textproduct: Salt Lake City

DISCUSSION

A weak shortwave trough is currently shifting across the region, bringing an area of showers to portions of central and southern Utah. CAMS suggest additional development ahead of this shortwave will occur across the southern mountains. Given surface dewpoints in the 30s to lower 40s and mediocre instability, expect this convection to be mainly outflow dominant, trending toward the adjacent lower desert areas through early evening. Main threat will be gusty, microburst winds in excess of 40 mph and brief heavy rain.

Attention will then turn to increasing potential for widespread heavy rain across the region from as early as late Saturday through at least Tuesday. A strong upper level trough shifting into the Pacific Northwest will combine with now Hurricane Rachel to bring deep tropical moisture into Utah, as early as Saturday night. Guidance has shifted quite a bit toward this phased solution, with only 10% of members now favoring a more progressive, drier solution.

How long the moisture sticks around is another question. Around 50% of members suggest the trough, along with PW anomalies on the order of 98+ percentile remains over the West through at least Tuesday night. The remaining 50% of members are more progressive, clearing the trough sometime Monday.

Regardless, confidence is high with 90% of members showing a variation that phases the strong Pacific trough with tropical moisture associated with Rachel, that Utah will see a period of moderate to heavy rainfall. Current guidance suggests 1 to 2 inches of rain across much of Utah, with locally in excess of 2.5-3.00 inches, particularly across southern Utah as the most probable range for the event. With colder temperatures associated with this Pacific trough, some higher elevation locations above 8500 feet may see light snow accumulations Tuesday.

Given it is only Tuesday, no products will be issued for this enhanced flash flood threat, but those with outdoor plans for the holiday weekend, particularly Sunday and Monday, should be prepared to make alternate arrangements as many areas of southern Utah such as slot canyons, normally dry washes, streams and areas near recent burn scars may see a heightened threat of flash flooding. Rises are also likely on all area streams and rivers.

AVIATION...KSLC

The SLC terminal will see VFR conditions throughout the day with some scattered clouds. Southerly winds are expected to shift to the northwest between 20Z and 21Z before returning to the south between 03Z and 05Z. There is a 20 percent chance that outflow from storms developing this afternoon over the higher terrain will bring periods of gusty and erratic winds, with this most likely occurring mid to late afternoon.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will prevail across the airspace through the evening with generally light and terrain driven winds. Isolated to widely scattered showers and thunderstorms will develop over the higher terrain this afternoon bringing lightning, brief mountain obscurations, and gusty and erratic winds to any areas they pass over through the early evening.

FIRE WEATHER

A weak system will bring isolated to widely scattered showers and thunderstorms to central and southern Utah through this evening. Relatively dry and warm conditions will segue to an increasing threat of widespread moderate to heavy rain as a strong Pacific system phases with tropical cyclone to bring deep tropical moisture to Utah. Moderate to heavy precipitation will begin as early as Saturday night and continue through at least Tuesday.

SLC WATCHES/WARNINGS/ADVISORIES

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