textproduct: Salt Lake City

KEY MESSAGES

- A couple of weak storm systems will bring generally light valley rain and mountain snow to northern Utah Monday night and Tuesday night. - A more substantial storm arrives by the end of the week into the weekend with the potential for widespread precipitation that could increase the risk of flash flooding.

DISCUSSION

The upper low that has brought showers to the area the last couple of days is now centered over southwest Wyoming as it continues to exit the area. Behind this low, showers have mostly dissipated over Utah this evening. A transient shortwave ridge will cross the area late tonight through Monday morning before southwesterly flow aloft increases ahead of the next trough which is currently noted over the PacNW coast. Fairly benign weather can be expected into early Monday evening. Temperatures on Monday will trend warmer, rising to near to slightly above normal across northern Utah but remaining below normal across the south.

The upstream trough will end up grazing northern Utah late Monday evening through Monday night. This will push a relatively shallow cold front into northern Utah. A quick round of showers is expected to accompany this front. The latest high-res models are not as enthusiastic about precipitation compared to the global models. For example, the 75th percentile of the REFS is only showing 0.15-0.3 inches in the Bear River Range, with generally less than 0.1 inches in the adjacent valleys and no measurable precipitation south of around Ogden. Meanwhile, the NBM 50th percentile has slightly higher amounts than that. Suspect the NBM will trend downward with the global deterministics trending towards a weaker cold front. With snow levels falling as low as 6500 feet near the Idaho border, some light snow accumulations can be expected over the higher terrain.

Cooler temperatures can be expected again on Tuesday behind the cold front, with northern Utah trending back to slightly below normal temperatures. Otherwise, any precipitation from the cold front will clear the area by around sunrise, leading to mostly clear skies during the morning through late afternoon. Southwesterly flow aloft will quickly redevelop as a second, weakening trough swings into the northern Great Basin. This trough will then eject across northern Utah Tuesday night, bringing another potential round of light precipitation to northern Utah. Deterministic models have this second trough trending slightly stronger, which falls in line with the first trough trending slightly weaker.

Thereafter, models are still pointing to an active pattern for the weekend into potentially early next week as a strengthening storm system over the PacNW phases with a second system originating farther west that taps into a plume of moisture. Latest global deterministics are introducing greater timing uncertainties in that the 18z GFS does not bring any precipitation into Utah until Saturday evening, compared to earlier runs and the EC which have precipitation beginning as early as Friday. Nevertheless, Sunday looks to be the wettest day at this time. However, there remains some model spread regarding how the large-scale pattern evolves through the weekend and how quickly the storm exits the area.

AVIATION

KSLC...VFR conditions are expected to persist through the TAF period with diurnal wind shifts. Chances for rain begin to increase around 03z later in the period, though chances at this time remain 20% or less.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist across the airspace through the TAF period. Around 00z, showers are forecast to move across northern UT, primarily impacting KLGU and potentially KOGD. At this time, chances of this occurring range from 40-60%.

SLC WATCHES/WARNINGS/ADVISORIES

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