After high pressure dominated eastern Utah for several days, moisture gradually increased ahead of an approaching system. This led to the development of isolated to scattered high-based thunderstorms.
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The episode as NWS GJT wrote it up.
After high pressure dominated eastern Utah for several days, moisture gradually increased ahead of an approaching system. This led to the development of isolated to scattered high-based thunderstorms. Given the dry air at the lower levels, gusty outflow winds were the primary threat from storms. The stronger storms produced gusty winds in excess of 58 mph across Grand County.
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 18, 10:30 AM MST, 3 hours 12 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 1130 AM MDT Tue Jul 18 2023 .SHORT TERM...(Today through Wednesday) Issued at 248 AM MDT Tue Jul 18 2023 It seems wrong to say it will be cooler today...but it will be. There isn't much solace in that since our highs will generally be 5 to 10 degrees above mid July normals. We broke or tied many records yesterday including the all time high at Grand Junction and today's may actually be in reach since it is only one away from the forecast of 102. Highs tomorrow will drop a few more degrees thanks in part to additional moisture that will be advecting in over the next 24 hours. Is this monsoonal moisture finally? Yes...but don't get used to it. The SubTropical High has been suppressed far enough eastward...over the southern Rockies on the 18/00Z H500 hand analysis map...that moisture from the Gulf of California is heading northward. The GOES ALPW imagery is showing one plume riding the periphery of the ridge across northern NV and UT this morning. The secondary plume from the GoCA is moving across Western AZ into the tip of NV. There is nocturnal convection in the northern plume associated with weak PV and a wind core aloft which should arrive to northeast Utah by sunrise and drift along our northern border through the morning. Heating will work on this moisture source and bring a noticeable uptick in convection this afternoon. The better coverage will be over the high plateaus and northward...mainly isolated coverage is expected southward due the proximity of the high pressure center and it is farther from the moisture plume. Though moisture is arriving we won't see monsoonal rains as the low layers remain extremely dry and the inverted V profiles will be favorable for pushing out gusty winds and progressive outflow boundaries. Isentropic surfaces show the secondary plume of mositure will arcing from S.NV across Utah to northern Colorado overnight. The transport vectors converge over our northern zones overnight where forcing from jet dynamics looks to keep diurnal convection going well into the early morning hours. Still not expected much QPF with these storms but the blanket of clouds will help keep heat in and temperatures tonight will be quite mild. With moisture established Wednesday will bring more afternoon showers and storms...possibly delayed a bit by clouds left over from the overnight activity. The moisture gradient continues to favor better storm coverage to the north while the lower valleys of the 4 Corners will be lucky to see even and isolated storm. Localized critical fire weather will still arise the next few afternoons thanks to the gusty winds and deep mixing in this hot airmass. This will mainly be in the central and south as the humidity will be slightly higher over the north. This is where we currently have bigger fires so any relief will be good. .LONG TERM...(Wednesday night through Monday) Issued at 248 AM MDT Tue Jul 18 2023 After a seemingly endless hot and dry pattern lately, scattered showers and thunderstorms are likely to develop across the higher terrain late this week. This pattern change is due to a plume of anomalous moisture with precipitable water values of 125 to 175% of normal nosing into eastern Utah and western Colorado from the west and southwest. This opening of the moisture tap is in response to a trough digging into the Pacific Northwest. As this occurs, the ridge flattens and becomes elongated across the southern Four Corners and southern Plains. The gradient in between the trough and the ridge tightens, which then increases the upper level winds and funnels moisture from the Pacific into the region as a result. Despite the increase in mid and upper level moisture, forecast soundings still reveal quite a bit of dry air in the lowest levels of the atmosphere... as evidenced by stout inverted V signatures. While showers and storms won't be completely dry, QPF is likely to be fairly limited overall, especially in the lower valleys. Thus, we'll need to continue to keep an eye on the potential for dry lightning and fire starts given critical fuels and gusty outflow winds. The good news? The increased cloud cover should provide at least a little relief from the extreme heat as of late, but it will still be hot with highs in the lower desert valleys reaching well into the 90s and low to mid 100s each day. Unfortunately, the anomalous plume of moisture is not expected to last long as the ridge is progged by ensembles to retrograde and amplify back into the Great Basin, Four Corners, and Intermountain West by this weekend. This synoptic evolution effectively cuts off the source of moisture and leaves the CWA mainly dry outside of the Continental Divide mountains through at least Sunday. With less clouds and storm activity, temperatures will climb back to well above seasonal normals. Looking ahead to early next week, there are some signs that another plume of moisture may try to work into the forecast area... with the potential to stick around for most of the week. We'll see how that pans out as we get closer, but the early && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1127 AM MDT Tue Jul 18 2023 VFR conditions are expected to prevail for the next 24 hours. A band of clouds and light showers is extending across the northern boundary with Wyoming, impacting KVEL and KHDN. The showers with this band may become thunderstorms this afternoon, and could bring gusty outflow winds. This band will drop south through the area over the next 24 hours. Otherwise, skies will be mostly clear with typical diurnal winds expected. Afternoon gusts up to 25 knots will be possible during the mid-to-late afternoon hours, but will quickly diminish as the sun sets. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...15 LONG TERM...MDM AVIATION...TGJT
Hazardous Weather Outlook National Weather Service Grand Junction CO 357 AM MDT Tue Jul 18 2023 COZ001>014-017>023-UTZ022>025-027>029-191000- 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- 357 AM MDT Tue Jul 18 2023 This hazardous weather outlook is for eastern Utah and western Colorado. .DAY ONE...Today and Tonight Thunderstorm development today will lead to a lightning and gusty outflow wind threat. Areas north of I-70 will see a better coverage of storms with mainly isolated storms occurring to the South. Localized critical fire weather will form again this afternoon mainly in the lower elevations of southern Utah and Colorado. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Thunderstorm development will occur each afternoon through the week before drier air returns for the weekend. Gusty outflow winds and lightning will be daily afternoon threats. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The Grand Junction radar (KGJX), 137 km away, was scanning. The volume nearest the first event began at 20:41 UTC.
1 thunderstorm wind. Local standard time, as filed.
A peak wind gust of 63 MPH was measured by the automated weather station at the Canyonlands Field Airport outside Moab.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Utah in 2023Every state in 2023This day in weather historyWarnings in Utah, July 2023
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: 1101707.