Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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339 FXUS65 KGJT 130833 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 233 AM MDT Mon May 13 2024 .KEY MESSAGES... - Afternoon showers and thunderstorms will once again form over the higher terrain. - An approaching disturbance will bring more widespread shower and storm activity Tuesday and Wednesday, with the San Juans most favored Thursday. - Temperatures will continue to warm through the week. && .SHORT TERM /THROUGH TUESDAY/... Issued at 230 AM MDT Mon May 13 2024 Aside from a few lingering showers, mostly clear skies and quiet weather has prevailed over eastern Utah and western Colorado over the last few hours. The showers will continue to taper off as subsidence associated with high pressure aloft builds in, bringing a quiet start to the workweek. Warm air associated with the ridging will allow temperatures to climb a few more degrees, running 4-8 degrees above normal for mid-May. This means low to mid 80s across the desert valleys and 70s to the higher valleys. Mountain towns may see highs running closer to normal this afternoon, as daytime heating works on moisture still pooled over the higher terrain and leads to another round of isolated to widely scattered showers and thunderstorms. This activity is expected to remain over the terrain and adjacent high valleys, with gusty winds, light to moderate rainfall, and maybe some small hail being the main threats. Activity will taper off with the loss of daytime heating, with Monday night once again being mostly quiet. In the meantime, a trough will be moving through the Pacific Northwest, and a cutoff low is forecast to move into Southern California. These two features will be the next weather makers for eastern Utah and western Colorado starting Tuesday afternoon. Previous guidance had the trough and cutoff low in phase as they moved into the region, leading to a broad area of showers and thunderstorms. The latest guidance has backed off a bit on this, tracking the trough through first on Tuesday before stalling out just to our east, while the low remains somewhere over the border between SoCal and Baja California. This will have an impact in the weather into the long term period, but keeping to the short term, this will bring unsettled weather Tuesday afternoon. Isolated to scattered showers and thunderstorms will once again pop over the higher terrain as daytime heating once again acts on residual moisture. A weak cold front associated with the trough will drop south through the CWA during the afternoon, bringing a band of more organized precipitation along with it. Behind the front, cooler and drier air will lead to a downturn in activity through the evening hours, along with lows Tuesday night into Wednesday approaching more normal values after a milder Monday night. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Issued at 230 AM MDT Mon May 13 2024 Any lingering convection looks to come to an end Tuesday night with a relatively quiet start to the day on Wednesday. However, Wednesday appears to be the most active day of the week in terms of showers and thunderstorms as the low pressure trough drops southward through the area, resulting in more widespread showers and thunderstorms. Storms may initially favor the high terrain Wednesday afternoon but will quickly fill in among the valleys as sufficient dynamics and forcing exist to allow storms to move off the terrain. There is somewhat of a split flow pattern here as the polar jet actually remains north of the region despite this trough moving southward through the area. The descending trough will actually meet up with and eventually merge with a cut off low that is parked over Arizona. The subtropical jet is rounding the base of this cut off low with fairly good jet support as a 120+ kt jet streak rounds its base through northern Mexico. So, it looks like this southern system is more of a player in this game than previously thought. Drawing more influence from the subtropical jet and our CWA stuck in the middle between the polar jet to the north and subtropical jet to the south, temperatures will remain milder with slight CAA with trough passage, but snow levels look to remain high. In fact, H7 temperatures peak in the 4C to 10C range during peak heating Wednesday afternoon and drop to as low as maybe 2C to 4C Wednesday night following trough passage. Therefore, not expecting much in the way of snow in the higher elevations with this system...maybe a couple inches at best at elevations above 11kft. So temperatures will still be relatively mild but cooler than Tuesday by about 5 degrees, bringing highs closer to normal. The trough is projected to be south of the Four Corners with the H7 and H5 low over eastern New Mexico and the Texas Panhandle by Thursday afternoon. H7 temperatures will quickly bounce back, returning to 8C to 10C by Thursday afternoon as WAA returns the above normal temperatures despite the northerly flow following trough passage. Enough moisture and instability will still linger in the trough`s wake to result in scattered thunderstorms Thursday afternoon, favoring the central and southern mountains, potentially drifting southward into adjacent valleys late in the day. Models seem to be in better agreement that a large ridge of high pressure will build in from the west and over the Great Basin on Friday, ushering in a much drier airmass and pushing the moisture out, resulting in mostly sunny skies and even warmer temperatures about 5 to 10 degrees above normal. The ridge axis moves east of the Divide by Saturday with southwest flow returning as a low pressure trough moves into the PacNW with a cutoff low forming off the SoCal coast. This will allow some moisture to advect in and result in some afternoon convection on Saturday, focused over the high terrain. Given the drier air mass, low levels will be dry so breezy conditions are possible with virga from any storm activity. There appears to be disagreement between models on how to handle these systems for the weekend and beyond so won`t put much stock in that yet. The better bet is to keep a drier and warmer trend with potential for isolated to scattered storms each afternoon over the high terrain. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1146 PM MDT Sun May 12 2024 Some light showers across the area will dissipate early this morning as drier and more stable air moves in with a high pressure ridge pushing in from the west. Partly sunny skies will prevail for Monday with some cumulus building over the high terrain in the afternoon as well as development of scattered thunderstorms, favoring the high terrain along the Divide. Brief gusty afternoon winds will occur Monday afternoon with VFR conditions and CIGS above ILS breakpoints. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...BGB LONG TERM...MDA AVIATION...MDA