Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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101 FXUS65 KGJT 272246 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 446 PM MDT Thu Jun 27 2024 .KEY MESSAGES... - Deep subtropical moisture will remain in place this evening with widespread showers and thunderstorms expected to continue. - Stronger storms have produced heavy rain, gusty winds, and hail to 1 inch in diameter. Localized severe storms and flash flooding are expected to continue this evening. - A Flood Watch remains in effect for much of eastern Utah and all of western Colorado from noon to midnight. - A Severe Thunderstorm Watch is also in effect until 9 PM MDT for all of eastern Utah and most of western Colorado. - Look for a slight downturn in thunderstorms on Friday before mostly dry weather returns for Saturday. The next push of moisture is expected to arrive Sunday. && .SHORT TERM /THROUGH FRIDAY NIGHT/... Issued at 446 PM MDT Thu Jun 27 2024 Deep subtropical moisture remained in place today and a pre- storm sounding launched at 20Z showed a precipitable water value of 1.09" with MUCAPE of over 1500 J/kg which is highly unusual for this area. DCAPE was 1100 and wind gusts to 52 mph have been observed as of 21Z. The Flash Flood Watch remains in place, and in addition, in coordination with SPC, a Severe Thunderstorm Watch has been issued with large hail and wind the primary threats. Storms which developed earlier this afternoon have generated flash flooding west of the Green River while a strong cell which moved through Moab prompted issuance of a Flash Flood Warning which resulted in a report of a debris flow over Hwy 191 at the entrance to Arches NP which closed the road. In addition to rain, this storm generated hail to 1" in diameter. A number of storms across the forecast area have prompted additional Flash Flood Warnings and Severe Thunderstorm Warnings in addition to several Special Weather Statements for near severe storm cells. Numerous showers/thunderstorms were working across central Utah and models suggested this activity is likely to hold together into the evening as modest divergence associated with the jet moving through the base of the trough over the northern Rockies provides some lift. Otherwise, instability and outflows from existing storms will continue to generate additional storms and based on moisture and CAPE values, some of these storms are likely to generate excessive rainfall and/or large hail and winds to 60 mph. Therefore, the Severe Thunderstorm Watch will continue to 9 PM MDT and the Flood Watch until midnight. During the latter part of the night, showers and thunderstorms will decrease and become more stratified in nature and therefore it`s unlikely that the Watch will need to be extended. High levels of moisture and lingering clouds will moderate lows which should settle out about 5 degrees above seasonal norms. Zonal flow sets in late tonight and will continue on Friday causing the subtropical moisture plume to shift southeast of the forecast area while drier air begins to infiltrate from the west. However, residual moisture will be sufficient to generate scattered to numerous showers and thunderstorms with the north favored. Enough shear remains across the north for a marginal threat of severe thunderstorms with wind and hail remaining the primary threats. As moisture levels fall, excessive rainfall becomes more localized, so a Flood Watch is unlikely, but will not be surprised if a few cells produce heavy rain. Temperatures are expected to rebound with highs for most locations climbing back above normal, but not by much. Drying continues into Friday evening, so expect storms to diminish at a faster clip than tonight. Given zonal flow aloft, overnight lows are expected to show little change as compared to Friday morning`s lows. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Issued at 446 PM MDT Thu Jun 27 2024 High pressure remains centered over Texas while a trough will be just off the West Coast at the start of the long term period. Moisture will continue to stream up from the south but the trough to our west does look like it`ll shunt the deeper moisture further to our east. This follows as models indicate some showers and storms but mainly along the spine of the Continental Divide. On Sunday, the trough will continue to slowly approach from the west and allow another push of monsoonal moisture to reach our CWA. By Sunday afternoon, PWATs will vary from 0.8 to 1.2 inches for just about the entire CWA...more down south, less up north. Weak impulses moving through the mean flow will be more than enough to allow scattered showers and thunderstorms to form. Favored areas include the southern valleys, and the San Juan and central mountains (60 to 80% chance). Elsewhere, chances range from 20 to 50%. The trough will have started filling as it begins to move across the CWA on Monday allowing another round of convection, in almost the exact same areas as those on Sunday. As of now, models are depicting another day of scattered convection but with the added support aloft, would think the convection would be a bit more intense. This may be a bit downplayed in current guidance so will need to keep an eye on the forecast as we get closer to Monday. Once the trough passes through, a wind shift will cause northerly winds to setup across the area allowing drier air to move in. Of note, models tend to dry out our CWA much too fast when this is forecast to occur. Once the hi-res models get their hands on this timeframe, there`s a good chance the PoPs will increase for both Tuesday and Wednesday. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1151 AM MDT Thu Jun 27 2024 Widespread showers and thunderstorms will continue through much of the TAF period. Storms will be capable of small hail and gusty outflow winds, as well as heavy rainshowers that will create TEMPO IFR conditions at terminals. Storms will taper off near sunset and VCSH/VCTS conditions are expected until around midnight MDT. VFR conditions are expected by daybreak at most terminals, with a few mid cloud ceilings hanging around on the terrain from leftover shower activity. && .HYDROLOGY... Issued at 446 PM MDT Thu Jun 27 2024 Deep subtropical moisture remained in place today as precipitable water values have verified in the 200 to 250 percent of normal range. Additionally, surface dewpoints were in the upper 40s and 50s with 60 degrees registered at KCEZ this afternoon. Given the abnormally moist atmosphere, several thunderstorms have produced excessive rainfall and Flash Flood Warnings have already been issued for the Moab area, Piceance Creek on the north end of the Roan Plateau and southwestern Paradox Valley. Consequently, the Flood Watches were warranted and will remain in effect for much of eastern Utah and all of western Colorado until midnight. Slick rock areas, slot canyons, and burn scars are at greatest risk for flooding, but urban flooding is also a concern. Be sure to monitor the latest forecasts and be prepared to take action should Flash Flood Warnings be issued for your area! && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Flood Watch until midnight MDT tonight for COZ001>014-017>023. UT...Flood Watch until midnight MDT tonight for UTZ022-025-027>029. && $$ SHORT TERM...NL LONG TERM...TGR AVIATION...TGJT HYDROLOGY...TGJT