Issue Date: Sunday, July 12th, 2020
Issue Time: 9:40AM MDT

— A LOW flood threat has been issued for the Southeast Plains and eastern Raton Ridge

Today will be quite the pattern change from the last couple of days. Moisture has returned to the state, which can be seen by the blue plume below. This moisture is helping create some morning fog and cloud cover over eastern Colorado where dew points are in the 50Fs and 60Fs. It’s also a bit windy over the eastern plains with south winds gusting between 25 and 35 mph. PW has risen to 0.64 inches over Grand Junction, which will mean that afternoon and evening storms will return to the forecast. Mid-level energy traveling around the High, including the shortwave marked with the orange “X” below, will allow a little better coverage of scattered storms over the lower elevations as well. As the shortwave (marked below) traverses eastward, it will help spark scattered storms over the Front Range and Southeast Mountains in conjunction with the diurnal flow. Inverted-V soundings indicate that storms that form will be capable of producing brief, gusty winds in addition to some lightning. Rainfall accumulations should be low, so flooding in not expected. As storms move into the adjacent plains, a little higher accumulation is anticipated along the Palmer and Raton Ridge.

Over eastern Colorado a lee trough sets up, which will create a dry line type feature over the eastern plains and mix out moisture back to its west. With dew points in the 60Fs to the east of this line, storms that move into the area or fire along the dry line will be capable of producing local, heavy rainfall even with moderate storm motion to the southeast. A few severe storms are likely with the main threats being large hail (up to 2 inches) and strong outflow winds, but a weak tornado may also be possible. A Low flood threat has been issued for the area from about 4PM to 11PM.

A second wave of weak storms will likely arrive to the western border later tonight. Upper dynamics associated with the shortwave to our northwest and mid-level energy rotating around the high will allow light rainfall to continue over the Northern, Central and San Juan Mountains through tomorrow morning. Flooding is not expected from these storms.

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:

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

A Low flood threat has been issued for the Southeast Plains as high dew points in the area will allow the severe thunderstorms to drop heavy rainfall. Max 1-hour rain rates just under 2 inches will be possible. The flash flood threats include flooding of local streams, roads, and low-lying areas. Local field ponding will also be possible. Large hail (up to 2 inches) and damaging outflow winds (up to 60 mph) will be possible under the severe storms that form with an outside chance of a weak tornado. The flood threat will start around 4PM and end around 11PM with lighter rainfall lingering a couple more hours.

Back west, as storms move off the mountains, max 1-hour rain rates will increase slightly to about 0.75 inches over the Palmer and Raton Ridges. Rain totals will be a bit lower over the lower elevation regions with surface moisture mixing out east throughout the day. Flooding is not anticipated with these storms.

Primetime: 1:30PM to 12AM

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

The Grand Valley will have its first wave of storms arriving just after 11AM this morning, so expect some light showers and storm accumulation/coverage increasing by later this afternoon. Max 1-hour rain rates up to 0.15 inches will be possible over the lower elevations with the main threat from storms being gusty winds and lightning. Over the higher elevations, isolated 24-hour totals up to 0.25 inches will be possible with more general rainfall totals in the 0.10 to 0.20 inch range. Again, the main threat from the afternoon/evening storms will be wind gusts up to 45 mph, but dangerous lightning will also be possible (beware hikers). Over the eastern mountains, low-level moisture looks a little better, so max 1-hour rain rates up to 0.40 inches will be possible. The overnight storms over the western mountains mentioned in the discussion aren’t expected to drop much rainfall, and increased cloud cover will likely keep low temperatures a little higher than they would normally be. Flooding is not expected.

Primetime: 11AM to Ongoing

Issue Date: Saturday, July 11th, 2020
Issue Time: 8:55AM MDT

— Flooding is NOT expected today

The visible satellite imagery below is showing some fog this morning over the northeast corner of the state where dew points are in the 60Fs. A little mixing and daytime heating should burn the fog off fairly quickly. Dry, westerly flow will continue over the state today with not much movement in the High from yesterday. This will again mix out the surface moisture from west to east throughout the day and place the higher dew points over the far eastern plains/southeast corner this afternoon. Some moisture has begun to make its way northward on the west side of the high (Utah, Arizona), and a disturbance over Wyoming (orange “X”) will swing south this afternoon with counterclockwise motion. This will help increase cloud cover across the norther border, but a decent cap at 700mb should keep storms from forming.

The cap may be able to break over the elevated regions of the Palmer and Raton Ridge, but even if a thunderstorm or two is able to pop, rain rates should be low enough to avoid flooding issues. With PW at 0.24 inches over Grand Junction (another daily record low), rainfall is not anticipated over western Colorado either.

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, Southeast Plains, Northeast Plains, Palmer Ridge, Raton Ridge, San Luis Valley, & Urban Corridor:

Temperatures over the plains will be slightly cooler today after a weak cold front moved through the area last night. It will be hard to notice the cooling as highs are still anticipated to be in the 90Fs. With dew points in the 50Fs over the far Southeast Plains and temperatures in the mid-90Fs, it’s to feel muggy once again. Expect cloud cover to increase across the northern border as the aforementioned disturbance moves south, which will bring a little relief from the afternoon heat. Thunderstorms are not anticipated over this area with the cap.

If a storm or two can break the cap over the Palmer Ridge and Raton Ridge, max 1-hour rain rates up to 0.50 inches will be possible along with gusty outflow winds. There is a better chance that only increased cloud cover occurs, but if the initial storms can produce a decent outflow boundary, it may be enough to help the subsequent cumulus break the cap. Flooding is not forecast.

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

Fire danger is elevated over the region as it has been very dry, it will continue to be dry, and fuels are exceptionally dry. The spread of rapid fire growth is less today, since surface wind speeds should remain below 10 mph. Thus, there is no Red Flag Warning, but still use caution with open flames and avoid burning. As for temperatures, it’s going to be hot again. The Grand Valley could reach 100F+, so similar to yesterday with maybe even a slight uptick in the afternoon highs. Rainfall is not anticipated, but some broken afternoon cloud cover is likely over the higher elevations.

Issue Date: Friday, July 10th, 2020
Issue Time: 10AM MDT

— Flooding is NOT expected today

Today’s weather can be described by one word: HOT! The strong ridge, with the high centered to our south, will produce some very high temperatures this afternoon. Expecting most metro areas, the Grand Valley, and eastern plains to hit the century mark, and if they don’t, they’ll come very close to it. The PW values across the state are quite low (new record low value for Grand Junction), and a mid-level cap just about 3km over eastern Colorado will keep afternoon rain out of the forecast. So, all the atmosphere will be able to muster is some broken cloud cover over the mountains and western Colorado this afternoon and evening. A little heavier cloud cover is expected across the southern border as the disturbance in the image below (over NM/AZ) makes its way northward. Rainfall from that disturbance is not forecast.

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:

Southeast Plains, Northeast Plains, Palmer Ridge, Raton Ridge, San Luis Valley, & Urban Corridor:

It’s going to be a scorcher this afternoon! Denver, Fort Collins, and Pueblo will all be able to reach that century mark making this the hottest day of the year so far (at the state level). Due to the slightly higher elevations of the San Luis Valley and Colorado Springs, high temperatures will be closer to the low-90Fs and mid-90Fs, respectively. Not expecting much cloud cover for relief from the heat either, so be sure to keep yourself hydrated.

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

Expecting the mountain valleys to reach the high 80Fs this afternoon with 70Fs for most mountain towns. Highs will likely reach the century mark or flirt with it over the lower elevations of western Colorado. Some gusty winds are anticipated over the Northern Mountains and Front Range, so a Red Flag Warning has been issued. West winds are expected to reach the 10 to 20 mph range with gusts up to 30 mph possible from 11AM to 8PM this morning. It will be too dry for any rainfall, but some broken afternoon cloud cover can be expected.

Issue Date: Thursday, July 9th, 2020
Issue Time: 10:10AM MDT

— A LOW flood threat has been issued for parts of the Northeast Plains

This morning’s water vapor imagery, below, shows a nearly zonal mid and upper-level flow is in place across the Rocky Mountain states. Very dry air is noted in Utah that will spread into western and central Colorado once again, limiting cloud cover and pushing temperatures above average again.

Things get more interesting farther east. A large cluster of storms is noted over South Dakota, which has sent a large-scale moist outflow boundary southwestward into eastern Colorado this morning. How moist? The Burlington observation station (Kit Carson County) is reporting a dew point of 63F under a low cloud deck. Meanwhile, the PW at Denver this morning was a meager 0.39 inches, well below normal, with a surface dewpoint of 33F! Farther east, the PW at North Platte (NE) was 0.88 inches, while Goodland (KS) measured an impressive 1.47 inches. In short, there exists a very sharp moisture gradient today across eastern Colorado. Furthermore, a surface low was noted over the western Oklahoma panhandle, which will re-develop further west in consistency with the warm season diurnal cycle in Colorado. This will help advect some of the aforementioned moisture back in the state. Instability, as measured by CAPE, will be in around 1,500 J/kg, though this number will be highly sensitive to the boundary layer moisture. A CAPE up to 3,000 J/kg would not be out of the question along the Kansas border. With 0-6km vertical wind shear increasing to 40+ mph today, there will be plenty of instability and dynamics to support rotating supercells. Large hail, up to 2.25 inches will be possible. The main limitation today will be the presence of a boundary layer cap that should limit storm coverage to the isolated/widely scattered variety.

Finally, regarding the threat of heavy rainfall, dewpoints above 55F are expected to persist along the NE/KS borders, with PW over 1 inch or even higher likely, at least locally. Our high resolution is suggested 40-60% chance of precipitation, though, it’s a setup where if storms fire, they will be capable of very heavy rainfall (along with the aforementioned severe weather). It appears the high-resolution guidance is underestimating rainfall rates today though precipitation chances look reasonable. Thus, a Low Flood threat is warranted for a small part of the Northeast Plains for this afternoon and into the overnight hours for isolated flash flooding and field/street flooding.

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:

Palmer Ridge, Northeast Plains, Southeast Plains:

Sunny west, with low clouds early out east. Temperatures warming up quick with isolated to scattered showers and thunderstorms likely this afternoon. Max 1-hour rain rate up to 1.9 inches along the Kansas border warrants a small area with a Low flood threat. Main hazards will be isolated flash flooding with field and street flooding likely under the strongest storms. Hail up to 2.25 inches will also be possible, along with tornadoes, mainly of the landspout variety given the low humidity below the cloud base.
Primetime: 3PM to 1AM

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

Mostly sunny and very hot today with temperatures continuing to run up to 10F above normal. An isolated thunderstorm cannot be ruled out for far eastern areas over the Urban Corridor. However, max 1-hour rainfall will be below 0.5 inches and gusty winds are the bigger threat with these storms. Flooding is not expected today.
Primetime: 1PM to 9PM