Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 180245
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
845 PM MDT Tue Oct 17 2017

.SYNOPSIS...A warming trend will continue through the middle portion
of the week. A weak storm system is forecast to cross the area
Friday, bringing cooler temperatures and mountain showers.

&&

.DISCUSSION...
Water Vapor Satellite shows a trough crossing the Northern
Rockies, transitioning to a shear axis from central California
into a closed low over the southern Pacific. 400-200mb MDCARS wind
observations place a 120-135kt cyclonic jet over the Pacific
Northwest which becomes anticyclonic over central Canada. GOES/SLC
00Z RAOB/HRRR indicate that precipitable water values vary from
0.10"-0.20" most locations, up to 0.25" over northwest Utah.

With the ridge flattening out, cirrus associated from the central
California shortwave and subtropical jet over the southern
Pacific continues to increase. Did bump up sky cover to partly
cloudy for many areas for at least part of the night per webcams
and latest satellite imagery.

It will be a warmer night due to increasing 850-700mb thickness,
cirrus and southwesterly flow. Still due to the dry airmass in
place outlying areas may dip a few extra degrees.

Going forecast in great shape. Updated diurnal T/RH curve based on
latest observations and guidance.

&&

.PREVIOUS DISCUSSION...
Mostly benign westerly flow aloft will continue through early
Friday, bringing generally quiet weather conditions to Utah and
southwest Wyoming. A ridge axis currently overhead per latest
water vapor imagery will slide east of the area tonight, while a
very weak shortwave currently in western Nevada will push through
central Utah. The only effect of this wave will be a few mid level
clouds in central/southern Utah tonight.

A stronger shortwave trough is forecasted to lift northeastward
from Las Vegas area across central and eastern Utah late tomorrow
into Thursday. A few models are wringing out light precip over the
central Utah mountains from this disturbance. Given the very dry
low-level profiles, it will be tough to get anything other than
sprinkles outside of the high terrain. Otherwise, Wednesday will
be another pleasant day for most areas with temperatures 5-10
degrees above normal.

Southwest flow aloft increases over the Great Basin Thursday in
advance of a developing longwave trough stretching from NorCal to
the Pacific NW. Stronger mixing should allow for the warmest
temperatures of the week, with most Utah valleys reaching the 70s
or around 10 degrees above normal.

The trough pushes inland Thursday, reaching Utah by mid-day
Friday and pushing a cold front through northern Utah and
southwest Wyoming during the day. Breezy conditions can be
expected by Friday afternoon, especially over the western deserts.
Models are in general agreement with keeping the core of cold air
at 500MB to our north, with a shallower front from the surface to
around 700MB that pushes through all of our area except far
southern Utah by Friday night. As has been the trend with recent
troughs, this system will be lacking moisture, and thus the best
chance of light precip will be over the higher terrain from around
Utah County northward, particularly over the Uintas. Snow levels
will approach valley floors, but not expecting to see anything in
the Wasatch Front given the mostly dry nature of the system. The
most noticeable aspect will be a ~20 degree drop in temperatures
from Thursday`s highs to Saturday`s highs.

Temperatures quickly rebound across the area Sunday as a dry
northwest flow aloft sets in and heights build in the wake of
Saturday`s trough passage.

Looking ahead to next week, global models are in agreement in
building a strong ridge over the Western US. This ridge is quite
persistent and actually strengthens further into the week. This
will likely bring an extended period of warmer-than-normal
temperatures and dry conditions for our area.

&&

.AVIATION...The dry/stable westerly flow aloft across northern Utah
will maintain VFR conditions under mostly clear skies through the
TAF period. Calm winds will become light out of the southeast
around 04z this evening.

&&

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

$$

PUBLIC...Rogowski/Van Cleave
AVIATION...Rogowski

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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