textproduct: Salt Lake City

KEY MESSAGES

- Showers and thunderstorms will develop Saturday, especially along and east of the I-15 corridor. In addition to potential for gusty winds, these storms will bring the threat of flash flooding to any rain sensitive areas over which they track.

- A broad approaching system will result in increasing southwesterly winds and gusts areawide. There is a 40-50% chance of gusts in excess of 45 mph in the West Desert Saturday, increasing to 60-80% Sunday.

- Unsettled conditions are expected Sunday through Tuesday as a large system and associated cold front moves through. This will result in periods of valley rain, accumulating mountain snow, and much cooler temperatures.

DISCUSSION

Expansive cloud cover is advecting through the region overhead as moisture increases within increasing deep southwesterly flow. A few light echoes are noted on area radars this morning, but little indication of much in the way of precip making it to the ground. As modest instability builds throughout the day, anticipate coverage of isolated convection to increase, primarily for areas along and east of Utah's high terrain. Otherwise, will see breezy conditions and another very mild day with afternoon highs peaking around 10-20 degrees above seasonal normal.

On Saturday a broader Pacific system will be pushing ashore along the California coast, while a preceding wave advects through overhead within the enhanced southwesterly flow. Models continue to concentrate moisture more in the eastern half of the area, generally along/east of the I-15 corridor and adjacent high terrain, with more modest amounts also noted roughly north of the I-80 corridor. Shower development is likely through the morning, with activity taking a more convective nature late morning into the afternoon as instability increases. Given enhanced deep layer shear as a result of the passing wave and enhanced southwesterly flow, a few storms may become more organized and pose a threat of gusty winds and small hail. Additionally, given the moisture, any stronger storm that tracks over a rain sensitive basin (burn scars, slot canyons, typically dry washes, slickrock areas) will pose a threat of flash flooding. Those with outdoor recreation plans to such areas should remain weather aware. Something of a dry slot will develop as the initial wave begins to shift out and the broad system continues to slowly churn inland, and as such will see precipitation chances decrease quickly from west to east through the late afternoon.

Aside from the precipitation/convection element of this pattern, the deep and strong southwesterly flow in the synoptic setup will also enhance lower level winds and gusts areawide. Winds will be more pronounced late morning on through the daytime hours as mixing strengthens. Widespread gusts in the 25-40 mph range will develop Saturday, with roughly a 40-50% chance of gusts in excess of 45 mph in portions of Utah's West Desert region. Gusts further increase Sunday as a cold front approaches, with chances of West Desert gusts above 45 mph increasing to 60-80%. Less confidence noted, but wouldn't be surprised to see other western valleys see some gusts at or above 45 mph, especially typical hotspots like the Tooele Valley or areas downwind of terrain features, such as the north end of the Oquirrh Mountains or Stansbury Mountains. Aside from potential to blow around any loose unsecured objects, winds will be capable of periods of reduced visibility due to blowing dust, and the southerly component will result in gusty crosswinds on travel routes such as I- 80.

Precipitation chances will gradually increase through Sunday afternoon as the broad system advances further into the Great Basin and an associated cold front approaches the local forecast area. Coverage will then become maximized along with frontal passage later in the evening and early overnight hours. Periods of enhanced post frontal showers then continue through Tuesday as subtle lobes of energy continue to rotate through within the deeper cyclonic flow churning through overhead. One large change in comparison to previous forecasts is that models have started to trend back towards the scenario in which the low cuts off from the northern stream, which in turn limits the depth of cold air and available moisture. The track also limits stronger west to northwest flow which would provide a favorable orographic boost to favored areas such as the Upper Cottonwoods. All that said, forecast water amounts have also trended downward. Much of Utah area mountains now sit around a 5-10% chance of 1" or more water, with the exception of the Salt Lake and Ogden area mountains which also dropped closer to the 10-20% range. In terms of precip type, snow levels will start around 7500 feet or so, only dropping to around 6500 feet by Monday morning. Snow accumulation amounts have also decreases, with forecast currently carrying a more widespread 2-4" for most Utah area mountains, and locally 8-12" in more favored areas such as the Upper Cottonwoods. There is around a 20% chance to see snowfall exceed 12" in those favored areas.

Temperatures will also fall as a result of this system, with afternoon highs back around 5-10 degrees below normal Monday and Tuesday. While they'll moderate back closer to normal by midweek, there is at least some signal in another potential system later on in the work week. Given a fair amount of differences this far out, little confidence in any sort of details.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions expected for all regional terminals today. Increased south to southwesterly breezes are expected across the airspace through this evening, with lighter terrain-driven winds redeveloping overnight. Gusty winds redevelop areawide with widespread gusts to 30 kts late Saturday morning. Scattered rain showers are expected to develop mid morning generally along and east of the Wasatch, with potential for TS developing after roughly 18z as instability increases through the afternoon.

SLC WATCHES/WARNINGS/ADVISORIES

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