469 FXUS65 KGJT 082049 AFDGJTArea Forecast Discussion National Weather Service Grand Junction CO 249 PM MDT Mon Sep 8 2025
.KEY MESSAGES...
- Expect isolated to scattered afternoon showers and thunderstorms focused over the higher terrain the next few afternoons with a small chance of storms lingering into the early morning hours.
- Thursday and Friday will see widespread showers and thunderstorms return with a passing system with temperatures cooling below normal.
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.SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 248 PM MDT Mon Sep 8 2025
The H500 08/12Z upper air analysis is showing general ridging over the western NOAM transitioning to a trough over the East. There is a cyclone that has snuck under the northern extent of the ridge which is hanging just off the CA/OR coast this afternoon. This parent low will only progress into NorCal over the next 48 hours though the trough will carve southward toward the Baja. This creates an set up for pulling moisture northward into the Rockies through the week with a tight gradient setting up near the CO/UT border...wetter to the East and drier to the West. The ALPW does show some moisture advecting northward into the SW Utah as height falls to the West induce the moist conveyor belt out of the monsoon region. Convection so far this afternoon is going about as planned firing mainly on the higher terrain up North and the divide mountains of the central and south. Some fairly decent shear and instability are in place but the 18Z RAOB suggest some capping to overcome. If it does northeast Utah into NW Colorado could again see some organized storms this evening. The Grand Valley was awoken overnight by a rogue nocturnal storm and this could happen again tonight as the back of wave lifts through and an upper jet begins to nose across eastern Utah. Confidence is not overly high so PoPs remain low but expect a least a decent ACCAS field with virga/light showers moving through our CWA during the morning hours which will blossom into more showers and storms tomorrow afternoon. PWAT shows a slight increase tomorrow...though nothing off the charts so coverage should be similar to today. Drier air filters in behind this overnight and will have to see if there are any waves or support to keep nocturnal activity going. Right now it looks dry. Temperatures stay near to slight above normal the next few days before they cool down as a wetter forecast arrives.
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.LONG TERM /WEDNESDAY THROUGH SUNDAY/... Issued at 248 PM MDT Mon Sep 8 2025
Low pressure digging down the West Coast will bring us one more day of summer-like conditions Wednesday. The jet streak rounding the southeast quadrant of the low will send abundant warm air and some gusty winds across the region. Relative humidities look to stay above critical fire weather thresholds, but some localized fire weather could materialize in our desert valleys along the state line. Pre-frontal showers and thunderstorms are expected too, so this will likely make fire weather a moot point. High pressure over the Great Plains will stall advancement of the low out of the Great Basin on Thursday. The jet remains overhead, so additional moisture filters in, creating more widespread shower activity on Thursday. Temperatures will remain warm, but also muted by cloud cover and showers. By early Friday morning, the low ejects eastward putting the CWA under jet exit region forcing and abundant moisture. This should bring widespread showers and thunderstorms to most of the CWA Thursday night and Friday. Cold air behind the front begins to invade and afternoon highs Friday should feel rather fall-like, especially with the damp conditions. Conditions in the wake of the front turn more progressive Saturday, with zonal flow producing additional precipitation chances on the terrain Saturday. Temperatures remain mild through the weekend, before warming some early next week. Transitory ridging will quiet things down on Sunday, before another weak disturbance delivers some additional shower activity Monday. While I`m sure warm conditions return this fall, there certainly is a seasonal shift arriving with this system.
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.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1133 AM MDT Mon Sep 8 2025
A thin layer of high level smoke is drifting through from upstream wildfires but this is not impacting surface visibility. Enough moisture remains in place that afternoon heating will spark more isolated to scattered showers and storms this afternoon and early evening. Confidence is not as overly high but did place PROB30 in the mountain and GUC sites where clouds are showing some vertical growth. There is also an outside chance of nocturnal storms forming over the western CWA after midnight and moving eastward through sunrise.
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.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None. UT...None.
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SHORT TERM...15 LONG TERM...LTB AVIATION...TGJT
NWS GJT Office Area Forecast Discussion