textproduct: Salt Lake City

UPDATE

Quick update AFD today due to widespread convection impacting the region.

Looking at the current mesoanalysis, SBCAPE values have increased through the morning, averaging 500-1000 J/kg based on the latest mesoanalysis. Deep layer shear is more than sufficient...with a broad area of 0-6KM shear in excess of 40-50 kts across the Beehive State. A dry slot will shift north and east with time, clearing convection across southern Utah by late afternoon.

Main threats today are small hail (less than 5% chance of hail in quarter size or larger), strong winds in excess of 58 mph with thunderstorms (5-10% chance across northern and eastern Utah) and localized flash flooding across portions of south central and southeastern Utah. The most at risk locations for flash flooding include Capitol Reef National Park, the Grand Staircase National Monument, the San Rafael Swell, western Canyonlands and Glen Canyon National Recreation Area.

The threat of flash flooding will end across southern Utah by 4-5 PM. The threat for organized convection across northern Utah, Uinta County, WY and eastern Utah will diminish after 5 PM.

Ahead of cold front crossing the region Sunday, expect a greater than 70% chance of wind gusts in excess of 45 mph across southwestern and west central Utah, the Sevier Valley and Castle Country. These areas will likely need wind advisories with this package.

Key messages and the aviation AFD are updated. The previous AFD follows for the remainder.

KEY MESSAGES

- A marginal risk for severe thunderstorms (5-10% chance of wind gusts in excess 58 mph) is outlooked for portions of northern and eastern Utah this afternoon and evening.

- Wind gusts in excess of 45 mph will occur across southwest and west central Utah, the Sevier Valley and Castle Country Sunday afternoon and evening.

- A storm system will bring unsettled conditions Sunday into Tuesday with periods of valley rain and accumulating mountain snow. The heaviest mountain snow is expected Monday into Tuesday.

- Freezing conditions will occur in the central and southern valleys Tuesday night into Wednesday morning and across most valleys including the Wasatch Front Thursday night into Friday morning.

DISCUSSION (Previous, issued at 1002 PM 04/10)

A broad storm system is moving onshore along the California coast this evening, putting Utah and southwest Wyoming under a breezy southwest flow aloft. This flow is drawing enough moisture northward for the development of scattered showers and thunderstorms early today, with many of these storms producing gusty winds, some in excess of 40 mph. A few light showers remain and will continue to dissipate into the overnight hours.

The California trough is on track to weaken significantly as it moves onshore, eventually crossing northern Utah Saturday afternoon and evening. The flow aloft is no longer expected to increase much with the passage of the trough, so the potential for wind gusts in excess of 40 mph has dropped to the 20 to 30 percent range. While it would not be surprising to see isolated gusts in excess of 40 mph, the areal extent and anticipated duration of these winds would not warrant a Wind Advisory. Associated showers and storms will be a bit more widespread compared to the last couple of days, but the best coverage will be confined to areas east of I-15, primarily over northern Utah. Still, any storms that move over rain sensitive areas could bring the threat of flash flooding.

As the weakening system exits the forecast area, another broad low will approach the California coast. Guidance appears to be converging on a solution for this low that would slowly track it across the Great Basin and eventually into Utah and southwest Wyoming Sunday into early Tuesday. There is high confidence that this will bring substantial cooling to the area, with highs below seasonal normals by Monday. The storm and associated cold front will also bring unsettled conditions and the potential for accumulating mountain snow, though totals overall look a bit less impressive than they have the past couple of days. This is because the system ultimately becomes a bit moisture starved and more guidance is showing the system weakening somewhat as it moves through, though not to the extent of the first system.

A drier zonal flow is expected to develop for the midweek period, but long range guidance is showing the potential for a colder storm system impacting the area by late in the work week, bringing a chance of snow for most valleys as well as the mountains for day seven.

REST OF UTAH AND SOUTHWEST WYOMING

Broadly VFR with isolated areas of thunderstorms causing brief drops into MVFR this afternoon into early evening. Winds will be more southwesterly across southern Utah with more of a westerly component to the north. Gusty synoptic winds through the day today falling overnight along the usual diurnal curve. Winds pick up again tomorrow from the south. More shower and thunderstorm chances on Sunday, but generally later in the day than we have seen today.

SLC WATCHES/WARNINGS/ADVISORIES

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