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FXUS65 KSLC 042204 AFDSLC

Area Forecast Discussion National Weather Service Salt Lake City UT 404 PM MDT Sat May 4 2024

SYNOPSIS
Southerly winds will continue to increase ahead of a storm arriving on Sunday. This storm will bring a cold front that will be precluded with strong wind gusts, particularly across western and southeastern Utah, on Sunday. Widespread valley rain and mountain snow will accompany the cold front with much colder temperatures. Conditions remain unsettled and cold through midweek.

.SHORT TERM (Through 12Z/6AM Monday)...The low pressure system that will bring our weather back to winter-like conditions is currently situated just off of the west coast between OR and CA.
This low will quickly move inland, with a potent cold front producing a stark transition to cooler temperatures, plentiful mountain snow, and weaker northwesterly winds on Sunday.

As the low continues to shift inland, southerly winds will continue to increase. Winds have been picking up this afternoon, with peak gusts into the 40s (mph) across the West Desert and into the 30s across portions of the Wasatch Front. Across these areas, winds will peak overnight, up to 60 mph in western Millard/Juab counties. This core of stronger winds will then shift eastward, with winds peaking across eastern valleys Sunday afternoon. A potential limitation in winds here is increasing cloud cover that would limit full mixing of H7 winds around 50kts down to the surface. Temperatures will also peak today, with current temperatures in the upper-70s along the Wasatch Front and mid-80s in lower Washington county.

The arrival of the cold front will greatly contrast today's weather. Abundant moisture combined with great mid-level and jet dynamics will produce widespread precipitation in the form of valley rain and mountain snow. The highest precipitation totals are expected across northern areas given more moisture availability and better dynamics. Snow levels, while initially quite high around 9000ft, will plummet behind the cold front down to around 5000ft by late Sunday night. Given antecedent warmth, snow may struggle to stick across lower elevations (roughly below 7000-8000ft), despite heavy snowfall rates along the front nearing 3 inches per hour. Thunder is also possible along this baroclinic zone, especially across higher terrain. This front will likely reach northwestern Utah early Sunday morning, also reaching the Wasatch Front by noon and southeastern Utah by Sunday evening.

Behind the front, winds will transition to west-northwesterly, thus terrain favored in this flow regime will do especially well snow-wise through Sunday night given a persistent moist, unstable environment.

Regarding QPF and snow totals (through Tuesday), many northern Utah valleys may see upwards of 0.8-1.4" of rain, with most central and southern valleys seeing quite a bit less, less than 0.25". The northern mountains can broadly expect 1-2" of liquid equivalent or 8-16" of snow with locally higher amounts in west- northwesterly favored areas such as the Upper Cottonwoods or Ogden-area mountains. Amounts could be even higher in the case of lake-enhancement...which is looking most likely along the northern Wasatch.

.LONG TERM (After 12Z/6AM Monday)...Our forecast through next week is largely unchanged for the first half of week where northwest flow persists behind an area of low pressure. The latter half of the week and into the weekend however, our forecast begins to become uncertain regarding the track of this same low. Deterministic models are continuing to show an area of high pressure pushing that low back toward our region and settling somewhere to the west. It's an interesting/odd progression for a low. When that progression occurs, how fast it happens and exactly how it'll impact Utah still is to be seen. Those with any plans over the weekend statewide that may be impacted by rain should certainly continue to keep updated on the latest forecast trends.

But back to the first half of the work week's forecast. Mountain snow showers, valley rain, thunderstorms and possible lake effect snow bands remain in the forecast across northern Utah (Nephi to the Idaho border) and southwest Wyoming for Monday, Tuesday and Wednesday. A winter storm warning is currently forecast through Tuesday for the northern Utah mountains and western Uinta Mountain ranges.

Snow on area benches in the Wasatch Front (and possibly in the Tooele Valley) continues to look pretty favorable Monday morning. In fact, snow may (20% chance) reach valley floors for some in the southern Salt Lake Valley and Utah County areas with snow levels forecast down to 4700 ft. At least though, any impacts from this would be short lived and minimal, as temperatures climb well above the freezing mark Monday.

Now speaking of temperatures, while they are above freezing we are well below normal for May 6th, 7th and 8th. Our temperature forecast across northern Utah remains forecast 15 to 20 degrees below normals. Monday and Tuesday's temperature forecast will be very similar while the coldest morning is forecast for Wednesday. Morning lows are expected below or at the freezing mark for several locations in the valleys (and well below freezing in the Wasatch Back and in the mountains). Headlines for a freeze warning for some valleys remain very possible if these trends persist.

Westerly winds Monday afternoon into the evening across the western Uinta Basin and for southwest Wyoming continue to look strong with speeds in excess of 30 mph and gusts exceeding 50 mph. As a result, a wind advisory will be issued for the western Uinta Basin while headlines are not being issued as high wind criteria is not quite met for southwest Wyoming.

Tuesday afternoon is looking like a favorable time frame for thunderstorm activity as a decent shortwave trough passes through northern Utah. Favorable amounts of instability and shear should be enough for at least a few thunderstorms to develop but what might be missing from the equation is enough moisture.

South of the Nephi area, modest weather conditions are forecast the first half of the week. The best chances for any precipitation is forecast for Tuesday and only for central Utah locations.

AVIATION
KSLC...Active period as a cool to cold season type storm approaches and moves through. With increasingly strong low level south flow, will see surface winds/gusts increase accordingly. Gusts likely maintained overnight into early Sunday, but could see some periods of low level wind shear if surface decouples and gusts drop.
Precipitation chances increase prior to sunrise, which should help carry strong gusts downward. By late morning, shower chances become increasingly likely ahead of cold front, though strong south flow may initially yield some downsloping off terrain, abating precip to an extent. Front passes early afternoon, with winds switching to northwest and gradually relaxing. Widespread precip continues with MVFR conditions fairly likely during times of heavier precip.

REST OF UTAH AND SOUTHWEST WYOMING
An anomalous cool to cold season system will approach and move through the region, resulting in active TAF period. As the storm approaches Saturday into early Sunday, most terminals will see increasing southerly winds and gusts, with gusts 30-45 kts possible at many terminals. If any terminals (generally those more sheltered) can decouple overnight, expect gusts to subside a bit, but in turn would see low level wind shear develop. As precipitation chances increase prior to sunrise, will see higher confidence in gusts being maintained. Precipitation chances become further elevated through the morning and afternoon as cold frontal boundary moves through. MVFR conditions likely in heavier precip, with IFR possible at higher elevation terminals where snow may mix in. Strongest winds/gusts will begin to subside following the frontal passage, with directions largely trending more west to northwesterly.

SLC WATCHES/WARNINGS/ADVISORIES
UT...Wind Advisory until noon MDT Sunday for UTZ101-102-122.

Winter Storm Warning from 6 AM Sunday to noon MDT Tuesday for UTZ110>112.

Wind Advisory from 6 AM to 10 PM MDT Sunday for UTZ114-120-121- 126>131.

High Wind Warning until noon MDT Sunday for UTZ115.

WY...None.

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