Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 041146
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
445 AM MST Mon Dec 4 2017

.SYNOPSIS...A cold Pacific storm system will slowly exit the area
today. Strong high pressure aloft will cover the western states
through the week.

&&

.SHORT TERM (THROUGH 12Z THURSDAY)...An upper trough remains in
place over Utah this morning, but will slowly slide east of the area
throughout the day. The airmass remains fairly unstable across
northern Utah with 500mb temperatures of -32C while at 700mb,
temperatures are currently near -13C. This cold air which arrived in
conjunction with the upper trough axis helped increased shower
activity late last evening. Currently, radar indicates showers still
ongoing from around Ogden south into the Salt Lake Valley, with some
enhancement of showers over the Great Salt Lake. Orographic
precipitation is also noted on radar along the northern and central
Wasatch Mountains as well as the Oquirrh and Stansbury mountains.
With the trough axis continuing to head east out of the area and
temperatures beginning to warm aloft, showers will gradually
decrease during the late morning through afternoon hours and end by
evening as a ridge starts to build into northern Utah. Although
there have been some lake enhancement of showers, a true lake-effect
event never managed to get organized overnight in part because winds
were not ideal, being too strong with some directional shear.
Although winds are forecast to gradually decrease this morning, the
window for a lake-effect event is quickly closing, as BUFR soundings
show a stable cap descending below 700mb by 15z. Have left Winter
Weather Advisories in place for the Wasatch Mountains where good
orographics will continue, otherwise all other highlights are gone.

Temperatures today will be much colder than it has been for a long
time. Some areas are already fairly well-mixed this morning owing to
the still gusty winds, and across northern Utah, aided by cloud
cover as well. For these areas, max temperatures are only going to
be a few degrees warmer than the current morning temperatures. As
skies clear tonight, temperatures will plummet pretty quickly. With
the ridge continuing to build into Utah tomorrow, the cold air will
become trapped in the valleys as inversions develop. On Wednesday,
models show a trough dropping into Wyoming on Wednesday along the
leading edge of the ridge. This is progged to bring a slight cooling
aloft as well as enhance the northerly MSLP gradient a bit over
Utah. Although this may weaken the inversions a bit, it will not be
enough to mix them out. As such, temperatures are forecast to remain
below normal across most valleys through midweek.

LONG TERM (After 12Z Thursday)...It`s a broken record in the long
term. Upstream ridging (blocking pattern) will dominate the period,
and that`s a high confidence outlook. It`s been so. At the least,
lower valleys won`t have snow on the ground to enhance the inversion
conditions that will persist, though haze is expected to continue to
build.

Have maintained a very gradual warming trend through the period as
WAA aloft is more than likely (temp trend more noticeable in the
upper elevations), while continuing to hold a more subdued
valley/basin trend due to sun angle and time of year.

Sorry to say, Global wave patterns don`t support much change in the
next few weeks...at the least.

&&

.AVIATION...Periodic high end IFR conditions in snow are expected
through 14z at the KSLC terminal, but no accumulations are expected
on untreated surfaces. CIGs are expected to gradually thin and rise
thereafter, but mountain obscuration of local terrain will most
likely occur through the remainder of day prior to breaking up this
evening.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Weather Advisory until 4 PM MST this afternoon for
     UTZ007-008.

WY...None.

&&

$$

Cheng/Merrill

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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