textproduct: Salt Lake City

KEY MESSAGES

- Scattered showers and thunderstorms Thursday afternoon and evening will result in localized gusty outflow winds in excess of 45 mph. Additionally, storms passing over rain sensitive basins may result in localized flash flooding.

- Widespread and significant critical fire weather conditions are expected Friday and Saturday as southwesterly winds near 40-50 mph will combine with hot and dry conditions.

- A strong cold front will cross the region later Saturday into Sunday bringing colder temperatures and the potential for patchy frost for the Cache Valley and Wasatch Back.

DISCUSSION

Another active day ongoing across the region. While moisture is on the decrease overall, there is sufficient lingering moisture to result in scattered convective development. SPC mesoanalysis shows early afternoon destabilization is already well underway with widespread 500-1000 J/kg CAPE and decreasing CIN. With effective shear also on the order of around 20-30 kts or so, seeing reasonable storm organization in what has developed across areas of southern Utah so far. That said, best shear is noted across areas of northern Utah (especially near the ID/WY border), and would anticipate any hail threat to be more likely in that area accordingly. Otherwise, think gusty outflow winds are once again the primary severe hazard with potential for gusts in excess of 50 mph. The current SPC Marginal Risk outlook highlights well the highest threat area. Aside from the severe threat, any stronger cells or trailing storms that track over rain sensitive areas will also bring a threat of localized flash flooding.

Moving into Friday more of a dry slot shifts over the area as a broad trough deepens into the Pacific. This will also result in an enhancement to southwesterly flow across the area, bringing widespread gusty conditions in the 30-50 mph range. The signal for the strongest gusts is noted over portions of southern to western Utah, and have opted to issue a Wind Advisory accordingly. With the strong winds and prolonged stretch of largely dry weather, this setup will allow for widespread critical fire weather conditions across Utah. Friday night into Saturday will see a largely dry cold front associated with the trough nudge partially into the area before retreating back northwest briefly. In turn, Saturday will be another day of widespread strong southwesterly wind gusts ahead of the front. The front will then gradually progress southeastward again Saturday into Saturday night, finally clearing out of Utah later Sunday. Best chance of showers or thunderstorms with the front and cyclonic energy within the trough appears to be portions of northern Utah and southwest Wyoming Saturday and Sunday, generally along and north of the I-80 corridor.

The airmass behind the cold front will be quite cool by late June standards. Forecast highs on Sunday for example are around 10 to 20 degrees below seasonal normal, which equates to upper 50s/low 60s for southwest Wyoming, upper 60s/low 70s for much of the Wasatch Front, and upper 70s to around 90 in southern Utah to lower Washington County. Forecast lows Sunday night into Monday morning actually get cold enough to note some frost potential in cooler sheltered valleys, particularly in the Wasatch Back and Cache Valley.

Looking at the upcoming week, it appears that a general southwesterly flow will largely be dominant. This will impart a gradual warming trend throughout the week with temperatures returning to near normal levels by midweek. Pattern does not look very favorable for much in the way of any moisture advection, so precipitation potential will be limited. Given the dry conditions and southwest flow (albeit more modest), will likely see localized areas of critical fire weather conditions return.

AVIATION

KSLC...Winds at the terminal are expected to shift to northwest between 20-21z. Scattered showers and thunderstorms between 20z-01z will likely cause gusty and erratic outflow winds at times. Wildfire smoke will continue to produce slantwise VIS reductions at times. Southeast flow will become dominant around 02z, but possibly as early as 00z with any lingering storm activity.

REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and thunderstorms will persist throughout the afternoon across Utah and southwest Wyoming, capable of producing gusty and erratic outflow winds in excess of 40-50kts. Wildfire smoke will continue to produce slantwise VIS reductions, particularly across central/eastern Utah.

FIRE WEATHER

A deepening trough of low pressure will gradually sink into the Great Basin Friday into Saturday, along with an associated cold frontal boundary. Deep and dry southwesterly flow will become enhanced ahead of this trough and front. Anticipate widespread daytime wind gusts 40-50 mph, with some gusts locally up to around 55 mph. Daytime humidity values will be very dry, likely falling to around 5-10% Friday, with only modest improvement to around 10-15% possible Saturday. Overnight recoveries also continue to look quite poor, with the only exception being locations that may receive some wetting rain from ongoing thunderstorm activity Thursday. Even then, would expect the very strong winds and dry airmass to overcome this, and as such high confidence in a significant critical fire weather pattern remains.

This front will largely be dry. The only locations that appear to see a favorable amount of available moisture are those in northern Utah, generally north of the I-80 corridor, and especially closer to the Idaho border. Outside of the areas closest to the Idaho border, the chance for wetting rains remain quite low.

The front will begin to push into northern Utah Friday night into Saturday, but retreat back northward quickly. It will then start making more notable southeastward progress Saturday evening into Sunday. It then looks to stall out somewhat along the high terrain of Utah, which may help prolong the gusty conditions ahead of it in portions of southern and eastern Utah particularly. By Monday it finally more or less progresses out of the region, but the overall deep flow shifts back to more of a general southwesterly dominant pattern. While winds and gusts will be much more modest than that of prior to the system passing and there will be a substantial cooldown, combination of dry southwesterly flow and warming trend towards midweek will likely maintain areas of elevated to locally critical fire weather conditions.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Red Flag Warning from noon Friday to midnight MDT Saturday night for UTZ478-479-482-484-488-489-492-495-497.

Wind Advisory from 9 AM Friday to midnight MDT Friday night for UTZ115-116-118-119-122-123-126>128.

Red Flag Warning from noon Friday to 3 AM MDT Sunday for UTZ493- 494-496-498.

WY...None.