Sunrise 6:20 AM   Sunset 8:27 PM Moonrise 3:04 AM   Moonset 2:18 PM

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FXUS65 KSLC 032201 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 401 PM MDT Fri May 3 2024

SYNOPSIS
An approaching storm system will bring much warmer conditions Saturday with strong afternoon winds for portions of Utah. A cold front will track into Utah Sunday. Lighter winds, cooler conditions, valley rain, and mountain snow are likely once the front pushes through.

.SHORT TERM (Through 12z/6AM Monday)...Satellite imagery shows a shortwave ridge continuing to shift eastward through the Great Basin and into Utah. Thus, skies will continue to clear heading into the late evening and overnight hours. Also seen is a strong closed low off the coast of British Columbia that will eventually produce winter-like conditions across much of our area later in the weekend.

The shortwave ridge axis will pass quickly to our east by mid Saturday morning, with increasing southerly flow as the aforementioned closed low pushes inland. In this pre-frontal environment, strong warm-air advection will produce Saturday high temperatures that are 10-20 degrees above Friday highs across all but far southern Utah. The main concern for Saturday, however, is gusty southerly winds across western valleys picking up in the afternoon and peaking overnight. Many western valleys will reach high-end Wind Advisory criteria (45-58 mph), with the highest gusts likely across western Juab and Millard counties, reaching upwards of 60 mph (70% chance in most areas). H7 winds around 50kts will likely mix well to the surface given steep lapse rates and a dry air mass, however increasing mid-level clouds could act to limit this mixing...therefore there is still some uncertainty in peak gusts at this time. This main core of winds will shift eastward by Sunday, with winds picking up Sunday morning across southeastern valleys, peaking Sunday afternoon. A High Wind Watch has been issued for these areas to highlight the highest risk areas.

A potent cold front will bring quite the contrasting weather to the area on Sunday, with a stark transition to much cooler temperatures, plentiful valley rain, snow down to 5000 feet, and weaker northwesterly flow. This cold front will be quite strong, also featuring the potential for thunderstorms along and behind the front on Sunday. This front will likely enter northwest Utah Sunday morning, reaching the Wasatch Front by mid day and southern Utah by evening.

Widespread precipitation will mainly begin along the frontal passage, with a few rogue showers possible just ahead of the front. Periods of heavy precipitation are possible, including heavy mountain snow. In terms of QPF through Monday, the Wasatch Front could see 0.8-1.4" of rain, with the northern mountains receiving upwards of 2" or more of liquid equivalent. These amounts could be even higher with any lake-enhancement late Sunday night. Snow levels, initially around 9000-9500 feet, will plummet with the frontal passage down to 5000 feet. The highest snow amounts up to 2 feet are expected in the Upper Cottonwoods and Ogden area mountains, given an extended period of unstable west to northwesterly flow and orographic enhancement behind the front.
Thus, Winter Storm Warnings have been issued for the northern mountains, especially given the potential for surface transportation impacts and unseasonable nature of the system.

In summary, expect strong warming and southerly winds ahead of the storm system late Saturday into Sunday, with an abrupt transition to winter-like conditions on Sunday.

.LONG TERM (After 12Z/6AM Monday)...Northwest flow will be our dominant flow pattern early next week behind the passage of a low pressure system and strong cold front. A series of shortwave troughs are forecast to track through the Intermountain West early in the week as the low tries to track to our northeast, which will bring valley rain showers, thunderstorms and mountain snow across northern Utah and southwest Wyoming. The exception here will be Monday morning; wherein snow levels are forecast to be low enough to bring snow to area benches in the Wasatch Front. Accumulating snow is quite possible though most likely to be an inch or less. There's a less than 40% chance for more than that at this point.

Otherwise, across most of northern Utah and southwest Wyoming, from Monday morning through Tuesday evening, on and off rain showers are forecast. What is a bit more favorable, unsurprisingly, is the persistent mountain snow. Snow amounts Monday alone across the northern Utah mountains are forecast to range between 5 to 12 inches (3 to 8 inches in the western Uintas) while amounts Tuesday will range from 4 to 10 inches (2 to 4 inches in the western Uintas). The confidence in snowfall amounts is lowest by the end of this event, on Tuesday evening.

Additionally, there remains potential for lake effect driven showers every morning from Monday through Wednesday which would bring additional QPF amounts to favored areas downstream. The latest guidance is favoring Wednesday morning, interestingly.

While strongest winds are forecast over the weekend, Monday afternoon looks to continue with that trend with some stronger winds for the Uinta Basin and southwest Wyoming, potentially impacting travel on I-80. Gusts in the 50+mph range are forecast and may warrant headlines in the future.

Dry conditions are forecast across central and southern Utah early next week with the exception of the central mountains and the Tushar Mountains where a few inches of snow are forecast.

Normally for early May, high temperatures for Salt Lake City will reach the upper 60s to 70 degrees. However, forecast high temperatures this Monday, Tuesday and Wednesday are forecast 15 to 20 degrees below average and will instead barely climb into the low 50s. A similar trend is noted for minimum temperatures. Temperatures are expected to be coldest Wednesday morning, so cold in fact that low temperatures are expected near or below the freezing for several valley locations. The EFI and Shift of Tails guidance support these anomalously cold temperatures for this time frame. If these trends persist, certainly freeze headlines would be warranted. If you need to plan ahead for agricultural reasons now is your time to plan for frost and freeze.

A fairly dry forecast remains in the forecast for the remainder of the week however toward the end of the week Utah may see some wrap around moisture associated with the same area of low pressure from earlier in the week. Deterministic models are showing this low tracking back through Utah Friday and bringing modest amounts of moisture with it. Positioning of the low and how much moisture it would bring are of course, pretty uncertain at this point. Right now eastern Utah and southwest Wyoming are the favored locations for any additional precipitation impacts.

AVIATION
KSLC..VFR conditions will remain in place through the valid TAF period. Northwesterly winds will prevail through the mid- evening, transitioning to a southerly flow around 04Z. South winds remain in place through the day tomorrow, with gusts up to 30kts expected by the early afternoon.

REST OF UTAH AND SOUTHWEST WYOMING
VFR conditions are expected across the area through the valid TAF period. Isolated showers across northern Utah will diminish through the early evening hours, giving way to mostly clear skies overnight. Tomorrow, winds will increase out of the south, with peak gusts across the West Desert expected to exceed 50 kts. Along the I-15 corridor, peak gusts will vary between 30 and 35 kts.

SLC WATCHES/WARNINGS/ADVISORIES
UT...High Wind Watch from Saturday afternoon through Sunday morning for UTZ115-122.

WY...None.

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