the chances of moderate and heavy rainfall. Post frontal upslope flow tomorrow morning will provide heightened chances for precipitation over the Southeast Mountains and eastern areas of the Southeast Plains. A strong resurgence of moisture over the area has issued a Low flood threat.  The heaviest precipitation is forecast to begin by 11PM and extends to sunrise tomorrow.  Slow steering flows overnight will allow storms to linger over areas for 2-3 hours.  Areas of moderate to heavy rainfall are not expected to be large, however storms centered over urban environments and burn areas create a higher risk of flooding.  High levels of soil moisture over the Southeast Mountains have also increased the flood threat to a Low.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

A cold front will pass over the northern border of Colorado mid afternoon today, initiating storms over the Cheyenne ridge at that time. Isolated storms are forecast over the Northeast Plains and Palmer Ridge this afternoon and tonight, but upper level steering flows between 20 and 30 mph will prevent high accumulations over the area. Isolated max 1-hour rainfall rates up to 0.75 inches are forecast over the northern Urban Corridor, Northeast Plains and Palmer Ridge. Brief afternoon storms are forecast over the Front Range, with max 1-hour rainfall rates up to 0.3 inches.  The highest chance for greater rainfall totals will be late tonight and early tomorrow morning over the Low threat area.  Max 2-3 hour rainfall rates up to 1.5 inches are forecast over the area.  The highest chances for flooding will be over Urban areas and recent burn areas.  Max 2-3 hour rainfall rates decrease over the Spring Creek burn area to 0.75 inches.  High levels of surface moisture and recent flooding over the area increase the chances for flooding over areas of the Southeast Mountains.

Primetime: 2PM to 5AM

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

Isolated afternoon storms are forecast over the high terrain, but fast steering flows will limit accumulation significantly. Isolated max 1-hour rainfall rates of 0.2 inches are forecast over the area today, with most of the lower elevations forecast to remain dry. Storms are expected to end over most areas early this evening, with chances extending over the Central Mountains and San Juan Mountains later into the night. Expect high temperatures to reach into the 90°Fs over the lower terrains once again today. No flooding is forecast over the area.

Primetime: 2PM to 7PM

Issue Date: Sunday, August 4, 2019
Issue Time: 10AM MDT

-A MODERATE flood threat has been issued for the 416, Junkins, Spring Creek, Hayden Pass and Lake Christine burn areas

-A LOW flood threat has been issued for portions of the Southwest Slope, San Juan Mountains, Grand Valley, Northwest Slope, Northern Mountains, Front Range, Central Mountains and Southeast Mountains

Expect similar weather statewide again today, but with a return of moisture over the northern mountain ranges and areas of the eastern plains. The subtropical high pressure remains overhead, with clockwise flow around the state once again. Embedded within the flow is a shortwave (“X” below) and local vorticity maximum that will move across Colorado today. This feature will provide lift and dynamical forcing for thunderstorms over the high country and eastern plains. Due to extra lift, rain will most likely be heavier than yesterday. Marked below on the visible satellite imagery is a surface high pressure system over the CO/NM border with a broad region of low pressure over the eastern plains. Wind flow around the two features will combine to produce downsloping flow over the Southeast Plains, creating a localized dryline over the area. This dryline will cap most storms over the Southeast Plains but provide a boundary for storms to form to the north. Thunderstorms are forecast over most of the high country as well as the Northeast Plains and Palmer Ridge.

Atmospheric moisture has increased over western Colorado from yesterday, with PW measuring 1.1 inches over Grand Junction this morning. Surface based moisture is very similar, but dewpoints over the high country have increased to the mid 40°Fs due to yesterday’s rain. Over the eastern plains surface moisture is similar to yesterday as well, but sunny skies this morning are likely to mix out low level moisture once again. The shortwave will pass over the high country during peak heating, which will create numerous thunderstorms capable of producing heavy rain. The system will arrive past the time of peak instability over the eastern plains, which should keep storms lighter. Steering flows over the mountains will vary between 10 and 20 mph, creating the primary threat of multiple storms over a 2-3 hour period. Recent rainfall over burn areas has increased the threat to Moderate over the 416, Junkins, Hayden Pass, Spring Creek and Lake Christine burn areas

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

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

Chances for precipitation are high throughout the area today. Heavier rainfall rates will once again favor the mountains to the south of I-70, however moderate and heavy rainfall is still possible over areas to the north. The primarily threat today is rainfall over a 2-3 hour period. Max 2-3 hour rainfall rates of 1.25 inches are forecast over the area, with rates up to 1.75 inches over the Southwest Slope and San Juan Mountains. Isolated areas of 1-hour max rainfall rates up to 1 inch are possible, but most areas will have max 1-hour rainfall rates of 0.5 inches. Rainfall will mostly be confined to higher terrain, with greater threats over steeper terrain and recent burn areas. Threats include flash flooding, debris flows and flooding of small rivers and streams.

Primetime: 11AM to 11PM

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

The highest chances of rainfall today will be over the Front Range and Southeast Mountains. Storms may move off of the Front Range this afternoon, but drier air underneath the storm base will limit severe weather potential over the Urban Corridor, Palmer Ridge and Northeast Plains. A few weak storms may move over the Raton Ridge this afternoon, but rainfall will be very limited as well. Max 2-3 hour rainfall rates of 1 inch are forecast over the Southeast Mountains and southern Front Range. Recent rain over the area will increase chances for flooding over these regions, with the highest chance over the recent burn areas. Threats include flash flooding, debris flows and flooding of small rivers and streams. The northern Front Range, Urban Corridor and eastern plains are expected to be drier once again today, with max 1-hour rainfall rates of 0.4 inches. The chance for measurable rain over these areas is confined to the upper elevations, Palmer Ridge and Northeast Plains.

Primetime: 1PM to 12PM