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FXUS65 KGJT 270556 AFDGJT

Area Forecast Discussion National Weather Service Grand Junction CO 1156 PM MDT Fri Apr 26 2024

KEY MESSAGES

- Widespread showers and thunderstorms expected again this afternoon. Moderate rainfall and small hail is possible.

- A potent system will move through the area this evening through Sunday morning bringing much cooler temps, valley rain and mountain snows to the region.

- Generally 6 to 12 inches of snow is expected above 9000 ft across most mountain ranges between today and Sunday morning.

SHORT TERM /THROUGH SATURDAY NIGHT/
Issued at 130 PM MDT Fri Apr 26 2024

A modest low pressure system is currently located over the Nevada/Utah state line placing us in prefrontal southwest flow.
Moisture continues to advect into the region within this flow allowing PWAT to almost reach 0.50" at GJT this morning. Lapse rates remain steep thanks to the shortwave that passed through yesterday.
Surface heating has cause convection to develop. There has been quite a bit of cloud cover this morning due to this moisture. The main uncertainty is how much instability can build with all of these clouds. Thus far there are a few thunderstorms so there is at least 100-200 j/kg in spots. Some models predicted upwards of 300 j/kg this afternoon, which is looking like a slim chance. If that can be realized then some small hail could occur with the strongest cells.
Pockets of moderate rainfall seem likely given the moisture values.
Scattered to widespread showers and storms will continue this evening and overnight across most of the forecast area as the low pressure approaches from the west. Snow levels are around 9-10 kft now, but may drop tonight closer to 8-9 kft so minor impacts are possible around the mountain passes.

Tomorrow morning the low pressure passes overhead and therefore large-scale lift is maximized. The low will drag a cold front through the region during this time as well. One thing the models have been hinting at for the last few runs is a an area of enhanced lift wrapping around the low from NE CO to NW CO then back to SE CO in the afternoon. Expect this will support a cluster of showers and or stratiform rainfall along with a few thunderstorms so chances continue. Snow levels hover around 7-8 kft tomorrow and tomorrow night. The low finally exits the region tomorrow evening so a majority of the precipitation shuts down. The moisture is not quick to leave so lingering orographic showers will continue through the night. The chances for snow to stick to the roads will be highest at night, which may impact travel in the mountains. Some higher valleys may receive snow will little to no accumulation. In general 6-12 inches is expected above 9 kft by Sunday morning.

LONG TERM /SUNDAY THROUGH FRIDAY/
Issued at 130 PM MDT Fri Apr 26 2024

In the wake of the large closed low ejecting northeastward into the central and northern Plains, a weak trailing shortwave embedded within northwesterly mid-level flow will act on residual moisture and keep orographically driven showers going across the higher elevations and adjacent valleys on Sunday. Given a lack of large scale forcing, showers and resulting QPF are expected to be light and generally around a tenth of an inch. Drier air advecting in will keep most of the lower desert valleys dry... allowing for a slight bump in temperatures. Higher up, lingering cool air will also mean some additional light accumulations of snow in the mountains, particularly along the Continental Divide. So with all of that being said, Sunday's weather offers some slight improvements in spots, but otherwise stays fairly unsettled overall.

Looking ahead to next week, the mean 500mb height pattern features a sprawling ridge across the northeast Pacific Ocean and troughiness over the northwest CONUS. That synoptic configuration generally will keep our CWA underneath west to northwesterly flow. Numerous waves are progged to clip the northern half of the forecast area through the remainder of the long term period, with potentially a stronger storm developing Wednesday into Thursday. This suggests that our unsettled pattern will more or less continue through the week with near daily chances of showers and possibly a few storms. This is especially the case across northeast Utah, northwest Colorado, and the Continental Divide mountains which will likely be closer to the storm track. Given the increased chances for clouds and showers there, temperatures should remain on the cooler side. Outside of those aformentioned areas though, like the lower desert valleys of eastern Utah and western Colorado, a mainly dry and increasingly warmer pattern is looking likely with temperatures climbing back into the 70s and even 80s. Safe to say, if you aren't happy with the upcoming weather pattern, chances are you won't have to go very far to experience something different.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
Issued at 1143 AM MDT Fri Apr 26 2024

Scattered showers and storms will roam across much of eastern Utah and western Colorado this afternoon and evening. While VFR should mostly prevail, brief periods of MVFR are probable near any showers and storms. Any stronger shower or storm can produce erratic and gusty winds. Scattered instances of ILS breakpoint ceilings are likely too, becoming more widespread later this evening and overnight. Isolated to showers likely linger through the night and into the morning hours on Saturday, with rain changing to snow for some of the high elevation terminals like KTEX and KASE. Longer periods of MVFR with brief periods of IFR are likely, especially in the mountains.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
Issued at 1125 PM MDT Fri Apr 26 2024

Widespread showers continue and will impact all terminals periodically through the next 24 hours. These showers will be capable of significantly reducing visibility, temporarily lowering ceilings below ILS breakpoints for most terminals, and producing gusty and erratic winds. KASE, KEGE, and KRIL will remain below ILS breakpoints for the next 24 hours with some breakouts from time to time. Chances for thunder returns after 18z tomorrow. Winds outside of showers will be under 10 knots and generally southerly to southwesterly. VFR to MVFR conditions will prevail for the next 24 hours, with periodic drops to IFR/LIFR with passing showers.



GJT WATCHES/WARNINGS/ADVISORIES

CO...Winter Weather Advisory until 6 AM MDT Sunday for COZ004-009- 010-012-013-018-019.
UT...Winter Weather Advisory until 6 AM MDT Sunday for UTZ023.

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