Issue Date: Friday, June 15, 2018
Issue Time: 09:30AM MDT

— Flooding is NOT expected today

Everything is coming together for the cool and wet weekend. In the water vapor imagery below you can see the trough that will start to drop into Nevada/Northern California later today. You can also see the subtropical moisture from Bud starting to creep north over the southwest. But for today, that low level moisture won’t quite make it into western Colorado for the next round of afternoon thunderstorms and showers.

Soundings at both Grand Junction and Denver show quite a bit spread between the temperature and dew point at the surface, which should lead to another day of gusty winds and limited rainfall from the thunderstorms this afternoon. A Red Flag warning is in place over Western Colorado through this evening due to dry thunderstorms (strong outflows and lightning) creating critical fire conditions. Rainfall coverage and totals over the southwest corner of the state are expected to increase overnight as remnants of Bud moisten the lower levels. Please check back to the FTB tomorrow for more specific details as a Flash Flood Watch and High Flood Threat Outlook have been issued for the San Juan Mountains and 416/Burro burn scars on Saturday.

Over the Northeast Plains, behind the cold front, dew points are increasing into the mid 50Fs. A bit of this moisture will mix out this afternoon, but there is still enough in place for moderate rainfall this afternoon. The front is expected to stall out over the Palmer Ridge later this morning, so these higher dew points won’t quite reach the Southeast Plains. This will make showers and thunderstorms more isolated over the Southeast Mountains. Behind the front, upslope flow will increase as will thunderstorm coverage over the Front Range. More storms are forecast to form over the Palmer and Raton Ridges later this afternoon. Storm motion will be to the northeast at 15-20 knots, so flooding is not a concern. Threats today include gusty winds, dry thunderstorms and small hail. Storm activity over the eastern plains should end by 11PM. There is no flood threat 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:

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

Upslope flow will return to the region favoring the Front Range, which should initiate thunderstorms over the higher terrains by this afternoon. Max 1-hour rain rates up to 0.75 inches/hour are possible near the CO/WY/NE border. However, the higher totals are expected to stay north of Colorado. Further south over the Palmer Ridge max 1-hour rain rates up to 0.6 inches/hour are likely. Due to limited low level moisture over the Southeast Plains, the storms that fire along the Raton Ridge will only have 1-hour rain rates up to 0.3 inches/hour. Storms will move east of Colorado by 11PM.

Primetime: 2PM – 11PM

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

Dry thunderstorms this afternoon will lead to critical fire conditions as they will produce lightning and gusty outflow winds (45-60 mph range). Thus, a Red Flag Warning is in effect until 9PM tonight. Max 1-hour rain rates this afternoon will be in the 0.05-0.15 inches/hour range with the highest rain rates over the southern/central mountains. After 10PM, the low levels will begin moisten as the subtropical moisture reaches the southwest corner of the state. This will increase rainfall coverage and intensity overnight in western Colorado with the most widespread activity over the San Juan Mountains. Totals over the San Juans by tomorrow morning will be in the 0.25-0.4 inch range favoring the south facing slopes. Flooding is not expected overnight, but please tune back into the FTB tomorrow morning as a Flash Flood Watch has been issued for Saturday over the San Juan Mountains and 416/Burro burn scars.

Primetime:  12:30PM – 11AM

Issue Date: 6/14/2018
Issue Time: 7:40 AM

NO FLOOD THREAT IS FORECAST TODAY.

Mid-level moisture is streaming into the state from the southwest as a result of high pressure aloft over New Mexico and an upper-level trough digging into the Pacific Northwest. This stream of moisture is sufficient enough to produce plenty of mid-level clouds this morning, and will support scattered thunderstorms across the state this afternoon and evening. Unfortunately for those looking for wetting rain, you will not find much of it today. The low-levels will remain too dry, especially over the High Country, where dry thunderstorms will produce plenty of virga, gusty winds, and cloud-to-ground lightning which could spark new fires.

East of the mountains, a little bit better low-level moisture is present, but not nearly enough to result in heavy rainfall. Strong, gusty winds and lightning will be the main impacts from thunderstorms today, with only brief periods of light-to-moderate rainfall as storms race off to the east-northeast. A couple of grass fires were started in Weld County last night, burning over 8,000 acres before being contained. Grass fires sparked by cloud-to-ground lightning will be a concern today, as well.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, jump below the map.

Zone-Specific Forecasts

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

Scattered high-based showers and thunderstorms are expected, producing more wind and lightning than rain. Plenty of virga will paint the sky, with brief periods of light-to-moderate rainfall underneath thunderstorms. Otherwise, the main story will be that high temperatures are a few degrees warmer than yesterday, with highs in the mid-to-upper 90s across the plains, and even a few 100+ readings in the Arkansas River Valley. Maximum rain rates from thunderstorms are as follows:

Front Range and Southeast Mountains: 0.05-0.15 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 0.25-0.5 inches/hour
Northeast Plains and Southeast Plains: 0.4-0.8 inches/hour

Timing: Noon – 11 PM, with a few storms rumbling over the Eastern Plains until 1 AM

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

Isolated-to-scattered showers/thunderstorms are expected today, producing very little (if any) rainfall. Most of the activity will remain south of I-70, but a few isolated storms over the Northern Mountains and Northwest Slope cannot be ruled out. Gusty winds and cloud-to-ground lightning will be the main concerns, with Red Flag Warnings in place across much of the area. Rain rates will remain below 0.15 inches/hour.

Timing: 11 AM – 11 PM

Issue Date: 6/13/2018
Issue Time: 8:12 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE NORTHEAST PLAINS, URBAN CORRIDOR, PALMER RIDGE, AND SOUTHEAST PLAINS.

Colorado is ground-zero for a battle between dry air and moist air, both in the mid-levels and at the surface. Shown in the water vapor imagery below is the mid-level battle, where moist air from the south is attempting to nudge northward into western Colorado. This moist air will make a valiant effort, pushing north towards I-70 over the High Country and Western Slope. This moisture will be sufficient enough to produce isolated, high-based showers/thunderstorms over southern and central portions of the High Country, producing very little rain (if any), with plenty of lightning and virga painting the sky.

The battle in the low-levels will take place east of the mountains, where east-southeasterly flow has pushed moisture rich low-level air into eastern Colorado. Dry air from the west will try to scour this moisture, with a dry line setting up along, or just east of, the foothills. The moisture, combined with daytime heating, will be enough to produce isolated-to-scattered thunderstorms, with the best coverage and intensity occurring east of I-25. A couple of the storms will become severe, with the potential to produce hail up to 1.5-2 inches in diameter and strong winds greater than 55 mph.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, jump below the map.

Zone-Specific Forecasts

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

Isolated-to-scattered thunderstorms will rumble today/tonight. Without a “trigger” in the mid-/upper-levels, it will be up to low-level convergence and daytime heating to produce adequate forcing for thunderstorm development. With south-southeasterly winds at the surface, the Denver cyclone is expected to aid thunderstorm development, likely kicking off a couple thunderstorms in the vicinity of the Denver metro area. Most storms will struggle to produce heavy rain thanks to dry air in the mid-levels zapping some of the potential, but hail clogging drainage and brief periods of heavy rainfall will likely produce a couple instances of street/field ponding in poorly drained areas. This is the culprit behind the low flood threat. Maximum rain rates are as follows:

Front Range: 0.05-0.25 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 0.5-1.0 inches/hour
Northeast Plains and Southeast Plains: 1.0-1.5 inches/hour

Timing: 2 PM – 11 PM, with a couple lingering thunderstorms over the Northeast and Southeast Plains until 2 AM

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

Dry and hot will be the main weather story today, with only a few isolated, high-based thunderstorms rumbling during the afternoon and evening hours south of I-70 where mid-level moisture from the south can have an impact. Dry air in the low-levels will keep rain rates low, so no flash flooding is expected. Maximum rain rates will be 0.05-0.10 inches/hour. North of I-70, expect dry conditions and mostly sunny skies to rule the day.

Timing: 1 PM – Midnight

Issue Date: Tuesday, June 12, 2018
Issue Time: 09:45AM MDT

— LOW flood threat for portions of the Southeast Plains, Palmer Ridge and Northeast Plains

Once again today, Colorado will be under westerly flow aloft, which should keep dry air in place over the majority of the state. There is a bit more moisture than the last couple of days to the west of Colorado (blue streaks below), so cloud coverage this afternoon over the higher terrains should be more plentiful when compared to the last few days. In the water vapor imagery below you can also see the start of the first northward push of the subtropical moisture at the southern AZ border. The 5880 meter ridge marked in the image will build north to the CO/WY border through this afternoon. Under the ridge and over the eastern plains, decent moisture will return this afternoon as winds shift from north to easterly and support upslope flow.

The best coverage for afternoon thunderstorms initiation will be over the southern Front Range, Southeast Mountains and Palmer Ridge. An isolated storm may also form over the Raton Ridge area. With dew point values in the 30Fs (west), storms are not expected to drop much rainfall. However, as storms move off of the mountains to the east this evening, they will encounter favorable moisture and dynamics for overnight convection over the plains. Threats include gusty winds, large hail and local heavy rainfall, which will could lead to street flooding and field ponding. The thunderstorms are expected to continue into tomorrow morning before crossing east over the Kansas border. With dew points in the mid-50Fs and slow steering winds, a Low flood threat has been issued for the Southeast Plains and portions of the Palmer Ridge and Northeast Plains through tomorrow morning.

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:

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

Upslope flow will return to the region, which should initiate thunderstorms over the higher terrains later this afternoon. Max 1-hour rain rates up to 0.7 inches/hour are possible this afternoon near the Palmer Ridge/Front Range intersect. Over the Southeast Mountains, mostly gusty winds and dangerous lightning are likely with precipitation totals under 0.1 inches. As convection spreads to the eastern plains this evening, thunderstorm and rainfall coverage will increase and continue into the morning hours. Max 1-hour rain rates up to 1.75 inches/hour are possible with local totals up to 2.1 inches over the Southeast Plains near the KS/CO border.

Primetime: 4PM – 8:30AM

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

Dense Smoke Advisory continues for the San Juan Mountains through noon today. Some smoke from the fire in Utah may also sneak into west, central Colorado. Rainfall is not expected today, but cloud cover will increase over the higher terrains this afternoon when compared to the last couple of days. This should help provide some shade from another day of above normal heat.