textproduct: Denver/Boulder

KEY MESSAGES

- Critical fire weather conditions are expected for the mountains and high valleys today. - Strong to severe storms possible across the eastern plains on today and Sunday. - Scattered coverage of showers and storms on Monday and most of next week across the plains.

- Elevated fire weather conditions possible for the mountains and high valleys most of next week.

DISCUSSION /Through Friday/

Issued at 217 AM MDT Sat Jun 20 2026

We've got quite an active day ahead of us, with critical fire weather conditions expected across the mountains and high valleys, and severe thunderstorms possible for our plains this afternoon/early evening.

Current water vapor satellite imagery shows a shortwave over Washington/Idaho. As this system treks east, it will help flatten the well advertised upper level ridge that has been dominating our weather pattern this past week. Winds across the high terrain will strengthen, with westerly wind gusts up to 40-45 mph possible throughout the afternoon. Due to the dry air mass in place, relative humidity values will plummet to 9-15%. A Red Flag Warning will be in effect from 11 AM to 9 PM today.

For the plains, a lee cyclone will develop in the morning ahead the incoming shortwave. Easterly flow at the surface will advect low-level moisture into the region, with dewpoint temperatures reaching up to the low 60s across parts of the eastern plains. Due to this, expect low clouds in the morning, which could affect initial storm development in the early afternoon hours. However, most hi-res guidance still favors the plains warming up to the low 90s. These hot temperatures combined with low-level moisture will allow instability to build. Storms are expected to develop off a boundary east of the Denver metro and track east through the afternoon, where they will encounter an environment favorable for all hazards. MLCAPE expected to build up to 2500-3000 J/kg, with deep layer shear of 40-50 kts. With steep mid-level lapse rates, supercells will have the ability to produce heavy rain, very large hail, and strong outflow winds. With PWAT values up to 1.5", localized flooding is possible. There is also a tornado threat, particularly for our far northeastern plains, where LCLs will be lower and SRH of ~150 m2/s2 is possible. Expect strongest storms to be out of the forecast area by 6-8 PM. However, recent CAMs do show the potential for additional thunderstorms exiting Wyoming and entering the northeastern plains later tonight.

With the arrival of the shortwave on Sunday, additional showers and thunderstorms are expected, but the strongest storms should be confined to the far eastern plains. Forecast soundings show the potential for elevated convection, with decent shear and mid-level lapse rates indicating large hail as the main threat with the strongest storms.

Next week continues to look active for the plains with daily chances for precipitation with the passage of multiple shortwaves. For Monday, there could be a few strong storms for the eastern plains. However, instability and shear profiles do not look as favorable as they do for the weekend. Unfortunately for the mountains, the upper level ridge over the southwestern U.S. will keep a dry air mass in place. Elevated fire weather conditions are possible throughout the week.

Ensemble guidance is in good agreement of below normal temperatures by Tuesday behind a cold front. Guidance has trended slightly cooler (besides the GEFS), with forecasted highs now in the upper 70s. However, warmer temperatures will return by the later half of the week.

AVIATION /18Z TAFS through 18Z Sunday/

Issued at 1152 AM MDT Sat Jun 20 2026

Current GOES-19 satellite imagery show cumulus clouds forming and moving over all three sites. Additionally, current observations show a boundary along the Palmer Divide as well as a weak cyclone centered to the south of KAPA over Douglas County.

Winds are light and near northerly at all three sites with winds expected to pick up in speed over the next few hours. As the boundary shifts north and eastward this afternoon, showers and thunderstorms will fire off starting as early as 19z with the highest chances continuing to look to be east of KDEN and KAPA. A shower/thunderstorm over these two terminals cannot be ruled out, especially early this afternoon. Nevertheless, there is a chance for wind gusts of about 25 to 30 kts from any outflow boundaries that could impact these two terminals.

Tonight, winds will stay gusty with a slight lean to the NW before a front pushes through between 02z and 05z turning winds to NNE. This front will increase gusts once again for a few hours at all three TAF sites. Low stratus clouds are in the forecast again for tonight impacting all three TAF sites with ceilings as low as 1000 to 1500 feet starting as early as 5z and lingering as late as 14z. Ceilings will lift by late morning as winds briefly turn to drainage. Tomorrow afternoon, the winds should be out of the NW and gusty with some gusts up to 25 kts looking likely for most of the afternoon.

BOU WATCHES/WARNINGS/ADVISORIES

Red Flag Warning until 9 PM MDT this evening for COZ211>214-217- 218.