Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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369 FXUS65 KGJT 131017 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 417 AM MDT Sat Jul 13 2024 .KEY MESSAGES... - Near-record daytime temperatures are expected today and Sunday, particularly in the valleys of eastern Utah and the Grand Valley in Colorado. - 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 SUNDAY/... Issued at 417 AM MDT Sat Jul 13 2024 Early morning radar imagery showed an area of virga/sprinkles over east-central Utah west of the Green River. Notably, looped reflectivity suggested the center of the dome of high pressure was roughly west of Hanksville which matched the positioning of the high according to latest operational models. Otherwise, aside from scattered areas of lingering altocumulus, skies were mostly clear across the forecast area. In the absence of cloud cover, temperatures will rapidly rise through the morning with afternoon highs expected to be near record levels again today. Highest impacts from heat continued to be in the valleys of eastern Utah and the Grand Valley of western Colorado where Heat Advisories remained in effect. The high pressure center drifts over southwest Colorado where it will remain today. With the high over Colorado it`s unlikely that there will be any appreciable increase in moisture over the forecast area. This seemed to be borne out by the HREF precipitable water (PW) field. Consequently, expect modest moisture over the San Juan Mountains and central Colorado portion of the Continental Divide will fuel another round of isolated to scattered afternoon/early evening showers and thunderstorms. Storm characteristics will be similar to yesterday`s with lightning, gusty winds and small hail the main threats. Diurnal cooling will bring an end to moist convection early this evening with all but a few lingering showers remaining after sunset. Models indicated an uptick in moisture tonight as the high center drifts east of the Continental Divide by 12Z/Sun. Increased moisture should yield unusually mild overnight lows. The HREF suggested a PW increase close to 0.30" from 00Z/Sun to 00Z/Mon. Operational runs were a bit less aggressive coming in closer to a 0.20" increase in PW. Am inclined to favor the operational runs as moisture flux doesn`t look all that impressive. In any event, increased shower/thunderstorm coverage appeared reasonable with the central and southern Colorado mountains favored. Despite the expected increase in clouds and shower/thunderstorm activity, models continued to indicate unusually hot conditions will persist for the areas in today`s Heat Advisory. Since the morning is likely to have few clouds over those areas and showers/thunderstorms are likely to be more distant, decided to extend the Heat Advisories through Sunday evening. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 417 AM MDT Sat Jul 13 2024 High pressure continues to drive the forecast through the coming week. The biggest change heading into Monday and Tuesday is increased subtropical mositure wrapping around the high and into the forecast area. Ensemble guidance continues to be very consistent with its projection of PWAT values 100-150% of normal during this period so while the coverage of afternoon showers and storms will increase with the additional moisture present, it is not looking like this system will pose an organized heavy rain threat. A shortwave trough passes through the Northern Plains on Wednesday and could nudge the surface high slightly westward. A brief drop in the moisture advection may occur as a result, but it picks right back up for the latter half of the week. Increase cloud coverage throughout the week will work to lower our high temperatures by a few degrees. However, temperatures remain well above normal through the forecast period. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1146 PM MDT Fri Jul 12 2024 Mainly VFR through the TAF period. Another day of scattered showers and storms in the southern mountains. Gusty outflow winds is the main TAF concern if showers/storms develop near the terminals (highest likelihood at KTEX and KDRO). && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Heat Advisory until 9 PM MDT Sunday for COZ006. UT...Heat Advisory until 9 PM MDT Sunday for UTZ024-027-029. && $$ SHORT TERM...NL LONG TERM...KAA AVIATION...KAA