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Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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881 FXUS65 KGJT 141138 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 538 AM MDT Wed Aug 14 2024 .KEY MESSAGES... - Scattered to numerous showers and thunderstorms will occur today mainly for areas along and north of I-70 as coverage begins to decrease with drier air moving in from the west. Gusty outflow winds, small hail, and frequent lightning are possible in addition to brief moderate to heavy rain. - Flooding threat will be reduced today given the drier air mass moving in, but still remains possible, especially with heavier rain rates in any stronger storms and in case of training. Saturated soils and steep terrain will be most susceptible to flooding. - Only isolated mountain storms are expected Thursday and Friday with dry weather elsewhere. Moisture begins to increase late this weekend. - Temperatures will remain a few degrees below normal today before beginning to rebound towards near and slightly above normal levels late this week into the weekend. && .SHORT TERM /THROUGH THURSDAY/... Issued at 354 AM MDT Wed Aug 14 2024 Isolated to scattered showers are continuing across the north early this morning behind yesterday evening`s shortwave trough. Drier air is beginning to work into the area from the west as skies are starting to clear out south of I-70. Even though drier air is beginning to advect in from the west, scattered to numerous showers and thunderstorms are expected to favor areas along and north of I-70 as the Pacific Northwest trough moves east across the Northern Rockies today. A 95 kt jet streak will accompany this trough passage as it lays across the northern areas, providing ample forcing for ascent for convection. We could see some stronger storms given the clash between the remnant moisture and incoming dry air as it tries to push this moisture out of the region, with more sun resulting in more surface heating to fuel the instability and act on the moisture in place. Some shear also will remain present across the north. So, storms today will be capable of strong gusty winds, small hail and frequent lightning in addition to brief moderate to heavy rain. SPC does have portions of northeast Utah and northwest Colorado, mainly north of I-70, under a marginal risk for severe storms, mainly due to the strong wind threat. Storm coverage will be noticably less for areas south of I-70 though as this drier air pushes in and this area is not in the favored area for ascent and forcing. Regarding the flooding threat, it will be reduced today given the drier airmass advecting in as well as reduced storm coverage. However, given the saturated soils from the last few days, especially yesterday, any storms that form will be capable of heavy rain rates where this moisture remains and if any storms exhibit training, this could lead to localized flooding especially in areas of steep terrain. So, something to keep an eye on today but it doesn`t appear widespread enough to warrant any Flood Watches. It is still important to remain vigilant and up to date on the latest developments as some storms could be stronger today given more surface heating to act on this moisture. CAPE values will range from 500 to 1000 J/kg along and north of I-70 with much less instability across southeast Utah and southwest Colorado. Mixing ratios also will be lower than yesterday but still in a modest 6 to 7 g/kg mainly across the northern and central areas with drier air at the mid levels across the south. Instability appears to peak late this morning into the early afternoon before stabilizing by this evening, but early morning showers and cloud cover across the north could result in a later start. Hi-res CAMs appear to favor convective initiation between 1 pm and 2 pm MDT with a reduction in storm coverage shortly after sunset, so the overnight period tonight is looking a bit quieter for once. Drier air mass will be fully entrenched across the area by Thursday with high pressure expanding to our south over Arizona and New Mexico and stretching across the Desert Southwest as most of the moisture exits to the east. The jet lifts north of the region so expect a sharp reduction in storm potential and coverage on Thursday. Only isolated storms remain possible Thursday afternoon over the high terrain, mainly across the north where the better forcing and moisture remains but overall, not anticipating much with mostly sunny skies across the region. Temperatures will be a few degrees below normal today but warmer than yesterday given more sunshine. We will see temperatures moderate to near normal by Thursday as this drier air mass takes over for the latter half of the week. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Issued at 354 AM MDT Wed Aug 14 2024 With limited moisture in place by Thursday night and high pressure in control, afternoon convection will begin to taper off not long after sunset and a generally quiet night should follow. These dry conditions will continue through Friday and into Saturday as the subtropical high remains centered directly to our south and eastern Utah and western Colorado remain cutoff from the monsoonal moisture plume. That said, waves passing through the flow around the high and a 60-70 knot jet to our north will provide enough dynamic support to see a few isolated to widely scattered showers or thunderstorms Friday afternoon. Areas north of I-70, particularly the higher terrain, will be most favored. The increased sunshine and decreased moisture during this period will also result in near to a few degrees above normal temperatures across the majority of the forecast area. By Saturday afternoon, the center of the high will have shifted east of the Divide, allowing flow to turn southwesterly across Arizona and Utah, dragging up some deep monsoonal moisture. The edge of this plume is forecast to be over eastern Utah, where some increased showers or thunderstorms will be possible during the afternoon and evening hours. After a few days of dry conditions, it`s likely that the main threats with these storms will be gusty outflow winds and lightning, rather than heavy rain, although a brief heavy downpour is not out of the question. As we move into the coming work week, we remain in a blocky, amplified pattern, with high pressure dominating the center of the country. Under this scenario, our sensible weather relies on where exactly the center of the high sets up on a day-by-day basis. A bit to the east, and the entire Western Slope winds up under the moisture plume. A bit to the west, and the moisture plume sets up over western Utah and we see sunny skies. Passing waves in the flow around the high will also have a hand in how widespread showers and thunderstorms are on any given day. As of now, deterministic and ensemble model guidance does keep above normal moisture in the area, with blended guidance reflecting this with higher PoPs through early next week. Temperatures look to remain near to a few degrees above normal. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 538 AM MDT Wed Aug 14 2024 Light rain showers will continue across the north through 14Z or so with VCSH across KVEL and KHDN, possibly KRIL. Elsewhere, clearing skies are evident with potential clearing behind these showers across the north after sunrise. Expect redevelopment of showers and thunderstorms mainly along and north of I-70, with VCTS more probable at KVEL, KHDN, KRIL, KEGE as well as higher terrain sites like KASE and KTEX this afternoon into the early evening. Elsewhere, mostly to partly sunny skies remain with drier conditions expected. VFR will prevail with brief MVFR or ILS conditions in any storms (mainly across the north) with strong gusty winds and brief heavy rain possible. Showers come to an end and skies should clear shortly after sunset. && .HYDROLOGY... Issued at 354 AM MDT Wed Aug 14 2024 Monsoonal moisture will keep showers and thunderstorms over the region today mainly focused on areas along and north of I-70 with rainfall rates of 1 to 2 inches per hour possible with storms. Flooding potential decreases today as dry air begins to advect into the region, though it`s still possible given the remnant moisture and forcing. Only isolated showers and storms are expected over the higher terrain Thursday and Friday with heavy rain becoming less likely. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MDA LONG TERM...BGB AVIATION...MDA HYDROLOGY...TGJT