486 FXUS65 KGJT 050609 AFDGJTArea Forecast Discussion National Weather Service Grand Junction CO 1209 AM MDT Fri Sep 5 2025
.KEY MESSAGES...
- Scattered showers and thunderstorms will bring some heavy rain, gusty winds, and lightning across the region this afternoon and evening. This trend continues into the weekend.
- Burn scar flash flooding will be possible through the weekend if any of the stronger cells with heavy rain move over more recent burn scars.
- Temperatures will remain around climatology before a warmup starts on Monday onwards.
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.SHORT TERM /THROUGH FRIDAY NIGHT/... Issued at 203 PM MDT Thu Sep 4 2025
PWATs have increased to 0.69 inches at the Grand Junction WFO this afternoon and this is noticeable with the increase in convection across the region. Weak rotation just to our west with an embedded shortwave is the impetus for this convection. Some heavy rain is falling under the stronger cells with plenty of cloud-to-ground lightning also detected. The main concern with any of this convection will be those heavy rainers moving over recent burn scars and the flash flooding threat. This threat will persist as long as the increased moisture remains in the atmosphere and convection continues. Convection will die down after sunset but some showers, maybe a few rumbles of thunder, will persist overnight.
More of the same is expected tomorrow with convection firing off the higher terrain very similar to today. The NAMNEST and HRRR are favoring southern portions of the CWA tomorrow afternoon but with plenty of available moisture and CAPE values mostly between 600 to 800 J/kg, convection will be possible across the entire CWA. Again, like today, main concerns will be some heavy rainers, lightning, and a few gusty outflow winds.
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.LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 203 PM MDT Thu Sep 4 2025
Monsoonal moisture will be well established over the region on Saturday, allowing for PWAT anomalies to peak around 150-175% of normal. As such, widespread showers and thunderstorms continue to be in the forecast on Saturday. The precipitation activity will be supported by a shortwave moving across the region through early Sunday. The support from the shortwave may increase the chances of heavier rainfall, which could raise flash flooding concerns over the new burn scars in the region. Relatively drier air in the northern most part of the region keeps PoPs lower there, and increases the chances of gusty outflow winds with storms. PoPs are expected to stay elevated through the night with the shortwave passage before Sunday`s afternoon convection begins. On Sunday, moisture remains but begins to make its way out of the area resulting in mostly terrain driven convection from the decrease in moisture and loss of upper-level support. PWAT anomalies fall closer to normal on Monday, leading to decreased coverage of terrain based convection through the early workweek. Increased cloud cover should keep daytime high temperatures down to 5 degrees below normal through the weekend, but the decrease in moisture next week should increase highs to near or just above normal.
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.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1153 PM MDT Thu Sep 4 2025
Light rain showers persist across southeastern Utah and southwestern Colorado with an occasional embedded thunderstorm. These will diminish through the overnight as they move up into central colorado. Showers and thunderstorms will increase again after 14Z, becoming scattered to widespread across the region along and south of the I-70 corridor between 18Z and 00Z, thereafter dying down to the southeast through the evening. Threats from these storms will be lightning and heavy rain along with gusty winds. Expect brief periods of MVFR conditions below ILS breakpoints along and south of the I-70 corridor at mountain TAF sites.
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.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None. UT...None.
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SHORT TERM...TGR LONG TERM...GF AVIATION...DB
NWS GJT Office Area Forecast Discussion