219
FXUS65 KSLC 170909
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
309 AM MDT Sat May 17 2025

.SYNOPSIS...A cold, winter-like system will impact the region
through Monday. High pressure will build into the area midweek,
bringing much warmer temperatures and a return to summer.

&&

.DISCUSSION...The forecast continues on as expected...with a cold,
winter-like trough approaching the region today...and a rapid
warm-up midweek. Early morning upper air and satellite analysis
indicates a strong shortwave trough is digging into the PACNW,
with the associated jet max clearly evident. Broad upper level
diffluence is noted across Oregon/norther California.

Expect this area of upper level diffluence and enhanced synoptic
scale lift to shift into the Great Basin this morning as the
shortwave trough crosses into the western Great Basin. HREF mean
SBCAPE values will approach 500 J/kg or so...with deep layer shear
near 35-40kts. As relatively high-based convection develops across
western and northern Utah, expect an attendant risk of microbursts
through the afternoon and evening.

Synoptic scale winds will also increase across western Utah this
afternoon and evening. With the probability of 45 mph + winds for
3 or more hours remaining at around 35% of so, elected not to
issue a wind advisory. There is some question despite the 40kt+
700mb flow of how quickly clouds move in and how much momentum
transfer there will be outside of microburst activity.

The associated cold front will cross into Utah this afternoon and
gradually progress across the state through Sunday morning. Expect
a band of moderate to heavy precipitation near and behind this
front, shifting to a more showery mode by Sunday afternoon. With
snow levels quickly falling to near 7000 feet behind the front,
expect a period of heavy mountain snow, especially above 8000ft
Sunday morning. Given seasonal routes have started opening for the
warm season, widespread recreation use ongoing in the higher
elevations and totals averaging 5 to 10 inches above 8000 feet,
issued a winter weather advisory for all Utah mountains.

Guidance continues to indicate a second shortwave trough will drop
into central and southern Utah Monday morning, bringing an
additional round of precipitation to these areas through Monday
afternoon. Current additional snow totals are under 2 inches in
most locations, so elected to end the winter weather advisory
Sunday evening...but this will need be monitored if amounts trend
up with later guidance.

Given this winter-like system, cold temperatures are expected
region-wide Sunday night into Monday morning. Portions of the
state will fall below freezing including the Cache Valley, eastern
Box Elder County, Juab and Millard Counties, the upper Sanpete
Valley and southwestern Utah, particularly in the outlying areas.
Issued a Freeze Watch for Sunday night/Monday morning...but
temperatures in some of these locations may fall below freezing
again Monday night into Tuesday morning. Those with sensitive
early season agriculture in these areas should be prepared for
multiple nights of below freezing temperatures and frost.

Following these cold temperatures, nature remembered to look at
the calendar and the heat will be on mid to late week as
temperatures surge to 10 to as much as 15 degrees above normal.
Guidance suggests little chance of precipitation after this cold
system through at least next weekend.

&&

.AVIATION....KSLC...Latest high-resolution model guidance
indicates isolated showers through 14Z which have a low-end
potential of causing occasionally variable winds. Otherwise, high
confidence in south winds through 20Z, gusty at times in the
20-30kt range in the early afternoon. From 20-24Z, gusty and
erratic winds possible in/near showers and isolated thunderstorms.
Wind shift to the W-NW is expected between 23-00Z with the
arrival of a cold front, with gusts 20-25kt post-frontal through
the evening. Increasing coverage of showers and a few
thunderstorms after 00Z, with persistent rain and isolated thunder
likely for the much of the remainder of Saturday night into
Sunday morning. Medium (~50% chance) for MVFR CIGs after 09Z
Sunday, with ~20% chance of IFR CIGs during this time. High
confidence in mountain obscuration beginning around 03Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Increasing shower/thunderstorm
coverage expected today from west to east, arriving across NW
Utah this afternoon, overspreading the Wasatch Front 00Z-03Z,
before expanding across western Utah 03-06Z, and finally central
Utah 06- 12Z. Gusty S winds anticipated Saturday afternoon ahead
of an eastward-expanding cold front that will overspread Utah and
SW Wyoming coincident with the above-mentioend arrival times of
the main precipitation shield. Isolated strong thunderstorms,
especially across northern Utah Saturday afternoon with
gusty/erratic wind threat. In advance of the front and precip
shield, gusty S-SW winds this afternoon into the early evening,
especially southern Utah. Along/behind the front, high confidence
in mountain obscuration, with medium (50%) chances for MVFR CIGs.
20-30% chance for IFR CIGs Saturday night-Sunday morning, with the
exception of extreme southern and southeast Utah where these
probs will be much lower.

&&

.FIRE WEATHER...Two main impacts today across the region. First,
gusty winds and low humidities are expected to develop by
afternoon and across western and southern Utah. As the upper level
disturbance continues to approach the region, high-based showers
and thunderstorms will develop. This will bring the attendant
threat of strong, gusty and erratic microburst winds. A strong
cold front will cross the region Sunday, bringing falling snow
levels (as low as 6500-7000 feet at times), widespread valley rain
and mountain snow through Sunday afternoon. Another round of
precipitation is likely across central and southern Utah Monday
morning into Monday afternoon.

As high pressure builds into the region midweek, temperatures
will quickly warm to around 10 degrees above normal...with little
threat of precipitation through next weekend.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Freeze Watch from Sunday evening through Monday morning for
     UTZ103-107-115-116-118-122.

     Winter Weather Advisory from 3 AM to 6 PM MDT Sunday for
     UTZ110>113.

     Winter Weather Advisory from 6 AM to 6 PM MDT Sunday for UTZ117-
     125.

WY...None.
&&

$$

Kruse/DeSmet

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