Sunrise 6:05 AM   Sunset 8:43 PM Moonrise 2:08 PM   Moonset 2:28 AM

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FXUS65 KSLC 171011 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 410 AM MDT Fri May 17 2024

SYNOPSIS
An active, unsettled pattern will continue through at least the first half of next week.

.SHORT TERM (THROUGH 12Z SUNDAY)...Just a few clouds so far this morning as Utah remains under a dry WNW flow aloft. Upstream, an upper trough is noted over the PacNW. This trough will track across Idaho and Montana today, pushing a relatively shallow cold front through northern and central Utah this afternoon and evening. Gusty postfrontal winds can be expected especially across portions of northern Utah and southwest Wyoming, but speeds should remain well below criteria for wind highlights. Despite the cold front, afternoon max temperatures should generally remain similar to or warmer compared to yesterday, due to better mixing and the idea that H7 temperatures start out warmer and do not cool until late in the day.

Latest CAMS are still hinting at the potential for some high-based showers near the boundary, especially across central Utah.
Instability is forecast to be on the low side today, with the HRRR only showing local areas with ensemble means of 100-250J/kg SBCAPE.
As such, the convection is not expected to be strong, but have maintained isolated thunderstorms across some localized high terrain areas as per the NBM. The greatest threat with the showers will be strong, gusty microburst winds owing to the dry boundary layer.
Looking at probabilistic guidance, though, the HRRR only has around a 10% chance of gusts 40 mph or greater in isolated areas, although feel that this might be slightly underdone.

The frontal boundary will weaken and stall tonight after it moves through central Utah. Tomorrow, the upper trough will have moved off into the northern Plains while the next upstream system begins to deepen into the PacNW. This will bring a return of southwesterly flow to Utah, lifting the boundary back northward. Convection is expected to develop again along the boundary, but with the low levels having moistened a bit, greater instability and an increased chance of measurable rain can be expected. However, that is not to say that the microburst threat is over. The HRRR probabilities show isolated 10-25% chances of gusts 40 mph or greater, greatest chance over west-central Utah.

.LONG TERM (After 12Z/6AM Saturday)...Models continue to trend in favor of a deeper longwave trough digging into the forecast area Sunday through Tuesday, favoring cooler and wetter conditions across at least the northern half of the region. Current deterministic guidance supports a cold front dropping into northern Utah some time late Sunday morning to early Sunday afternoon, progressing through much of Utah by Monday morning. Initial lack of significant moisture will allow for the front to progress through the area without causing much in the way of precipitation, however, at least isolated to widely scattered showers will be possible along the boundary.
With a colder airmass in place, Monday will feature temperatures that are 5 to 15 degrees colder than the day prior (about 5 to 10 degrees below average for this time of year). Precipitation is likely to be tied to the frontal boundary, where coverage may be greater as the environment becomes more moist. Again, the best chances for precipitation may be confined to the northern half of the area, but we'll dial in those details soon.

There is some uncertainty with how far south this front will progress, which is continuing to introduce around 7-8 degrees of spread in the temperature forecast for the St. George area for Tuesday. At the very least, there is higher confidence in more extreme cooling across the northern half of the area, with lesser confidence over the southern and eastern halves.

A brief break in activity is forecast heading through Wednesday as the initial trough lifts out of the area. However, just upstream models indicate potential for another trough to drop out of the PacNW region. With another trough following quickly in the wake of the aforementioned, should see cooler and wetter weather prevail through the second half of the week.



AVIATION
KSLC...VFR conditions are expected over the KSLC terminal through the valid TAF period. Gusty northwesterly winds are expected during the afternoon hours, and may begin to gust out of the west to southwest around 15-20kts before 18Z.

REST OF UTAH AND SOUTHWEST WYOMING...Gusty afternoon winds out of the west to northwest are expected across at least the northern half of the forecast area today. VFR conditions will prevail across the region with increasing mid-level clouds during the afternoon hours across central and southern Utah. Isolated showers will be possible in this area, and will have the potential to generate gusty and erratic outflow winds in excess of 35kts.

FIRE WEATHER
A storm system will graze northern Utah today, pushing a cold front through northern and central Utah this afternoon and evening. This front will be accompanied by gusty winds, while high-based showers could lead to isolated strong microbursts. The boundary will gradually lift back to the north through the day on Saturday, accompanied by isolated to widely scattered showers and thunderstorms. Southwest winds increase again on Sunday ahead of the next storm system which will continue to bring unsettled weather to the area through at least the early part of next week.

SLC WATCHES/WARNINGS/ADVISORIES
UT...None.
WY...None.

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