textproduct: Salt Lake City

KEY MESSAGES

- Near record to record heat expected through Wednesday.

- Gusty southwesterly winds and single-digit daytime relative humidity will result in a period of critical fire weather conditions across portions of southern Utah on Wednesday.

- Isolated to widely scattered high-based thunderstorms bring the threat of strong to severe wind gusts and small hail Wednesday afternoon and evening, mainly across high terrain and northern Utah.

DISCUSSION

An anomalously strong ridge currently overhead will continue to amplify through Tuesday, which will yield some of the warmest temperatures of the year tomorrow afternoon. Highs will once again challenge daily records across the region, with temperatures soaring around 20 degrees above seasonal normals. Avoid strenuous outdoor activity if possible, and be sure to have a way to keep cool during this anomalous warmth.

A shift in the pattern from persistent heat and bone-dry conditions is still expected mid-week as a shortwave trough digging into the PacNW shunts the ridge eastward. This will introduce stronger southwesterly flow across the region Wednesday, resulting in widespread afternoon wind gusts between 25-40 mph across Utah and southwest Wyoming. Strongest winds are expected across the West Desert and portions of southwest Utah, which when combined with very low humidity, will produce a period of fire weather conditions across these areas. See the Fire Weather section below for additional information on this threat.

Mid-level moisture advection is expected on the backside of the exiting ridge on Wednesday, yielding a pretty substantial increase in PWATs across the region; PWAT anomalies across Utah and southwest Wyoming peak around 125-150% of normal by Wednesday afternoon. Concurrently, the aforementioned PacNW shortwave trough is expected to brush northern Utah on Wednesday afternoon, and when coupled with intense daytime heating will produce sufficient forcing for scattered high-based convection. Convection may develop first across the high terrain, but coverage is expected to expand northeast through the afternoon. Early high- res model data indicates a very favorable environment across central and northern Utah (including the Wasatch Front) for both strong to severe wind gusts given DCAPE values around 1400-1600 J/kg, as well as small hail given substantial shear and high mid- level lapse rates.

Thunderstorm activity wanes across the region late Wednesday as a drier airmass quickly moves in behind the shortwave. Cooler conditions prevail on Thursday behind the exiting system, with temperatures moderating closer to seasonal normals across the region. More zonal flow is expected to develop across the western US on Friday, allowing temperatures to rise back to around 10 degrees above average areawide. More uncertainty in the forecast exists this weekend as models work out the evolution of another trough moving into the northwest. Still around 80% of ensemble members show a drier solution that would only knock temperatures down slightly for the weekend, but there is still 20% that show a much stronger cooldown with better chances for precipitation.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will persist for the entire airspace through the period. Dry and stable conditions with clear skies will continue with light and diurnally driven winds.

FIRE WEATHER

A strong area of high pressure will dominate the region through Wednesday. This ridge will result in record heat and very dry conditions. Daytime humidity minimums will fall to single digits to low teens, and overnight recoveries through midweek will be minimal.

An approaching system will result in increasing south to southwesterly winds Wednesday. Widespread gusts of 25-40 mph are expected to develop through the afternoon and evening. In areas where fuels are sufficiently dry, this will result in locally critical fire weather conditions (particularly fire weather zones 495, 496, and 497 below around 8000 feet). Additionally, increasing mid level moisture will bring the threat of isolated high-based convection Wednesday afternoon and evening. This activity is expected to largely be dry in nature, carrying the threat of lightning, and gusty erratic outflow winds. Coverage of this activity will be highest on the high terrain.

A dry cold frontal passage will occur Wednesday night into Thursday. Temperatures across northern Utah will cool around 10-15 degrees, and across southern Utah temperatures will cool up to around 5 degrees. Daytime minimum relative humidity values will remain very low, with widespread single digit to low teen values into the weekend. Overnight recoveries will improve marginally, on the order of 5-15% wetter than previous days. There is then potential for another cold frontal passage Saturday or Sunday, but models continue to diverge on specific details at this time.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Fire Weather Watch from Wednesday afternoon through Wednesday evening for UTZ495>497.

WY...None.