textproduct: Salt Lake City

KEY MESSAGES

- High temperatures across the region peak today, with many daily, monthly, and all- time records being challenged, particularly over northern portions of the area.

- Temperatures will gradually become less hot during the upcoming week as monsoonal moisture moves into the area. This will increase the threat of precipitation and thus flash flooding, particularly over southern Utah, for much of this week.

DISCUSSION

We are on record temperature watch this afternoon and evening across Utah and southwest Wyoming as an anomalously strong ridge of high pressure amplifies across the Rockies. 700 mb temperatures are forecast to maximize around 20-22C late this afternoon; to put this in context, the highest 700 mb temperature ever recorded from an upper air sounding at KSLC stands at 20.2C, observed on 7/13/2002. Also of note, the current 20.2C record coincides with one of the most significant and widespread heatwaves for our area, and resulted in SLC recording its second occurrence on record of an all- time high temperature of 107 degrees. Other locations such as Logan and Evanston are also likely (over 90% chance) to see highs shatter their current all- time records of 103 and 95, respectively. Park City will also near its all-time record of 99 today, but with lower probability to meet or exceed it, around a 30% chance.

Extreme Heat Warnings continue through Monday morning for most of the region, but will be allowed to drop off across southern Utah as a surge of monsoonal moisture begins to move into the area and limits daytime highs due to increasing cloud cover. The Extreme Heat Warnings continue Monday into Tuesday morning for the remainder of Utah and southwest Wyoming given highs only cool a couple degrees through Monday. Overnight lows also remain warm, around the mid-70s for most locations, exacerbating heat impacts through this period.

We will see inklings of this monsoonal surge today as isolated high-based showers and thunderstorms develop across southwest Utah this afternoon and evening. Given lower-levels remain dry today, main impacts from any cells that develop include gusty and erratic outflow winds to 50 mph as well as dry lightning strikes. Otherwise, monsoonal moisture becomes widespread across central and southern Utah on Monday with PWATs approaching 1" across the area. Deep moisture will continue to become more widespread the remainder of Utah on Tuesday and linger through the remainder of the week. When coupled with overall light upper-level steering flow, this pattern will result in an increased flash flooding risk through this week, particularly for central and southern Utah. Areal coverage of storms will vary each day, resulting in varying levels of flash flood risk through the week. Regardless, conditions will be favorable for the threat of flash flooding especially for slot canyons, normally dry washes, and recent burn scars.

AVIATION

KSLC...VFR conditions with diurnally normal winds persist. There is a 20-30% chance of southerly gusts 20-25 kts or so between 07-14Z Monday. Winds then expected to shift northwesterly between ~18-20Z Monday. There will then be potential for southerly outflow wind gusts between, with timing most likely between 23Z Monday to 04Z Tuesday.

REST OF UTAH AND SOUTHWEST WYOMING...Isolated to scattered afternoon showers and thunderstorms will develop across portions of southern and central Utah. This will bring potential for gusty and erratic outflow winds, with decreasing threat noted at areas further north nearer the Idaho border. Aside from this, winds largely anticipated to follow a typically diurnal pattern, with modest gusts 20-25 kts or so at typically breezy or exposed terminals. Conditions expected to remain VFR, though any stronger storm directly atop a terminal may result in brief reductions to CIGS/VIS.

FIRE WEATHER

An anomalously strong area of high pressure moves overhead today, resulting in record heat and very dry conditions across the region. Some increasing mid-level moisture ahead of our main monsoonal moisture push will result in isolated high- based showers and thunderstorms this afternoon and evening across southwest Utah, capable of producing gusty and erratic outflow winds and dry lightning strikes. Monsoonal moisture overspreads most of central and southern Utah on Monday, allowing for more scattered storm coverage with potential for heavy rainfall under stronger cores. Showers and thunderstorm become widespread across the state by Tuesday, bringing flash flood concerns and increasing chances for wetting rains through the remainder of the week.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Extreme Heat Warning until 6 AM MDT Tuesday for UTZ101>108-114- 116-118>121.

Extreme Heat Warning until 6 AM MDT Monday for UTZ115-122- 128>131.

WY...Extreme Heat Warning until 9 PM MDT Monday for WYZ021.