Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 272243
Area Forecast Discussion
National Weather Service Salt Lake City UT
443 PM MDT Mon Mar 27 2017
.SYNOPSIS...An upper trough will cross the region tonight through
Tuesday. A second storm is expected late Thursday into Saturday.
.SHORT TERM (Thru 12Z Thursday)...The axis of the elongated upper
trof is centered along the western UT border this afternoon with
widespread precip across much of the CWA. Convection has developed
over the southeastern CWA east of the srn center of the trof
which eventually becomes the primary center as it drops se into
nern AZ by 12z Tue.
The associated surface front has advanced to roughly a Duchesne to
St George line and will shift into the eastern CWA this eve.
Showers will accompany this feature into the east but these are
expected to taper off once the low level flow increases out of the
nw. The precip will persist in areas favored by low level nwly
flow overnight and will taper off on Tue as the upper low moves
away to the east. Also an area of wrap around precip will persist
to the west of the weakening nrn center as it shifts into swrn WY
Snow levels have lowered to around 6000 ft or so behind the front
but any impacts so far appear to be limited to areas above 8000
ft. This will change tonight as the airmass continues to cool and
snow levels lower to near the valley floors. Any impact tonight
however should still be mostly limited to areas around 6000 ft
and higher, but this will involve the passes along I-15 as well as
the Wasatch Back and swrn WY. Current Winter Weather Advisory is
on track and have expanded it into these other areas for tonight
into Tue morning.
Gusty northerly winds have developed over nwrn UT and these are
forecast to spread across the entire CWA overnight. Winds over the
west deserts should stay sub advisory. The downslope areas in ern
UT could see isolated advisory level gusts in the most favored
locations but with the upper low digging south, there appears to
be limited upper support as winds aloft veer to a little nely
overnight. The gap areas of Washington Co look to get the
strongest winds tonight into tomorrow morning and have issued an
advisory for this area.
Precip will taper off on Tue with it lasting the longest over the
nern CWA. Expect a break in the weather on Wed with temps warming
back up as short wave ridging advances into UT.
.LONG TERM (After 12Z Thursday)...The GFS has now moved towards the
EC solution of the storm system tracking farther west and south for
Thursday into Friday. This will bring the precipitation into
Northern Utah slower by about 6 hrs and will also direct the coldest
air aloft to head towards southwest Utah. The EC is a little farther
east with the 700 mb baroclinic zone across central Utah then heads
back northwest across the SL valley towards NW UT at 06Z Friday.
Meanwhile the GFS has the 700 mb baroclinic zone over southwest Utah
stretching back northwest into NE NV. this difference is significant
in that the EC has easterly flow aloft at 700mb developing between
06-12Z which would be warm advection over the cooler northwest
surface component which could lead to a period of heavy rain for the
Wasatch Front and Mountains. The GFS places this heavier warm
advection band farther west over Dugway proving ground. Have leaned
towards a blend of the two with a slight edge to the EC for now as
the run-to-run consistency of the models has been very poor. The
evolution of this closed low forming over the southern portion of
Utah has yet to be resolved and as a result will keep confidence low.
With the warm advection pattern across the north the valleys will
escape seeing any snow while farther south over southwest Utah the
700 mb temperatures will be cold enough for snow from about midnight
Thursday night through midday Friday above elevations of 4500 ft.
The GFS is much slower than the EC in having the closed low exit the
region and hangs moisture back across the eastern two-thirds of the
CWA through Saturday evening while the EC is faster with drying
developing by midday Saturday. Since the GFS had the drier solution
in the first place and has wobble the most have leaned toward the
drier solution of the EC.
The operations run of the EC continues to show another shortwave
moving across the CWA Sunday afternoon while the EC ensemble shows
very little reflection of this feature. Since the EC ensemble is
more in line with most members of the GFS have gone with the dry
forecast for Sunday and Sunday night but hedged towards climo for
Monday as uncertainty increases.
.AVIATION...Light and variable winds at the SLC terminal will become
northerly by 23-00Z. MVFR conditions are expected to prevail through
02Z with a 40 percent chance of lingering through 04-06Z. Cigs will
likely increase to VFR levels from 06-09Z but then have MVFR
conditions between 09 and 13Z. There is a 30 percent chance that
the MVFR conditions will not occur between 09-13Z.
UT...Winter Weather Advisory until 10 AM MDT Tuesday for UTZ006>010-
Winter Weather Advisory until 4 AM MDT Tuesday for UTZ518.
Wind Advisory from midnight tonight to noon MDT Tuesday for
WY...Winter Weather Advisory until 10 AM MDT Tuesday for WYZ021.
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