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Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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546 FXUS65 KGJT 131947 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 147 PM MDT Sat Jul 13 2024 .KEY MESSAGES... - Near record heat continues through tomorrow, especially for the desert valleys of eastern Utah and the Grand Valley in Western Colorado. Heat Advisories remain in place. - Showers and thunderstorms remain in the forecast over the higher terrain throughout the next 7 days, although the greatest coverage will occur tomorrow and Monday. - Temperatures will begin to cool off somewhat midweek onward, although they will remain around 5 degrees above normal. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 145 PM MDT Sat Jul 13 2024 Based on current satellite imagery, the center of the dome of high pressure is located over eastern Utah, somewhere south of Moab. Models have a good grip on this, although they are struggling a little with the ongoing afternoon convection. The moisture present is fairly modest, with this morning`s 12z GJT sounding coming in with a PWAT of 0.59 inches, and dew points at this hour in the mid to upper 30s. But, with strong differential daytime heating and a modest 500 J/kg of CAPE, it`s enough to fire showers and thunderstorms off the higher terrain across the region. Dry surface layers, as indicated by this morning`s Inverted-V sounding, with keep gusty outflow winds as the main threat, followed by frequent lightning and small hail. A brief heavy shower is possible. Thus far these showers and storms have remained anchored to the terrain, and are slowly drifting in a clockwise direction around the above- mentioned center of the high. This will continue through the afternoon before things die off with loss of heating after sunset. With the high nearly directly overhead today, look for some of the hottest temperatures of the week, with the exception being areas that see clouds and showers. The center of the high is expected to continue drifting east through the evening and into the overnight, pulling the moisture plume on its western edge along with it. This plume will set up shop over eastern Utah and western Colorado beginning late tonight, and is expected to remain in place through the next few days. Models remain consistent on PWATs increasing to 100-150% of normal, although much of this moisture will remain aloft, as it takes time to mix out the dry surface layers. This means there will be an increase in shower and storm coverage tomorrow afternoon, especially over the terrain, but the main threats will remain gusty winds and lightning, with lesser chances of small hail and brief heavy rain. The expansion in cloud and storm coverage tomorrow afternoon will bring high temperatures down a few degrees compared to today, but with the lower desert valleys still expected to see highs of 100-110 degrees, the Heat Advisory remains in place through 9PM tomorrow evening. Additionally, the increasing moisture will keep nighttime lows tonight and tomorrow night even more mild than we`ve seen in previous days, with the desert valleys again see the worst of it with forecast lows in the mid 70s. This means minimal relief from the heat if you don`t have some form of cooling available to you. Remember to stay hydrated and avoid doing outdoor activities during the heat of the day if possible. Relief is in sight as we move into the coming work week. && .LONG TERM /MONDAY THROUGH FRIDAY/... Issued at 145 PM MDT Sat Jul 13 2024 The high pressure ridge will be situated slightly east of the area by Monday, allowing for sub-tropical moisture to circulate around the high as PWAT anomalies rise up towards 100 to 150 percent of normal. Monday and Tuesday appear to be the more active days in terms of shower and thunderstorm activity with more scattered to widespread coverage. Additionally, shortwaves will move through the flow, causing the high pressure center to retrograde a bit back to the south and west heading into Tuesday. These shortwaves may also result in stronger storms with gusty outflow winds and small hail the primary concerns. The moisture increase is enough to increase cloud cover and cool things down a tad (by about 5 degrees compared to this weekend), but not quite robust enough to warrant widespread heavy rain threat. Some locally moderate to heavy rain is still possible with some storms but gusty outflows seem like the better bet with drier air already trying to sneak back in by Tuesday afternoon as the high retrogrades westward. Temperatures will still be hot though despite the moisture and storm increase, staying 5 degrees above normal on average compared to almost 10 above normal currently. By Wednesday, the high pressure ridge axis will be over the Great Basin to our west, with enough lingering moisture to warrant daily afternoon showers and storms over the high terrain. A bit of an increase may occur late next week as more shortwaves round the top of the high through the Northern Rockies and down the Front Range, acting on leftover moisture to warrant better storm potential. The high however remains to our west so not seeing any new moisture advection, just recycled moisture under the high. Temperatures stay around 5 degrees above normal through the end of the week for much of the area with near normal temps for the higher terrain and southwest Colorado where better chance for storms remains. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1142 AM MDT Sat Jul 13 2024 VFR conditions are expected at all TAF sites today with high cloud bases, keeping CIGS well above ILS breakpoints during the next 24 hours. Storms are beginning to develop over the northern side of the ridges of the eastern Uintas and northwest San Juan mountains. Expect storm coverage to remain scattered today, favoring the southern and central Colorado mountains as well as the eastern Utah mountains with gusty outflow winds 40 to 50 mph and small hail possible. Showers/storms should dissipate by sunset. && .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...BGB LONG TERM...MDA AVIATION...MDA