Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 051619
Area Forecast Discussion
National Weather Service Salt Lake City UT
919 AM MST Mon Dec 5 2016
.SYNOPSIS...A cold front will stall across central Utah this
afternoon and further weaken. A second, colder storm system will
bring snow and the coldest temperatures of the season to most of
Utah and southwest wyoming for midweek.
.DISCUSSION...Morning water vapor and H5 analysis continue to
depict a broad long wave trough encompassing much of the northern
CONUS this morning, anchored by a parent upper low over
Saskatchewan. A progressive short wave clipped northern Utah
earlier this morning surging a strong but relatively dry cold
front south along the Wasatch Front bringing light snow and gusty
winds, but a marked clearing trend is occurring N-S over the north
under rapidly rising MSLP and post front subsidence. The surface front
continues to surge south across central/southern Utah, but has
largely become removed from both the mid level baroclinicity
draped from Utah County east across Strawberry Reservoir, and the
parent short wave now translating east across central Wyoming.
Thus, the frontal dynamics are weakening and have noted rapidly
decreasing trends in areal coverage of light snowfall, now
primarily tied to the H7 baroclinicity.
Trimmed PoPs for this morning across much of the area in this
latest update, lowered QPF/snowfall, and trimmed clouds towards
latest trends. Also warmed temps along the Wasatch Front by a
degree or two as current obs are only a degree or two from
forecast afternoon highs.
Focus of shift moving forward shifts upstream to the next upper
low (currently over southern Britcol) and the short term forecast
details regarding the next round of snow tomorrow afternoon, and
the coldest temps of the season come midweek.
No other updates made or planned. Previous Discussion below...
.PREVIOUS DISCUSSION...A break in precipitation is expected
tonight, before the next upstream wave currently along the
British Columbia coastline digs into the Great Basin during the
day Tuesday. The models have been trending slower with this wave,
and as such have lowered POPs later tonight into Tuesday morning
across most areas, however did retain chance POPs across northern
Utah north of I-80 Tuesday morning where warm advection may bring
a period of light snow. This second wave is forecast to cross
northern Utah Tuesday afternoon and evening bringing a period of
light snow to northern and central Utah with modest accumulation
The more noteworthy aspect of this second wave will be the much
colder airmass which follows. 700mb temperatures Wednesday morning
are forecast around -18C Wednesday morning, which will keep max
temperatures Wednesday in the low to mid 20s across most northern
and central valleys, and single digits in the mountains.
Flow aloft is progged to shift to westerly by Thursday morning as
a warm front moves through, advecting a moist airmass back into
the forecast area. This will allow precip to redevelop over
northern Utah, persisting through Friday before temperature
advection becomes more neutral. Maxes are expected to run at least
a few degrees above climo by Friday afternoon with the warmer
airmass and enough flow to erode any inversions.
Global models then indicate a cooling trend for northern Utah and
southwest Wyoming with a cold front settling in during the day
Saturday as a weak wave grazes the forecast area. A good jet over
Idaho should keep a bit of instability around for a few showers.
EC/GFS then keep a somewhat active pattern going through day seven
with another weak wave moving through in zonal flow. Because the
models continue to disagree quite a bit with regard to the timing
and strength of this next wave, have opted to keep POPs near climo
for days six and seven.
.AVIATION...VFR conditions are expected to prevail at the SLC
terminal. Cigs around 7000 ft AGL should prevail through 19z-20z,
with clearing from the north behind as snow showers dissipated near
the airport. Northwest winds are expected to continue throughout the
day before switching after 03z to a southeast direction.
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