Sunrise 6:28 AM   Sunset 8:21 PM Moonrise 11:46 PM   Moonset 7:28 AM

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FXUS65 KSLC 271117 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 517 AM MDT Sat Apr 27 2024

SYNOPSIS
An upper low crossing the region will maintain cool and unsettled conditions through tonight. A gradual warming trend will follow Sunday into Monday, with another series of mostly dry cold fronts crossing the region beginning midweek.



.SHORT TERM (Through 12Z/6AM Monday)...Early morning satellite imagery and objective analysis show an upper low spinning across southern Utah, with a TROWAL structure wrapping around the north side of this low across northern Utah. This feature is maintaining a broad area of stratiform precipitation across much of northern Utah west of I-15 within a light easterly flow. Meanwhile precipitation is more showery across central and southern Utah in closer proximity to the upper low.

As the upper low slowly progresses eastward this morning, the region of warm advection across northern Utah will persist, and likely spread south with time into west central and southwest Utah. As the upper low continues east this afternoon, the flow aloft will transition to northwesterly as the airmass slowly dries. Lingering moisture coupled with daytime heating will support afternoon convection mainly east of I-15. Temperatures this afternoon will run roughly 10F below climo in the wake of the upper low.

A general northwest flow aloft will persist through Sunday, with a weak embedded wave bringing a small chance of showers across mainly northern Utah/southwest Wyoming. Rising heights and warming aloft will allow temperatures to rebound 5-8F across the area Sunday afternoon, remaining slightly below climo for late April.

.LONG TERM (After 12Z/6AM Monday)...Active weather resumes over the northern half of the forecast area on Monday as a series of troughs begin sweeping across the PacNW/ northern Rockies region. There is some uncertainty in the progression of this active storm track and just how far each expected trough progresses into Utah, however, what once looked like a week of relatively inactive weather is seeming to lack support from guidance. While we are expecting a warming trend through the week, it is likely that the aforementioned troughs will curb the warming trend and even bring periods of cooling over at least the northern half of the area.

Monday through Tuesday morning, models maintain good agreement on a trough progressing across southern ID/ northern UT region. Not only will this trough interact with the existing lower level moisture, it will also advect more moisture into the region. While guidance does not point toward any significant precipitation accumulation, there will be enough energy and moisture to kick off isolated to scattered showers, and perhaps an isolated thunderstorm, during the afternoon hours on Monday and through a portion of the overnight hours. The quickly progressing trough is expected to depart the region overnight, allowing for drying conditions on Tuesday. That said, can't rule out a stray shower in the mountains. A cold front will drop into northern Utah Monday evening through Monday night, setting up Tuesday to see cooler temperatures (right around, or just below, seasonal normals).

Late Tuesday forward is where the real uncertainty begins. A second trailing shortwave trough is anticipated to follow behind the aforementioned from late Tuesday through Wednesday, however, models are seeming to struggle with the amplitude of this trough. The portion of the forecast where this is driving the most uncertainty is the temperature forecast, with the precipitation forecast being the secondary uncertainty. About 65% of ensemble members show a trough deep enough to drive another cold front into at least the northern half of the forecast area, with about 20-25% of those members supporting a much deeper trough that would drive a cold front into southern Utah. The remaining 35% of ensemble members produce a much shallower trough that wouldn't bring much of a front at all... in fact, some members support the start of a warming trend. Model output of high temperatures range from 54 to 67 (25th to 75th percentile) for Wednesday in SLC and from 59 to 74 for Thursday. For Cedar City, these temperatures range from 62 to 74.
Quite a bit of uncertainty at this point, however, odds are favoring a more shallow trough that would impact the northern half of the area while the southern half remains unscathed.

From a precipitation perspective, again, not looking at any signals for significant forecast precipitation. What will be the most likely outcome at this point in time is a round of scattered mountain showers across northern Utah and adjacent valley areas/ southwest Wyoming.

Heading into the late week/ weekend, there is uncertainty in how quickly the aforementioned trough exits the region and whether or not ridging will establish over the western U.S. At this point in time, it's a nearly 50/50 split between trough vs
ridge
so continue to monitor forecasts through the upcoming week.



AVIATION
KSLC...Low CIGs and rain showers will continue through the morning and early afternoon hours today over KSLC. Showers will become a bit more scattered as we move into the late afternoon hours, however, local mountain obscuration is expected to continue through the evening hours. Clouds begin clearing slowly during the overnight hours. Otherwise, northerly winds are expected to be the dominant flow pattern, however, periods of variable/ south flow will be possible while showers persist.

Rest of Utah and Southwest Wyoming...A storm system will continue to bring low ceilings and mixed precipitation across the region today.
A mix of VFR and IFR to LIFR conditions are expected across the area, with the most likely areas to see poor conditions due to mixed precipitation at the KBCE and KEVW terminals. Persistent, widespread precipitation will become more showery as we head through the afternoon hours, with conditions drying from north to south. That said, northern Utah and southwest Wyoming will continue to see precipitation and poor conditions through the evening hours.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Winter Weather Advisory until 6 AM MDT Sunday for UTZ111-112.

Winter Weather Advisory until 6 PM MDT this evening for UTZ113- 117-125.

WY...None.

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