textproduct: Salt Lake City

KEY MESSAGES

- Near record to record heat expected through Wednesday.

- Locally elevated fire weather conditions will be possible in portions of Utah through Tuesday given very anomalous heat, single digit humidity, and poor overnight recoveries.

- Locally critical fire weather conditions may develop Wednesday afternoon and evening as winds increase and very dry and anomalously warm conditions are maintained.

- Isolated to widely scattered high-based thunderstorms will bring the threat of microbursts to the region Wednesday afternoon and evening.

DISCUSSION

An expansive area of ridging is currently centered over Arizona with ridge axis extending northward through the forecast region. In turn skies are clear to mostly clear, and temperatures are already quite mild. 700 mb temperatures associated with the ridge peak around 14C to 15C, driving anomalous warmth at the surface with forecast daytime highs through Wednesday generally 15F to 25F above seasonal normal. SLC will see favorable odds to hit or exceed 90F each day, and St. George will see a greater than 50% chance to hit 100F Tuesday when the heat is expected to peak. Temperatures this warm are more akin to what would be expected for early July, and as such would anticipate some locations to see records met or broken. While the night will still offer some relief, those who work outside or otherwise have strenuous activities planned during the daytime should be sure to have a way to stay cool, take breaks when needed, and stay hydrated.

Models have come into fair agreement on the progression of a trough shifting inland from the PacNW for the middle of the week. Ahead of this feature, deep south to southwesterly flow will increase on Wednesday. This will result in breezy conditions during the day Wednesday with widespread gusts in the 25-40 mph range. There is around a 40% chance of wind gusts exceeding 45 mph locally in some portions of areas such as the West Desert region and Castle Country. If winds trend upwards, may need to consider Wind Advisories in subsequent forecasts. As this feature approaches and nudges the ridge eastward, it will also help advect modest amounts of mid level moisture into the region. With strong heating in the afternoon, some areas of instability will form and yield some high-based convection. Given the well mixed boundary layer, this activity will be capable of gusty erratic dry microburst type winds. They will also be drier in nature, with minimal chances of true wetting rains from them. Coverage of this isolated to scattered convection remains primarily over high terrain and adjacent areas downstream.

The cold front will start to push southward through the area Wednesday night into Thursday. What meager moisture was available earlier will have largely diminished by the time the front starts to push through, so anticipate the frontal passage to be dry. The baroclinic zone is actually fairly pronounced, do expect to see a fairly marked cooldown following the frontal passage, potentially accompanied by a brief period of gusty winds right as the front passes. The cool air associated with the trough will moderate more substantially further south in Utah, so the overall temperature decrease will be less notable. Still, across the northern half of the area expect afternoon highs to fall around 10F to 15F lower than the previous days, and up to around 5F at areas across southern Utah.

Models still generally support another trough translating eastward through the W CONUS over the weekend, though uncertainty in the exact evolution remains. Around 40% of ensemble members support more of a dry and grazing type of trough, with a more muted and brief cooldown. Another 40% have a similarly dry setup, but a slightly more amplified trough with a bit more of a cooldown. The final 20% represent the deepest solution, a scenario which would see the best chances of a stronger cooldown and modest precipitation chances. The deeper scenario would also offer the best chance of seeing some cooler air sticking around a bit into the upcoming work week, but as always will have to watch and see where things trend as we approach the weekend.

REST OF UTAH AND SOUTHWEST WYOMING

Winds will be largely light and terrain-driven today and overnight, the exception being westerly gusts to 20-25kts across southwest WY this afternoon. VFR conditions will prevail with mostly clear skies.

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.