FTB 08-12-2020: High Fire Danger Continues with Severe Storms Returning to the Northeast Plains

Issue Date: Wednesday, August 12th, 2020
Issue Time: 10:30AM MDT

— Flooding is NOT expected today

Today will be similar to yesterday’s setup as dry air remains anchored over the western 2/3rds of the state. With the high pressure ridge to the south of Colorado, dry air over southern Utah will continue to flow into western Colorado and spread eastward. Meanwhile, a trough is moving into the Pacific Northwest, which is increasing the height gradients and upper-level winds over the western US. The combination of dry air and gusty surface winds will once again create elevated fire danger for western Colorado today, so a Red Flag Warning has been re-issued for the Grand Valley, Southwest Slope, Northwest Slope, and Central Mountains.

Some surface moisture has banked its way up against the foothills and over the plains of eastern Colorado due to outflow from last night’s storms. This has increased surface dew points into the 50Fs for much of the plains, as indicated on the image below. However, soundings show this moisture is quite shallow, so it should have no problem mixing out from west to east with diurnal heating. Weak showers and a few isolated storms are still expected to fire over the Continental Divide this afternoon, and could produce some gusty winds again as they dissipate across the Urban Corridor. With slightly higher moisture and instability east, storms that can make it into the Northeast Plains should strengthen, and a couple severe thunderstorms could develop with moderate wind shear in place. The severe storms could create strong outflow winds and severe hail as well. Due to moderate upper-level flow, storms should be moving east fairly quickly, and with a little less moisture available than yesterday, flooding is not expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Strong storms are possible over the northeast corner of the state later this afternoon. Max rain rates up to 1.4 inch are possible under the stronger storm cores, but quick storm motions decrease the chances for flooding. Gusty outflow winds up to 60 mph and severe hail up to 1.5 inch in diameter could accompany the strongest storms.

Little to no chance for storms over the Southeast Plains and Urban Corridor, but as storms move off the higher terrain, they could produce some gusty downbursts. Higher chances of storms and clouds exist farther north.

Primetime: 12PM to 9PM

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

Guidance is showing a higher chance for some storms over the high terrain this afternoon. Unfortunately, without much moisture, they will most likely produce only gusty outflow winds. With the hot and dry conditions continuing, along with wind gusts 30+ mph, a Red Flag Warning has been re-issued along the northwest portion of the state. Keep up to date on wildfire-related road closures (https://cotrip.org/home.htm) and evacuations from their social media pages (linked below). Smoke from the wildfires will also impact air quality for the central and northern mountains and valleys, especially overnight.

Pine Gulch Fire: https://www.facebook.com/PineGulchFireCO
Grizzly Creek Fire: https://www.facebook.com/GrizzlyCreekFireCO

FTB 08-11-2020: Thunderstorms for the Eastern Plains & High Fire Danger for Western Colorado

Issue Date: Tuesday, August 11th, 2020
Issue Time: 8:50AM MDT

— Flooding is NOT expected today

Increasing west-southwest flow aloft today will continue to entrain the dry air mass over the majority of the state (yellow/orange below). This will produce lower precipitation chances back to the west and over the mountains. Additionally, the dry air is expected to move into the adjacent, eastern plains helping mix out surface moisture from west to east, which will set up a dry line over the eastern border counties. Along and east of this line will be the main focus for heavier rainfall this afternoon and evening, and upper dynamics are favorable for a few severe thunderstorms to develop. Expect the haze to continue as well over northern Colorado with the ongoing fire activity.

A weak shortwave is also expected to move through the flow, which will help enhance lift and increase wind speeds as it moves overhead. Without much surface moisture to work with, “storms” that can fire back to the west will likely produce strong outflow winds and little to no rainfall. The increased wind speeds from the feature are also expected to somewhat mix down to the surface, which will escalate fire danger with the low relative humidity values over western Colorado. A Red Flag Warning has been issued for the western border counties and Central Mountains from noon to 8PM. As the shortwave arrives to the eastern plains this afternoon, it will help kick off the convection. Severe thunderstorms that develop will be capable of producing strong wind gusts and severe hail. PW values will be around 1 inch, but faster steering flows to the east/southeast and more scattered coverage of the stronger storms means that no flood threat will be issued.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

Temperatures will be back on the rise today after a nice cool down over portions of eastern Colorado yesterday. Rainfall chances are close to zero over the mountains and I-25 corridor, although areas with increased cloud cover this afternoon over the mountains may see a sprinkle or two. As the clouds move off the mountains into the adjacent plains, the breeze should pick up. Best chance for rainfall will be over the border counties along and east of a dry line. Max 1-hour rain rates up to 1.4 inches will be possible along with strong wind gusts (up to 55 mph) and large hail (up to 1.5 inches) for the severe storms that develop. Faster storm motion and smaller coverage of the heavier rain cores will mean that no flood threat is issued.

Primetime: 2PM to 9PM

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

High fire danger is forecast today with a Red Flag Warning issued for the border counties and Central Mountains from noon to 8PM. Southwest surface winds are forecast to be between 10 and 20 mph with gusts up to 30 mph possible as relative humidity values continue to sit in the low teens and single digits. Haze is expected to continue and the HRRR model shows a lot of near surface smoke over the Grand Valley and portions of the Central Mountains, which will lower the air quality. Hot temperatures are also forecast with the Grand Valley reaching the upper 90Fs, Durango near 90F, and the mountain valleys in the mid to upper 70Fs. Again, the dry air will keep precipitation chances near zero.

 

FTB 08-10-2020: Upslope Flow will Ignite Some Storms for the Plains

Issue Date: Monday, August 10th, 2020
Issue Time: 10:10AM MDT

— Flooding is NOT expected today

Mid-level and upper-level flow continues to be weak today, as Colorado is situated between a broad trough to the north and an elongated, weak high pressure region to the south (see image below). This will allow slow storm movements today. Additionally, a summertime cold front has banked its way up against the Front Range this morning, which has increased surface dew points back into the low 50Fs along the Urban Corridor and Northeast Plains. However, the Denver sounding this morning shows this surface moisture is very shallow, which has only increased the PW value to 0.53 inches (still below average). Some clouds and showers have developed over the Palmer Ridge and east to the Kansas border this morning (blue & white on the water vapor satellite image below), which lines up with the location of the cold front and some upper-level lift. This cold front will likely not make it much further south today. Cooler daytime high temperatures are expected behind the cold front for the northern plains. A surface low pressure is sitting over southeastern Colorado, which is helping more moist easterly flow impinge on the eastern side of the Palmer Ridge. This low pressure area will sit over southeastern Colorado today and reinforce the weak surface moisture up against the Front Range mountains and Palmer Ridge along with the northeasterly upslope flow behind the cold front. With diurnal heating, some of the shallow surface moisture will mix out, but enough moisture should stick around to increase chances for rainfall over eastern Colorado. Storms are expected to fire over the Front Range this afternoon and make their way east, but limited moisture (40Fs and 50Fs dew points) and instability will keep rain rates low. The main threat will be gusty outflow winds. Flooding is not expected today.

Continued dry air over the desert southwest will be trying to push its way into southwestern Colorado, but the driest air should stay southwest of the state, which will allow some afternoon clouds and showers to once again develop over the high terrain. However, no flooding is expected.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

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

The biggest change today is the 10F cooler high temperatures for the Urban Corridor and Northeast Plains behind the cold front. However, this cold front will allow some isolated storms to fire over the Front Range and Palmer Ridge this afternoon, with the highest chances for storms over the Palmer Ridge. With limited surface moisture, these storms should stay fairly weak with max rain rates up to 0.8 in/hr over the Palmer Ridge. Gusty outflow winds up to 50 mph are also possible with storms this afternoon and evening. Lower rain rates, up to 0.4 in/hr, are forecast over the Front Range and Urban Corridor. These storms will slowly make their way east into the plains, where higher moisture closer to the eastern border of Colorado could increase max rain rates up to 1 in/hr. It is possible some additional storms may fire near or after sunset as the nocturnal low-level jet pushes moisture back west overnight. Due to the placement of the surface low pressure over the Southeast Plains, lower chances for storms exist over the Southeast Mountains and Raton Ridge due to dry westerly surface winds.

Primetime: 12PM to 2AM

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

Mostly sunny and warm today, with high temperatures a few degrees above average. Clouds and showers could form over the high terrains, similar to the last few days. Flooding is not expected, as only isolated sprinkles are forecast.

Primetime: 12PM to 7PM

FTB 08-09-2020: More Dry Air & Heat

Issue Date: Sunday, August 9th, 2020
Issue Time: 10:05AM MDT

— Flooding is NOT expected today

Today’s weather setup is similar to yesterday, as Colorado is situated between a broad high pressure ridge to the southeast and a broad trough to the north (see image below). The shortwave that initiated storms along the northeastern and eastern border of Colorado yesterday is now moving up into Minnesota. Strong mid-level flow is largely confined within the trough to the north of Colorado. Weak (10-20 mph) mid-level southwesterly/westerly flow is present over Colorado today, as indicated by the 500 mb analysis overlaid on the satellite image below. Some mid-level energy and moisture are creating some clouds over southern Colorado (blue on water vapor image below). This mid-level energy will increase chances for light showers over the southern mountains today. However, dew points are quite dry over Colorado this morning, with 10Fs over northwestern Colorado and 30Fs over southern Colorado. This dry surface air will limit rain accumulation at the surface. The Grand Junction sounding this morning shows a record low PW value of 0.26 inches, which shows just how dry the airmass is over western Colorado. No flooding is expected today.

The eastern border of Colorado is the only place where some moisture is able to hang on, where dew points are in the 50Fs. Farther west over the Urban Corridor, the air is much drier, with dew points in the 30Fs and a below-normal Denver PW value of 0.43 inches. A broad area of low pressure will remain over the plains of Colorado, but small pressure gradients will generally favor weak westerly and northerly winds over the plains. This will not allow higher moisture east of Colorado to be pushed west into Colorado, so much of the low-level moisture that exists along the eastern border of Colorado this morning will be mixed out with diurnal heating today. In fact, temperatures will climb to near-record levels along the Urban Corridor and plains regions today. There still exists a low chance of thunderstorms developing along the eastern border of Colorado today, but the limited moisture will cut down on instability and potential rainfall from these storms. No flooding is expected.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Northeast Plains, Urban Corridor, Palmer Ridge, & Southeast Plains:

Partly cloudy and hot, and locations near the eastern border could see a storm or two fire where low-level moisture is able to stay in place. Storms will be fighting plenty of dry air, so max rain rates should stay under 0.5 in/hr. Flooding is not expected with these storms. Near-record high temperatures are expected for the Urban Corridor, with a high of 98F forecast for Denver and a high of 99F forecast for Fort Collins.

Primetime: 1PM to 8PM

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

Mountain clouds and showers are possible this afternoon, with the highest chances of cloud cover and showers over the San Juan Mountains. Northern regions will likely just see some clouds and smoke from the Pine Gulch Fire. Extremely dry air at the surface will limit any rainfall to high elevation locations, where up to 0.05 inches of rain could fall. No flooding is expected. A fire danger still exists for much of western Colorado due to the continued dry weather.

Primetime: 11AM to 8PM