Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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665 FXUS65 KGJT 020530 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 1130 PM MDT Wed May 1 2024 .KEY MESSAGES... - A cold front will cool temperatures 5-10 degrees across much of the region Thursday. - Valley rains and mountain snow this afternoon will move east of the Divide by midnight. 1-2 inches of snow is expected above 9000 feet, with some higher peaks getting more. - Scattered showers and thunderstorms will be capable of producing small hail, lightning and gusty winds this afternoon and early evening. - Warm and dry conditions return for the weekend ahead of more unsettled weather early next week. && .SHORT TERM /THROUGH THURSDAY NIGHT/... Issued at 256 PM MDT Wed May 1 2024 The persistent low pressure system centered along the Canadian Border about the Alberta-Saskatchewan-Montana triple point continues to dominate the weather pattern keeping the longwave trough in place across the Western CONUS. A stronger shortwave and cold front is moving under the low supported by a 100kt jet aloft. This shortwave looks to be enough to finally eject the low to the east by Thursday evening, bringing changes to our weather in the next week. The tight northerly pressure gradient at H500 is producing 60kt zonal winds aloft across eastern Utah and Western Colorado. A band of showers is tracking northwest to southeast across the region associated with the right entrance region of the jet. With the dry inverted-V sounding from this morning, little of the precip is reaching the ground, but the showers/virga is effectively mixing the strong westerly winds to the ground with 30 to 45 mph gusts have been reported across the northern and central portions of the region. These showers will continue to push through to the southeast across the region in sync with the right entrance region of the jet, moving east of the Divide by late this evening. The actual cold front with this system will start into the region in the Uintas late this afternoon, working its way to the southeast through the evening hours before stalling out on the San Juans in the overnight. Look for the morning low temperatures 10 to 15 degrees cooler tomorrow than this morning in the areas north of the San Juan Mountains. The skies clear out overnight with sunny dry weather on tap for at least the morning. By noon we`ll start seeing some mid to high clouds moving down from the northwest ahead of the next shortwave trough due into the region Friday morning. The clouds will generally stay to the north of the I-70 corridor, and though the sun will feel warm south of I-70, temperatures will remain about five degrees below normal through the day behind the frontal boundary. There is a very slight chance for showers to initiate over the northern mountains overnight Thursday, but these will likely hold of until the morning. With the strong zonal flow aloft continuing over the region, look for more gusty west winds again tomorrow afternoon. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Issued at 256 PM MDT Wed May 1 2024 The progressive pattern will continue to impact eastern Utah and western Colorado through the long term period. Due to the polar jet`s seasonal migration north, showers will continue to miss the lower elevations of the Four corners region. That said, the next mid-level trough in the series begins to impact the area early Friday morning and will continue to generate showers through the afternoon according to model consensus. The lifting mechanism initially is produced from overrunning and jet divergence, but transitions to vorticity advection and orographics as the trough passes over the north during the day. Accumulations across the Elkhead, Park, Flat Top and eastern Uinta mountains are expected to be light, generally from 1 to 3 inches above 8500 feet with locally higher amounts. Timing of the cold front associated with this wave is expected to allow temperatures to rise a couple of degrees north of the I-70 corridor and around 5 degrees to the south. Subsidence on the backside of the trough with a transitory ridge building over the area ahead of a closed low off the coast of the Pacific Northwest will result in a break in the weather Friday night. On Saturday, the low to the west moves ashore over southern Oregon causing the area to fall under broad difluent southwest flow aloft. Meanwhile, strengthening southwesterlies will drive the cold front northward and out of the forecast area with much warmer air filtering into the region during the day. Lingering moisture is expected to yield isolated to scattered showers and thunderstorms over the mountains of the Continental Divide Saturday afternoon while the remainder of the region remains dry and warmer with highs climbing to around 10 degrees above normal. From Saturday night to Sunday the closed low moves over the Great Basin. Pre-frontal height packing ahead of the impressive cold front associated with this system will result in windy conditions from late morning Sunday into the early evening. Moisture arrives over northeast Utah early with showers becoming likely for the eastern Uinta Mountains during the afternoon with more scattered activity north of the I-70 corridor and far northwest Colorado. 12Z operational models were in better agreement and all indicated the low will pass over the area Sunday night driving it`s cold front eastward to the High Plains by 12Z Monday. Consequently, this will be the most active phase of the storm and snow levels will be lowering to between 6 and 7 Kft. The moisture wrapped system is expected to continue to generate showers over the northern and central Colorado mountains and northwest plateau on Monday. Snowfall accumulations from this system have the potential of reaching advisory levels across the Flat Tops and the Elkhead and Park Ranges. Temperatures cool a bit in the warm sector of the storm on Sunday due to clouds and virga/showers, but should still run 5 to 10 degrees above normal while overnight lows will considerably milder than normal due to mixing associated with frontal passage. However, on Monday highs are expected to fall by 5 to 10 degrees below normal as the colder air takes hold of the region. A secondary mid-level short wave trough sweeps over the area Monday night into Tuesday and as a result, the chance for showers over the northern mountains and northwest Colorado plateau will continue. Any additional accumulations will be light as it stands now. Overnight lows Tuesday morning will be colder, but at this time it doesn`t appear they will approach freezing for areas with sensitive vegetation. Highs moderate a few degrees but will continue to run just a little below seasonal norms. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1130 PM MDT Wed May 1 2024 The last of the remaining showers primarily along the Continental Divide mountains will continue to clear out to the south and east over the next few hours. MVFR/ILS breakpoint ceilings will hang on during that timeframe too before mostly dissipating by sunrise. On Thursday, another disturbance will brush across the northern tier of eastern Utah and western Colorado. This will bring more clouds back into the picture, especially north of I-70. Ceilings should mostly stay above ILS breakpoints, however. Farther south, mostly sunny skies will prevail. Winds will once again become breezy during the afternoon hours with gusts of 25 to 35 mph common. Winds settled down again not long after sunset. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...DB LONG TERM...NL AVIATION...MDM