Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 101032

Area Forecast Discussion
National Weather Service Salt Lake City UT
332 AM MST Sun Dec 10 2017

.SYNOPSIS...Strong high pressure aloft will remain the dominant
weather feature across the western states through at least the
middle of next week.


Water Vapor Satellite shows a ridge progressing into the Interior
West from the West Coast. 400-200mb MDCARS wind observations
place a 100-125kt anticyclonic jet from off of British Columbia
through central Canada and into the Upper Midwest. GOES/SLC 00Z
RAOB/HRRR indicate that precipitable water values vary from
0.05"-0.10" mountains and many southern and eastern valleys to
0.10"-0.20" northern valleys.

With the ridge sliding eastward, ridgetop temperatures will trend
higher toward +4C or +5C early this week. 00Z KSLC RAOB showed a
5.1C inversion in place with a base near 865mb and a top around
750mb, lower and stronger than 24 hours ago. There was also a
reinforcing subsidence inversion noted at 650mb.

Synoptic pattern will continue to support inverted conditions
through the short term portion of the forecast. Visit our website
and social media, along with Utah DAQ`s website and social media
for actionable tips to lessen the trajectory of worsening air
quality. The majority of Utah DAQ sampling stations are currently
placing air quality into the yellow or moderate category with a
gradually worsening trajectory during the past 48 hours.

Besides the Cache Valley, with dry conditions stratus and fog not
an immediate concern due to lack of snowpack for most valleys.
There is a chance that as this event ramps up, a narrowing diurnal
thermal range may start to saturate the lower levels again across
closed valleys and lower basins, potentially developing over the
Great Salt Lake first.

The global models are in good agreement through Wednesday but
then the EC shows little more of a brush by system Thursday,
although it has become less definitive with this feature in recent
runs so sided with the GFS. Kept the trend of valley inversions
in place through Friday. By Friday night the EC has a fast moving
disturbance with -6C degrees 700mb temps across nrn Utah. Although
this is a little weaker than the forecast from 24 hrs ago,
decided to leave minimal PoPs for nrn Utah and southwest Wyoming
for the time being.

More importantly, this may be just enough cooling to erase the
inversion or at least weaken it across nrn Utah, especially in the
Cache Valley. Have decided to go without haze in the Wasatch Front
forecast for the weekend. Since both the GFS and EC have a
disturbance for Saturday have gone closer to the SuperBlend
temperature forecast for the GSL desert and Cache Valley as the
inversion will possibly be turned over. However, models appear to be
waffling a little on the breakdown of the ridge so confidence
remains low on temperature trends.

Have adjusted winds up some across southwest Wyoming Friday and
Saturday afternoons, but not quite strong enough for them to show up
in the zone forecast.


Light southeast or calm winds will prevail at the SLC
terminal through about 17-18Z before shifting to the northwest, but
remaining light as well. High end MVFR or VFR conditions in haze
will occur throughout the Taf period.





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