Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 222124

Area Forecast Discussion
National Weather Service Salt Lake City UT
324 PM MDT Sun Oct 22 2017

.SYNOPSIS...A weak cold front will move through the area tonight,
curbing the warming trend for tomorrow before high pressure
rebuilds through the middle of the week. A storm system will
move through Utah and southwest Wyoming Thursday before high
pressure returns for the upcoming weekend.


.SHORT TERM (Through 00Z Thursday)...The ridge off the Pacific
coast has flattened in response to a trough moving over the top of
it, leaving Utah and southwest Wyoming under a mild zonal flow
this afternoon. In a warm advection regime, temperatures have
warmed considerably, with maxes running in excess of 10F of what
was observed yesterday, putting them at values up to 5F above
seasonal normals.

The weak Pacific Northwest trough is currently moving through
Idaho and Montana, but the only impact to the forecast area has
been some high and mid level clouds over far northern Utah and
southwest Wyoming. This system is expected to bring a shallow
frontal boundary into the area tonight, which will act to curb the
warming trend for all but southeast Utah tomorrow.

Behind the exiting system, high pressure will quickly rebound
during the day Monday and build through midweek. This will result
in dry conditions and continued warming of the airmass. However,
developing inversions will limit valley warming at least somewhat,
though maxes should still be around or a few degrees above
seasonal normals there.


.LONG TERM (After 00Z Thursday)...Med range models have come into
a little better agreement on the digging short wave for Thu altho
differences remain. The 12z GFS was even farther east with the
system indicating just some airmass cooling and a shift to
northerly winds for our CWA Thu, but little cloudiness and no
precip. The EC remains deeper with the trof and has a better
defined cold front for Thu, but it has trended towards the GFS
backing off considerably from its 00Z run and is not as cold. It
is also indicating much less qpf for Thu than the 00z run.

Given the trends in the guidance, would suspect that the GFS is
going to verify better here, but in deference to the EC, have
kept some slight chance pops in the grids altho have trimmed them
from the prev forecast. Have pops limited to the far nrn CWA Wed
night then across the nrn CWA for Thu. Confidence is still low for
this portion of the forecast in spite of the model trends.

A dry and gradually warming northerly flow is forecast for the
remainder of the long term period with strengthening inversions as
the upstream ridge gradually shifts into the Great Basin and the
flow gets light over UT.


.AVIATION...Winds at the SLC terminal are expected to switch to the
northwest around 22-00Z, though there is a 30 percent chance that
winds simply remain southerly through the afternoon. Ceilings will
start lowering between 23Z and 05Z, with a 50 percent chance that
ceilings drop below 7000 feet.




SHORT TERM...Traphagan
LONG TERM...Wilensky

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