textproduct: Grand Junction

KEY MESSAGES

- Unseasonably warm and dry conditions continue through much of the seven-day forecast.

- Periods of light mountain rain/snow is possible north of Interstate 70 Wednesday through Sunday. The potential for minor winter weather impacts is confined to the spine of the Park Range.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 231 PM MST Mon Dec 15 2025

Conditions remain quiet today as a ridge sits over us. Skies are clear and high temperatures continue to sit 10-20 degrees above normal region-wide. The pattern begins to shift tomorrow though. Another AR is flowing through the PacNW, and per water vapor imagery, may be slightly ahead of schedule compared to ECMWF and GEFS forecasts. The leading edge of this moisture is on a northeastwards track around the backside of the western CONUS trough as of now, but over the next 24 hours, deterministic models are anticipating the upper-level flow to transition to zonal, if not east-southeasterly through the Intermountain West. This pulls the stream of moisture southwards into our CWA, but even then, additional moisture will get caught up on the Sierra Nevada range. As this pool of moisture is quickly depleted, little more than cloudy skies will be able to develop.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Issued at 231 PM MST Mon Dec 15 2025

Models are mostly in good agreement Wednesday with high pressure off the SoCal/Baja coast and troughing over the Great Lakes putting eastern Utah and Western Colorado under a northwesterly flow. A shortwave system moves in through the Pacific Northwest Wednesday morning, passing over the region that evening into Thursday morning. Models diverge on timing with the European and the European ensemble running six hours behind the GFS and GEFS. OF note, H500 winds go from 40 kts in the morning to 75 kts by evening with gradient tightening with the approaching shortwave. Look for winds picking up through the afternoon and continuing through the evening into the overnight gusting 30-40 mph generally north of I-70, spreading into the central Colorado mountains, and gusting 55-70 mph over the peaks of the northern and central Colorado mountains. This system also has strong jet support supporting a cold front with a GFS jet core of 155kts+ and the European 175kts+. The left exit region of the jet passes over the northern and central mountains Wednesday evening frontal boundary for the GFS and early Thursday morning for the European. H700 temps drop about 8-10C northwest to southeast across the region with the surface front only pushing south to the San Juans. Guidance is only dropping surface temps 5-8F between Wednesday and Thursday, but we could see drops more in the range of 10-15F should this occur. Atmospheric river (AR) moisture with this system looks impressive with IVTs over 300kg/m/s, but this is mostly reflective of the strong flow aloft, and not so much deep moisture. Pwats remain below 0.6 inches. Current guidance still has light to moderate snow possible over the Park Range and light snow across the other northern mountains extending south into the Elk Mountains. This latest run of the models is showing this system to be a much stronger system than previous runs though it still lacks moisture, and with the drastic change from the previous runs, confidence is low for mountain snow accumulation. Holding off on any headlines with this system to see the next run of the models has to say. Stay tuned on this one as it could get exciting.

As the nose of the jet slides east and the right exit region crosses the region, subsidence will kill any heavier showers, but light orographic showers may persist over the northern mountains Thursday. Another shortwave passes to the north Friday evening into Saturday keeping the tight gradient aloft across the region. Look for gusty winds over the higher terrain Thursday evening through Saturday. The AR moisture stays mostly to the north as does the jet and any upper- level dynamics , but does brush the northern mountains. With a more zonal flow and warm air advection, snow levels rise to about 8,000 feet with rain falling below this elevation. Again, not a lot of precipitation is expected from this system with only a slight chance for minor impacts on Rabbit Ears Pass Friday night and Saturday.

Of interest, the AR pushes south to the LA Basin Sunday to bring moisture into the Desert Southwest and southern Colorado mountains, but guidance hasn't picked up on this yet. Early next week we could see some showers farther south, but we'll just have to wait to see. Otherwise, the weather pattern seems to stay unsettled through the extended period with weak systems passing every few days.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 919 PM MST Mon Dec 15 2025

Passing high cloudiness and light winds are again expected to dominate the TAF forecasts over the next 24 hours. There is a 20 percent probability or less of ground fog impacting the KGUC airfield overnight.

GJT WATCHES/WARNINGS/ADVISORIES

CO...None. UT...None.