Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 140941
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
341 AM MDT Mon Aug 14 2017

.SYNOPSIS...A cold front will move into northern Utah today then
stall across central Utah tomorrow. A warming trend will follow
for the remainder of the week.

&&

.SHORT TERM (THROUGH 12Z WEDNESDAY)...
Water Vapor Satellite shows a trough extends down the interior
west from a deep closed low over the Gulf of Alaska. One embedded
wave is pivoting northeast over Idaho, while the next approaches
from southwest Oregon. 400mb-200mb MDCARS wind observations place
a 80kt-110kt cyclonic jet down the British Columbia coast into
southern Oregon. GOES/SLC 00Z RAOB/HRRR indicate that precipitable
water values vary from 0.35"-0.55" west central Utah and the
mountains to 0.75"-1.00" most other valleys.

During the short term period height falls occur today into tomorrow
with the best height falls occurring ahead of the approaching
aforementioned wave late tonight into tomorrow morning. Trailing
energy associated with the strong Polar Jet will help define the
building trough overhead tomorrow morning. Storm looks nice and
sharp in the upper levels, and has notable Potential Vorticity
values in the upper and middle levels.

Natural evening drainage from Idaho into northern Utah has allowed
the cold front to sneak through Wendover and Salt Lake City as of
this writing. Mid August heating will encourage this shallow boundary
to retreat northwest mid morning through afternoon.

This system will bring the threat of showers and storms mainly to
the north later today into tomorrow. A noticeable cooldown is
expected through midweek. Gusty northwest winds aided by upstream
virga/precipitation could become a factor with the front late day
and evening, considering dewpoint depressions near 40F during
peak heating and 3mb-6mb pressure rises with the surging cold
front. This is especially true across the West Desert, Great Salt
Lake, and Point of the Mountain. Ahead of the cold front, gusty
southwest winds will occur thanks to 30kts 700mb flow, a building
southerly pressure gradient and pressure falls.

Interestingly, it may be cool enough to see some flakes mix in
with rain at the highest of Utahs ridges late tonight into
tomorrow.

.LONG TERM (AFTER 12Z WEDNESDAY)...
Brief zonal flow is expected to quickly turn to the southwest
during the day Wednesday as a weak trailing trough crosses the
forecast area. This will bring enough instability for a few
showers and thunderstorms, primarily over the higher terrain.

After Wednesday, model solutions diverge. Latest ECMWF shows high
pressure rebounding over the forecast area with a drier west to
northwest flow persisting into the upcoming weekend. Meanwhile, the
GFS keeps the ridge axis much farther east, allowing shortwave
energy from a weak Pacific trough to eject into the area. This would
keep a bit more moisture and instability around, along with the
resultant showers and thunderstorms. Though the EC has been the more
consistent model, have kept some POPs in to account for the GFS
solution as it seems a bit more believable this time of year in this
type of pattern. By Sunday night/Monday, all global models show the
Pacific trough moving into the Great Basin, so have raised POPs a
bit during this time.

With the influence of high pressure, the warming trend in
temperatures should continue into the first part of the weekend,
with maxes running near to slightly above seasonal normals.

&&

.AVIATION...
The SLC terminal will see VFR conditions through the morning with
increasing high clouds. Northwest winds are expected to return to
the southeast between 14Z and 16Z before shifting back to the
northwest between 20Z and 22Z as the main cold front moves
through. However, there is a 40 percent chance of northerly winds
persisting throughout the day.

&&

.FIRE WEATHER...
ERC values are below the 50th percentile across southern, south
central and eastern Utah. Values are higher, varying from 50th
through 79th percentile across north central and northern Utah.

Warm with a drying today ahead of a cold front which will cross
from northwest Utah today, making it into south central Utah by
tomorrow morning before stalling and weakening. Suspect critical
fire weather conditions will occur tomorrow afternoon and evening
as southwest winds become gusty. A Red Flag Warning remains in
effect for near Dixie, Fire Weather Zone 497.

Behind the cold front late this afternoon and evening, expect to
see virga/showers enhance frontal winds especially west desert,
near large bodies of water, and areas favored in northerly flow
such as Point of the Mountain.

Most areas will see cooler and more moist conditions midweek
before a gradual warming and drying trend occurs late week.
Chance for showers and storms increase from the north today into
tomorrow as a trough crosses the Great Basin.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Red Flag Warning from noon today to 8 PM MDT this evening for
     UTZ497.

WY...None.
&&

$$

SHORT TERM/FIRE WEATHER...Rogowski
LONG TERM/AVIATION...Traphagan

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

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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