Sunrise 6:13 AM   Sunset 8:08 PM Moonrise 1:55 AM   Moonset 11:50 AM

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FXUS65 KSLC 012033 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT Issued by National Weather Service Grand Junction CO 233 PM MDT Wed May 1 2024

SYNOPSIS
A cool but relatively stable airmass will reside across much of Utah and southwest Wyoming today. The exception will be southern Utah where scattered showers will persist through this evening as a cold front moves out of the region. A relatively cool and unsettled pattern will persist through the remainder of the week, with the next weather system affecting northern Utah and southwest Wyoming Thursday night into Friday.

.SHORT TERM (Through 12Z/6AM Friday)...Showers have developed a bit further west and south than most guidance indicated as the tail end of the lingering frontal boundary continues to push southward across southern Utah. Increased the PoPs in the near term to expand coverage westward towards Bryce Canyon, with the coverage remaining scattered south of a line from Bryce Canyon to Capitol Reef through Canyonlands NP. These showers seem largely driven by instability as lapse rates remain steep this afternoon upwards of 8 to 9 C/km. This shower activity is fairly light with mostly gusty winds upwards of 30 to 40 kts due to showers and virga in some areas. These showers are expected to continue moving southwest to northeast with the areal coverage slowly drifting southward and out of the area by this evening. A shortwave trough is pushing through across the north behind this boundary with some CAA entering northwest Utah in the west-northwest flow as H7 temps drop to between -7C and -9C. This should allow overnight lows to drop below freezing across much of the area. However, a Freeze Warning remains in effect for those areas that are most susceptible, which includes East Box Elder County and the Utah Valley (UTZ103 and 106). Even though other lower elevations fall near to below freezing, they haven't reached their average last freeze dates, so no products remain in effect for those areas.
While there is some concern with cloud cover, it looks to remain scattered overnight which shouldn't impede those areas mentioned in the Freeze Warning from reaching those conditions.

Temperatures on Thursday will rebound quite nicely as the cold air retreats northward and WAA pushes in from the west and southwest.
Highs should warm up by about 5 degrees compared to today under a westerly flow aloft with dry conditions expected. We are still under the influence of the upper level trough that is still sitting over the Intermountain West and Northern Rockies with yet another shortwave moving across the north Thursday night into Friday morning. This will generate some shower activity with some high elevation snow but amounts at this time look minimal with a few tenths to maybe an inch or two in the higher elevations of the western Uintas and Bear River Range. Much of the central and southern areas should remain dry throughout Thursday into Friday morning.

.LONG TERM (After 12Z/6AM Friday)...The long-term period begins with another shortwave trough grazing northern Utah, bringing isolated showers to the northern third of Utah and southwest Wyoming on Friday before drying out in the evening and overnight.
A shortwave ridge will then build across Utah on Saturday, but this feature will be transient as another strong closed low forming off the coast of the PacNW begins to move inland.
Increasing southwesterly flow is also expected on Saturday along with strong warm-air advection with H7 temperatures reaching +7C by Saturday evening. Ensemble guidance suggests H7 winds reaching around 35-50kts across southwestern UT, with surface wind gusts approaching High Wind Warning criteria (50kts)...something that will need to be monitored in the coming days.

As the closed low continues inland, this will bring a potent cold front through our forecast area later in the weekend. The main impacts with this front will be a quick transition to northwesterly winds, onset of widespread precipitation, potential for thunderstorms along the frontal boundary, and snow levels dropping to around 5500-6500ft. Winds could be quite gusty behind the front; ensemble guidance suggests a mean of around 20-30kts at 700-mb, though the GFS is a bit more anomalous, reaching 45kts over northern Utah. Precipitation chances will likely continue through Monday as the parent trough continues to shift over the western US, as well as the chances for afternoon thunderstorms given steeper lapse rates under the cold core. H7 temperatures will drop quite a bit with this trough, down to around -6C to -9C.

There is still a lot of uncertainty regarding the timing of the cold front. This could move through as early as late Saturday evening (21% of ensemble members) or as late as Sunday evening (another 21%). The most likely solution is Sunday morning to around mid day. The rest of the coming week looks to remain cooler following Sunday's strong cold front with a few shortwaves moving through the northwest flow on the backside of the upper level trough, keeping scattered showers early to mid next week in place across the northern areas.

AVIATION
KSLC...Northwesterly flow will continue, with gusts to 20kts possible mainly during the afternoon. Light, southeasterly flow is expected around 09-10z. VFR conditions will prevail.

REST OF UTAH AND SOUTHWEST WYOMING
Northerly to northwesterly winds will prevail through the afternoon and evening across the area, becoming gusty to around 20-25kts, especially across eastern areas. These northerly winds will weaken, becoming light and diurnally-driven overnight. VFR conditions will prevail.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Freeze Warning from midnight tonight to 9 AM MDT Thursday for UTZ103-106.

WY...None.

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