396
FXUS65 KSLC 240909
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
309 AM MDT Fri May 24 2024

.SYNOPSIS...A stable airmass across northern Utah will transition
to a more active pattern beginning today. Widespread
precipitation is expected north of I-70 late today into Saturday
evening. A cool, stable airmass will shift into the area for
Sunday, followed by a substantial warming trend early next week.

&&

.SHORT TERM (Through 12Z/6AM Sunday)...Zonal low extends across
the Great Basin/Colorado Plateau region early this morning,
between a shortwave trough exiting the region and crossing the
northern High Plains, and an upstream trough digging along the
British Columbia coastline. A weaker perturbation is also noted
off the northern California coast roughly along 130W. At the
surface, a shallow cold front has pushed through southern Utah
overnight while the associated low level baroclinic zone remains
largely stalled further north across central Utah.

The shallow surface boundary will mix/retreat northward early
today, allowing a return to warm and breezy to windy conditions
across southern Utah by this afternoon. Further north, a more
stable airmass will remain across northern Utah, however airmass
modification will allow temperatures to trend roughly 10F warmer,
and reach the upper 60s to low 70s along the Wasatch Front.

The shortwave feature off the California coast will spread inland
late today through tonight. Moisture ahead of this wave will
spread into the forecast area, largely along the slowly
retreating low level baroclinic zone. This will bring an increase
in showers and thunderstorms this afternoon and evening with the
greatest coverage across central Utah, and more isolated coverage
on either side of the baroclinic zone. This activity will
initially be high based with little measurable precip but a
threat for microburst winds, however as we transition into the
evening measurable precip will become more common with these
showers and thunderstorms.

The British Columbia shortwave will then dig through the Pacific
Northwest, northern Rockies and northern Great Basin late tonight
through Saturday. Precipitation will be fairly widespread across
northern and central Utah through at least early Saturday
afternoon, while coverage across the south remains more spotty
during the afternoon hours. Snow levels will remain above 8500
feet with any appreciable accumulation confined to the highest
elevations of the Wasatch Range as well as the Uintas. Precip
totals across the northern valleys including the Watch Front will
most likely range from 0.20-0.35 inches, with lesser amounts
across central Utah. As the trough axis continues east late
Saturday, any lingering precip should wind down by early Saturday
evening, and a transition to a more summer-like pattern begins.

.LONG TERM (After 12Z/6AM Sunday)...Beginning on Sunday, a return to
summer-like weather will begin to make an appearance across Utah and
SW Wyoming in the wake of our departing storm system with
temperatures beginning to rise. A more substantial increase in
temperatures will begin on Monday, when temperatures will rise ~10F
across the north and ~5F across the south. Deterministic and
ensemble guidance is in good agreement in building a high pressure
ridge across the region through early next week, and this feature
will be responsible for the warming/drying trend. The warmest day of
the period (and the year to date) is now most likely on Tuesday.
This is when high temperatures will soar into the upper 90s across
Lower Washington County to the upper 80s across the Wasatch Front.
Latest NBM shows a 27% chance of reaching 90F at SLC on Tuesday.
With enough southerly downslope influence and enough sunshine, this
probability could be a bit conservative.

Forecast certainty does begin to wane slightly by midweek, as
differences emerge regarding the evolution of the mid-level ridge as
well as potential interactions with an incoming PacNW trough, with
notable strength and timing differences apparent across the solution
space. By Wednesday, 80% of the solution space shifts the ridge axis
off to the east, suggesting a slight cooling trend will emerge. As
we head into the Thursday-Friday timeframe, around 1/4 to 1/3 of the
solution space drops a trough across the Northern Rockies, with a
similar sliver of the remaining solution space representing either
zonal flow or the ridge simply staying put. Through this analysis,
we see 3 possible forecast outcomes in the Thursday to Friday
timeframe. We`ll call scenario 1 the outcome that keeps the ridge in
place; and this would imply maintenance of warm/dry conditions.
Scenario 2 with its transition to the zonal flow regime would suggest
temperatures cooling back down near seasonal normals across the
north along with little change in temperatures across the south.
Additionally, a low chance for a few showers/storms across northern
Utah/SW Wyoming may accompany said pattern shift. Finally, scenario
3 with the stronger Northern Rockies trough would suggest
temperatures cooling to slightly below normal across northern
Utah/SW Wyoming with only modest cooling across southern Utah, along
with higher chances for showers across the north. At present, all 3
scenarios are essentially equally possible forecast outcomes, and
the official blended/calibrated forecast falls more in line with
scenario #2 and its zonal flow regime. As we get closer to this
period of greatest uncertainty, we`ll continue to monitor trends to
observe which one of these outcomes becomes the most dominant
outcome.

&&

.AVIATION...KSLC...Increasing mid and high VFR clouds will be
common this morning along with southerly winds. Models suggest a
brief wind shift to the SW between 19Z-20Z before shifting to the
more typical NW between 20Z and 21Z. Yesterday`s cold front will
move back north this afternoon, and showers associated with it are
expected to develop towards 00Z, with occasional showers persisting
through Saturday. Model consensus suggests these showers will force
an earlier than usual wind shift to the S, with gusty S winds
continuing through much of the night Friday night. Better than a 90%
chance for VFR conditions through 09Z Saturday morning, but lower
CIG trends emerge after 09Z Saturday morning with showers. Chances
for MVFR approach 40% after 12Z Saturday.

.REST OF UTAH AND SOUTHWEST WYOMING...Increasing mid and high VFR
clouds will be common this morning as yesterday`s cold front moves
back north this afternoon, and showers associated with it are
expected to develop towards 00Z, with occasional showers persisting
through Saturday. Most shower activity will be across central and NE
Utah, but isolated showers possible as far north as near the Idaho
border and as far south as the southern mountains. Gusty S-SW winds
will develop south of the warm front across southern Utah this
afternoon. After midnight tonight, pockets of MVFR CIGs and mountain
obscuration become more common across central and NE Utah associated
with showers.

&&

.FIRE WEATHER...A cold front will remain stalled across central
Utah today. To the south of this front, warm dry and breezy to
windy conditions will persist across southern Utah. Meanwhile to
the north of this boundary, a more stable airmass will remain
across central and northern Utah. Despite this, temperatures will
trend a few degrees warmer over northern and central Utah today
as the airmass modifies. Moisture increasing along and north
of this boundary will bring an increase in showers and
thunderstorms over central and northern Utah this afternoon and
evening, with more isolated coverage over the south. Initially
these storms will be high based and accompanied by gusty
microburst winds afternoon, with a better chance for wetting
rains later on into the evening.

A low pressure system will cross the region late tonight through
Saturday, bringing widespread precipitation across northern and
central Utah, with more spotty coverage of precipitation across
the south. Wetting rains will be likely with this system across
the northern half of the state, before the system exits the area
Saturday evening. A cool airmass will remain in place Sunday,
followed by a substantial warming and drying trend early next
week. By Tuesday temperatures will approach 10 degrees above
normal as a summer-like pattern sets in. A dry cold front will
cross the area Wednesday into Thursday, bringing a slight
cooling trend but little if any precipitation.

&&

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

$$

Seaman/ADeSmet

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