Issue Date: Wednesday, September 4th, 2019
Issue Time: 8:45AM MDT

— Flooding is NOT expected today

Temperatures will be back on the rise again today without a cold front to provide any relief from the heat. The one saving grace from hot temperatures will be the increased cloud cover over the state (areas of blue shading in the water vapor imagery below), which may keep some areas a couple of degrees cooler than they normally would be. For the majority of the state, the broken cloud cover is expected burn off significantly with a few hours of heating, which will allow some (limited) instability to build for another round of afternoon and evening storms. Similar pattern to yesterday with the 500mb high in place over the southwest corner of the state. This is pulling in several disturbances across the state from the west and southwest. Expecting another wave to travel though the flow this afternoon and help spark more widespread storm coverage over the mountains with a little activity spilling into the adjacent eastern plains (Palmer Ridge/Northeast Plains). Steering flow speed will be slow to moderate and direction will be westerly over the mountains with storms gaining a little bit of a southerly component over the eastern plains as they rotate around the high.

Not quite as much moisture to work with today with westerly flow aloft washing out moisture from west to east. This will act to decrease dew points a bit over western Colorado when compared to yesterday. Thus, high-based storms that are able to form will produce more wind and virga than measurable rainfall. Over eastern Colorado, surface winds will also be more southerly as the trough passes to the north (just west of the orange “X” below). PW was measured at 0.89 inches at Denver, but most of moisture was located in the mid and upper levels of the sounding. Thus, high-based storms today may produce brief, windy conditions. There is also a slight cap above 500mb, but not thinking it is strong enough to suppress convection over the immediate adjacent plains. A stronger cap is in place over the eastern plains and with instability decreasing by the time storms reach this area (sunset), storms are expected to dissipate quickly. Flooding is not forecast for storms that form 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, Central Mountains, San Juan Mountains, Urban Corridor, Northeast Plains, Palmer Ridge:

Best chance for measurable precipitation this afternoon over the mountains will be over the southern Front Range, San Juan Mountains and eastern Central Mountains. Brief winds and moderate rainfall will be possible with thunderstorms that from with max 1-hour rain rates up to 0.4 inches possible. Trailing storms may cause storm totals up to 0.6 inches along and near the Continental Divide. As storms move into the adjacent plains, they will have the best chance for survival along the elevated terrains of the Palmer Ridge. Max 1-hour rain rates up to 0.6 inches will be possible with rain rates decreasing to 0.25 inches/hour over the northern Urban Corridor. There is a slight chance for a storm to move into Weld County that forms over the Cheyenne Ridge, if the cap can break, max 1-hour totals up to 0.9 inches will be possible. However, there is less than a 30% chance of this happening. Flooding is not forecast and the main threats from storms today will be wind, lightning and isolated, moderate rainfall.

Primetime: 1PM to 11PM

Northwest Slope, Grand Valley, Southwest Slope, Northern Mountains, Southeast Mountains, San Luis Valley, Raton Ridge, Southeast Plains:

Expecting more cloud cover than rainfall over the Northern Mountains, Southeast Mountains and Raton Ridge. Should a storm be able to form, less than 0.05 inches of rainfall is anticipated. The Southeast Plains and San Luis Valley should be clear this afternoon with temperatures in the 90°Fs and 80°Fs, respectively. A little bit of cloud cover is likely over the Northwest/Southwest Slope and Grand Valley with the disturbances moving in from the west. Highs will still be able to reach the upper 80°Fs and 90°Fs over these western lower elevations with 70°Fs over the higher elevations.

Issue Date: Tuesday, September 3rd, 2019
Issue Time: 11AM MDT

–A LOW overnight flood threat has been issued for the Junkins, Hayden Pass and Spring Creek burn areas

The ridge axis is slightly to our west today with the 500mb high anchored over the state, which will produce weak northwest flow over eastern Colorado and southwest/westerly flow over western Colorado. A passing trough will push a cold front (blue dashed line) through the state, and reduce high temperatures over the northern half of Colorado. As much as a 10°F to 15°F drop in high temperature from yesterday is expected over the Northeast Plains and Urban Corridor. Highs are expected to drop between 2°F and 4°F over western and southern Colorado where morning sunshine will allow temperatures to increase quickly again throughout the morning. As far as moisture goes, it remains low over Denver and Grand Junction this morning with PW measuring around 0.5 inches over both locations. Expecting an increase in moisture post frontal passage with some higher moisture sneaking into the southwest corner as well. Mid to upper level moisture and energy can be seen by the cloud cover over Utah, and is expected to move over Colorado on and off throughout the week (orange line below). Behind the front, post frontal upslope flow will continue to increase surface moisture with easterly flow at the surface.

The highest chances for precipitation today will be over the San Juan Mountains, Southeast Mountains, Central Mountains and the Front Range with the eastern plains remaining capped. Moisture behind the cold front will return dew points up to 60°F over and to the south of the southern Front Range. Residual surface moisture (40°F dew points) and incoming mid-level moisture will provide more wetting rainfall to the San Juan and Central Mountains today. Pockets of moderate instability will allow thunderstorms to initiate over the eastern mountain ranges this afternoon. Overnight, post frontal upslope flow continues over the Southeast Mountains, which will provide nearly continuous rain over the area until early tomorrow morning. A Low flood threat has been issued for the Junkins, Spring Creek and Hayden Pass Burn areas for precaution. Threats include debris flows, mud slides and flooding of small rivers and streams if this nearly stationary, overnight convection tracks overhead. Rainfall over dry soils elsewhere should be gradual enough that a Low flood threat is not needed outside of the 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:

San Juan Mountains, Southwest Slope, Central Mountains, Southeast Mountains, Front Range, Raton Ridge:

Afternoon thunderstorms are expected over these regions with storms extending into tomorrow morning over the Southeast Mountains. Isolated totals up to 0.1 inches are forecast over the San Juan Mountains, high elevations of the Southwest Slope and northern Front Range. Higher levels of moisture within the post frontal upslope flow area will increase chances of rainfall over the Central Mountains, Southern Front Range and Southeast Mountains. Isolated areas of max 1-hour rainfall rates up to 0.75 inches are forecast over Central Mountains, southern Front Range and Southeast Mountains for the rainfall overnight. Isolated storm totals up to 1.5 inches are possible over the Southeast Mountains with the overnight convection, and if the storms set up over the recent burn areas, flash flooding of local streams, debris slides and mud flows will be possible.  This threat will extend until early tomorrow morning.

Primetime: 2PM to 4AM

Grand Valley, Northwest Slope, Northern Mountains, Northeast Plains, Palmer Ridge, Urban Corridor, Southeast Plains, San Luis Valley:

Most of the forecast area should remain dry today with a slight chance for a brief thunderstorm moving off of the mountains into the Urban Corridor and Raton Ridge.  Isolated maximum 1-hour rainfall rates of 0.2 inches are forecast for these storms. The remaining areas of the region should remain dry with little to no chance for precipitation today.  Afternoon cloud cover should decrease temperatures by 2°F-4°F over the western areas and by as much as 10°F to 15°F over the Northeast Plains, Urban Corridor and Palmer Ridge.  Wind gusts up to 30 mph are possible over the eastern plains with the passage of the cold front this morning.

Primetime: 2PM to midnight

Issue Date: 9/2/2019
Issue Time: 7:05 AM

NO FLOOD THREAT IS FORECAST TODAY.

Record high temperatures fell yesterday, and more are likely to fall today, as the strong high pressure continues its grip on the region. Abundant sunshine and relatively little cloud cover will allow for maximum solar heating today, and the dry air will leave the state with very little chances for respite. The San Juan Mountains and Southeast Mountains will see a couple isolated, high-based storms develop during the afternoon/evening hours, but little (if any) rainfall will reach the surface. Instead, gusty winds and occasional cloud-to-ground lightning will be the main impacts. There is also a less than 10% chance, much like yesterday, of an isolated storm or two over the Palmer Ridge, and adjacent Northeast/Southeast Plains; most likely, it will be just a bit of late afternoon cloud development. Other than those two scenarios, I hope everyone enjoys the heat and sunshine, because that is what Mother Nature has in store for Colorado.

Today’s Flood Threat Map

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

Zone-Specific Forecasts

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

Sunny skies and hot temperatures will be the main weather story today. A couple isolated, high-based thunderstorms have a less than 10% chance to rumble over the Palmer Ridge and adjacent Northeast/Southeast Plains. IF a storm develops, the main impact will be a brief period of light-to-moderate rainfall (less than 0.20 inches/hour) and gusty winds.

Timing: 2 PM – 8 PM

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

Abundant sunshine and near-record temperatures will rule the day across the vast majority of the area. A couple isolated, high-based thunderstorms will rumble over the San Juan Mountains and Southeast Mountains, but very little rainfall will make its way to the surface. Instead, the main impacts from any activity will be gusty winds and occasional cloud-to-ground lightning. Rain rates will be less than 0.10 inches/hour.

Timing: Noon – 9 PM

Issue Date: 9/1/2019
Issue Time: 7:10 AM

NO FLOOD THREAT IS FORECAST TODAY.

The first day of Meteorological Fall is going to feel more like the middle of summer today, as strong high pressure sits overtop the southwestern United States. High temperatures will be a couple degrees warmer than yesterday and will flirt with record highs in a few locations. The heat and abundant sunshine will be the main weather story today, while the sidebar will be a couple isolated, high-based thunderstorms. The strong high pressure will suppress most thunderstorm activity, but there are two areas to mention:

Front Range, Southeast Mountains, San Juan Mountains, Raton Ridge, and immediately adjacent areas along I-25 and south of I-70: Strong daytime heating and orographic effects will be the driving forces behind a couple isolated thunderstorms. Gusty winds, cloud-to-ground lightning, and brief periods of light-to-moderate rainfall will be the main impacts. Small hail will be possible in stronger storms.

Palmer Ridge, Northeast Plains, and northern Southeast Plains: A weak dryline will result in some surface convergence over the area, although it remains to be seen whether there will be enough to overcome the strong high pressure aloft. One or two isolated thunderstorms cannot be ruled out. IF a storm (or two) forms, the main impacts will be gusty winds, brief periods of light-to-moderate rainfall, cloud-to-ground lightning, and hail up to 1.0 inches in diameter.

For more details on timing and rain rates, please see the zone-specific forecasts below.

Today’s Flood Threat Map

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

Zone-Specific Forecasts

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

Mostly sunny skies and hot temperatures will be the main weather story today. A couple isolated, high-based thunderstorms will rumble over areas adjacent to the higher terrain and south of I-70. A couple thunderstorms are also possible along a weak dryline over the Northeast Plains, Palmer Ridge, and Southeast Plains.

Brief periods of light-to-moderate rainfall (less than 0.25 inches/hour), gusty winds, and hail (up to 1.0 inches over the Plains, smaller near the higher terrain) are the main threats.

Timing: 2 PM – 11 PM

Front Range, Southeast Mountains, San Juan Mountains, and Southwest Slope:

Mostly sunny skies will rule the start of the day, with fair weather cumulus building through the afternoon and early evening hours. A few isolated thunderstorms will develop thanks to daytime heating and orographic effects, mainly south of I-70. Gusty winds, brief periods of light rainfall (less 0.15 inches/hour), and cloud-to-ground lightning will be the main impacts from any thunderstorm development.

Timing: Noon – 9 PM

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

Plenty of sunshine and hot temperatures are expected, with a few clouds bubbling over the mountains during the heat of the afternoon. The San Luis Valley will see some high clouds from isolated storms over nearby mountains.