Issue Date: Monday, July 22, 2019
Issue Time: 10:05AM MDT

–A MODERATE threat is issued for portions of the Southeast Mountains and Raton Ridge.  This threat includes the Spring Creek, Hayden Pass and Junkins burn areas

–A LOW threat is issued for portions of the Front Range, Urban Corridor, and Palmer Ridge

Moderate to heavy rainfall will return today over the Southeast Mountains and Raton Ridge, adding additional moisture to saturated soils.  The high pressure ridge aloft continues to move its way to the east and is now centered over the CO/NM border (marked “H” in the water vapor imagery below).  Mid and upper level flow on the backside of the high (yellow lines below) will bring in moisture from the southwest, providing chances for afternoon thunderstorms over the high country.  A large region of surface high pressure over the Northern Great Plains today will provide cooler surface winds and moderate moisture advection to the eastern plains from the east-southeast.  A small region of low pressure is expected to form over the San Luis Valley again this morning and into the early afternoon, pulling moisture up and over the Southeast Mountains from the Southeast Plains.

Morning and early afternoon cloud cover will keep temperatures cooler over the eastern plains, thus limiting instability this afternoon for potential thunderstorm growth. West of the Continental Divide, dry surface conditions and sunny skies this morning will confine thunderstorms to the high county, allowing another hot day over the valleys of the western slope. Upslope flow over the Front Range and Palmer Ridge will provide a chance for thunderstorms over the area.  Storms may move over the Urban Corridor and Palmer Ridge this afternoon, but upper level steering flows out of the north-northeast at 15-20 mph will prevent storms from traveling far over the eastern plains.

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:

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

Chances for afternoon thunderstorms are high again today over the Front Range, Urban Corridor, Southeast Mountains and Raton Ridge. Upper level moisture will return from the west today and combine with upslope flow from the east to provide lift over the Continental Divide. A Moderate threat has been issued for the Southeast Mountains and Raton Ridge, including the Hayden Pass, Junkins and Spring Creek burn areas. Chances for thunderstorms will begin around 1PM, but the primary threat will be from 4PM to 11PM. Max 1-2 hour rainfall rates between 1.5 inches and 1.75 inches are forecast over the areas of Moderate threat. Ground conditions are likely close to saturated due to moderate and heavy rain over the weekend, which greatly increases the chances for flash flooding, especially over recent burn areas. Threats include: flash flooding, debris flows, mud slides, flooding of small streams and rivers, and flooding of roadways.

Thunderstorms are forecast to begin over the Front Range around 1PM and travel eastward over the Urban Corridor between 3 and 4PM. 1-hour rainfall rates up to 1.5 inches are forecast over the Urban corridor, with 1-hour rainfall rates up to 1 inch over the Front Range. Heavy rain over the weekend enhances chances for flooding even with lower rainfall rates. Storms may additionally form over the Palmer Ridge mid-afternoon, but upper level winds and insufficient instability will limit the storms from traveling far to the east. Primary threats include: flooding of small rivers and stream, flooding of roadways and low laying intersections, and field ponding. The Northeast and Southeast Plains are not forecast to have severe weather due to cloud cover this morning. Small thunderstorms may travel over the Southeast Plains early this evening but max 1-hour rainfall rates are forecast to be 0.75 inches.

Primetime: 1PM to 11PM

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

Afternoon thunderstorms are forecast over the high country today. Mid-level moisture will return throughout the day from the south-southwest, aiding upslope flow to produce thunderstorms. Convergence over the San Luis Valley will provide a chance for thunderstorms over the climatologically dry area. Max 1-hour rainfall rates up to 0.75 inches is forecast over the area. Thunderstorms are primarily forecast over the San Juan Mountains, Central Mountains and Northern Mountains, favoring the high elevations. Max 1-hour rainfall rates of 0.6 inches is forecast over these areas. Storms tracking near the 416 burn area could produce 0.5 inches in an hour, but flooding is unlikely. High temperatures up to 100°F are forecast over the Grand Valley and Southwest Slope again today.

Primetime: 12PM to 7PM

Issue Date: Sunday, July 21, 2019
Issue Time: 10:15AM MDT

— A HIGH flood threat has been issued for the Spring Creek burn area

— A MODERATE flood threat has been issued for portions of the Palmer Ridge, Southeast Plains, Raton Ridge and Junkins burn area

— A LOW flood threat has been issued for portions of the Front Range, Urban Corridor, Northeast Plains and Hayden Pass burn area

Another day of heavy rain is forecast today as strong upslope flow returns to the east of the Continental Divide. The high pressure ridge that was centered over the Baja Peninsula yesterday shifted eastward and is now positioned over the AZ/NM border. This will bring in drier air to the west of the Divide, thus limiting the chance for thunderstorms over the west today. PW has increased drastically over the eastern plains due to heavy rain yesterday. PW was measured at 0.83 inches over Denver this morning and increases to 1.2 inches over the eastern border. West of the Divide, PW values decrease to 0.4 inches over the Grand Valley and San Juan Mountains. Dewpoints this morning (green contours below) measure in the 50°Fs along the foothills and increase into the 60°Fs over the eastern border, providing ample moisture for afternoon and evening thunderstorms. Surface moisture is expected to remain high over the eastern plains throughout the day.

At the surface, a thermal low (“L” below) is expected to form early this afternoon over the San Luis Valley, creating strong upslope flow along the Front Range, Palmer Ridge and Southeast Mountains. Strong thunderstorms are forecast to form over these areas early this afternoon. Northwesterly steering flows at 20-25 mph will keep storms moving at a moderate pace, however continual upslope flow will cause storms regenerate and train over the same areas. Thunderstorms will favor the Southeast Plains and Palmer Ridge as they move off of the higher terrain. A Flash Flood Watch has been issued over portions of the Southeast Mountains and Wet Mountains, including the Hayden Pass, Junkins, and Spring Creek 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:

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

Severe thunderstorms are forecast this afternoon and into the early morning.  Storms will form over the Front Range early this afternoon and move to the south/southeast over the Urban Corridor mid-afternoon.  Multiple rounds of thunderstorms can be expected over the area, ending around 8PM.  Max 1-hour rain rates up to 1.75 inches and max 3-hour rain rates up to 2.25 inches may be possible over the region, with heavier rates favoring the Urban Corridor. Threats include flooding of small streams, roads and low lying intersections with the threat decreasing after 6PM.

Over the Palmer Ridge, Southeast Mountains, Southeast Plains and Raton Ridge, max 1-hour rain rates up to 2.5 inches (east) and 1.5 inches (west) are possible.  Isolated 2 to 3 hour totals up to 3.5 inches are possible by early morning. Storms are expected to begin around 2PM and extend until 2AM, with later storms favoring the Southeast Mountains. High rain rates may cause flash flooding of rivers/arroyos, road flooding, and field ponding. Over steep terrain and burn areas threats include debris slides, mud slides, and landslides.

Primetime: 2PM to 2AM

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

Incoming dry air from the west and ample sunshine is expected to mix out surface moisture throughout the day.  Isolated weak thunderstorms are possible over the Northern, Central and San Juan Mountains.  Max 1-hour rainfall rates of 0.1 inches are forecast over the high terrain.  It’s going to be hot over all the forecast zones today, reaching up to 100°F over the Grand Valley, with high temperatures in the 80°Fs and 90°Fs over the other regions.

Primetime: 1PM to 7PM

Issue Date: Saturday, July 20th, 2019
Issue Time: 10:55AM MDT

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

PM update: Only slight changes to the forecast at this time over the eastern plains. The cold front has moved faster to the south than originally forecast, resulting in a shift south for the High and Moderate flood threat. There is also a slight eastward shift of the Moderate flood threat. Strong surface flow out of the northwest will help storms remain more stationary, therefore rain rates look to increase over the area with max 1-hour rain rates up to 2.75 inches possible. Isolated totals greater than 3.5 inches are still forecast by morning. The heavy rainfall threat for the eastern plains is forecast to end after 1 AM. 

There will be a drastic change in weather today after a couple days of hot temperatures and dry conditions. Heavy rain expected over the eastern portion of the state behind a slow moving cold front. This feature will keep most of the Northeast Plains capped and bring some cooler temperatures back into the forecast behind it. Upper level high pressure zones over the Baja Peninsula and Texas Panhandle will combine with low level moisture behind the front to pull in high moisture from the Pacific. Shown in the water vapor imagery below is a shortwave (marked with an “X”) embedded on the backside of the high pressure system. This feature is forecast to move eastward today/tonight, which will help provide lift and generating a low level vorticity maximum over the eastern plains for overnight rainfall. The surface low that is currently positioned over the CO/KS border will deepen throughout the day as it gains upper level support from the passing shortwave.

Moisture is expected to increase drastically throughout the day over eastern Colorado and into the evening as dewpoints in the mid 60°Fs are advected around the east and north side of the low. PW is forecast to reach between 1.25 and 1.4 inches this afternoon over Denver, nearing the max values seen this time of year. Post frontal upslope flow east of the Continental Divide will provide lift for thunderstorm generation, and slow steering winds (10 mph to the E and SE) will allow for some very high accumulations. Surface based CAPE is forecast to be greatest along the Front Range and Urban Corridor as well as over the Southeast Plains. High levels of instability will create a chance of severe thunderstorms over these areas with the greatest threat over the Southeast Plains and eastern Palmer Ridge. Mid-level moisture is expected to increase throughout the day west of the Continental Divide as well with the shortwave passing over the area this afternoon. Surface moisture is expected to stay fairly low, with dewpoints measured in the 30°Fs and low 40°Fs this morning, but there should be enough moisture for thunderstorms over the higher elevations. Fire danger will also be reduced.

Slow steering winds under storms today (east) will produce some very high rain rates, so flooding is likely with threats being street flooding, flooding of low lying areas and field ponding. Over the higher terrains, including the Junkins and Spring Creek burn areas, mud flows, debris slides and flash flooding will be possible. Thunderstorms look to persist over the Southeast Plains tonight along the boundary with enhanced lift by the shortwave marked below. The MCS is expected to create several flooding hazards with nearly stationary storms over a 2 to 3 hour period. In addition to the threats mentioned above, arroyo flooding and flash flooding of local streams will be possible. The threat ends around 1AM, but light showers will likely persist into tomorrow morning. A High/Moderate flood threat has been issued for today.

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

Severe thunderstorms are forecast this afternoon and into tonight over the two regions mentioned above with a High/Moderate flood threat issued. Storms will form over the Front Range just after noon, and move their way east throughout the afternoon and into tonight. The northeast corner of the state looks to remain capped, so eastern plain activity will likely be along the front and south. With nearly stationary storms, the threat today will be 1 to 2 hour totals (west) and 2 to 3 hour totals (eastern plains). Max 1-hour rainfall rates up to 1.8-2.0 inches are forecast over the Front Range and Urban Corridor. Threats include flooding of small streams, roads and low lying intersections with the threat decreasing after 9-10PM. Over the steeper terrains and aforementioned burn areas, debris slides, mud flows and flash flooding are possible.

Over the Palmer Ridge, Southeast Plains and Northeast Plains max 1-hour rainfall rates up to 2.25 inches are possible. Isolated 2 to 3 hour totals greater than 3.5 inches are possible by morning. Reminder, this threat extends overnight with the flood threat decreasing after 1AM. These high rain rates will cause flash flooding of rivers/arroyos, field ponding and road flooding. Some severe storms are also possible earlier in the evening with gusts up 65 mph and hail up to 1.5 inches diameter as additional threats. Lingering showers are possible through tomorrow morning.

Primetime: 2PM to 1AM

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

With an uptick in moisture, though not as great over western Colorado, afternoon and evening thunderstorms return to the forecast. Storms will favor the San Juan Mountains and will likely be more confined to along and near the Continental Divide over the Northern and Central Mountains. Max 1-hour rainfall rates up to 0.8 inches are forecast over the eastern San Juan Mountains and southern/eastern Central Mountains. Max 1-hour rain rates will drop to the 0.25 to 0.5 inch range over the Northern Mountains. Lingering dry air at the surface will limit precipitation over the lower elevations of the forecast area. Storm are expected to dissipate after sundown with the decrease in instability.

Primetime: Noon to 10PM

Issue Date: Friday, July 19th, 2019
Issue Time: 8:25AM MDT

— Flooding is NOT expected today

Almost a completely clear morning, but there is some light, broken cloud cover over the higher terrains in the northwest corner of the state. Cloud cover will increase over the northern mountains this afternoon with this disturbance, so that may provide some relief from the heat. Not much change in the forecast from yesterday. A dry air mass will remain intact over the state, which will keep conditions dry and hot. Flow aloft will become more southwesterly throughout the day, but with dry air also to our west and southwest, there will be little change in available moisture for afternoon storms. As anticipated, flooding is not forecast. There is relief from the heat coming tomorrow for eastern Colorado as a cold front starts to drop through early tomorrow morning. It won’t affect western Colorado as much, but high temperatures are still anticipated to drop off a couple of degrees.

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:

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

It’s going to be another scorcher with temperatures over the lower elevations reaching 100°F – 106°F. There may be some more afternoon cloud cover when compared to yesterday, but still expecting that to be patchy. A light shower may be possible over eastern Park County/northern Teller County this evening, but with high bases only expect a sprinkle or two with some light wind.

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

The Red Flag Warning continues for another day over Moffat County. Critical fire weather is expected to end as moisture slowly increases over the area tomorrow into Sunday. So use caution with open flames for another day with the breezy conditions. Highs today will likely increase about 5°F from yesterday, so keep yourself hydrated.