Monsoonal moisture lingered across eastern Utah and, when paired with daytime heating, led to scattered showers and thunderstorms. In addition to brief heavy rain, gusty outflow winds were common with storms.
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The episode as NWS GJT wrote it up.
Monsoonal moisture lingered across eastern Utah and, when paired with daytime heating, led to scattered showers and thunderstorms. In addition to brief heavy rain, gusty outflow winds were common with storms.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Grand Junction, CO wrote its last area forecast discussion before the first event at Jul 23, 1:09 PM MST, 2 hours 48 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 209 PM MDT Thu Jul 23 2020 .SHORT TERM...(Tonight through Friday night) Issued at 124 PM MDT Thu Jul 23 2020 The summertime Southwest Monsoon pattern continues over our region with a plume of higher than normal moisture feeding north between a synoptic scale trough to our west and an upper level ridge to the southeast. The weak convective system and its remnants that moved northeast across eastern UT into far western CO has finally dissipated and places that were cloudy are now warming up and destabilizing. Surface dewpoints, even in the mountains, are in the 40s to mid 50s. An axis of 0.70-1.00 inch precipitable water is analyzed from southeast UT across western CO. Early afternoon most unstable CAPE is running 500-1500 J/kg. It's hard to pick out any individual minor shortwave upstream until you get down to southeast AZ. However, there is an upper level jet max over the area helping to provide some dynamical support for the otherwise terrain driven convection. Mean flow will continue to move storms to the northeast at 15 to 20 mph and this will be a positive factor in lowering the threat for flash flooding today. While diurnally driven convection will die down after sunset, a remnant circulation associatied with mesoscale convective sytem generating over eastern AZ late today will move north over the Four Corners and up over western CO after midnight and into Friday morning. This activity will likely delay destabilization in its wake Friday, but with no change to the flow or reduction in moisture, expect another round of afternoon terrain initiated convection with storms capable of producing heavey rain moving off to the northeast. Maximum temperatures will remain below normal with the cloud cover and shower activity. .LONG TERM...(Saturday through Thursday) Issued at 124 PM MDT Thu Jul 23 2020 The current weather pattern will continue through Tuesday, and in fact there is agreement with precipitable water values increasing to over an inch for much of the area Sunday through Tuesday as the tropical plume of moisture is tugged on by a synoptic scale trough over the Pac NW and the stationary closed low near CA. Surface dewpoints will also continue in the 40s and 50s. Our national center is forecasting between 3 and 5 inches of rainfall for the San Juan mountains through Tuesday with lesser amounts to the north. This looks reasonable and we will continue to monitor daily trends and timing of convective development and systems for the possibility of flash flood watches, especiall for burn scar areas. Even though storms are expected to be caught up in a general steering flow of 10 to 20 mph, areas with repeated rainfall will become increasingly susceptible to flash flooding as well. Right now, it appears that areas south of I-70 will remain the areas with greatest coverage of thunderstorms and rain, while northeast UT and far northwestern CO may get through the next 5 days without seeing more than a few sprinkles. Extended range models and ensembles agree on the Pac NW trough sliding east early next week and allowing the subtropical upper level ridge to slide to the west over our region. Therefore, confidence is relatively hight that the southerly flow will transition to a drier westerly regime Wednesday for a day or two before a possible return to the monsoon pattern. Depending on the extent of cloud cover on any given day, high temperatures could run a few to as much as 15 degrees below normal Sunday through Tuesday, before returning to near normal Wednesday and Thursday in the drier air. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 1140 AM MDT Thu Jul 23 2020 Isolated thunderstorms will increase in coverage early this afternoon, materializing over higher terrain and drifting northeast. Brief periods of heavy rainfall, gusty outflow winds and lightning are expected with stronger storms. Showers and thunderstorms will be more common over TEX, GUC, MTJ, and ASE this afternoon before weakening tonight. However, some lingering mountain showers are likely to persist after sunset, with additional thunderstorms moving into the area from AZ and NM overnight. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...BM LONG TERM...BM AVIATION...ERW
Hazardous Weather Outlook...UPDATED National Weather Service Grand Junction CO 229 PM MDT Thu Jul 23 2020 COZ001>014-017>023-UTZ022>025-027>029-241200- Lower Yampa River Basin-Central Yampa River Basin- Roan and Tavaputs Plateaus-Elkhead and Park Mountains- Upper Yampa River Basin-Grand Valley-Debeque to Silt Corridor- Central Colorado River Basin-Grand and Battlement Mesas- Gore and Elk Mountains/Central Mountain Valleys- Central Gunnison and Uncompahgre River Basin- West Elk and Sawatch Mountains-Flat Tops- Upper Gunnison River Valley-Uncompahgre Plateau and Dallas Divide- Northwest San Juan Mountains-Southwest San Juan Mountains- Paradox Valley/Lower Dolores River- Four Corners/Upper Dolores River-Animas River Basin- San Juan River Basin-Southeast Utah-Eastern Uinta Mountains- Eastern Uinta Basin-Tavaputs Plateau-Arches/Grand Flat- La Sal and Abajo Mountains-Canyonlands/Natural Bridges- 229 PM MDT Thu Jul 23 2020 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...This Afternoon and Tonight Isolated to scattered thunderstorms will occur this afternoon and evening. A few strong storms are possible from about mid- afternoon through the early evening. Lightning, small hail, gusty winds, and brief heavy rain will all be possible...particularly over eastern Utah and southern Colorado. .DAYS TWO THROUGH SEVEN...Friday through Wednesday Isolated to scattered thunderstorms are possible each day with best coverage south of Interstate 70. Heavy rainfall from the strongest storms will become increasingly likely through the weekend, along with gusty winds and lightning. These hazards are mostly likely from early afternoon through the mid evening hours. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The Grand Junction radar (KGJX), 190 km away, was scanning. The volume nearest the first event began at 22:58 UTC.
1 thunderstorm wind. Local standard time, as filed.
A peak wind gust of 59 mph was measured by the automated weather station at the Vernal Regional Airport.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Utah in 2020Every state in 2020This day in weather historyWarnings in Utah, July 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 896645.