A midlevel disturbance trekked across the region. This feature tapped into low-level moisture to produce scattered showers and thunderstorms.
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The episode as NWS GJT wrote it up.
A midlevel disturbance trekked across the region. This feature tapped into low-level moisture to produce scattered showers and thunderstorms. The stronger storms produced gusty winds in excess of 70 mph at the Cortez Municipal Airport.
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 Aug 15, 10:31 PM MST, 2 hours 42 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 1131 PM MDT Sun Aug 15 2021 .SHORT TERM...(Tonight through Monday night) Issued at 154 PM MDT Sun Aug 15 2021 Radar has started lighting up with some beefy cells popping over the Uncompahgre Plateau and La Sals. A subtle wave is moving through the mean flow and is allowing convection to be a bit more organized from what we've seen over the last few days. As moisture remains higher south of I-70, those areas can expect some brief, heavy rain and gusty outflow winds while areas north can expect to see more wind than rain. While H7 winds remain light, radar indicates the storm moving at around 10 to 15 mph from the northwest to southeast. Good news as this will keep the storms moving especially over burn scars so flooding risks, while still there, will be a bit less. Short range guidance brings most of the convection to an end by sunset with a few showers lingering under the wave as it continues to drop to the south and eventually out of the CWA by daybreak. Hazy conditions have moved back in as well but the good news, for the next 24 hrs at least, is that the densest smoke from fires out west will stay to our north and west. Hopefully this trend holds. Tomorrow, the much touted upper level trough and surface cold front will be just off the PacNW coast. The ridge of high pressure will start to deform with the ridge axis shifting to our northeast as the trough gets closer. Lower levels will see little change to current PWATs while midlevels will see a bit of drying. This will lend itself to a decrease in convection with only the San Juans and the Divide from Vail Pass southward, being favored for convection. Warm temperatures and hazy skies, especially for eastern Utah, continue. .LONG TERM...(Tuesday through Sunday) Issued at 154 PM MDT Sun Aug 15 2021 The base of the much discussed Pacific trough finally comes ashore on Tuesday, flattening the ridge over the Great Basin and shifting winds to more southwesterly across eastern Utah and western Colorado. With this wind shift, deeper monsoonal moisture will finally be able to stream into the area, with forecast PWAT values increasing to near an inch across western portions of the CWA by Tuesday evening, and over an inch across eastern Utah by Wednesday. Convection will be limited on Tuesday, however, thanks to a shortwave ridge being pushed out ahead of the trough. The best chances of convection will be over central and eastern Utah, where the moisture pool will be deepest. Confidence is high that Wednesday will be the day for clouds, cooler temps, and widespread precipitation. Models are in good agreement that PWATs will increase to between 0.80 and 1.20 inches across much of the CWA, and that the surface front will move through during peak heating. Plenty of dynamic support is expected with the frontal passage, and while antecedent cloud cover may temper the amount of instability a bit, conditions look very good for widespread shower and thunderstorm activity the area Wednesday afternoon. Temperatures for this period are expected to run 5-10 degrees below average. Unfortunately, forecast confidence drops substantially after Wednesday as models still disagree on the evolution of the upper level trough. The EC ensembles continue to favor a slower closed low solution that would have widespread showers and storms continue through the day Thursday before the trough finally lifts northeast. On the other hand, the GFS ensembles have a much more progressive trough that lifts out overnight Wednesday, with only a few lingering showers possible Thursday afternoon. Models have been consistently having issues with the evolution of this system, and in fact a few days ago the solutions were totally flipped. The EC was more progressive and drier, while the GFS was slower and wetter. Hopefully, over the next few days, the models will come into better agreement as to how the second half of the work week will play out. When the trough does finally lift off to the northeast, flow will become more zonal and high pressure will begin to build back in. This will keep conditions drier and allow temperatures to rebound to at or above average for the weekend. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) Issued at 1131 PM MDT Sun Aug 15 2021 Lingering showers and thunderstorms will continue to push southeastward before dissipating in the overnight hours. Despite moist convective activity, VFR conditions are likely to persist as the lower levels of the atmosphere remain dry, which will keep ceilings high and rain rates low. Showers and thunderstorms redevelop this afternoon as instability increases with rising temperatures. Included mention of rainfall at KTEX, KGUC and KDRO where southward moving cells are most likely to impact flight operations. Gusty outflow winds are possible at all TAF sites during the afternoon and evening. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...TGR LONG TERM...BGB AVIATION...NL
Hazardous Weather Outlook National Weather Service Grand Junction CO 348 AM MDT Sun Aug 15 2021 COZ001>014-017>023-UTZ022>025-027>029-161000- 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- 348 AM MDT Sun Aug 15 2021 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Thunderstorm development will occur again this afternoon and evening. Some storms will be capable of brief heavy rainfall rates and others capable of producing gusty outflow winds in excess of 45 mph. Thicker smoke looks to move into northern portions of Utah and Colorado which could affect air quality conditons. .DAYS TWO THROUGH SEVEN...Monday through Saturday Thunderstorm coverage will become more widespread by mid week as a larger storm system moves through the region. The threat of heavy rainfall rates or prolonged precipitation could impact burn scars and lead to other runoff issues. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1221 AM MDT MON AUG 16 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1157 PM TSTM WND GST 2 NW MONTROSE 38.51N 107.90W
08/15/2021 M49 MPH MONTROSE CO ASOS
&&
GJTThe Grand Junction radar (KGJX), 199 km away, was scanning. The volume nearest the first event began at 08:11 UTC.
1 thunderstorm wind. Local standard time, as filed.
A peak wind gust of 71 MPH was measured by the automated weather station at the Cortez Municipal Airport.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2021Every state in 2021This day in weather historyWarnings in Colorado, August 2021
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: 967338.