Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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853
FXUS65 KSLC 131044
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
344 AM MST Wed Nov 13 2024

.SYNOPSIS...High pressure over the area will track east of the
area later this afternoon. A weakening storm system will act to
curb the warming trend over the area through Friday. Another
relatively weak storm system will impact the area over the
upcoming weekend.

&&

.SHORT TERM (Through 12Z Friday)...As yesterday`s quick hitting
storm system rapidly makes its way into the central United
States, high pressure is moving over Utah and southwest Wyoming
this morning, with the ridge axis nearly overhead. As this
happens, another storm system is approaching the Pacific coast,
and a few high clouds associated with the system are streaming
into the area.

The ridge will continue east today, with the ridge axis moving
over western Colorado during the afternoon hours. This will be in
response to the Pacific trough moving onshore as it weakens. What
is left of the system is expected to move over the top of the
ridge tonight into early tomorrow, bringing a rather weak and dry
front into far northern Utah, acting to curb the warming trend
just a bit. Thus, we`ll see maxes near climo today and up to 5F
above seasonal normals for Thursday, making it the warmest day of
the week. Southerly winds will be on the increase during the day
Thursday as yet another Pacific storm system makes its way
onshore.

.LONG TERM (After 12Z Friday)...Two storm systems will cross the
area during the long-term period, with the first bringing mountain
snow and even minor valley snow accumulations late Friday into
Saturday. More uncertainty lies with the second system, though this
one has the potential to be colder and wetter than the first.

The first storm system will take the shape of a longwave trough
diving south into the western US, becoming split over the Great
Basin with the parent trough moving eastward across Utah and a
closed low forming well to our southwest. This closed low will track
far to our south even as it eventually moves eastward, thus will not
have any impact on our area. The parent trough, however, will bring
precipitation chances and cooler temperatures to much of the area,
particularly across northern UT and southwest WY where the best
dynamics will be located. Cold air will filter into the area late
Friday through Saturday morning, dropping 700-mb temperatures to
around -10C and thus increasing snow chances down to valley floors
(the exception being St. George). Any valley accumulations (<5000ft)
should be minor as it will take time to transition from rain to snow
overnight, with a 15% chance of seeing >1" of snow at KSLC
(~4200ft). Currently, northern mountain accumulations are likely to
remain sub-advisory, though we could see this change a bit more in
the coming days due to shifts in the longwave pattern or mesoscale
effects. Central and southern Utah will see less precipitation,
likely less than 0.1" of water equivalent even in the mountains.

After a brief break in the action on Sunday, another storm system is
likely early next week, though there is plenty more uncertainty
surrounding this one. We can generalize this uncertainty by grouping
the forecast into two separate scenarios, where the main difference
is the amplitude of the trough and thus how far south into southern
UT it reaches. Scenario 1 (56% of ensemble members) favors a deeper
trough, which would bring much colder temperatures and modest
precipitation to much of the state. For example, 700-mb temperatures
could drop to around -14C across northern UT, which would likely
produce the coldest temperatures of the season so far. Chances for
accumulating northern valley snow are higher with this scenario;
currently, the NBM suggests a 40% chance of >1" in Salt Lake City
(6% chance of >6").

Scenario 2 (44% of ensemble members) features a shallower trough
that grazes across northern UT. This would likely limit impacts to
northern areas, with 700-mb temperatures still dipping down to -10C
across the north. In contrast, southern UT wouldn`t see much of a
cooldown, if at all.

Heading into mid-week, nearly all ensemble members favor a ridge
setting up over the western US, though it`s unclear how long this
ridge could potentially last.

&&

.AVIATION...KSLC...Southeasterly winds are likely to last through
the valid TAF period, with occasional gusts to 20kts through the
afternoon (20-01z). VFR conditions will prevail.

REST OF UTAH AND SOUTHWEST WYOMING...Winds will remain largely light
and terrain-driven, with occasional gusts to 20-25kts out of the
south this afternoon at many sites. VFR conditions will prevail at
nearly all locations. Fog may develop at KLGU (60% chance) and KHCR
(30% chance) early this morning before 15z, which could produce
periods of LIFR conditions.

&&

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

$$

SHORT TERM...Traphagan
LONG TERM/AVIATION...Cunningham

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