Sunrise 6:33 AM   Sunset 8:25 PM Moonrise 2:32 AM   Moonset 1:13 PM

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FXUS65 KSLC 021519 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 359 AM MDT Thu May 2 2024

SYNOPSIS
A relatively cool and unsettled pattern will persist through the remainder of the week, with the next weather system bringing showers to northern Utah and southwest Wyoming Thursday night into Friday. A rapid warmup Saturday will precede a strong storm system and associated strong cold front that will arrive this weekend. This system will bring strong, gusty winds and snow to the mountains.

.SHORT TERM (Through 12Z/6AM Saturday)...Early Thursday morning analysis reveals the continued presence of an energetic jet stretching across the region with a pair of departing disturbances across MT/WY. Meanwhile, another upstream impulse can be seen entering the PacNW at this time. This wave will race eastward today and propagate into southern Idaho this afternoon. Most likely scenario then depicts this system briefly amplifying across northern Utah and SW Wyoming through Friday before exiting to the east Friday night.

Showers associated with this incoming system are expected to commence across northwestern Utah early this afternoon, before scattered showers gradually overspread northern Utah and SW Wyoming during the remainder of the afternoon hours. This activity will persist through the evening and much of the overnight hours, centered across northeast Utah and SW Wyoming. The bulk of the activity this afternoon and evening will largely occur north of I-80, although we can't rule out an isolated shower occurrence south of this delineation. NBM and SPC calibrated thunder probabilities indicate a 10-20% chance of lightning across northwest Utah, with lightning probabilities elsewhere under at or below 10% with this system, suggesting most of us will not experience lightning and thunder activity. With steep low to mid- level lapse rates this afternoon and modest 700mb flow in the 20-30kt range, a few cells will be capable of producing gusty outflow winds, with a 50% chance for gusts in the 30-40 mph range with the strongest cells, mainly across northwest Utah and stretching east across the Great Salt Lake.

Model consensus suggests a few, light showers will continue across northeast Utah and SW Wyoming Friday morning into the early afternoon hours. In terms of snowfall, most likely range is in the 1 to 3 inch range above ~6500 feet elevation, with a few isolated totals upwards of 6 inches possible on the high end of the distribution (10% chance) at the highest peaks or where showers are the most persistent.

In the wake of this system, a shortwave ridge axis will move into the Great Basin Friday night, bringing a brief return to tranquil conditions late Friday afternoon through Friday night beneath strong mid level warm advection.

.LONG TERM (After 12Z/6AM Saturday)...Distinctly different weather conditions are expected for each weekend day, with Saturday more like summer and Sunday more like a chilly spring or winter day in the mountains. A stout longwave trough with a closed low will track into the PacNW Saturday. A shortwave ridge axis will track east of Utah early Saturday, and as the aforementioned trough digs through the day, winds aloft will increase. Strong warm air advection and strong southwest winds will build into Utah, especially for the afternoon. With largely clear conditions to start Saturday, lows will be in the 30s for many valleys. As flow increases, with roughly 50 knots at 700 mb likely by the evening, afternoon highs will climb more than 35 degrees from morning lows throughout southwest Wyoming and Utah.

National Blend of Models 50th percentile, or 50% chance of being reached or exceeded, for maximum wind gust Saturday is almost 50 knots at Milford and St. George and over 50 knots at Cedar City.
That 50 knot threshold would be High Wind Warning criteria for those valleys. At least Wind Advisory criteria winds are likely. Blowing dust will be a threat with winds of that magnitude. That number drops of some further north, with the Tooele valley around 45 knots and the Salt Lake Valley around 30 knots. Flow aloft will peak Saturday night into Sunday as the trough approaches. That will likely be the peak in mountain wind gusts, where gusts exceeding 65 knots are likely throughout western Utah. Valley winds will taper off some Saturday night, but stay strong until a baroclinic zone pushes through Sunday.

Variance with ensemble guidance is around the trough axis, coming from timing differences with ensemble members. There is high confidence that the cold front will track into western Utah Sunday morning. There is some uncertainty in precisely when, but it is most likely that the cold front will push into the urban corridor either late in the morning or early in the afternoon. Strong pressure falls, cold air advection, and precipitation will come with the front. There is a low, roughly 15%, chance for isolated thunder and lightning near the front. Conditions will stay warm enough for valley precipitation to be rain through the day, with snow levels initially around 8000 feet, dropping to 5000-5500 feet into Monday.
Post-frontal west to northwest flow will bring orographic enhancement for some places. Snow ratios will start rather low, but increase as colder conditions push in, with dense, wet snow to start transitioning to less dense snow into Monday.

Water content of 1-2 inches is likely for the northern mountains.
Snowfall totals will be highly related to elevation within the mountains, with much of the northern mountains from roughly 6-12 inches, but localized totals of more than 20 inches. Precipitation will generally be lighter to the south. Valley rain will last through the day for most of Utah once the front tracks through.
Before the trough exits, there is a low chance for snowflakes to reach valley floors early Monday.

The trough will lift Monday with conditions drying through the day.
Several shortwave troughs could bring more precipitation through the week, with the first for Tuesday.

AVIATION
KSLC...Light southeast winds will prevail through around 19Z when winds likely begin a transition to northwest. Guidance now favors a slow transition, initially southwesterly then northwesterly by mid-afternoon. At the same time, there is a 40% chance that winds remain southerly throughout the day. Clouds will increase for the afternoon and evening. A cold front will bring isolated to scattered rain showers from roughly 06-12Z. VFR conditions could lower into MVFR range with rain showers, with a 10% chance of vicinity lightning.

REST OF UTAH AND SOUTHWEST WYOMING
Light winds with clear or mostly clear conditions will last through the morning. Winds will be gusty much of the afternoon, especially for southwest Wyoming and southern Utah, with southwest to northwest gusts around 30 knots.
Clouds will increase for the afternoon and evening in southwest Wyoming and northern Utah. Isolated to scattered rain showers are likely from roughly 03-15Z. VFR conditions could lower into MVFR range with rain showers.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Freeze Warning until 9 AM MDT this morning for UTZ103-106.

WY...None.

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