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Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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533 FXUS65 KGJT 122114 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 314 PM MDT Fri Jul 12 2024 .KEY MESSAGES... - Near-record daytime temperatures are expected today and Saturday especially in the lower valleys. - Afternoon showers and thunderstorms will develop over higher terrain each day throughout the seven-day forecast with an increase in coverage expected early next week. - Temperatures remain elevated beyond the weekend, but some relief is expected from cloud cover and shower activity as monsoonal moisture is forecast to return early next week. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 314 PM MDT Fri Jul 12 2024 High pressure continues to sit to our west, directing a northerly flow across the area. This is allowing the heat dome to persist, with warm air advection to continue through the weekend as the high pressure shifts directly overhead by Saturday. Near record high temperatures are possible across the area with triple digit heat across eastern Utah and west-central Colorado valleys, in fact we are already there this afternoon. The Heat Advisory remains in effect through Saturday and made no changes to the coverage area or timing due to the uncertainty of sub-tropical moisture return on Sunday and what kind of impact increased clouds and storm activity will have on the high temperatures for Sunday. This is something for later shifts to re-evaluate. In this heat, make sure to limit your exposure and stay hydrated. Storms continued to develop again across the southern mountains like yesterday, except a little bit further west across the Abajos and La Sals. The HRRR seemed to have a better handle on the timing and coverage of storms so nudged the PoP fields towards the HRRR as well as hi-res WRF to better reflect these trends in the forecast. Storms were hot to begin with on radar but have since cooled down, but gusty outflow winds of 40 to 50 mph and lightning appear to be the primary concerns. The air mass is very dry as evidenced by our 12Z GJT inverted V sounding and relative humidity in the single digits to teens in the lower valleys. These storms also have a tendency to drift into the adjacent southern valleys but are collapsing as they do, so again, gusty outflow winds will be common. Storms appear to be driven by daytime heating, steep lapse rates upwards of 9C/km, quite a bit of DCAPE and a little bit of shear, so small hail is also possible. Storm activity should die down by sunset with a similar story expected for Saturday with highs a bit hotter than today and similar storm coverage over the high terrain with high pressure directly overhead. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Issued at 314 PM MDT Fri Jul 12 2024 By Sunday the high pressure that has been bringing all the heat will be centered roughly over the Four Corners. This means Sunday is likely to be yet another scorcher, especially for the desert valleys where highs in the low 100s are once again forecast. That said, by Sunday we are also expected to tap into a plume of monsoonal moisture rotating around the high, with PWATs forecast to climb to 100-150% of normal. This will lead to increased storm coverage over the higher terrain, and an increase of clouds overall, which may put a slight damper on temperatures, but only by a few degrees compared to the days previous. In addition, the prolonged period of hot and dry weather prior to this monsoonal push means surface levels will be extremely dry and will take some time to moisten. Therefore, the main threats with any storms will be gusty outflow winds and lightning, with the potential for some small hail or a very brief downpour. A trough dropping through the Northern Plains Monday into Tuesday will nudge the high back westward somewhat, cutting us off from the moisture plume once more. The moisture that did advect in on Sunday and Monday will stick around for a bit, being recycled each afternoon and leading to daily showers and thunderstorms favoring the terrain. This increased storm coverage should continue to nudge temperatures down a few degrees through the week. Highs on Sunday and Monday will run around 10 degrees above normal, dropping to around 5 degrees above normal by mid to late week. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1118 AM MDT Fri Jul 12 2024 Under high pressure, look for generally clear skies this afternoon and evening. A few storms are possible in and around the San Juans, so have included VCTS for KTEX, KDRO, and KGUC. Winds will be northerly and gust up to around 20 knots this afternoon, before dropping and once again becoming light and terrain driven. VFR conditions will prevail. Main threats with any passing shower or storm will be gusty outflow winds and lightning. Construction near the runway at KGJT has led to periods of reduced visibility, so have included a tempo group to account for this. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Heat Advisory until 9 PM MDT Saturday for COZ006. UT...Heat Advisory until 9 PM MDT Saturday for UTZ024-027-029. && $$ SHORT TERM...MDA LONG TERM...BGB AVIATION...TGJT