textproduct: Salt Lake City

KEY MESSAGES

- Strong wind gusts will be possible with thunderstorms Friday. A categorical Marginal Risk (level 1 of 5) of severe weather across portions of southeast Utah for this severe wind gust potential.

- Thunderstorms may result in isolated flash flooding Friday if tracking over rain sensitive basins of southern Utah such as slot canyons and dry washes.

- Elevated to locally critical fire weather conditions will develop across portions of the Henry Mountains and San Rafael Swell Friday afternoon due to gusty winds and low relative humidity.

- Precipitation and wetting rain becomes more widespread across northern Utah Friday night into Saturday. Accumulating snowfall in excess of 4" is expected for the Uintas above around 10000 feet.

DISCUSSION

The broad low which has remained across the western US for several days will finally begin more of an eastward progression through the Great Basin through Friday. Already seeing moisture associated with this increasing, as evidenced by area radars picking up on shower activity across southern Utah. With increased cloud cover and the low helping to shift the ridge, temperatures are running a bit cooler today and will peak at levels lower than yesterday's high.

As the core of the low continues to shift east, synoptic forcing for ascent will increase across the area, initially favoring southern Utah with coverage later on shifting to areas further north. In general this moisture is more concentrated around the mid levels, supporting higher based showers and thunderstorms. As such, given mean afternoon destabilization on the order of around 100-300 J/kg along with 25-35 kts bulk shear, will see activity capable of producing gusty and erratic outflow wind gusts. In general, think most activity will support gusts in the 35-50 mph range or so. However, it does appear a corridor of enhanced DCAPE may develop across portions of south central to southeast Utah, supporting around a 5% chance of severe gusts in excess of 58 mph. For this area, the SPC has indicated a categorical "Marginal Risk" of severe weather, risk level 1 of 5. As activity shifts further north later in the day, waning instability and increasing saturation should begin to limit the gusty wind threat.

While storms Friday afternoon are expected to be somewhat higher based in nature, there still will be a nonzero threat of locally excessive rainfall in any storm that becomes more organized. Generally, anticipate this to mostly be a threat to more rain sensitive basins such as slot canyons and dry washes across southern Utah. As such, opted to add "Possible" to the Flash Flood Potential Rating for many southern Utah parks and recreation areas. Those planning recreation in such places will want to keep an eye on the weather, or consider alternatives on other less rain sensitive locations.

Late Friday evening on into Saturday the low will start to eject more northeastward through Utah and into southwest Wyoming and northwest Colorado. The highest concentration of moisture will wrap around into the core of the low, which will also have favorable synoptic forcing even with more limited instability. As such, should see a more persistent area of showers and stratiform rain across northern Utah and southwest Wyoming as the low gradually tracks through. Models continue to support fairly widespread amounts of around 0.10" to 0.25" for much of the Wasatch Front, and potential for an area more in the 0.50" to 1.00" range where a deformation axis may set up around the low. Right now the rough consensus for such a band is around the Weber/Davis County area, though the exact track of the low will dictate where it ultimately may set up. Also think there could be a favorable upslope component with the low shifting east of the terrain, allowing benches to squeeze out a bit more. The EFI also highlights the Uintas on through Uinta County, WY with signal for climatologically anomalous precip, which tracks with the current forecast low progression. Currently have around 0.50" to 1.00" water for these areas, but wouldn't be surprised to see some locally higher amounts.

Despite it being the end of May, this storm system does actually look to have enough cold air with it to result in some high elevation snow. That said, outside of any rate driven reductions, snow levels don't look to far much lower than around 9500 feet at best. Given the signal for higher water amounts across the Uintas, the higher locations generally above 10000 feet look to actually see accumulating snowfall. Generally these amounts are in excess of 4", with potentially up to 10" in the higher reaches, though mild antecedent conditions and dense nature of the snow will likely help to limit accumulation to an extent. While no Winter Weather headlines appear necessitated, those planning recreation in the high Uintas or travel through open seasonal roads such as Mirror Lake Highway should be prepared for snow.

Temperatures through the weekend fall to around 5-10 degrees below seasonal normal as the low moves through. This looks to be short lived though, as ridging then appears favored to become the increasingly dominant influence on the forecast area once again. With that, forecast carries a warming trend through the upcoming week along with limited precipitation chances.

REST OF UTAH AND SOUTHWEST WYOMING

Gusty/erratic winds will impact the region with showers/isolated thunderstorms moving from south to north, developing over central Utah around 21Z and quickly moving north across northern Utah/SW Wyoming, exiting to the north between 02-03Z. Wasatch Front terminals will be impacted between mainly 22Z-02Z. Most gusts will be in the 25-35kt range, but can't rule out isolated gusts up to 45kt. Brief reductions in visibility due to BLDU may accompany some of this activity. Rain then overspreads northern Utah and SW Wyoming overnight through Saturday morning with widespread MVFR CIGs, isolated IFR CIGs and mountain obscuration from central Utah northward. Conditions gradually improve through the afternoon as steady, widespread rain transitions to scattered showers/isolated thunderstorms across northern Utah.

FIRE WEATHER

Southerly wind gusts Friday around 25-35 mph in combination with minimum humidity values around 15 percent will result in elevated to locally critical fire weather conditions across eastern valleys where fuels are sufficiently dry. Additionally, an area of low pressure will gradually move in and lift northeastward through Utah Friday into Saturday. For Friday this will result in showers and thunderstorms during the afternoon to early evening, with activity initially favored over southern Utah, shifting northward late evening into the overnight hours. This system will provide around a 30-60% chance of wetting rains for the southern and central mountains, 40-70% chance for northern mountains, and a greater than 80% chance for the Uintas. Additionally, temperatures will be cool enough with the system to bring accumulating snow to the high Uintas, with 4" or greater expected above 10000 feet, and locally up to 10" possible in the higher reaches.

Following the low pressure system departing, high pressure is favored to build back into the region and become the dominant weather influence. This will start a warming and drying trend from Sunday onward into the upcoming week. Temperatures will push to around 5 to 10 degrees above normal, and afternoon humidity values will largely fall back into the low teens to single digits.

SLC WATCHES/WARNINGS/ADVISORIES

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