Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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414 FXUS65 KGJT 252103 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 303 PM MDT Tue Jun 25 2024 .KEY MESSAGES... - Isolated showers and storms thrive for another evening, before the mid-week moisture surge returns... - Showers become widespread Wednesday/Wednesday night thanks to a plume of deep subtropical moisture. - Flooding and Flash Flood potential ramps up during this anomalously moist period. && .SHORT TERM /THROUGH THURSDAY/... Issued at 300 PM MDT Tue Jun 25 2024 Like clockwork, storms are firing off high terrain, feeding off abnormally moist atmospheric conditions. Despite PWAT anomalies running over 150%, this morning`s inverted V sounding suggests high based storms this afternoon with potential for some impressive outflow winds (i.e. in excess of 50 mph). In addition, current mesoanalyses indicate DCAPE contours over 1500 J/kg for much of the Western Slope, also supporting strong downward momentum and thus, strong surface winds. While small hail is still possible, heavy rainfall and training storms favor flooding and flash flooding threats, too, rather than severe hail. Satellite imagery already illustrates the plume of deep subtropical mositure creeping back into the southwest corner of the forecast area. Said progression will only continue overnight, thanks to the PacNW low nudging inland and pushing the broad ridge of high pressure eastward. By Wednesday morning, moisture content is progged to run in excess of 200% of normal, peaking around 250% of normal by Wednesday night. Surplus moisture will support orographic showers Wednesday morning; however, perturbations rippling along synoptic flow will boost lifting mechanisms and may support longer lasting thunderstorms Wednesday afternoon. WPC has eastern Utah and western Colorado under a marginal risk for excessive rainfall, which favors the potential for flash flooding across the Western Slope. One caveat, though, may be the longevity of those early morning showers and whether or not we see lingering cloud cover. If clouds do hold, surface temperatures will be hindered, as well as instability for storms to feed off of. Thus, in this case, widespread showers are still possible, but storm intensities decrease, resulting in a dampened threat for flash flooding. I have held off on any flood watch highlights for tomorrow due to said uncertainty. Regardless, winds ramp up aloft Wednesday night into Thursday as pressure gradients are squeezed between the broad trough to the northwest and ridge (now) to the southeast. Jet dynamics and the approaching trough may support more organized convection by Thursday afternoon. We don`t see too many days with defined helicity swaths draped across the CWA. That, along with CAPE values ranging from 1500 to 2000 J/kg, suggest strong thunderstorm development, especially along a frontal boundary dipping in from the northwest Thursday evening. A Flash Flood Watch may be warranted for Thursday`s convection, so stay tuned as high resolution guidance trickles in. Thursday looks like the most active day this week, and best potential for severe thunderstorms, so stay tuned for updated watches and warnings. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Issued at 300 PM MDT Tue Jun 25 2024 The trough responsible for providing an extra punch of synoptic lift on Thursday pushes off to the east Friday morning. This will help scatter out some of the remaining convection, but the northern half of the forecast area will likely see continued convection through Friday evening (45-75% chance) with pulses of shortwave energy continue to advect through the mid-level flow. Even though the forcing becomes less organized after Thursday night, PWAT values remain elevated at 120-200% of normal until early next week. Daytime heating and orographic lift will lead to scattered showers and storms in the high terrain each afternoon/evening, with coverage increasing on Sunday evening as more moisture surges into the region. Recent model runs are trending towards stronger moisture advection (especially the GEFS) so we will have to keep an eye on this period in the coming days. Otherwise expect seasonal temperatures with some fluctuations depending on cloud cover and coverage of precipitation. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1058 AM MDT Tue Jun 25 2024 VFR conditions are forecast through the TAF period with light westerly breezes today. Isolated to scattered showers and thunderstorms will develop over the higher terrain this afternoon with brief periods of MVFR near the storms. Winds become light drainage winds this evening as the showers die down. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...ERW LONG TERM...KAA AVIATION...TGJT