Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 190354

Area Forecast Discussion
National Weather Service Salt Lake City UT
954 PM MDT Sun Sep 18 2016

.SYNOPSIS...The dry and stable westerly flow over the region will
persist through Monday evening. A weather disturbance lifting
northeast into the Great Basin will draw moisture north into the
state, with the greatest impact across extreme southern and
eastern Utah midweek. A new and much stronger storm system will
impact most of the area late in the week.


.SHORT TERM (Until 18Z Wednesday)...The dry and stable westerly
flow aloft across the region will generate one more day of warm
and dry conditions Monday.

Tuesday looks to be a transitional day as the upper low parked off
the northern Baja coast opens up and lifts northeast will drawing
moisture north into the southern Great Basin. Trajectories of the
advancing moisture and the remnant dynamic features associated
with the decaying upper low would put the best threat for precip
across extreme southern Utah through east-central Utah beginning
Tuesday afternoon and continuing through the overnight hours. The
remainder of the state will remain dry with temps running a little
above September norms.

.PREVIOUS LONG TERM (After 18Z Wednesday)...Lingering moisture
could allow for isolated to widely scattered showers/thunderstorms
on Wednesday afternoon, but the party really gets started
Wednesday night as a large trough pushes into the Great Basin.
Models have generally trended deeper and further south in the 12Z
runs, while still keeping good instability and forcing across
northern Utah, so have generally increased POPs and sky cover
across the board for Wednesday night and Thursday. It remains to
be seen whether models consistently keep this trough further
south, so have not gone too crazy with POPs/sky over southern
Utah, but confidence continues to grow for a good precipitation
event and significant cooling across the northern half of the CWA.

In addition to trending deeper with the trough, models have also
kept precipitation going longer across northern Utah into Thursday
night and Friday. The biggest impact with this trend is that the
northern mountains could see accumulating snowfall in the
7,000-10,000 foot range after the coldest low level air pushes in
Thursday night. Have increased POPs through this time frame as
well, though again it will take a few more runs to gain confidence
in this solution.

The trough is slow to exit, but eventually slides east of the area
on Saturday. Models continue to promote the idea of a cool but
generally dry northwest flow for Sunday/Monday.


.AVIATION...The dry and stable westerly flow aloft will maintain
the VFR conditions under clear skies throughout the TAF period.
Southeast winds will persist overnight, then turn more southerly
with a slight increase in speeds during the morning. A shift to
a northwest wind will likely be a bit later in the afternoon on


.FIRE WEATHER...Warm and dry conditions will persist through Monday.
The only area of significant winds during this time period will be
across the northern Wasatch mountains and Uintas on Monday where
gusts in excess of 30 mph are likely. Min RH values will likely
bottom out into the upper single digits across southern half of Utah
Monday while RHs in the lower teens will be common farther north.

A low pressure system with tropical connections will opening up and
move northeast across at least the southern half of Utah Tuesday in
to Tuesday night with widespread wetting rains likely over the
southeast quarter of the Fire District. However, models are in
disagreement with where this system will track and therefore low
confidence in where the greatest rain amounts will occur. Best
threat at this time appears to be south of I-70 and east of I-15.

In the wake of the this tropical system will be a cold trough moving
in across the region late Wednesday night and impact the entire
region through Friday. Snow levels will lower to 7K ft MSL by Friday
morning from about I-70 northward. This storm system will
potentially be the season ending storm across the northern third of
the fire district with accumulating snow likely down to 7K ft MSL.
farther south snow levels will be higher but still a good threat of
wetting rains Thursday into Friday.





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