Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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018 FXUS65 KGJT 300931 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 331 AM MDT Thu May 30 2024 .KEY MESSAGES... - Slightly cooler, more seasonable temperatures today and Friday in the wake of a cold front which continued to push southward across the area early this morning. - Chances for isolated to scattered showers and thunderstorms remain along the higher terrain of the Continental Divide through early next week. - Temperatures climb back above normal this weekend and a building ridge next week suggests temperatures are likely to climb even higher by midweek. && .SHORT TERM /THROUGH FRIDAY/... Issued at 331 AM MDT Thu May 30 2024 The cold front was just south of the I-70 corridor at 08Z this morning according to latest surface observations. Aside from scattered alto-cumulus clouds there was little else to mark its presence. The mid-level trough that drove the front southward had pushed east of the Continental Divide by this time so it`s unlikely that the front will move much farther south. As a result, cooler temperatures will impact the central and northern zones of the forecast area today with little change across the south. Dry zonal flow sets in behind the trough, though models indicated that enough moisture remains to fuel some instability driven showers/thunderstorms over the Divide with the southern and central ranges favored. The subcloud layer remains dry so this activity will continue to generate more wind than rain. Diurnal cooling brings an early end to moist convection this evening followed by decreasing clouds. Conditions will show little change Friday, though models indicated less shower and storm coverage during the afternoon. Temperatures are expected to be a little warmer across the north with highs running near persistence elsewhere. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Issued at 331 AM MDT Thu May 30 2024 Starting with the bottom line up front, the longwave pattern just doesn`t want to let go of the spring weather with deep troughs digging down into the western states and move on to a summer pattern. The models keep building a strong ridge in over the Intermountain West late in the period, but with each successive run of the models, pushing the formation of the ridge further into the future with guidance sending mixed signals. What this spells for eastern Utah and western Colorado is continued warm weather on the dry side with afternoon buildups of isolated to scattered virga, showers and thunderstorms resulting from diurnal heating and initiated by orographic lift. Some days will see more activity and other days will see less. There is general agreement on a warming trend over the weekend and into next week with temperatures reaching 10-15 degrees above the climatological mean for early June across the region and hitting the century mark in the lower desert valleys by mid week. Heat risks may become a concern in these areas and will be something to watch. Looking at the synoptic pattern, the longwave trough continues across the northern CONUS and southern Canada keeping eastern Utah and Western Colorado under a zonal flow with transient ridges and shortwave troughs. With the last shortwave that passed to the north of the region out on the Plains Friday evening, the next shortwave trough will be just moving into the Pacific Northwest. Lacking jet support, this next shortwave will move slowly east along the Canadian Border, passing north of the region Sunday into Tuesday. The models were in general agreement with this trough pulling a significant surge of moisture off the Pacific inland over the northern States and into the northern Utah and Colorado to feed continued afternoon convective activity over the northern mountains. Guidance hasn`t picked up on this moisture plume, low balling probabilities of precipitation (PoPs) below 20%. Afternoon PoPs closer to 50% seem more reasonable across the higher terrain of the northern half of the region. In the latter half of next week the European ensemble wants to build a ridge in off the Pacific from the west while the GEFS builds the high north out of Mexico over the Western States with a cutoff low off Baja; two very different scenarios with significantly different outcomes. Additionally, the upper level analysis of the models, above 400 mb, indicates yet another deep trough digging south over the eastern Pacific to erode a ridge over the western CONUS. With all these discrepancies, there is low confidence in this extended forecast beyond about Tuesday. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1130 PM MDT Wed May 29 2024 Expect VFR conditions and generally light terrain driven winds through the TAF period. The exception will be light afternoon virga showers mostly through the central and southern Colorado mountains producing gusty outflow winds. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...NL LONG TERM...DB AVIATION...DB