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Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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818 FXUS65 KGJT 182048 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 248 PM MDT Thu Jul 18 2024 .KEY MESSAGES... - Temperatures are expected to remain a few degrees above normal with daily thunderstorm chances through the remainder of the week with a slight drying trend late in the weekend. - Threats from thunderstorms will mainly be from gusty outflow winds though a few storms will be capable of producing small hail and moderate to heavy rainfall rates. Overall flooding threats remain low. - The combination of high based storms, gusty outflow winds and lightning will also keep a threat of new wildfire starts in the picture. && .SHORT TERM /THROUGH FRIDAY NIGHT/... Issued at 248 PM MDT Thu Jul 18 2024 The persistent area of high pressure is currently centered near west-central New Mexico / east-central Arizona this afternoon, resulting in another round of diurnally-driven showers and thunderstorms across the Western Slope. Convection has been slightly stronger than this time yesterday with some pea-sized hail and a quick three-tenths of an inch of rain reported on the Uncompahgre Plateau. Even with a PWAT less than the mean value of 1.43 inches on this morning`s 12Z GJT sounding, what moisture remains trapped in the atmosphere is more than sufficient for producing storms today, as well as keeping the brief potential for slightly heavier rainfall rates present. The ridge will begin to slowly retrograde westward tonight and into Friday, allowing today`s precipitation to largely diminish overnight before activity redevelops by midday Friday. We are expecting a slight uptick in storm coverage on Friday as a shortwave trough rounding the backside of the main low to the east brushes the Continental Divide. PWATs will increase to 120 to 150 percent of normal which could bring better potential for heavier rain. Even so, the low levels will remain dry so gusty outflow winds and small hail will be the primary concerns from convection. Friday night looks to be quiet though a lingering shower cannot be ruled out. Temperatures through the short term won`t fluctuate much given the continued presence of the ridge overhead. Overall, readings will trend slightly above normal for the lower elevations and near normal in the mountains. Overnight lows tonight and Friday night will be mild for mid July. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Issued at 248 PM MDT Thu Jul 18 2024 Anomalously low heights will be settling in East of the Rockies which will drive the SubTropical High well back to the West into a least the middle of next week. Ensemble anomaly tables show higher than normal PWAT extending north of the Gulf of Cali into the eastern Great Basin...effectively shutting down a direct tap to the monsoon into the Rockies. Instead we will continue to advect recycled moisture through the ridge which will keep the daily thunderstorm chances in the forecast but limit the widespread heavy rainfall and flood threat. I would have to guess that extended scenario will be similar to the past few days in the northerly flow pattern. Storms should favor the higher terrain for initiation and drift southward as they regenerate with a few storms surviving into adjacent valleys. Overall the precipitation outlook for the many of the lower valleys is not favorable and it will be very hit or miss as storms move off the hills. There is some hope that by late next week a stronger system arriving the PacNW will begin to nudge the high eastward and this could lean the moisture plume farther into the Great Basin. Temperatures remain fairly static and will continue to run near to above normal through the period. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1122 AM MDT Thu Jul 18 2024 Moisture has increased a tad and this should lead to an uptick in thunderstorm coverage today with an early start already indicated on current radar/satellite trends. Gusty outflow winds will continue to be the main threat with only a very low probability of MVFR or lower conditions developing. Showers and a few storms may linger during the overnight hours but the coverage will be limited. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...MMS LONG TERM...15 AVIATION...TGJT