textproduct: Salt Lake City

KEY MESSAGES

- Temperatures will stay mild for Memorial Day, with scattered afternoon showers with a few thunderstorms developing over the higher terrain. Any storms that develop will be capable of producing gusty and erratic winds.

- Strong southerly winds are expected to develop over central and southern Utah from Tuesday through Thursday, raising concerns for near-critical to critical fire weather conditions. Peak winds will shift from a portion of western Utah on Tuesday to the eastern Utah valleys on Wednesday and Thursday.

DISCUSSION

A weak shortwave disturbance will push into Utah from the south through the remainder of today and through the overnight hours, helping to initiate an organized area of scattered showers and isolated thunderstorms. Initially, showers and thunderstorms will be tied to the mountainous terrain and adjacent valley areas (as is currently being observed via satellite and radar). As more robust lift is introduced into the region, coverage of showers will expand across southern Utah this evening and continue into the overnight hours, eventually shifting northward into the Uinta Basin by early Tuesday morning. With moisture being relocated farther northward by Tuesday, the potential for showers and thunderstorms will be greatest from about western Emery County north to northeastward to Uinta County, Wyoming. The main threat with these showers/ thunderstorms will be the potential for brief downbursts to create wind gusts in excess of 40-45 mph. Brief moderate rainfall rates will also be possible, however, flash flooding is not expected as the near- surface environment remains very dry.

Coincident with this weak shortwave disturbance moving through the area through Tuesday, a deep upper-level low will drop into the Great Basin region through Tuesday and a portion of Wednesday, remaining quasi-stationary through the end of the week. As we remain on the eastern periphery of this feature throughout the week, enhanced southerly winds are expected to develop across a portion of southern and central Utah from Tuesday through at least Thursday afternoon. For Tuesday afternoon, the strongest winds in the forecast area will be expected across Utah's west-central valley areas, particularly western Millard County and a portion of northwestern Beaver County. These strong winds will migrate into the eastern valleys by Wednesday morning, and will remain over the eastern valleys through at least Thursday afternoon. Model guidance is placing a high probability (70-90% chance) for wind gusts in excess of 45 mph over western Emery and Carbon Counties for both Wednesday and Thursday afternoon. Additionally, there is upwards of a 30-40% for isolated wind gusts in excess of 55 mph from Huntington southward through Ferron late Wednesday and Thursday mornings through the early afternoon. Given that the moisture tied to this area of low pressure will be west of the forecast area, surface conditions are anticipated to remain largely dry through the upcoming week. These dry conditions will pair with the strong southerly winds and dry fuels to create critical or near-critical fire weather conditions across a portion of central and southern Utah from Tuesday through Thursday.

Again, most of the moisture tied to this system will be located over the central Great Basin which will keep daily precipitation chances low through at least Thursday. The only areas that will see anywhere from a 15-30% chance of showers and thunderstorms will be far western Utah near the Nevada border. As this system finally begins to lift out of the region around Friday/ Saturday, we'll see chances for precipitation begin to increase over the northern area, but still only remaining in the 15-30% range.

Aside from the more impactful weather, temperatures will be trending downward into Tuesday and Wednesday, remaining stagnant on Thursday, then trending down again into Friday as the center of the low pressure system moves through the region. Warming temperatures and drying conditions will spread over the region Saturday forward as weak high pressure develops over the area once again.

REST OF UTAH AND SOUTHWEST WYOMING

Isolated to scattered high based showers will develop through the afternoon, especially off of Utah's high terrain, drifting north thereafter. In the vicinity of these showers, erratic and gusty outflow winds around 30-40 kts may develop. Additionally there is around a 10-20% chance of lightning in this activity. Isolated to scattered shower chances are maintained especially along/east of the high terrain overnight into Tuesday, with high based convection once again developing through the afternoon.

FIRE WEATHER

Isolated to widely scattered showers and thunderstorms will continue to develop through the remainder of the daylight hours across much of Utah's high mountainous terrain along and east of the I-15 corridor. Any significantly developed showers will carry potential to produce strong outflow winds in excess of 45 mph alongside low chances for wetting rains. Expect an area of scattered showers and isolated thunderstorms to continue through the overnight hours across central Utah (mainly east of the I-15 corridor), pushing into the Uinta Basin by the early morning hours on Tuesday. Moisture and instability will linger over the northern region through Tuesday, bringing more potential for isolated to scattered showers and thunderstorms.

Strong southerly winds are expected to begin developing on Tuesday afternoon, primarily over the western half of Utah. Wind gusts in excess of 30 mph pairing with relative humidity around 13-17% will create areas of near-critical fire weather conditions, with isolated critical fire weather conditions developing where fuels are critically dry in southwest and west-central Utah. These strong winds will shift into the eastern Utah valleys on Wednesday and Thursday (mainly in central and southern Utah) and will pair with relative humidity around 10-15% to create critical fire weather conditions for multiple days. There is generally high confidence that critical fire weather conditions will develop across western Emery and Carbon Counties, with moderate confidence in similar conditions developing in eastern Garfield and Kane Counties. After Thursday, a cooling and moistening trend is expected into Friday with conditions warming and drying from Saturday forward.

SLC WATCHES/WARNINGS/ADVISORIES

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