textproduct: Salt Lake City

KEY MESSAGES

- Near record to record heat builds in through the start of the week.

- 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.

- A more unsettled pattern sets in by mid week, resulting in a return of isolated thunderstorm chances across the area.

DISCUSSION

Quiescent conditions across the region this Sunday as a strong ridge of high pressure is gradually shifting inland from the California coast. A few high clouds are sneaking through on the periphery of the ridge, but its increasing influence will keep the area dry and mild with afternoon highs around 5-15 degrees above seasonal normal.

The ridge becomes more centered from the Desert Southwest into the Great Basin by Monday, gradually shifting eastward by mid week. In turn temperatures increase with afternoon highs pushing 15-25 degrees above normal, with the warmest appearing to likely be Tuesday. For SLC, there is around a 90% chance of hitting 90F on Tuesday, and a 70-80% chance even Monday and Wednesday. Similarly lower Washington County sees around a 50% chance of hitting 100F Monday, increasing to around 70% Tuesday. Given hot temperatures more or less areawide, these values will likely break records in many locations. Given the early nature of this heat, those working outdoors or with outdoor plans should be sure to stay hydrated and have a way to stay cool.

Models still largely support a pattern change by midweek, though still with some differences in potential scenarios. That said, the favored solution (~80% ensemble membership) is one in which a cutoff to near-cutoff trough pushes ashore. Of those, half bring this feature inland quick enough to bring some mid/upper level moisture back by Wednesday, and the other half has a slower progression with this moisture Thursday. The remaining 20% of members has a weak grazing system with very limited moisture. Leaning towards the favored solution(s), expect at least some development of isolated afternoon convection Wednesday and/or Thursday. Given the mid/upper nature of the moisture, what does form will likely be high based, in turn yielding minimal wetting rain chances but some threat of dry microbursts. Coverage is expected to be highest over the high terrain and adjacent areas downstream. Aside from the convective potential, the increasing south to southwesterly flow ahead of the trough will enhance the general background winds, with widespread daytime gusts likely in the 20-35 mph range. While temperatures will remain above normal, a cooling trend starts by Thursday.

Uncertainty still remains quite high for the pattern evolution into the weekend. Around 30% of ensemble members carry a moderately deep trough which would be the coolest/moistest potential scenario. Another 30% carry a weaker more grazing trough. 30% then just gradually deepen a trough through the PacNW, and the final 10% rebuild ridging over the area. So, once again would focus on trends, though some type of troughing is at least slightly favored at this time.

REST OF UTAH AND SOUTHWEST WYOMING

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

FIRE WEATHER

A very strong ridge of high pressure will gradually build into the region through midweek. Given the strength of the ridge, near record to record heat is expected across Utah. The airmass associated with it is also very dry, and daytime minimum relative humidity values are forecast in the single digits to low teens. Overnight recovery also looks quite poor through midweek, especially across the southern half of Utah where humidity may only increase upwards 10% or so. Following a midweek system overnight recoveries will improve slightly, though daytime minimums will still largely remain in the single digits to teens.

Wind gusts will be more modes, around 20-25 mph, Monday and Tuesday while the ridge is more overhead. A trough is favored to start advancing through the Great Basin by Wednesday, increasing deep south to southwesterly flow over Utah. This will yield a corresponding increase to wind gusts, with widespread daytime gusts around 20-35 mph. This will result in elevated fire weather conditions, particularly for fire weather zones with fuels approaching critical (495/496/497). Depending on the exact speed of the trough, similarly gusty winds may develop Thursday. Additionally, what little moisture is associated with this system will be mid to upper level, and result in around a 10-20% chance for isolated high based convection Wednesday and Thursday afternoon. This activity will have minimal chances of wetting rain, and with the dry and high based nature carry a threat of gusty erratic outflow winds.

SLC WATCHES/WARNINGS/ADVISORIES

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