textproduct: Salt Lake City

KEY MESSAGES

- Gusty west to southwest winds with gusts in excess of 30 mph will combine with very low relative humidity values to bring critical fire weather conditions to areas of central and southern Utah east of I-15 on Saturday.

- Widely scattered showers and thunderstorms, mostly dry, will develop over northern Utah during the day Saturday, with the best chances near the Idaho border. Strong outflow winds in excess of 50 mph can be expected with these storms, along with dry lightning.

- High pressure will rebuild for early next week, keeping conditions very dry with a steady warming trend in temperatures. The potential for heat related illness could increase for some valleys by the middle of the upcoming week.

DISCUSSION

The persistent Pacific ridge moved east of the area into Colorado today as a disorganized trough made its way into the Great Basin. The center of that system is now near far northwest Utah with the associated boundary near a KTMT-KEVW line. Widely scattered showers continue over northern Utah and southwest Wyoming this evening, with these storms producing little if any rainfall. Gusty winds will be the primary threat with these storms, which will tend to diminish overnight as the center of the trough lifts northwest into Idaho.

There is relatively high confidence that the approach of a trailing wave from the storm system Saturday afternoon will combine with daytime heating to produce another round of showers with at least a few thunderstorms focused near the Utah/Idaho border. Given the continued dry nature of the airmass at lower levels, there is concern that coverage of dry lightning will be enough to produce critical fire weather conditions. South of the cold front, breezy west to southwest winds will continue to persist through Saturday afternoon, combining with the dry airmass to produce areas of critical fire weather conditions.

The trough and its associated cold front will also bring a noticeable cooldown, particularly for northern Utah where maxes Saturday will be up to 10F less warm than today's values. In a lingering unsettled airmass, Sunday's temperatures will not be much different than Saturday. However, the Pacific ridge is expected to rebuild over the Great Basin to start the work week, bringing a steady warming trend in temperatures. By midweek, there is potential for temperatures to get hot enough to increase the risk of heat related illnesses for some valleys, including the Wasatch Front.

AVIATION...KSLC

Isolated showers may result in gusty outflow winds prior to around 07Z Sat, but otherwise expect S winds to prevail into the day along with VFR conds. Winds expected to shift NW around 17-19Z Sat, but isolated to scattered high-based thundershowers late afternoon into the evening could result in gusty outflow winds (likely from the west) to around 35 kts. VFR conds anticipated to still prevail, with a low (5% chance) that something atop the terminal could briefly bring MVFR VIS.

REST OF UTAH AND SOUTHWEST WYOMING...At southern terminals, clear skies with modestly gusty daytime winds (up to around 25 kts) expected. For northern terminals, high based showers will bring potential for gusty erratic outflow winds through 09Z or so Sat, though VFR conds anticipated to persist. After a lull, expect isolated to scattered thundershower development mid afternoon into the evening, bringing renewed threat of gusty erratic outflow wind gusts up to around 35 kts. VFR conds still largely expected to persist, though there is a low (~5%) chance any stronger cell moving directly over a terminal could briefly reduce VIS to MVFR range.

FIRE WEATHER

A low pressure system is moving into the area late this evening and will cross the area through Saturday, bringing a cooling trend. The airmass will remain very dry across central and southern Utah, with the axis of gusty winds shifting to areas east of I-15. A Red Flag Warning remains in effect for these areas Saturday afternoon and evening. Although winds will be a bit weaker across southwest and west central Utah Saturday, fire weather conditions will remain elevated, and local pockets of critical fire weather conditions are possible.

High based showers and dry thunderstorms are expected to develop across northern Utah Saturday afternoon and evening in association with the passing trough, with the greatest coverage of storms near the Utah/Idaho border. Strong outflow winds in excess of 40 mph will be possible, with a few gusts approaching 60 mph. The areal coverage of dry lightning continues to be uncertain, so will keep the Fire Weather Watch in place for northwest Utah (zone 478).

High pressure will strengthen across the region beginning Monday, bringing a warming trend, with a return to hot and very dry conditions by midweek.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Fire Weather Watch from Saturday afternoon through Saturday evening for UTZ478.

Heat Advisory until 6 AM MDT Saturday for UTZ104-105.

Red Flag Warning until 3 AM MDT Saturday for UTZ492-495.

Red Flag Warning from noon to 10 PM MDT Saturday for UTZ482-484- 488-489-493-494-496-498.

Red Flag Warning until midnight MDT tonight for UTZ497.

WY...None.