Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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783 FXUS65 KGJT 272132 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 332 PM MDT Sat Apr 27 2024 .KEY MESSAGES... - Showers and isolated thunderstorms continue this afternoon and evening with another round expected on Sunday. - Additional mountain snow through tonight can leave high mountain passes snow-covered and slick. Winter Weather Advisories remain in effect through 6 AM MDT Sunday. - Drier and warmer weather returns next week, but additional disturbances can bring more showers across the northern tier. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 332 PM MDT Sat Apr 27 2024 GOES-East water vapor imagery shows a large sprawling closed mid-level low pressure system spinning over the Four Corners this afternoon. Underneath the low, plenty of clouds and widespread showers with counter-clockwise large scale motion are being observed across eastern Utah and western Colorado via visible/IR satellite and the KGJX WSR-88D, respectively. As expected, the clouds and showers have largely kept surface based instability to a minimum with temperatures several degrees below normal. The only exceptions to that are across the fringes of the CWA in extreme northwest Colorado, northeast Utah, southeast Utah, and southwest Colorado where less clouds and more sun have resulted in a bit more instability. Unsurprisingly, it`s those locations that will be favored for any stronger shower or thunderstorm activity this afternoon and evening. In fact, we`re already seeing several lightning strikes in northeast Utah near Vernal where storms have tapped into the higher instability. With those stronger cores, gusty outflow winds and small hail are a possibility in addition to the lightning threat. Elsewhere, light and intermittent stratiform showers will be the rule, with plain rain falling below 7000 to 8000 feet and snow falling above. In terms of accumulating snow, that will mainly be confined to above 9000 feet, primarily in the eastern Uintas and along the Continental Divide mountains where Winter Weather Advisories remain in effect. Latest webcams reveal roads that are largely free of snow, which makes sense given the time of day and time of year. That being said, high mountain passes could become snow-covered and slick again towards and after sunset with the loss of daytime heating and any additional snow that falls. Winter Weather Advisories will expire at 12Z Sunday morning as our storm system lifts out to the north and east. Most showers will diminish by late tonight, but a few could linger into the morning hours on Sunday. In the wake of today`s system, a weak trailing shortwave embedded within northwesterly flow will interact with residual moisture and daytime heating to kick off another round of showers and possibly a few storms late Sunday morning into Sunday afternoon. This wave will be battling dry air advection and a lack of large scale forcing for ascent, so showers won`t be quite as numerous as the last few days. Most showers will be tied to the terrain with the aid of orographic lift, but some showers may drift off into the lower adjacent valleys. QPF will mostly be light and add up to around a tenth of an inch... a bit more or a bit less depending on elevation. Given a smaller footprint of showers, expect less clouds, and a little more sun, allowing for temperatures to bump back up closer to seasonal norms. With the loss of daytime heating, showers are expected to diminish fairly rapidly after sunset, giving way to a drier and warmer day to start the work week on Monday. && .LONG TERM /MONDAY THROUGH FRIDAY/... Issued at 332 PM MDT Sat Apr 27 2024 Flow becomes zonal on Monday as this weekend`s storm moves to the Upper Midwest, forced east by a mid-level short wave trough ejected from a closed low off the coast of British Columbia. The regional airmass will be largely drier in the westerlies promising quiet weather Monday morning while temperatures climb several degrees above normal during the day. However, model consensus indicated the potential for convective showers over the northern mountains in the afternoon as modest moisture moving ahead of the previously mentioned short wave filters in throughout the day. The short wave trough moves eastward Monday night driving a cold front across the northern half of the forecast area. Meanwhile, moisture and lift along and north of the front is expected to bring another round of precipitation to the northern mountains and northwest Colorado plateau with a chance for showers over the central Colorado mountains and the eastern Uinta Mountains. A bit of a lull in activity is expected Tuesday as flow again becomes zonal in the wake of the disturbance, though scattered instability showers are possible, mainly over the Elkhead, Park and Flat Top Mountains. Despite the passage of the cold front, temperatures are expected to be near, or only a few degrees cooler than on Monday across northeast Utah and northwest Colorado and a few degrees warmer along the I-70 corridor and south. On Wednesday, models were in good agreement showing a positive tilt trough moving over the Intermountain West and Great Basin causing flow aloft to shift to the southwest. As this plays out, moisture ahead of the trough overruns the stalled front over the northern portion of the forecast area resulting in a good chance for showers, especially for the northern and central mountains of Colorado. Meanwhile, a tightening of the pressure gradient ahead of the approaching disturbance will bring breezy conditions to the northern zones Wednesday afternoon and evening. Cloud cover and showers should bring a few additional degrees of cooling to the north while areas to the south can expect little change in temperature and little chance for precipitation. The forecast is less clear for the remainder of the week as the ECMWF slows the eastward progress of the mid-level trough as compared to the Canadian and GFS solutions which were more progressive. The latter two models suggested little chance for additional showers Thursday and Friday while the ECMWF depicted active weather Thursday and Thursday night and lingering Friday with the north again favored. Model blends indicated chance precipitation for the Continental Divide, and particularly for the northern Colorado mountains Thursday and Friday and this seemed to be the appropriate forecast for now. Given trough passage sometime at the end of the week it stands to reason Thursday, and to a lesser extent Friday, will be cooler. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1144 AM MDT Sat Apr 27 2024 A spring storm will bring mountain snow and scattered showers and thunderstorms to the region through this TAF period. Intermittent IFR/ILS breakpoint conditions can be expected as gusty winds, small hail, and snow present numerous challenges to aviation today. Thunderstorm activity will taper around sunset, as will shower activity, but lingering clouds and moisture will still produce some opportunity for IFR conditions in the mountains tonight and into Sunday morning. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Winter Weather Advisory until 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...MDM LONG TERM...NL AVIATION...TGJT