Remnants from Tropical Storm Harold lifted across the Desert Southwest. This, combined with already abundant subtropical moisture, resulted in widespread showers and thunderstorms across western Colorado.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS GJT wrote it up.
Remnants from Tropical Storm Harold lifted across the Desert Southwest. This, combined with already abundant subtropical moisture, resulted in widespread showers and thunderstorms across western Colorado. Storms were slow moving and produced heavy rain. As a result of the heavy rain, some flooding and debris flows occurred in portions of Gunnison, Garfield, Mesa, and Montezuma counties.
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 24, 10:35 AM MST, 2 hours 25 minutes earlier.
Area Forecast Discussion National Weather Service Grand Junction CO 1135 AM MDT Thu Aug 24 2023 .SHORT TERM...(Today through Friday) Issued at 417 AM MDT Thu Aug 24 2023 The center of what was Tropical Storm Harold was located over Winslow, AZ as of 0930Z this morning. Meanwhile, what could be considered one of its outer bands was bringing light/moderate rain to much of southeast Utah and southwest Colorado early this morning. Harold will continue to bring cool, wet weather across the forecast area for the next three periods as it slowly moves northeast to the Four Corners today, then over west-central Colorado tonight and finally over north-central Colorado Friday. Moisture entrained within Harold, on top of that advected northward from the Mexican plateau, is expected to drive precipitable water levels to between 1 and 1.4" across the forecast area which, to put it into context, approaches 250% of normal for some areas according to ECMWF ensembles. This of course raises the potential for excessive rainfall and localized flooding. However, the cloud shield over the area is unlikely to lift, inhibiting available CAPE with the HREF showing 500 J/Kg on average with pockets approaching 1,000 J/Kg significantly reducing the threat of excessive rainfall. Therefore, in agreement with the previous shift, will hold off issuing a Flood Watch as the threat appears relatively low for widespread excessive rainfall. That said, localized mud/debris flows are possible for susceptible areas including recent burn scars. Nocturnal showers and embedded storms are likely tonight as Harold tracks over the area with more of the same on Friday. Expect significantly cooler temperatures today as clouds limit solar insolation and showers add diabatic cooling to the mix. As a result, afternoon highs today and Friday are expected to fall several degrees below normal. In contrast, clouds will limit escape of long wave surface radiation keeping overnight lows relatively mild. .LONG TERM...(Friday night through Wednesday) Issued at 417 AM MDT Thu Aug 24 2023 By Friday evening, the wave associated with the remnants of Harold will be traversing northwest Colorado and eventually moving out into the Plains. Between the upper level dynamic support in the form of this wave, and the deep moisture still pooled across eastern Utah and western Colorado, shower activity will last through the night. On Saturday morning, a ridge of high pressure pushes into the region, bringing an end to the overnight convection. Ample moisture will remain across the Western Slope through the weekend, with forecast PWATs in the 120-170% of normal range. With increased sunshine expected under the ridge, enough instability should build to fire showers and thunderstorms off the higher terrain in the afternoon, although coverage will be significantly less compared to previous days. Weak flow aloft will lead to slow movers and the continued threat for heavy rain and flash flooding. Over the course of the weekend, the high pressure that has been sitting over the Plains the last several days will work its way west. The high will center itself over the Four Corners by Sunday morning, and should shift into western Arizona and southern California by Monday evening. This will cut off any monsoonal moisture from flowing north into the Great Basin, and forecast PWAT values do decrease somewhat through the weekend and into the coming week. Tuesday looks to be the driest day of the period, with PWATs coming in at right around normal for this time of year, roughly 0.50- 0.70 inches. This is still plenty of moisture to keep afternoon convection in the forecast through the weekend and into early next week, although the main threats with this storms will transition away from heavy rain and back toward gusty outflow winds as a surface dry layer builds in. These drier conditions will stick around through midweek, with temperatures slowly climbing to around 5 degrees above normal. Low temperatures will remain mild and above normal through Saturday, before dropping to more normal values as drier air works in and clear night skies replace clouds and showers. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 1131 AM MDT Thu Aug 24 2023 Cloud cover has limited atmospheric instability this morning but the arrival of the system in the 4 Corners and some sunshine occurs this afternoon...widespread shower and thunderstorm activity is expected. Most TAF sites will be impacted with temporary ILS to MVFR conditions as these storms move through with moderate to heavy rainfall rates and gusty winds. This system will continue to roll through the area overnight into Friday with MVFR cigs possible in some valley locations by sunrise. Shower and thunderstorm activity will remain widespread through tomorrow as well. && .HYDROLOGY... Issued at 417 AM MDT Thu Aug 24 2023 Remnants from Tropical Storm Harold, currently situated over east- central Arizona as of 09Z/Thu will begin to move over southeast Utah and southwest Colorado today before spreading over the remainder of the region on Friday. ECMWF ensemble means indicated that this surge of moisture could raise precipitable water levels to between 1 and 1.4" across the forecast area today, tonight and Friday which equates to somewhere between 180 and 230% of normal. Though Harold will be much weakened by the time it arrives over the area, it should still supply enough dynamic forcing to generate widespread shower and thunderstorm activity. The threat of heavy rain rises significantly with this system as developing storms should be efficient rain producers and slow moving which may result in localized mud and debris flows and potential flash flooding. Locations at greatest risk are recent burn scars, areas of steep unstable terrain and those with poor drainage. WPC has much of our area under a marginal risk, with slight risk now expanded to include southeast Utah and southwest Colorado for Thursday. Cloud cover Thursday morning is likely to inhibit stronger convection from developing early in the day, limiting the flash flood potential to localized and not as widespread. Therefore, opted not to issue a Flash Flood Watch at this time. While localized flash flooding is possible, the potential for more widespread flooding will have to be monitored with the latest guidance and trends. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && SHORT TERM...NL LONG TERM...BGB AVIATION...TGJT HYDROLOGY...GJT
Hazardous Weather Outlook National Weather Service Grand Junction CO 435 AM MDT Thu Aug 24 2023 COZ001>014-017>023-UTZ022>025-027>029-251045- 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- 435 AM MDT Thu Aug 24 2023 This Hazardous Weather Outlook is for northwest Colorado, southwest Colorado, west central Colorado, east central Utah, northeast Utah and southeast Utah. .DAY ONE...Today and tonight. Remnants of Tropical Storm Harry will move across the region during the next 36 hours. Deep moisture associated with this storm raises the potential for excessive rainfall potentially leading to localized debris/mudslides and flash flooding. However, cloud cover will mitigate this threat to a significant degree. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. The heavy rain threat continues on Friday with Harold finally exiting the area Friday night. Drying begins this weekend and will continue early next week. Consequently, thunderstorms will be incrementally decreasing each day, eventually becoming confined to the higher elevations, mainly along the Continental Divide by Monday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected today or tonight, however spotters are encouraged to relay rainfall amounts or any observed flooding to the National Weather Service in Grand Junction.
The national radar mosaic for the moment the first event began.
7 flood, 1 debris flow. Local standard time, as filed.
A CoCoRaHS observer southwest of Redvale reported flooding as a result of heavy rain from thunderstorms. Over an inch of rain was recorded, which led to partial erosion of the observer's irrigation ditch.
The emergency manager reported flooding at the intersection of 25 and L Roads northeast of downtown Cortez as a result of heavy rain from thunderstorms.
Daniels Hill (a section of Gunnison County Road 3) was damaged and unpassable due to flooding from heavy rain. The road remained closed until the following afternoon.
The emergency manager reported that heavy rain from thunderstorms led to minor flooding across portions of Cortez, including some basements in homes along Highway 491 and Veterans Park.
Heavy rain from thunderstorms over the Grizzly Creek Fire burn scar resulted in the ponding of water along portions of I-70 with a mud and debris slide reported near mile marker 120.6 I-70 was closed in both directions from 1800 on the evening of the 24th to 0000 on the 25th.
Heavy rain from thunderstorms led to 6 inches of water flowing over 12th Street and Park Avenue in Rifle.
Heavy rain from thunderstorms flooded a basement at the intersection of 5th Street and Ute Avenue in Rifle.
Heavy rain from thunderstorms resulted in minor flooding/ponding of water on portions of I-70 near mile marker 56 going east towards De Beque.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2023Every state in 2023This day in weather historyWarnings in Colorado, August 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: 1113841, 1113840, 1113794, 1113797, 1113799, 1113802, 1113804, 1113836.