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Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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092 FXUS65 KGJT 140528 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 1128 PM MDT Tue Aug 13 2024 .KEY MESSAGES... - Numerous showers and scattered thunderstorms continue today with coverage decreasing tomorrow. Gusty outflow winds, small hail, and frequent lightning are possible. - Heavy rain rates with storms will bring an enhanced threat of flash flooding and debris flows today. Saturated soils and steep terrain will be most susceptible to flooding. - Only isolated mountain storms are expected Thursday and Friday with dry weather elsewhere. Moisture begins to increase late this weekend. - Temperatures will remain near to several degrees below normal before beginning to rebound. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 245 PM MDT Tue Aug 13 2024 This morning`s cloud cover and lingering showers did the trick, with a large swath of light to moderate rain continuing to lift into northwest Colorado. This has helped dampen instability this afternoon, with only scattered thunderstorms thus far as MUCAPE maxes out between 500 and 1000 J/kg. Any stronger cells today have been pretty shallow, indicating heavy rain rather than the threat of gusty winds or hail. The potential for more than rain will still be there through the evening as additional storms begin to fire in the wake of this morning`s activity. CAM models have initiated fairly well given the active morning, with these latest cells joining with a cluster of showers and embedded storms moving into northeast and east-central Utah later this evening. From sunset onwards this activity will push through western Colorado before gradually washing out near the Divide around midnight as the accompanying shortwave aloft exits the forecast area. While some additional light showers may linger overnight, mostly dry weather is expected to prevail with the loss of daytime heating and with the departure of the wave. Based on how the day has unfolded, confidence has increased that the potential for flooding and / or debris flows will be more localized rather than widespread, so opted to not issue any flood watches with this afternoon`s package. Additionally, lift provided by the shortwave has resulted in some quicker storm motion. All the same, be sure to stay tuned this evening for any short-duration flood advisories or warnings. A downturn in convection is expected on Wednesday as flow aloft shifts to the west, advecting drier air into the region. PWATs on Wednesday afternoon are projected to drop to around 80% of normal south of I-70 while the northern tier of the forecast area sits right around normal. The main trough tracking through the Intermountain West will finally swing east into the Northern Great Plains on Wednesday. Its base and accompanying 70 to 80 kt jet will skirt the north and, since this will be where the better moisture resides, the majority of storms will be focused here. We should see a bit more wind than heavy rain with storms as the deeper moisture gradually erodes but, regardless, can`t rule out small hail and brief heavy rain with any convection. A transitory ridge begins to build on Wednesday night so quiet, and slightly cooler, conditions can be expected. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 245 PM MDT Tue Aug 13 2024 Desert Southwest high shifts across Arizona and New Mexico on Thursday, which drapes the ridge axis across the CWA. In addition, a shortwave rolling atop the ridge will support a southerly drift of a 70-80 kt upper level jet across the northern half of the forecast area. With dry air mixing in under the ridge, our moisture source feeding afternoon convection dwindles. Thus, despite support aloft, afternoon thunderstorms will have much less moisture to feed off of. Higher terrain across the Unitas and Elkhead/Park Ranges have a better chance of seeing isolated to scattered storms by the afternoon/evening. Elsewhere, dry and warming conditions prevail. Temperatures follow suit, warming through the end of the week. Highs are projected to climb back above normal by Friday, thanks to the warmer and dry air mass. The center of high pressure will continue to nudge east into the weekend, pushing far enough east to allow eastern AZ and central UT to fall back under a plume of tropical mositure on Saturday. The western edge of the CWA appears to fall right along the moisture gradient, so confidence is low for how much measurable precipitation will be able to work its way to the surface for our four eastern UT counties. Nonetheless, the positioning of said high will, at least, open the gates to recycling tropical moisture around the ridge. Thus, recycled moisture and/or the monsoon plume sliding overhead would allude to increasing PoPs though the end of the weekend. From Monday onward, a Rex Blocking pattern is looking like a plausible solution, such that, high pressure will be blocked over the Desert Southwest/Southern Plains for several days. As subtle waves roll over the top of the ridge, we`ll see some wobble in the high`s center. These shifts will dictate how much (or if at all) the CWA falls under the monsoon plume. If the ridge remains offset to our east, the Western Slope will be more or less trapped under a southwest regime, maintaining near to slightly above normal temperatures and precipitation for several days. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1123 PM MDT Tue Aug 13 2024 An area of stronger showers and storms will work through the central mountains over the next hour or two, bringing reduced visibility, brief heavy rain, and lightning to KASE, KEGE, and KGUC. Skies are clearing behind this area of convection. Scattered showers across the north will bring occasional periods of light rain to KVEL and KHDN over the next 2-4 hours as well. Another stronger area of convection is tracking along the CO/NM border, bringing light to moderate rain and lightning to KCEZ and KDRO. This area is showing signs of weakening though, and like the more northerly area, clear skies are building in behind this area. Winds will remain generally light and terrain driven over the next 24 hours, although afternoon gusts of 20-25 knots will be likely, and gusty, erratic winds are possible around storms. Afternoon convection will be focused across the north tomorrow, as well as over the higher terrain. VFR conditions will prevail. && .HYDROLOGY... Issued at 245 PM MDT Tue Aug 13 2024 Monsoonal moisture will keep showers and thunderstorms over the region through tomorrow with rainfall rates of 1 to 2 inches per hour possible with storms. This morning`s cloud cover has largely limited the intensity of convection thus far, so the potential for flooding and debris flows remains localized. All the same, be sure to stay tuned to the latest forecast for any flood highlights. Flooding potential decreases on Wednesday as dry air begins to advect into the region, though it`s still possible. Only isolated showers and storms are expected over the higher terrain Thursday and Friday with heavy rain becoming less likely. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MMS LONG TERM...ERW AVIATION...TGJT HYDROLOGY...TGJT