textproduct: Salt Lake City

KEY MESSAGES

- Near record to record setting heat builds in through early next week, with afternoon highs around 15-25 degrees above normal.

- Combination of anomalous heat, single-digit daytime RH and poor overnight recoveries, and modestly gusty winds will result in areas of locally elevated fire weather conditions.

- The next chance of isolated precipitation arrives midweek, as some flavor of trough helps to shift/flatten the ridge.

DISCUSSION

A pleasant start to the weekend underway, with satellite only displaying some mid to high altitude clouds filtering through overhead in the northwesterly flow. A subtle grazing impulse within this flow will help bring temperatures down a degree or two most places outside of southern Utah, but in general still expecting afternoon highs around 5-10 degrees above seasonal normal. A few isolated showers/thunderstorms may develop across portions of southeast Utah, but most areas will remain dry.

Over the next several days an expansive ridge of high pressure will shift into the region, with its influence expected to peak Monday and Tuesday. Subsidence associated with the ridge will keep precipitation chances more or less nil, and result in potential record setting heat with afternoon highs 15-25 degrees above normal. To contextualize the strength of the ridge, 700 mb temperatures are progged to increase to around 15C or so. This would well exceed the climatological 90th percentile of 9C, and per SPC sounding climatology would even exceed typical 700 mb temperatures of mid summer. Thankfully being May this won't result in quite the oppressive levels of heat one might expect if this were to arise in summer, but all the same we'll be looking at better than 50% odds to see the first 90F day in the SLC area, and 100F day in St. George. Temperatures will still cool at night and offer some relief, but given these are the hottest temperatures of the year so far, those working outdoors or recreating should be sure to have a way to stay hydrated and stay cool.

Scenarios for the post-ridge pattern evolution from midweek to the end of the work week haven't changed markedly. Around 45% of ensemble members maintain a cutoff low off the California coast and largely dry conditions locally. Around 25% of members have this feature push inland and phase partially with the northern stream, offering the best odds of precipitation (which still isn't much) and is the coolest scenario. The remaining 30% do little aside from strengthen the northern stream sufficiently to flatten the ridge and offer a slight cooldown. In all scenarios the ridge at least moderates and shifts enough to allow some cooler temperatures in comparison to the record warmth earlier in the week.

Uncertainty in the midweek pattern evolution translates onward towards the weekend, with ensembles still diverging on potential weather scenarios. Around 35% bring a deeper, cooler, and wetter trough into the region. 30% have a weak and dry grazing system, and the remaining 35% have a slightly more amplified but still dry trough shifting through. Given the high degree of uncertainty and being a week out, would focus on trends for now.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will persist for the entire airspace through the period. Dry conditions and largely clear skies will continue. Modest northwesterly surface winds this afternoon will trend light and diurnally driven this evening on through the remainder of the valid TAF period.

FIRE WEATHER

Modestly breezy northwest winds will persist across portions of the Wasatch Plateau, Castle Country and the Swell, and the Uinta Basin through the evening. Any isolated shower or thunderstorm will quickly diminish through the evening hours.

An anomalously strong ridge of high pressure will build into the region through the middle portion of the upcoming week. Temperatures across Utah will push close to if not exceed record levels, and the ridge will result in very dry conditions. Across most of Utah daytime minimum humidity values will fall to single digit values, to at best low teens across portions of the Wasatch Front and northern high terrain. Overnight humidity recovery will also be quite poor, especially across the southern half of Utah. Wind gusts will generally be modest, with some pockets of gusts generally in the 20-25 mph range Monday and Tuesday. If winds increase, this could result in areas of locally elevated fire weather conditions, especially in zones 495/496/497 where fuels are approaching critical. With wind gusts on Wednesday forecast to increase more into the 25-35 mph range or so, some locally critical areas could develop if fuels become sufficiently dry.

There is uncertainty on the exact pattern evolution in regards to the influence of a trough Wednesday and Thursday, but it is likely to at least result in a modest increase in mid level moisture. While isolated in nature, there is around a 10-20% chance of high based afternoon convection forming over the high terrain. With limited moisture, this activity would likely be dry in nature and also carry potential for gusty and erratic outflow winds.

Moving onward from the end of the work week and into the weekend temperatures will decrease given the weakened ridge, and while daytime minimum humidity will remain single digit to low teens, overnight recoveries will improve somewhat. Models show potential for another trough over the weekend, with around 35% supporting a deeper and possibly wetter system. The remaining are more modest and grazing in nature, offering a slight cooldown and minimal precipitation chances. In all cases, an uptick in daytime winds would be likely.

SLC WATCHES/WARNINGS/ADVISORIES

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