FXUS65 KGJT 122339 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 539 PM MDT Sun May 12 2024 .KEY MESSAGES... - Showers and thunderstorms, favoring the northern valleys and mountains along the Divide, will continue this afternoon and again, tomorrow. - A disturbance will bring more widespread showers and storms Tuesday and Wednesday, then favoring the San Juans on Thursday. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 155 PM MDT Sun May 12 2024 The area of low pressure that brought the rain, storms, and mountain snow has shifted to the Plains where the precip continues. In our neck of the woods, plenty of mid to upper level instability remains in the atmosphere as indicated by some steeper lapse rates and widespread CAPE values around 300 to 600 J/kg. This instability has been realized as radar is showing plenty of convective cells across the area, favoring the northern valleys. Cyclonic flow around the low is causing these cells to move almost directly from north to south. A few lightning strikes have been noted under the stronger cells and that will be the biggest concern along with some gusty winds of 35 to 45 mph. Heading towards the evening hours, the atmosphere will return to more stable conditions as convection ends. A few clouds will persist as temps drop to the usual mid May values. For tomorrow, another day of convection but coverage should be somewhat less than seen today. Forecast Skew-Ts are showing shallow inverted V profiles so we should see some virga and the occasional gusty outflow. Cumulus clouds will be common over the higher peaks as the afternoon wears on. Flow will become more zonal allowing daytime highs to slowly start increasing. Highs will be about 4 to 6 degrees warmer than those seen today. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Issued at 155 PM MDT Sun May 12 2024 Zonal flow will kick off the long term period as a trough of low pressure quickly pushes across the Northern Rockies on Tuesday. Moisture will increase in earnest across the forecast area as the trough's axis dives farther south with PWATs jumping to 150 to 200 percent of normal by Tuesday afternoon. Even with the better broad scale ascent remaining well to our north, the abundance of moisture paired with daytime heating will result in numerous showers and storms on Tuesday. We're not out of the woods yet when it comes to mountain snow but, with 700mb temperatures remaining in the 4 to 8 degree C range over the higher terrain, snow levels will generally be above 11kft. Convection could drive these levels locally lower but little impact or accumulation is expected. The trough undergoes a bit of a split as the northern wave's axis slides across the north on Wednesday while the southerly feature hang back over southeast Utah and southwest Colorado into Wednesday night. So, after a brief downturn in shower activity Tuesday night with the loss of daytime heating, thunderstorms will redevelop for Wednesday with scattered to numerous coverage expected. An additional couple inches of snow will fall along the higher terrain favoring the southern and central Colorado mountains with wetting rain likely elsewhere into Wednesday evening. Confidence is lacking going into the latter half of the work week as there are some discrepancies regarding if the trough exits by Thursday. Guidance does favor a strong ridge of high pressure building off the West Coast which would help usher the trough out of the region. As a result, a shift towards drier weather is favored at this time, though residual moisture paired with orographics would lead to daily showers and storms over the higher terrain each afternoon. Another large trough develops upstream towards the end of the long term but it's too early to get excited about such things. Temperatures will be a grab bag through the long term as various systems approach and move across the area. Tuesday's highs will trend well above normal before dropping back down to slightly below normal before values become unseasonably warm once more by Friday. Overnight lows will generally be mild for mid May through the period. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 539 PM MDT Sun May 12 2024 Scattered showers and thunderstorms will continue this evening and remain in the vicinity of most northern and central TAF sites through 03Z. Storms will be capable of producing brief MVFR conditions in addition to gusty outflow winds of 35 to 45 kts. Activity diminishes tonight as weak ridging slides over- head with CIGS remaining above ILS breakpoints into Monday morning. Another round of scattered thunderstorms will develop after 18Z Monday, favoring the higher terrain along the Divide. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...TGR LONG TERM...MMS AVIATION...TGJT