Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 191034

Area Forecast Discussion
National Weather Service Salt Lake City UT
434 AM MDT Wed Oct 19 2016

.SYNOPSIS...A cool northwest flow will prevail across the region
today, with high pressure following for the remainder of the
week. Southwesterly flow will develop over the weekend with
moisture spreading into the region by early next week.


.SHORT TERM (through 00z Saturday)...The shortwave trough which
crossed northern Utah and southwest Wyoming late Tuesday afternoon
and Tuesday evening continues to translate eastward and away from
the forecast area early this morning. 700mb temps near -5C have
proven sufficient for a couple of convective bursts off the GSL
over the past hour or two, however with 500mb temps warming
instability is expected to become too shallow to support
additional development by morning, and have kept any mention of
showers out of the forecast for now.

Low amplitude mid level ridging currently situated along the
Pacific Northwest coast will build inland and amplify today,
eventually becoming situated across the forecast area for the
remainder of the week. Surface ridging will result in one more
cool night with frost possible in outlying areas of the Wasatch
Front tonight into Thursday morning, otherwise with rising heights
and warming temperatures aloft max temps are forecast to rebound
to near or slightly above seasonal norms by Friday.

.LONG TERM (After 00z Saturday)...A warm and dry southwest flow will
prevail through the weekend with better mixing expected by Sunday as
surface high over the north pulls east and southeast surface
gradient combines with the southerly flow aloft. Temperatures will
be about 5-10 degrees above normal Sunday. The GFS shows some
showers breaking out Sunday afternoon over the higher terrain but
this looks too fast and have leaned toward the EC which does not
show QPF and yet is slightly deeper and faster with the trough along
the west coast.

The early part of next week should see unsettled weather across much
of the CWA with both the EC and GFS showing a weak ejecting wave
lifting northeast Monday. The EC is stronger and colder with this
initial wave but with so much uncertainty over the eastern Pacific
decided to use a blend of models and go with slightly above normal
PoPs from Monday afternoon through Tuesday. By Tuesday night there
is about 60-70 meter standard deviation difference at 500mb in the
GFS ensemble members across Utah. The EC 500mb heights are about 70
meters lower than the GFS at this time as well. The EC has a
shortwave ridge developing along the west coast as it starts to
carve out a closed low between 130 and 140 W at 40 N while the GFS
keeps the trough progressive with lowering heights moving towards
Utah. Due to these differences have gone with near climo PoPs
Tuesday night through Wednesday night.  These uncertainties in the
global models are most likely due to how they are handling the
interactions of the typhoons in the western Pacific and the northern
jet stream.


.FIRE WEATHER...Dry and cool weather will occur today but then
warming is expected into the weekend. The clearing index values will
lower in the valleys today and across all areas Thursday as an
inversion builds over the region. Southwest transport wind will
increase Friday so higher elevations will see improvement to the CI
values but the valleys will remain trapped under the inversion
through Friday except for the southwest valleys where mixing is
likely to develop. Low RH values will occur across the southern half
of Utah`s valleys Thursday and Friday while only the northern
mountains will experience the sub 20% RH values on Thursday and

Southwest winds pick up across western valleys this weekend. This
will result in good to excellent CI values. Moisture spreads into
the region Sunday night through Tuesday and depending on which model
pans out may see more unsettled weather into Wednesday. Temperatures
will cool from 5-10 degrees above normal this weekend to about
normal levels early next week.


.AVIATION...Isolated showers could cross the SLC terminal through
12Z. Cigs expected to be between BKN035 and BKN070 through 12Z with
a 40 percent chance of lifting above BKN070 by 11Z. Light and
variable winds through 12Z due to the showers then southeast from
12Z until 17Z. Northwest winds after 17Z.





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