Issue Date: Thursday, September 12th, 2019
Issue Time: 8AM MDT

— Flooding is NOT expected today

Cool start to the morning behind the cold front with most low temperatures overnight not above 50°F. The exception is over the southeast corner of the state where temperatures are still in the mid to upper 50°Fs. The visible satellite imagery below shows some cloud cover (and gravity waves) over the northern mountains, and some clouds over the eastern plains. The eastern cloud cover is associated with the exiting trough, so expecting this to clear up by about noon with plentiful sunshine forecast for the rest of the day. The cloud cover to the north will also start to clear out as upper level winds gain more of a northwesterly component this morning and advect in a dry air mass. PW has dropped off drastically at Denver already (about a half inch since 6PM last night). With PW values both east and west of the Continental Divide under a half inch the rest of the day and subsidence (sinking motion) behind the trough, rainfall is not anticipated today. With severe clear weather forecast, flooding is not expected.

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:

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

Expecting clouds, fog and lingering precipitation to start to end with the morning heating. However, gusty winds will continue over the northern high terrains through this afternoon. Dry air and subsidence will nix the chances for measurable rainfall today and help create clear skies by noon. Cooler high temperatures are also forecast with highs in the 70°Fs over the lower elevations and upper 50°Fs to mid-60°Fs for the mountains.

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

Clouds are expected to decrease over the eastern plains throughout the morning as the trough moves eastward. Gusty winds will continue over the northern high terrains through this afternoon with winds also picking up over the Northeast Plains throughout the morning. Those winds should start to taper off during the late afternoon. High temperatures are forecast to be in the 70°Fs for the lower elevations and low 80°Fs for the southeast corner of the state with clear skies. Rainfall is not forecast today, but an increase in cloud cover is likely over the Raton Ridge and Southeast Plains overnight associated with a disturbance moving through New Mexico. This should help keep low temperatures a little bit warmer than they normally would be over this region. At this time, not thinking there will be any measurable rainfall with these clouds, but a sprinkle or two can’t be ruled out.

Issue Date: Wednesday, September 11th, 2019
Issue Time: 9AM MDT

The infrared imagery below shows the strong trough to our west with a little dry air (break in rainfall) between this system and the one from yesterday. Large ascent out in front of the trough is marked with the orange “X”. There is still some ongoing rainfall this morning associated with the disturbance over eastern Colorado. Snow is also being reported over the highest elevations of the eastern San Juans with just fog over the Northeast Plains. Expecting this disturbance to continue to move eastward and weaken throughout the morning. As the strong trough and jet move overhead this afternoon, gusty winds are forecast with the cold front, tightening surface gradient and thunderstorms that develop. Wind gusts up to 45mph are forecast for western Colorado/high terrains with gusts up to 40 mph along the front over the eastern plains tonight. Not expecting the cold front to drop though until later this afternoon (west) and tonight (east), but some very cold temperatures are forecast overnight with a little bit of snow for the highest elevations. Largest accumulations (a couple inches above 10,000 feet) will be possible over the northern high terrains by tomorrow morning with some lighter accumulations as you move south. A cool start to Thursday morning, statewide, will finally allow it to feel more like fall.

As far as rainfall today, storms look to favor the northern half of the state with a couple isolated storms possible over the far Southeast Plains. Storm motion is forecast to be quick to the northeast with the jet overhead, but trailing storms should help produce greater accumulations with less instability able to develop over western Colorado and the mountains. Over eastern Colorado, a surface low develops over the far Northeast Plains. This should dry out the low levels to the south of its location, but keep higher moisture on its north and east side. This should limit storm coverage over the Southeast Mountains as the trough passes through.

PW was measured at 0.73 inches at Denver this morning, which should increase as the low develops. Thus, stronger, more widespread storms will be possible over the northern portion of the Urban Corridor, Front Range and Northeast Plains. A couple of these storms may become severe over the Northeast Plains with large hail and damaging winds as the main threats as daytime heating and dynamics will be better over the area. A boundary is forecast to set up somewhere over the eastern plains, so a couple weak thunderstorms will be possible again this afternoon over the Southeast Plains where the cap can break. With better moisture over Kansas, flooding is not anticipated. Additional weak, overnight storms will be possible over the Northeast Plains with the cold front dropping south and upper level support from the trough. So forecasting some fog tomorrow morning as well over the northeast quadrant of the state. Flooding is not forecast today due to the speed of the storms with the jet overhead.

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, Northern Mountains, Northwest Slope, Grand Valley, Urban Corridor, Northeast Plains:

Best chance for rainfall and highest totals will be over these regions. Trailing storms will allow for some decent accumulations over the Northwest Slope and Northern Mountains. The former very much needs the wetting rain, but both areas are the in either the D0 or D1 drought categories. Isolated storm totals up to 1 inch will be possible by tomorrow morning with some snow over the Northern Mountains (above 10K feet). Over the northern Front Range, Central Mountains and Grand Valley, max 1-hour rain rates up to 0.25 inches will be possible.

As storms move into the northern Urban Corridor and develop over Northeast Plains, totals should increase with higher moisture on the north side of the surface low. Max 1-hour rain rates up to 0.75 inches (west) and 1.5 inches (east) will be possible. A couple storms may become severe near the Nebraska border with large hail (up to 1.75 inches) and damaging winds also being a threat. The main severe threat will stay north, but a couple of these stronger storms will be possible near the Nebraska border. Linger showers and weak thunderstorms will be possible overnight with the cold front sliding south and upper level support from the passing trough. Flooding is not forecast due to the quick storm motion to the northeast.

Primetime: 9AM to 2AM

Southwest Slope, San Juan Mountains, San Luis Valley, Southeast Mountains, Raton Ridge, Palmer Ridge, Southeast Plains:

Better dynamics and moisture will be to the north for western Colorado, but rainfall is still forecast for the San Juan Mountains, Southwest Slope and Southeast Mountains with PW at Grand Junction at 0.67 inches and rising. Storm motion should favor the southwest facing slopes for accumulation with light rainfall anticipated for the San Luis Valley as well. Max 1-hour rain rates up to 0.75 inches (west) and 0.25 inches (east) are possible with totals under 0.1 inches for the San Luis Valley. Storm rain rates should be little lower near the 416 burn area and with only gradual rainfall forecast over the longer duration, so flooding is not anticipated at this time.

Dry air to the west should keep the Raton and Palmer Ridge dry this afternoon with only increasing cloud cover forecast along a convergence boundary. Temperatures will be able to reach the 90°Fs again, so I’m sure they’re looking forward to the cold front dropping through tonight. A couple of weak thunderstorms will also be possible over the Southeast Plains along the convergence boundary created by the surface low. Max 1-hour rain rates up to 0.75 inches will be possible with storm rainfall total slightly higher.

Primetime: 1PM to 9PM

Issue Date: Tuesday, September 10, 2019
Issue Time: 10:30AM MDT

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

A strong shortwave trough is expected to move over western Colorado today bringing widespread thunderstorms and gusty winds to the area. Moderate levels of mid-level moisture can be seen in the blue and white colors over Utah in the mid-level water vapor imagery below. Embedded within the jet stream (orange line below) are a series of shortwaves that will move over western Colorado throughout the afternoon and well into tomorrow morning. These features and enhanced lift from the jet stream will bring widespread showers and thunderstorms over the west. PW was measured at 0.53 inches this morning over Grand Junction and is forecast to increase up to 0.75 inches this afternoon. Most of the moisture is concentrated in the mid-levels, which will keep storms high based this afternoon, so gusty winds in the storm vicinity area likely.

With the jet overhead steering flows are expected to be greater than 30 mph out of the southwest, so max 1-hour rainfall rates will be limited to 0.5 inches with most areas receiving rates closer to 0.25 inches. These fast flows will also create sustained wind gusts up to 35 mph over and to the west of the Continental Divide with wind gusts up to 55 mph possible in the vicinity of the stronger thunderstorms. The heaviest rainfall is expected over the Southwest Slope and San Juan Mountains where PW is expected to increase up to 1.1 inches briefly this afternoon, so a Low flood threat has been issued for the 416 burn area. Storms tracking over the burn area will be capable of reaching max 1-hour rainfall rates up to 0.4 inches with 2-3 hour totals capable of reaching 0.6 inches. Threats include debris flows, mud slides and flooding of small rivers and streams.

Low pressure remains over the Southeast Plains this morning with downsloping flow off of the Southeast mountains creating a dryline (red dashed line below) over the area. This feature will provide lift for early afternoon thunderstorms which will be capable of producing moderate rainfall rates, large hail and gusty winds. Steering flows are expected to be slow (8 mph – 13 mph) out of the south/southwest. This will cause storms to sit over the area with max 2-3 hour rainfall rates up to 1.4 inches possible. Storms are also expected to move off of the Front Range and over the northern Urban Corridor and western Northeast Plains this afternoon and tonight, but rainfall rates are forecast to be below flood threat criteria. Flooding is not forecast over these areas 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:

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

Widespread storms are expected to begin around noon over the southwest corner and along the CO/UT border. Storm coverage will then extend to the entire forecast region early this afternoon. Fast winds within the jet stream will keep storms moving quickly with max 1-hour rainfall rates of 0.5 inches possible over the Southwest Slope and San Juan Mountains. Multiple storms that track over the area will be capable of producing 2-3 hour totals up to 0.75 inches. Storms that track over the 416 burn area will be capable of causing mud slides, debris flows and flooding of small rivers and streams. The threat for the burn area will extend until sundown, but a few isolated showers are expected overnight and into tomorrow morning.  These showers are not forecast to cause flooding problems.

Max 1-hour rainfall rates of 0.25 inches are possible over the remaining forecast areas. These rates will decrease to 0.1 inches overnight as instability decreases. Sustained wind gusts up to 35 mph are possible with maximum wind gusts up to 55 mph within the vicinity of stronger storms this afternoon and early this evening. Flooding is not forecast outside of the 416 burn area.

Primetime: Noon to 9am

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

Storms coming in from the west are expected to reach the Front Range by 3 pm. Moisture will be low by the time they reach the area, so max 1-hour rainfall rates of 0.2 inches are forecast over the northern Front Range. As the storms move off of the mountains they will pick up moisture from the Northeast Plains and Urban Corridor, which will increase 1-hour max rainfall rates over the northern Urban Corridor and western Northeast Plains up to 0.75 inches. Storms will begin around 3 pm over the Front Range and exit the northern Colorado border by 10 pm. To the south a few isolated storms over the Southeast Mountains are possible this afternoon with max 1-hour rainfall rates of 0.1 inches.

The heaviest rainfall for the eastern regions today will be to the east of the dryline forming over the Southeast Plains this morning. Slow steering flows will allow storms to produce up to 1.4 inches over a 2-3 hour period. Large hail and wind gusts up to 55 mph are possible within the storm vicinity. Storms are expected to begin around noon and end by 8 pm tonight. Flooding is not forecast over the area.

Primetime: Noon to 10pm

Issue Date: Monday, September 9th, 2019
Issue Time: 10:20AM MDT

–Flooding is NOT expected today

The shortwave trough that provided widespread precipitation yesterday has moved over central Great Plains (“X” below). This system has left behind high surface moisture, which has created a large region of fog over the eastern plains and Urban Corridor this morning. This surface moisture is expected to mix out as zonal flow of dry air makes its way over Colorado from the west. This advection of dry air and subsidence behind the trough will keep most of the state dry and sunny today. There is a slight chance for precipitation over the far eastern plains this afternoon associated with a dryline set up (dashed orange line below). Chances of precipitation are on the low end, but a couple storms maybe produce isolated areas of rainfall up to 0.75 inches along the Colorado/Kansas border this afternoon. Additional storms are possible over the Northeast Plains and northern Urban Corridor overnight due to a low level jet streak passing over Wyoming. This will provide upper level support in a moderate moisture environment. Flooding is not forecast 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, Northern Mountains, Northwest Slope, Northeast Plains, Palmer Ridge, Southeast Plains:

Expecting a 3°F to 5°F temperature increase from yesterday with a building ridge and mostly sunny skies. There is a slight (10%-20%) chance of some weak thunderstorms over the northern mountain ranges this afternoon from upslope flow of residual surface moisture, but cloud cover and maybe some brief wind is more likely with the low dew points. Isolated totals up to 0.1 inches may be possible for the stronger storms. The highest chance (30%-40%) for isolated thunderstorms today is over the far eastern plains to the east of the dryline over Prowers and Baca County. Max 1-hour rainfall rates up to 0.75 inches are forecast for the stronger storms. There is an additional chance for a few isolated storms overnight for the Northeast Plains and northern Urban Corridor due to a low level jet streak passing over Wyoming. Max 1-hour rainfall rates up to 0.5 inches are forecast for these storms. Flooding is not forecast today.

Primetime: 1PM to 3AM

Grand Valley, Central Mountains, Southwest Slope, San Juan Mountains, San Luis Valley, Southeast Mountains, Raton Ridge:

Storms are very unlikely today with dry air and building high pressure over the area. Expecting high temperatures to increase 3°F to 5°F from yesterday with dew points dropping into the teens and single digits. Wind gusts will remain well below critical fire weather, but caution is still needed with open flames due to the drying out vegetation over the last month or so. Sustained winds between 10 and 15 mph with gusts up to 20 mph are possible out of the west/southwest near the Continental Divide. Flooding is not forecast today.