Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 221126

Area Forecast Discussion
National Weather Service Salt Lake City UT
526 AM MDT Fri Sep 22 2017

.SYNOPSIS...A cold core upper low will drift slowly east across the
Great Basin through the weekend. Below normal temperatures are
expected across the region, with periodic valley rain and mountain
snow concentrating on the northern half of Utah and southwest
Wyoming throughout the weekend.


.SHORT TERM (THROUGH 12Z MONDAY)...A broad upper low will continue
to move slowly across the western CONUS through the weekend, keeping
a cool and moist airmass in place over the forecast area. The
current mean position of the low center is near Boise per satellite
imagery and latest RAP analysis. The associated surface cold front
has now made it past a line extending from near Kanab through Price
to near Vernal and is expected to stall there this morning. However,
the front has started to weaken as the shortwave disturbance
embedded within the low which helped progress the front across the
area yesterday has lifted north of the area. As a result,
precipitation along the boundary has started to diminish and is now
confined primarily across the Wasatch Plateau, Uintas, and southwest

Meanwhile, another weak vort lobe noted on satellite imagery is
rotating into northwest Utah currently, and this has caused showers
to redevelop across the northwest deserts. These showers should
gradually lift northeast through the morning hours. Snow levels
briefly reached the higher valleys overnight, and could still do so
this morning in heavier showers. Otherwise, snow levels should
remain near 6000ft across northwest Utah.

Another vort lobe currently rotating across the Sierra Nevada is
expected to swing through west-central through northern Utah this
afternoon. As this one will track deeper into Utah, this should
strengthen the cold front later this afternoon and push it through
the remainder of the forecast area this evening. Valley rain and
mountain snow should re-ignite along this boundary as it
strengthens, but mainly the northern portion, since a dry slot will
be working its way into southeastern Utah.

Precipitation is expected to wane overnight. The upper low becomes
more consolidated for the weekend, and as the low center approaches
western Utah on Saturday, precipitation will tend to redevelop. The
GFS and EC are coming into closer agreement with the track of this
closed low, taking it across southwest Utah Saturday night, then
lifting northeast. Moisture wrapping around this low will bring
widespread precipitation, especially to favored areas such as the
western valleys, central and southern mountains, Uintas, and
southwest Wyoming during the weekend.

.LONG TERM (After 12Z Monday)...With the center of the cold upper
level low beginning to lift north and east to start off the next
week, the amount of available energy decreases. Northerly flow aloft
associated with the low will help to usher in some relatively warmer
temperatures behind the low. Global extended forecast models are in
good agreement about the whole weather pattern into early Tuesday
morning. Thereafter, the models diverge on solutions about timing
and placement of another trough dropping through the Great Basin and
where it will end up.

700mb temperatures warm gradually from near -2C late in the weekend
to +3C to +4C by mid week, with a subtle bit of dry air becoming
pulled in from the south and west. Extended models differ quite
drastically by mid week with the ECMWF dropping a closed low
southward through the Great Basin by Wednesday, while the GFS
amplifies a strong off shore Pacific ridge pattern and extends the
trough to the east oriented more north-south. While the EC continues
with this cut off Low feature through the end of the week, the GFS
tries to further strengthen a ridge across the Western U.S. The
extended forecast had more influence from the EC due to the
performance as of late being more consistent run to run while the
GFS has flip flopped more often than not. This being said, the most
current run of the ECMWF does have a more different solution than
the previous version, so some changes are being introduced at the


.AVIATION...MVFR ceilings will continue to persist at KSLC
through the early morning, before slowly scattering out during the
mid to late morning hours. Southeasterly winds will likely stay in
place before switching to the northwest after 16z. Expecting cigs to
improve above 7000 feet by 19z-20z.


.FIRE WEATHER...A cold front remains stalled across south-central
through northeast Utah this morning as a slow-moving storm system
continues to cross the Great Basin. Valley rain and mountain snow
showers will continue across mainly northern Utah today, while
breezy southwesterly winds will be common across southeast Utah once
again ahead of the cold front. Precipitation will wane overnight
while the cold front pushes through the remainder of the fire

A cool and moist airmass will remain in place through the weekend.
Valley rain and mountain snow will increase again Saturday into
Sunday, across much of the area except far southern and southeast
Utah. A general drying and warming trend looks to be in store for
the first half of the work week.


UT...Winter Weather Advisory until noon MDT today.




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