Weather Service Report


516 
FXUS65 KSLC 280957
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
357 AM MDT Thu Mar 28 2024

.SYNOPSIS...A potent cold front will move into northern Utah this
afternoon before stalling and weakening over northern Utah this
evening. Cool and stormy conditions will then persist through
early next week as a Pacific trough impacts the area. 

&&

.SHORT TERM (Through 12Z/6AM Saturday)...High pressure is moving
over the central United States as a trough spins near the Pacific
Northwest coast. An ejecting wave out ahead of the trough has
brought a cold front into Nevada this morning, with a decent band
of precipitation accompanying it. Ahead of the boundary, winds are
starting to pick up over Utah and southwest Wyoming, and will
continue to do so through the morning. Winds will be strongest in
west central and southwest Utah, where a Wind Advisory is
currently in effect. Anticipating a good amount of gusts in excess
of 40 mph as these winds peak during the day, which will result in
some travel difficulties. 

The front is on track to slide across northern Utah during the
afternoon into the early evening, undergoing frontogenesis as it
does so. As a result, a potent line of valley rain/mountain snow
with a few embedded thunderstorms will make its way across the
area, with some heavy rates anticipated along the band. The heavy
snow (with a high chance of rates in excess of an inch an hour)
will bring noticeable travel difficulties to the higher terrain 
of northern Utah along with some significant accumulations. Going
Winter Weather Advisory covers this threat well. There is a medium
chance the rates will be high enough to lower snow levels down to
the benches, with a low chance (20 percent or so) of some flakes
in the valleys.

By the evening, the front is expected to make its way into central
Utah before stalling and weakening. Associated precipitation will
diminish significantly during the evening and overnight hours, but
some precipitation will still persist along the band. The
associated Pacific Northwest trough is expected to remain fairly
stationary as the initial front moves through. However, by Friday
morning there is high confidence that the low will merge with
another low moving toward the California coast. As this merger
occurs, the system will link up with the stalled boundary and push
it back northward as a warm front Friday afternoon and evening.
This will bring some initial accumulations, but these will be
generally on the light side. 

.LONG TERM (After 12Z/6AM Saturday)...On Saturday, a deep positive 
tilted trough will be digging southward along the California coast. 
Associated with this, a somewhat diffuse baroclinic zone will remain 
draped from southwest to northeast across Utah, with guidance 
suggesting somewhere possibly near the I-15 corridor or so. This 
boundary looks to initially retreat north/westward through the day, 
though given it'll be dependent on how/where the larger trough 
moves, it's exact position and motion remains a bit uncertain. While 
this boundary will likely serve as a focus for a bit more 
precipitation, strong moisture/energy advection within southwesterly 
flow on the leading edge of the trough will be sufficient for 
widespread scattered precipitation across much of the state 
regardless. On the warmer side of the boundary (south central into 
southeast Utah), enhanced H7 flow will promote gusty surface winds, 
with afternoon gusts likely in the 30-50 mph range.

Later in the day on into Saturday night, the Pacific trough looks to 
begin to pivot inland. As it does so, baroclinicity along the 
boundary becomes enhanced, and jet support becomes maximized 
especially across portions of southwestern Utah. With a bit more 
residence time of these favorable ingredients, a period of higher 
precipitation rates are expected, and as a result a marginal risk of 
excessive rainfall is realized across the southwestern most corner 
of the state. For higher elevations, this will translate to a period 
of heavy snowfall with rates potentially exceeding an inch per hour, 
especially for orographically favored mountains in the strong 
southwesterly flow.

Moving through Sunday, the baroclinic zone advances west to east 
across Utah as the trough continues its inland trajectory. As it 
does so, once again anticipate a period of more focused 
precipitation along/near the cold frontal boundary. Colder H7 
temperatures will also begin to lower snow levels following the 
frontal passage, though as a whole conditions look mild enough to 
generally favor valley rain and mountain snow. That said, higher 
elevation mountain valleys such as the Wasatch Back will see some 
potential for some light accumulations, especially with any rate 
driven cooling and associated lowering of snow level. Precipitation 
will gradually become less widespread moving overnight through 
Monday as deep layer moisture decreases, and forcing becomes more 
instability driven as the trough axis moves overhead.

Overall the evolution of the flow through this period remains a bit 
more complex than a more typical trough progression, and thus 
uncertainty in specific amounts/timing/etc. remain a bit higher than 
usual. Still, good confidence is noted on a generally wet and cooler 
pattern through the weekend. If nothing else, mountains still see 
favorable odds to add a decent amount of water to the snowpack, with 
total SWE from Saturday morning onward to event cessation ranging 
roughly 0.50"-1.50" (using NBM 25th to 75th percentile QPF). Locally 
up to 2.00" of water will be possible at some of the more typically 
favored locations such as the Tushars or Upper Cottonwoods.

Moving towards the middle of the week, deterministic and ensemble 
guidance continue to generally favor a transition to milder/drier 
weather with ridging nosing in from the west, despite a trailing 
lobe of the trough lingering into the Desert Southwest. Towards the 
back half of the work week however, models diverge fairly evenly on 
whether the ridge remains dominant or if things trend back towards 
more unsettled weather.

&&

.AVIATION...KSLC...Gusty southerly winds increase through Thursday 
morning ahead of an approaching cold front. A few prefrontal showers 
are possible, with frontal timing most likely ~20-22Z or so. A 
period of gusty northwest winds, rain (~20% chance of lightning), 
and MVFR conditions are likely to accompany the initial frontal 
push. Lingering rain showers and gradually improving conditions 
expected thereafter into the evening, with activity becoming 
increasing isolated overnight into early Friday, and winds relaxing 
and shifting back southerly.

.REST OF UTAH AND SOUTHWEST WYOMING...An approaching cold frontal 
boundary will result in increasingly gusty southerly winds at most 
area terminals. At northern terminals, will also see shower chances 
increase through the morning ahead of the front. The front is 
expected to push through northern terminals through the early 
afternoon, bringing a switch to northwesterly winds, and a period of 
reduced conditions most likely to MVFR. At far northern or more 
elevated terminals (i.e. EVW/LGU/HCR), chance of snow mixing in will 
yield associated chance for further reduced conditions to IFR at 
times of heaviest precip. Conditions gradually improve through the 
evening following frontal passage, with decreasing precipitation 
chances. With the front expected to stall somewhere across central 
Utah, southern terminals primary impact will remain continued 
stronger southerly winds.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 6 PM MDT this evening for UTZ110.

     Winter Weather Advisory from 9 AM this morning to 9 PM MDT this 
     evening for UTZ111-112.

     Winter Weather Advisory from noon today to midnight MDT tonight 
     for UTZ113.

     Wind Advisory from 9 AM this morning to 6 PM MDT this evening 
     for UTZ115-122.

WY...None.
&&

$$

SHORT TERM...Traphagan
LONG TERM/AVIATION...Warthen

For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity

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Western Regional Climate Center, wrcc@dri.edu