Sunrise 6:07 AM   Sunset 8:13 PM Moonrise 4:16 AM   Moonset 5:59 PM

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FXUS65 KSLC 060955 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 355 AM MDT Mon May 6 2024

SYNOPSIS
A cold, unsettled pattern will continue through midweek across much of the region...bringing significant northern mountain snow accumulations. A gradual warming and drying trend is expected across northern Utah late in the week. This warm-up may be slower across southern Utah as a remnant low remains in place across the area.

.SHORT TERM (Through 12Z/6AM Wednesday)...An unseasonably cold, elongated upper low continues to progress east across the northern Utah/southwest Wyoming early this morning. A fairly broad area of precipitation across northern Utah is being driven in large part by the upper circulation passing overhead, with some orographic enhancement and perhaps a little influence from the relatively warm waters of the GSL as -8C to -9C 700mb air spreads overhead.
Snow levels are generally just off the valley floor, but are falling within heavier showers/bands of precipitation.

This area of forcing will move east through sunrise, however quickly on its heels is a plume of low/mid level warm advection spreading across southern Idaho and far northwest Utah, on the back side of the parent low. This region of forcing will spread across northern Utah/southwest Wyoming this morning, bringing another round of organized precipitation. Valley floors will again see a mixture of rain and snow dependent on precip rates, while elevations above roughly 4500 feet see predominant snow. This snow will be heavy at times across the higher terrain of northern Utah, where a Winter Storm Warning remains in effect.
Precipitation will trend showery this afternoon as shortwave ridging temporarily builds overhead.

Temperatures will remain well below climo across the forecast area today, with max temps remaining confined to the low-mid 50s across the northern valleys (10-15 degrees below climo), and low 70s around St George and Bullfrog.

Late tonight into Tuesday an upstream shortwave trough will quickly dig into the region bringing another round of precipitation to the I-15 corridor and adjacent terrain across northern and central Utah. Snow levels will again flirt with the valley floors, with accumulating snowfall persisting across the higher terrain. Current Winter Storm Warning expires midday Tuesday, and may need to be extended depending on whether the snowfall Tuesday remains impactful. The re-enforcing shot of cold air will also trend temperatures 5F or so cooler over northern Utah Tuesday, where max temps will remain in the mid to upper 40s.
Meanwhile temperatures across southern Utah will trend 2-5F warmer. With this colder air mass spreading into the region, the potential for a hard freeze exists late Tuesday night across at least outlying portions of the Wasatch Front and may require headlines.

.LONG TERM (After 12Z/6AM Wednesday)...Our active pattern over the next few days will start to subside as the trough responsible for the unsettled weather will become positively tilted across the Rockies on Wednesday. Given that a light northwest flow will remain in place Wednesday morning along with some moisture advection from the north, lake effect snow is still a possibility (~30% chance) to the south and east of the GSL. Otherwise, the synoptic forcing begins to deteriorate with relatively drier conditions unfolding.
Temperatures will remain 15-20 degrees below normal across northern Utah and ~10 degrees below normal for southern Utah.

As this positively tilted trough lingers across the Rockies on Thursday and a ridge builds into the PNW, flow aloft will gradually become more easterly. Flow aloft looks to remain light with cold air advection fairly marginal resulting in a limited potential for enhanced easterly canyon/downsloping winds across northern Utah, but these parameters will be worth monitoring to see if future guidance starts to trend towards a more impactful scenario.

Guidance has trended towards a scenario in which the parent trough shifts to the east, but a cutoff low develops across the Great Basin over the weekend (~87% of members). This weak cutoff low would keep low PoPs across the area through the weekend with a gradual warming trend, whereas a more prominent ridge nosing in from the PNW would lead to much drier and warmer conditions. Additionally, with the cyclonic flow centered over the southern Great Basin and anticyclonic flow to our northwest, easterly winds aloft would continue. As stated previously, the strength of enhanced canyon/downsloping wind parameters will be monitored closely.

This low looks to gradually decay by early next week with 80% of members indicating a quieter pattern as ridging spreads into the Great Basin from the PNW.

AVIATION
KSLC...MVFR conditions will persist across the KSLC terminal through midday as light rain and snow continue with reduced CIGs and mountain obscuration. Two main rounds of precipitation will move through the terminal. The first, already ongoing, will move out by ~10Z with another arriving ~13Z and lasting through ~20Z.
Conditions improve to VFR after the second round of precipitation with VCSH continuing through the afternoon. Light and variable winds will transition to a gusty west/northwesterly wind during the day.

REST OF UTAH AND SOUTHWEST WYOMING
MVFR/IFR conditions across northern Utah/SW Wyoming will persist through midday as light rain and snow reduce CIGs and VIS, at times. Southern Utah will dry out with a few snow showers exiting the high terrain and VFR conditions developing and remaining throughout the day. Winds will become gusty out of the west/northwest and persist throughout the day.



FIRE WEATHER
An unseasonably cold storm system will continue to bring periods of accumulating mountain snow and low elevation rain across northern and central Utah today through Tuesday. Any precipitation across southern Utah will remain more spotty.
Temperatures across northern Utah will run 10 to 15 degrees below normal today and again Tuesday, while temperatures across southern Utah remain 6 to 10 degrees below normal. With these cool and unsettled conditions, daytime relative humidity will remain elevated with excellent overnight recovery.

A shift toward warmer and drier conditions is expected beginning late this week, however a fair amount of uncertainty remains regarding how quickly this trend will become established. Roughly half the guidance begins building a strong area of high pressure with a more robust warmup heading into the weekend, while the other half maintains a weakening low pressure area across the region resulting in a slower warm-up.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Winter Storm Warning until noon MDT Tuesday for UTZ110>112.

WY...None.

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