Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 151002

Area Forecast Discussion
National Weather Service Salt Lake City UT
402 AM MDT Fri Sep 15 2017

.SYNOPSIS...A cold front will bring cool showery conditions to
northern and central Utah and southwest Wyoming today. A milder
southwesterly flow will return for the weekend. Another
unseasonably cold storm system will impact the forecast area next


Water Vapor Satellite shows a weakening lifting wave over south
central Wyoming, with a cold pacific trough approaching from the
northwest. MDCARS 400mb-200mb wind observations show a 50-75kt
cyclonic jet over eastern Utah. Meanwhile an 75-125kt cyclonic jet
is over the western states, becoming anticyclonic across the
eastern two thirds of Canada. GOES/SLC 00Z RAOB/HRRR indicate
that precipitable water values vary from 0.30"-0.50" mountains to
between 0.90"-1.10" west of the Wasatch range.

Height falls aloft across the north today with the trough
building in from the Pacific Northwest. This will drive a cold
front, currently from near Evanston to Dugway, through south
central Utah today. The core of the trough pivots over the north
this evening, which should provide a final push of the boundary
through the state. In fact, by tomorrow morning, canyon winds may
be gusty across southern Utah. This is supported in the low
levels with an 8mb northerly pressure gradient across the state.
However a bit higher at 700mb flow will be westerly so not
thinking this will be an impactful event.

While there will be some instability showers around post frontal,
deeper convection is expected to form along the boundary across
north central Utah midday, sliding southeast during the afternoon.
Locally heavy rainfall is possible for a short duration in these
areas. PoPs significantly decrease post frontal across the north
by afternoon. Slightly increase PoPs again overnight to account
for the upper level trough passage. Snow Levels will remain at or
above 9kft during the time precipitation is expected. With
dynamics passing mainly to our north, have no precipitation
mentioned near the Arizona border.

Strong height rises occur tomorrow with the trough pivoting to the
northeast. With timing cant rule out a few showers across
northeast Utah and southwest Wyoming early in the morning, but
then the remainder of the short term period will be dry. This will
be the beginning to a warming/drying trend.

Cyclonic flow will remain in place at the mid levels beginning
the long term period, though stability will be attempting to
return between the departing low and approaching amplifying trough
diving in from the NW. Can not rule out a few showers across the
northern mountains during peak differential heating hours Sunday,
but as a whole, quite benign and near seasonal wx will dominate
into early week (sensibly).

The primary focus of the long term period keys in on the evolution
of the next northern branch trough, its amplification, timing, and
support as the long wave settles into the Great Basin region
through midweek. EC/GFS have slowly trended a bit towards each other
over the last few runs, namely depicting a highly amplified feature
with the primary upper low over southern Canada. Current timing of
the attendant cold frontal passage falls into the Tuesday timeframe
using a blended outlook, with precip coincident and focused across
the north. Several factors detract from enhancing more than an
isolated/scattered precip potential currently, with timing and
run to run consistency being forefront. Need this run to run
consistency to improve prior to enhancing the message much more than
expectations of yet another unseasonably cool and somewhat wet period
across the area midweek.


A cold front stretching from SW Wyoming into far western Utah
continues to slowly approach the KSLC terminal, with the next band
of showers/isolated thunderstorms advancing rapidly in front of
this feature. Gusty outflow winds are not much of a threat with
passage of any storms, rather lightning potential looks to be the
primary impact through 13z. Light south winds currently in place
are expected to switch to the northwest with frontal passage
between 14-15z, with moderately gusty post frontal winds taking
form through the remainder of the morning hours.


Most stations are now reporting an ERC at their 50th percentile
or lower, and the trend has been for decreasing ERC`s during the
past 3 days.

A stronger storm will cross the northern Rockies today, impacting
mainly northern and central Utah. A cold front is forecast to push
through the state by evening. Expect cool and unsettled
conditions especially north of Interstate 70. The stronger
activity may bring lightning, and locally gusty/erratic winds and
brief heavy downpour. The snow level will fall from 11kft this
morning to 9kft this evening.

Warming and drying occurs tomorrow through Monday ahead of the
next broad cold Pacific Northwest storm. Gusty winds both ahead of
and behind the cold front Tuesday, which may bring locally
critical fire weather conditions across the south if fuels can
sufficiently dry out. Cooling and moistening again for the middle
of next week.





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