Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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896
FXUS65 KSLC 230855
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
255 AM MDT Mon Oct 23 2017

.SYNOPSIS...High pressure rebuilds through the middle of the
week. A storm system will move through Utah and southwest Wyoming
Thursday before high pressure returns for the upcoming weekend.

&&

.SHORT TERM (THROUGH 06Z THURSDAY)...
Water Vapor Satellite shows an amplifying ridge along the west
coast with a strong disturbance moving into the Upper Plains.
400-200mb MDCARS wind observations place a 150-175kt
northwesterly jet from British Columbia into the northern Rockies.
GOES/SLC 00Z RAOB/HRRR indicate that precipitable water values
vary from 0.25"-0.33" mountains and far southern valleys to
0.50"-0.85" northern valleys.

Strong height rises are occurring over the Pacific Northwest and
northern Rockies behind the aforementioned storm system. While the
storm is well to our northeast, its strong enough to support the
passage of a shallow cold front, currently making its way through
south central Utah per the enhanced northerly pressure gradient
and pressure rises. With the dynamics so far removed from the
region, not expecting any precipitation. Rather, a slight cooling
trend and gusty winds particularly in the higher terrain, and
typical canyon/downslope areas.

With a 10mb northerly pressure gradient, an area to watch for
near-advisory wind gusts is the outlying sections of Washington
County. While there is a nice pressure gradient in place, pressure
rises wash out this morning, and there is little support aloft. So
for now feel comfortable with gusts just below advisory criteria.
Pressure gradient increases a bit tonight as does 700mb flow. The
strongest winds in this area is therefore expected overnight
tonight into tomorrow morning.

A benefit from this cold frontal passage is maintaining good air
quality with sufficient flow. Come tomorrow and Wednesday,
building inversions will develop with warming aloft, with many
valleys failing to realize the full amount of warming. Luckily it
appears that there will only be two stagnant days before the next
system.

.LONG TERM (AFTER 06Z THURSDAY)...
The GFS model has continued the dry northerly flow setting in
Thursday with the main trough dynamics remaining well east of the
CWA with the nose of the jet aimed for NW Colorado. Meanwhile, the
EC is farther west with this digging trough over the northern
Rockies with the nose of the jet at 18Z Thursday aimed at the
Wasatch Front. Have taken a blend of the two models at this time
as the GEF operational leaned towards the EC, but the GEFS
ensemble mean was much more like the GFS. As a result, have backed
off some on the PoPs for Thursday and removed them completely for
late Wednesday night.

A modest surface high is forecast to move over the CWA from late
Thursday through the weekend with a dry northwesterly flow aloft.
Despite the 700mb temps rising between 5 and 7 degrees C between
Friday afternoon and Sunday afternoon, the northern valleys temps
are probably going to straight line with very little change, while
warming of about 5 degrees is expected across the southern valleys.
This will be a result of a modest valley inversion setting up across
the north.

&&

.AVIATION...
The surface winds at SLC terminal have been very light and variable
as the typical SE drainage winds are fighting a developing northerly
surface gradient. The northerly winds, albeit light, should develop
between 11 and 13Z this morning and remain in place through this
evening. Mid level clouds will thin by about 15- 16Z. VFR conditions
will prevail through the TAF period.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

SHORT TERM...Rogowski
LONG TERM/AVIATION...Struthwolf

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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