Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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501 FXUS65 KGJT 292152 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 352 PM MDT Mon Apr 29 2024 .KEY MESSAGES... - A disturbance passing to our north will bring rain showers and mountain snow to the northern half of the CWA tonight. Snow accumulations of 1-3 inches are possible. - Afternoon winds will remain gusty this week, as a series of disturbances along the jet stream impact the region. - A brief cool spell on Thursday in the wake of a cold front will drop temperatures, before things warm back up heading into the weekend. && .SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 347 PM MDT Mon Apr 29 2024 Satellite imagery shows the models are tracking well with the low descending out of the Gulf of Alaska off the coast of British Columbia into the Pacific Northwest, a weak longwave trough across the western CONUS to the Great Lakes producing a zonal flow across eastern Utah and Western Colorado, and the last low pressure system that pass through the region Saturday exiting stage right up over the Great Lakes into Canada. Our weather will be impacted through this week by disturbances passing to the north in the longwave pattern bringing continued unsettled weather to the areas generally north of the I-70 corridor. Currently the westerly flow is driving the residual moisture in the region onto the terrain producing scattered light orographic showers along and north of I-70, and isolated showers to the south. Guidance hasn`t picked up on the orographic effects and had to pencil in PoPs to cover the northern areas. Warm air advection aloft has capped these showers below about 500mb, and with the plentiful residual moisture in the area generating significant cloud cover preventing diurnal heating, stronger showers or storms are unlikely to develop this afternoon. A shortwave passes to the north this evening into Tuesday morning bringing showers and an isolated thunderstorm across the northern areas with some snow accumulation possible above 9,000 feet. Expect up to an inch snow accumulation possible in the eastern Uintas, and a few inches possible on the Flat Tops, and on the Park, Elkhead and Gore Ranges. Behind this disturbance, a band of drier air pushes into the area by afternoon to clear out the skies and heat the surface temperatures to near normal or a little above normal that will increase mixing the winds aloft down to the surface. Look for westerly winds across the region tomorrow afternoon around 20-25 mph gusting 30 to 35 mph with the stronger winds across the northern two thirds of the region. As a second shortwave digs deeper into Idaho and Wyoming overnight Tuesday, winds aloft increase to near 70 kts at H500 across the northern areas and more like 40 kts across the southern areas with the tightening pressure gradient. Would not be surprised to see a few strong overnight gusts lee of higher terrain, but again, none of the guidance seems to pick up on it. This is something to watch in the short term. Otherwise, look for a few isolated light showers overnight in the northern mountains going into Wednesday morning. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Issued at 347 PM MDT Mon Apr 29 2024 The pattern remains progressive Wednesday as the positive tilt mid- level trough shifts eastward over the Great Basin during the day. Models drive the cold front associated with this system east- southeastward across the northern half of the forecast area before the days out, and the boundary may drift farther south than earlier runs had indicated. Moisture running northeastward ahead of the system combined with surface convergence, good dynamic forcing at the mid and jet levels will lead to numerous showers and embedded thunderstorms by Wednesday afternoon with the northern Colorado mountains favored, though chances are good for the eastern Uinta Mountains, the northwest Colorado plateau and the central Colorado mountains as well. Areas to the south will see little to no chance for precipitation. Cooler temperatures appeared reasonable for Wednesday, especially for the northern and central zones with frontal passage. That said, not confident models are cooling it enough for areas along and north of the I-70 corridor, so replaced NBM with bias corrected ConsAll which appeared more reasonable and has shown better verification numbers. The trough axis moves to just east of the Continental Divide by 12Z/Thu while the cold front is driven to the southern CO/UT borders. The evening period will remain active for the previously mentioned locations with coverage decreasing late Wednesday night. Twenty-four hour snow accumulations approach advisory levels for the Park Range, but only for areas above the treeline, so will not issue highlights for this event unless later runs warrant reconsideration. NBM seemed a bit out of step with latest operational runs on Thursday which only indicated slight to low chance PoPs over the Elkhead and Park with little chance elsewhere. In contrast, NBM holds onto to middling chance PoPs over the northern and central Colorado mountains and adjacent valleys throughout the day. Check back tomorrow and I`m certain we`ll be looking at markedly reduced chances for additional showers on Thursday. What is more certain however, is that temperatures will dip by around 10 degrees for the entire forecast area, or around 5 to 10 degrees below normal. Another fast moving system impacts the north on Friday bringing another round of rain, snow and embedded thunderstorms for the northern and central Colorado mountains and, to a lesser extent, their adjacent valleys. This system moves out quickly with conditions improving Friday night. The weekend outlook appears pretty favorable for those looking to get out and recreate. A transitory ridge moves overhead on Saturday as a low deepens over the West, then shifts east on Sunday as the western low begins its approach. Models not in good agreement with the positioning of the low center, but this doesn`t appear to be a factor for our weather until early next week. Consequently, aside from some isolated moist convection over the Continental Divide, dry and warm weather is expected with the lower valleys climbing into the 80s with 70s in the higher valleys and upper 50s and 60s in the mountains. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1159 AM MDT Mon Apr 29 2024 A weak disturbance moving over northwest Colorado will bring lowered ceilings for KHDN. There`s a slight chance for showers at KHDN through 21Z, but odds didn`t favor mentioning in the TAF. Meanwhile, ceilings below ILS breakpoints at times at KASE and KEGE may slow traffic into those airports this afternoon. Breezy west and southwest winds will be common for most sites into the evening. A more energetic disturbance moves over the area tonight with showers almost certain at KHDN in the early morning hours. This activity is likely to bring ceilings to ILS breakpoint levels, but impact on visibility less certain. Elsewhere, winds will drop off and VFR conditions continue during the remainder of the period. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...DB LONG TERM...NL AVIATION...NL