textproduct: Salt Lake City

KEY MESSAGES

- Widespread moderate to heavy rainfall threat increases late Saturday through Sunday as a remnant tropical system and associated deep moisture lift through and interact with an approaching trough. Widespread water amounts of 1 to 3 inches are forecast, with locally higher amounts in excess of 3 inches possible, particularly in high terrain and areas along and northwest of the circulation track.

- There is also a wind threat associated with this storm, particularly in the higher terrain, with ~50% chance of wind gusts in the mountains near the circulation gusting 50+ mph and ~30% chance of wind gusts 58+ mph.

- A closed low will slowly meander across the Great Basin Monday through Wednesday with scattered showers and thunderstorms remaining and snow levels falling to 8500-9000 feet.

DISCUSSION

Temperatures across the area remain mild with low 80s once again for KSLC. Convection is currently ongoing across portions of central and northern Utah, primarily in the terrain. These storms are generally weak with high bases and frequent lightning. These storms will fizzle out after sunset as they lose their diurnal forcing. Tomorrow will see some more isolated convection develop similar to today along with increasing southerly winds as a trough to the northwest starts to gradually move closer. Winds will increase even more on Saturday, particularly across the west desert where there is ~50% chance of wind gusts 50+ mph and ~25% chance of gusts 58+ mph.

The remnants of Tropical Storm Rachel in the eastern Pacific will bring widespread precipitation resulting in a flooding threat as well as a severe threat from thunderstorms and strong winds associated with the post tropical circulation. Currently, Tropical Storm Rachel is situated ~915 miles west of the southern tip of Baja California. The current track of this storm bring Rachel into the northern Baja Saturday night as a tropical storm. This track then continues into the Mojave before moving into southern Utah during the day on Sunday.

Scattered showers and thunderstorms start to move into the Utah, but the main event holds off until Sunday when the circulation center of the post-tropical remnants of Rachel move into Utah. The current NHC forecast has the mean track of this circulation moving into southern Utah during the day on Sunday before traversing into northern Utah by Sunday evening. The track of this circulation will be pivotal regarding the details of this forecast. Generally, areas along and northwest of this track will see the highest probability of heavy rain, and areas to the southeast will see the greatest potential for gusty winds. Additionally, there could be a severe component Sunday morning across southern Utah as the circulation moves through and discreet convection develops. Hodographs suggest rotation with the potential for some isolated brief tornados.

Overall rainfall amounts from Rachel are between 1-3" with some locations, particularly southerly facing mountain aspects of 3"+. Remnants from Rachel will be moving out of the area by Monday, but the closed low to our west will continue to meander across the region through the middle of next week with most scattered showers and thunderstorms remaining possible.

HYDROLOGY

Widespread precipitation of 1 to 3 inches, locally in excess of 3 inches, particularly across southerly facing mountain aspects, between late Saturday and Monday morning. Expect many area waterways including streams, rivers, normally dry washes, creeks, and slot canyons to have rising, fast flows by Sunday evening. Current forecasts do not bring any rivers to flood stage, but this will be monitored as the fine details of heavy rain bands become more confident. Those with activities near rivers, streams, creeks and recent burn scars should closely monitor the forecast over the next several days. Those with outdoor plans Sunday onward that include any travel near waterways across Utah should consider alternate plans. Scattered showers and thunderstorms will remain possible through at least Wednesday, but these rates will generally be lower, but areas that receive a lot of precipitation during the weekend will be much more sensitive to any additional rainfall.

AVIATION

KSLC...The SLC terminal will see VFR conditions through the TAF period. Expect the typical switch from northwest winds this afternoon to southerly winds this evening. On Friday, there is an increased likelihood that winds remain southerly into the afternoon, or even become southwesterly briefly in the late afternoon as winds at the surface align with the winds aloft. While there is not a high enough chance for a prob 30 group in the TAF, a few high based showers may develop in the vicinity of the terminal after 1800UTC.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail across all regional terminals, with generally light diurnally-driven winds through the TAF period. Isolated showers and thunderstorms will redevelop over the higher terrain this afternoon and again on Friday afternoon. These storms could bring some gusty and erratic winds, lightning, and a brief mountain obscurations.

FIRE WEATHER

Warm conditions will persist for the next couple of days across the area. Isolated showers and thunderstorms will be possible, primarily across the terrain over today and tomorrow with frequent lightning being the primary threat. Southerly winds will start to increase tomorrow across the area with min RH in the mid to low teens across western Utah that could lead to locally critical fire weather conditions. Winds increase more on Saturday as an area of low pressure to our west gradually moves closer.

Tropical remnants from Tropical Storm Rachel in the eastern Pacific will begin to move into the area on Saturday with scattered showers and thunderstorms, but the bulk of the moisture will hold off until Sunday when the post-tropical circulation moves into the Great Basin with widespread heavy precipitation expected, particularly for areas along and northwest of the circulation. High winds will also be a threat near the center of this circulation.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...None.