textproduct: Salt Lake City

KEY MESSAGES

- Temperatures continue to warm across the forecast area through midweek.

- The threat of strong gusts (40-50mph) and lightning increases tomorrow afternoon across southern and central UT as high-based storms develop with an incoming system.

- An active pattern develops late Wednesday, continuing into the weekend.

DISCUSSION

Current satellite imagery indicates a dry airmass situated across much of the forecast area. To our southwest, mid-level water vapor imagery indicates a plume of moisture associated with a shortwave trough within the southern stream beginning to stream into AZ, creeping into extreme southern UT. Currently, all this will amount to is increasing cloud cover across southern and central UT through the morning hours with northern UT and southwest WY following in the late evening/overnight hours.

Through tomorrow, the aforementioned shortwave will continue progressing east with time. Upper level and potentially some mid level cloud cover will persist across primarily southern and central UT through the afternoon, though this is not expected to limit daytime heating substantially. Modest forcing will arrive to southern UT in the mid to late afternoon hours, spurring convective development across southern UT and higher terrain of central UT. While higher PoPs are generally confined to higher terrain given better moisture quality / higher RH, scattered dry thunderstorms are forecast to develop across southern and central UT lower terrain. Given lapse nearly reaching dry adiabatic, inverted-V soundings are quite abundant west and somewhat east of I-15 tomorrow afternoon, supporting a gusty wind threat. DCAPE is somewhat limited, however, with generally scattered 40-50mph gusts possible with perhaps a couple severe gusts (>58mph). This limitation is primarily due to the aforementioned cloud cover moving in well ahead of the main forcing, limiting mixing and overall PBL height.

There also exists a low-confidence scenario for some localized flooding along the UT/AZ border, primarily across the Telegraph Flats. Deep layer shear roughly 30-40kts and PWAT's ranging from 0.6- 0.8" of water could result in some longer-lived storms, especially if any storm that forms gets hung up on the terrain. However, as stated earlier, this scenario is extremely low-confidence at this time and will be monitored throughout the day tomorrow.

Following the passage of the shortwave to our south, transient upper ridging settles in across the area and will slide southeast by Wednesday afternoon as a trough to our north flattens the ridge. Some mid-level moisture is expected to remain in place Tuesday afternoon yielding terrain driven showers into late Wednesday morning / early afternoon. Most lower elevation locations will remain dry through Wednesday afternoon.

Forecast confidence has increased regarding the evolution of the cutoff low that will stall off the CA coastline Wednesday before progressing inland Thursday evening through the weekend. Compared to yesterday where confidence was 50/50 regarding the cutoff low phasing in with the first trough mentioned in the paragraph above, ensemble cluster guidance now indicates zero members that support this solution and indicate the northern stream trough progressing east well ahead of the cutoff low. This has generally allowed the system to become warmer, with rain expected across nearly all locations within the forecast area with the initial push Thursday evening into Friday afternoon.

Forecast confidence as we enter Friday afternoon into the remainder of the weekend, however, decreases substantially due to both the northern stream and southern stream remaining extremely active. Numerous shortwave impulses progress east across all pieces of long range guidance, with ensemble clusters indicating a 45% chance of the cutoff low continuing south and not phasing into another incoming northern stream shortwave. The other 55% has the cutoff low phasing in with the incoming northern stream trough Saturday into Sunday. Both outcomes yield extremely different results, where the latter will result in a deepening trough ejecting northeast across the Great Basin, bringing more precipitation to the forecast area. The former will result in a higher chance that the cutoff low continues sliding southeast down the CA coastline before progressing inland toward AZ, potentially resulting in a notable decrease in precipitation from what is currently in the forecast. Changes are expected to occur with future forecast packages as details are ironed out regarding what will happen this weekend.

REST OF UTAH AND SOUTHWEST WYOMING

Light, terrain-driven winds will prevail with VFR conditions and increasing high clouds overnight. High-based showers will begin to push into far southern Utah as early as 16z Monday. These showers will be capable of producing gusty and erratic outflow winds and isolated thunder/lightning at KCDC, KSGU, KBCE, and perhaps KU52 on the northern periphery during the afternoon.

SLC WATCHES/WARNINGS/ADVISORIES

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