FXUS65 KGJT 261743 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 1143 AM MDT Fri Apr 26 2024 .KEY MESSAGES... - Isolated showers continue this morning with more widespread showers and thunderstorms expected again this afternoon. - A potent system will move through the area Friday evening through Sunday morning bringing much cooler temps, valley rain and mountain snows to the region. - Winter Weather Advisories remain in effect above 9000 feet for 6 to 12 inches of snow. Advisories in UT begin at 6AM this morning while CO advisories begin at 6PM this evening, both continue through 6AM Sunday. && .SHORT TERM /THROUGH SATURDAY/... Issued at 154 AM MDT Fri Apr 26 2024 Light showers continued overnight as a weak wave moved across the area. These showers will continue through the morning hours though shortwave ridging is expected to limit coverage to a degree. This all changes as we head into the afternoon, however, thanks to an approaching trough and surface cold front. Like yesterday, CAPE values will be on the order of 300 to 600 J/kg across much of the CWA while lapse rates will be around 8C/km. QG forcing is also showing a decent amount of lift across the CWA so with all these ingredients in place, we can expect another day with numerous showers and thunderstorms. Forecast Skew-Ts continue to show an inverted V profile but not as deep as yesterday though DCAPE values do reach 400 J/kg so some stronger downbursts are certainly possible. Heading into the high country, some snow will fall as the snow level will sit around 9K feet. Of course, any stronger convection could drop these snow levels noticeably. Either way, daytime heating will limit any impacts to roadways as snow will melt there giving way to some wet roads. As the day progresses and the trough continues to approach the CWA, a midlevel closed low will form just west of the Four Corners region. Upper level support in the form of a 100-110kt jet will be rounding the base of the trough Friday afternoon and the wind speeds entering the trough will be just about equal to those exiting the trough meaning the trough and front will be slow moving. The end result will be a prolonged precip event with banded precip setting up (where exactly is the tricky bit) and accumulating mountain snows and precip for the valleys. Precip will continue overnight Friday with accumulating mountains snows for almost all of the higher terrain. Models continue to paint 6 to 12 inches of snow so the Winter Weather Advisories will remain in effect. Precip continues Saturday across the CWA and with all the cloud cover, precip and west through northwesterly flow, high temps will be about 10 to 15 degrees below normal late April values. By Saturday evening, the broad area of low pressure will be more over eastern CO than the Western Slope but alas, precip will continue. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Issued at 154 AM MDT Fri Apr 26 2024 By Saturday evening, the low will have moved east of the Divide and out onto the Plains of northeastern Colorado with wrap- around moisture keeping orographic snow showers going overnight into Sunday morning in the northern and central Colorado mountains. The northwesterly flow aloft behind this system and lingering moisture will support isolated to scattered showers in the mountains through Sunday before tapering off in the evening. The Colorado mountains above 9,000 feet can expect another two to four inches accumulation from Saturday evening into Sunday evening. Since daytime temperatures will stay around freezing Saturday under overcast skies on Vail Pass and at the high elevations in general, the mountain roads won't have a chance to warm up through the day. Look for the mountain roads to remain slick and messy overnight into Sunday even though not much snow will fall overnight. Models are in good agreement with a general longwave trough setting up to the north across the western CONUS to the Great Lakes that remains in place for the coming week. The zonal flow across eastern Utah and Western Colorado will generally be dry with breezy westerly winds each afternoon, but a series of shortwave systems moving through the longwave to the north will brush the northern mountains spawning isolated to scattered showers each afternoon in the Elkhead, Park and Gore Mountains, and on the Flat Tops. Otherwise, look for mostly clear skies and warm temperatures across the region with most of the clouds that do form staying mostly over the mountains each afternoon. Model agreement continues through the week, but beyond Monday, wide dispersion shows up in the ensembles that average out to the continued zonal pattern, but confidence is very low on the solutions. This spells the possibility of one of the shortwaves passing to the north digging deeper into the area to possibly impact the central and even the southern mountains with showers. The run-to-run consistency is is also not consistent; where 24 hours ago models were in agreement predicting H500 heights of 576 to 579 over the region which would spell very warm days by mid week, the most recent runs are now showing these heights in the 570 to 573 range, much more moderate. We'll just have to wait and see how this one plays out. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1143 AM MDT Fri Apr 26 2024 Scattered showers and storms will roam across much of eastern Utah and western Colorado this afternoon and evening. While VFR should mostly prevail, brief periods of MVFR are probable near any showers and storms. Any stronger shower or storm can produce erratic and gusty winds. Scattered instances of ILS breakpoint ceilings are likely too, becoming more widespread later this evening and overnight. Isolated to showers likely linger through the night and into the morning hours on Saturday, with rain changing to snow for some of the high elevation terminals like KTEX and KASE. Longer periods of MVFR with brief periods of IFR are likely, especially in the mountains. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Winter Weather Advisory from 6 PM this evening to 6 AM MDT Sunday for COZ004-009-010-012-013-018-019. UT...Winter Weather Advisory until 6 AM MDT Sunday for UTZ023. && $$ SHORT TERM...TGR LONG TERM...DB AVIATION...TGJT