Granger, Utah Weather Forecast Discussion

613
FXUS65 KSLC 252044
AFDSLC
Area Forecast Discussion
National Weather Service Salt Lake City UT
244 PM MDT Thu Sep 25 2025
.SYNOPSIS...A slow moving storm system moving across the Desert
Southwest over the weekend will bring increased moisture and
instability, primarily for southern Utah, but gradually shifting
north and east. A cold front may impact the area by the middle of
next week.
&&
.SHORT TERM (Through 12Z/6AM Saturday)...A broad trough has moved
onshore over California this afternoon, with moisture making its
way into southwest Utah out ahead of it. Satellite derived PWs are
in the 0.6 to 0.7 inch range over southwest Utah, and noticeably
drier elsewhere. The position of the low is also providing some
lift and shear over southwest portions of the state, and
predictably some showers have started to develop. A few of these
storms could be strong to severe during the remainder of the
afternoon and early evening, producing gusty winds and hail. Given
the moisture, any storms that develop will also be capable of
producing heavy rain that could lead to flash flooding, leading to
a probable in the Flash Flood Potential for Zion National Park
this afternoon. Elsewhere, conditions are mostly dry and
relatively mild with maxes averaging 5F above normal for this time
of year.
The low is expected to meander southward down the California coast
tonight into tomorrow morning before making an eastward turn into
Arizona during the afternoon. Moisture is expected to increase
further and spread northward. CAPE will be a bit higher with
improved jet support but overall shear will be a bit less. Thus,
tomorrow`s convection will remain focused over southern Utah with
some storms expected over the higher terrain of northern and
central Utah as well. The weakening of the ridge and proximity of
the low will also bring highs a bit closer to seasonal normals
for Friday afternoon.
.LONG TERM (After 12Z/6AM Saturday)...The pattern continues to look
more fall-like, with a couple of synoptic systems expected to
dictate our sensible weather over the long-term period.
On Saturday, the rotating closed low centered over roughly Yuma, AZ
will finally start to shift northeastward, with increasing moisture
from south to north expected across southern to central Utah. Model
soundings suggest a fairly saturated profile through all but the
lowest levels on Saturday afternoon, and combined with relatively
slower storm motions and PWATs near 180-200% of normal, this will
likely produce an elevated flash flood threat for prone areas.
By Sunday, this closed low will transform into an open wave crossing
N-AZ/S-UT, resulting in abundant moisture spreading across Utah and
southwest Wyoming (near ~200% of normal). Combined with synoptic
lift as the wave passes overhead, expect higher coverage of showers
and thunderstorms on Sunday, particularly Sunday afternoon.
Interestingly, the ECMWF EFI is highlighting south-central to
southeastern Utah during the 00z Sun-00z Mon period for fairly
abnormal QPF...potentially due to better lift and appreciable
instability across this area as compared to Saturday. Thus, as you
might guess, expect another day of elevated chances for flash
flooding in those prone areas, with a Marginal Risk for excessive
rainfall on both Saturday and Sunday. Finally, temperatures will
trend a few degrees cooler by Sunday, particularly for southern Utah.
To begin the work week, the synoptic pattern will begin to evolve as
a strong trough over the Gulf of Alaska starts to shift into the
western US. Overall diffluent flow within this still-elevated
moisture will result in yet another active day with showers and
thunderstorms, particularly across northern areas. Unlike prior
days, however, this increasing southwest flow will promote quicker
storm motions which could help reduce the threat of flash flooding,
particularly on Tuesday. While ensemble agreement is slowly
increasing with regards to the timing of this trough as it shifts
towards us, ensemble members still remain split 60-40 between a
slightly slower solution (60% chance) and slightly faster solution
(40% chance). Another area of uncertainty is the amplitude of this
trough, which will ultimately affect how much of Utah sees a cold
front move through the area in the mid-week timeframe.
Beyond Wednesday, forecast confidence in the longwave pattern
decreases, but model guidance overall favors a drier air mass with
gradually increasing temperatures moving forward. To summarize the
long-term period, expect an elevated flash flood threat through at
least Sunday, with showers and thunderstorms still continuing within
increasing southwest flow ahead of a longwave trough next week.
&&
.AVIATION...KSLC...Light northwest winds will last through roughly
04Z when winds transition to the southeast. Clouds will increase,
with scattered to broken clouds in VFR range from around 04-18Z.
There is around a 20% chance for rain showers that would be capable
of enhancing wind speeds with varying directions from 09-15Z.
.REST OF UTAH AND SOUTHWEST WYOMING...Showers and thunderstorms will
be capable of locally heavy rain and gusty, erratic outflow winds
for most of southern Utah through 06Z. Clouds associated with that
storm system will increase further north, with scattered to broken
clouds in VFR range building into northern Utah by 04Z. Largely dry
conditions will last from 06-18Z throughout southwest Wyoming and
Utah, although there is around a 20% chance for rain showers in
northern Utah from 09-15Z. Winds will be relatively light, but
showers and thunderstorms will be capable of enhancing speeds and
altering directions.
&&
.FIRE WEATHER...A broad low pressure system is currently centered
over California, but is bringing an increase in moisture and
instability to southwest Utah, where showers and thunderstorms
will continue to be a threat through the early evening. Any storms
that develop will be capable of producing gusty winds as well as
brief heavy rainfall. The trough will track slowly east over
Arizona and New Mexico over the weekend, gradually weakening as it
does so. This will allow the deeper moisture over southern Utah to
be drawn upward, expanding the coverage of afternoon showers and
thunderstorms, particularly over the higher terrain, through the
weekend. High pressure will temporarily bring drier and more
stable conditions to start the upcoming week before another trough
potentially brings a cold front through the area for the middle of
next week.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&
$$
SHORT TERM/FIRE WEATHER...Traphagan
LONG TERM...Cunningham
AVIATION...Wilson
For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

NWS SLC Office Area Forecast Discussion