654 FXUS65 KGJT 090946 AFDGJTArea Forecast Discussion National Weather Service Grand Junction CO 346 AM MDT Tue Sep 9 2025
.KEY MESSAGES...
- Expect isolated to scattered afternoon showers and thunderstorms focused over the higher terrain through Wednesday with a small chance of storms lingering into the early morning hours.
- Thursday and Friday will see widespread showers and thunderstorms return with a better chance of wetting rains. Temperatures will cool to below normal levels.
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.SHORT TERM /THROUGH WEDNESDAY/... Issued at 346 AM MDT Tue Sep 9 2025
As the back edge of a shortwave continues to lift through northeast Utah and northwest Colorado, showers and storms continue to pop up as enough instability and lift remain. Once again, thunderstorms developed across east-central Utah and tracked into the Grand Valley of west-central Colorado during the early morning hours. These storms have since weakened considerably with some light rain and gusty winds but lightning was fairly frequent with this convection earlier with some pockets of heavy rain rates, although the storm motion was fairly quick, so precipitation amounts were around 0.20 or less.
These showers will be more isolated through sunrise with accas left in its wake, an indicator of instability. PWAT continues to increase ever so slightly today with CAPE between 300 and 500 J/kg. There looks to be some CIN as well though so some areas may continue to remain capped, so will likely need to overcome this to realize stronger convection. Regardless, scattered showers and thunderstorms are expected to develop over the high terrain by afternoon with some storms spreading over the valleys late in the day. Looks like similar coverage to yesterday with gusty winds and frequent lightning the primary concerns with pockets of wetting rain possible but less likely as low levels remain dry. The HRRR is more aggressive with convection this afternoon while the NAMNest is less so and keeps activity mainly over the high terrain. Something to keep in mind. Conditions look to dry out behind this wave tonight as southwest flow increases ahead of a low pressure system that develops out west over Northern California, pumping dry southwest flow into the Desert Southwest and Great Basin. There is nothing definitive to suggest that convection will continue overnight tonight like the last couple nights but something to monitor.
On Wednesday, conditions start off dry with breezy southwest winds across eastern Utah and western Colorado near the UT-CO border ahead of this low. High pressure remains to our southeast over eastern New Mexico, which does allow monsoonal moisture to push across southwest Colorado up the central Divide late Wednesday afternoon and evening. This will result in a bit better coverage of storms late in the day on Wednesday. Increasing clouds and moisture should put a damper on near critical fire weather conditions which could be localized due to the gusty winds along the UT-CO border. Chance of wetting rain increases for the San Juans and central mountains by late Wednesday afternoon and evening due to this increasing moisture but imagine gusty winds will remain primary threat with storms until better moisture arrives Thursday. Temperatures will remain warm and above normal through Wednesday, before a cooldown arrives.
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.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Issued at 248 PM MDT Mon Sep 8 2025
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 /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1152 PM MDT Mon Sep 8 2025
Isolated storms will still continue overnight mainly across areas north of I-70 but cannot completely rule out a stray thunderstorm or two developing in the early morning hours across the I-70 corridor from KCNY to KGJT. Included PROB30 group at KVEL and KHDN to account for this. We will still keep SCT to BKN cloud cover along and north of I-70 through sunrise with clearing skies across the south. Another round of scattered showers and storms is expected to develop Tuesday afternoon with higher terrain sites favored. Winds will generally be southwesterly with gusts of 15 to 25 kts possible during the afternoon. VFR conditions are expected to prevail with brief MVFR possible in any shower/storm.
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.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None. UT...None.
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SHORT TERM...MDA LONG TERM...LTB AVIATION...TGJT
NWS GJT Office Area Forecast Discussion