Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 252159 CCA

Area Forecast Discussion
National Weather Service Salt Lake City UT
356 PM MDT Mon Sep 25 2017

.SYNOPSIS...Warmer and drier conditions will exist across the area
through midweek. The next upper low will develop over western
Arizona Tuesday, then turn back to the north and impact much of
southern and eastern Utah during the latter half of the week.


.SHORT TERM (through 00Z Friday)...As one closed low moves away
tonight across Wyoming, another will develop over the very southern
tip of Nevada by Tuesday evening. Residual moisture and cold
temperatures aloft have resulted in the cumulus cloud build up
across northern Utah this afternoon, but as the cold low moves
farther away tonight the skies will clear after sunset. A couple of
light snow showers are still possible over the Uintas early this
evening, as one final cold trough aloft moves across but they too
will die with sunset.

Tuesday will be dry across the entire CWA and temperatures will warm
another 4-7 degrees, but still be about 5-10 degrees below normal
for September 26.  The closed low will track into NW Arizona
Wednesday and as it does will tap some moisture from New Mexico and
wrap it northwestward into southeastern Utah by Wednesday morning
and across most of southern Utah by the end of the day. The LI
lowers to -2 in spots across southern Utah by late in the day so
have included thunderstorms for the afternoon and evening for this
part of the CWA. Noticed that the PWs get up to 2/3 of an inch so
not too bad for this time of year so increased the QPF some as well
as broadened the areal extent of scattered showers for Wednesday
night and Thursday.

The EC tracks the 500 mb low a little farther east than the GFS but
not sure what is  pushing it farther east so leaned towards the GFS
solution which had the support of the NAM and SREF.

.LONG TERM (After 00z Friday)...The upper lifting northeast through
southern/eastern Utah Thursday will be in the process of slowly
winding down before exiting the state by early Friday. The latest
runs of the GFS and ECMWF have switched places, with the GFS
taking a track to the west of the ECMWF. Both models are showing
the best support for lift along the eastern flank of the low,
though the GFS proximity to the central mountains will likely
generate more terrain-based precip through Thursday evening.

Lingering light precip across northeast Utah/southwest Wyoming
late Thursday night through early Friday should end as a shortwave
ridge moves into the area from the west for late Friday through
early Saturday.

Amplification of the upper ridge near 150W will allow the next
trough to deepen as it enters into the Pacific Northwest late
Saturday. This trough will likely remain focused on the northern
Rockies as it tracks east late in the weekend. The associated
low-level baroclinic will push south into northern Utah, bringing
some precip and cooler temps to the far north Saturday night
through early Sunday.

Low confidence exists concerning the evolution of the pattern
early next week. The GFS is by far the more aggressive model as it
brings a deep/cold trough across the region beginning Monday. The
ECMWF also develops a trough, but holds it well over the Pacific
Northwest/eastern Pacific during the first half of the week. The
resultant strong southwest flow aloft in this model would generate
warm and mostly dry conditions early in the week. Both models have
struggled to show much run-to-run consistency, thus the reason for
the low confidence in the model solutions.


.AVIATION...VFR conditions will prevail at the KSLC terminal through
the valid TAF period. Northwesterly winds currently in place are
expected to switch back to the southeast between 03/04z.


.FIRE WEATHER...Upper low finally moving away tonight will leave
Utah between systems for Tuesday. However, the RH will remain
elevated not only Tuesday but through the entire week. The next
closed system will develop over the far southern tip of Nevada
Tuesday night. This system will then track northeast into south
central Utah Wednesday wrapping moisture around to the
northwest across eastern and central Utah. Wetting rains will
accompany some of the showers over the central and eastern
portions of the area.





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