Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 191051
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
351 AM MST Sun Nov 19 2017

.SYNOPSIS...High pressure aloft will remain over the region
through the balance of the weekend. A weak weather disturbance
will graze northern Utah on Monday, followed by even stronger
high pressure aloft returning midweek.

&&

.SHORT TERM (Through 00Z Thursday)...A broad, low amplitude mid
level ridge extends from the Pacific Coast inland across the Great
Basin early this morning. Meanwhile at the surface, high pressure
remains centered from southeast Idaho across northern Utah and
into western Colorado. This is associated with a low level cold
and stable airmass, which will likely modify slightly today but
otherwise maintain valley inversions across most of northern and
central Utah. Southwest Wyoming as well as the Bear River Valley
failed to warm out of the 20s on Saturday, and although the
airmass will likely modify somewhat, have gone well below guidance
in these areas today, keeping max temps in the low to mid 30s.
Elsewhere warmed the remainder of the valleys across northern and
central Utah 3-5 degrees from what was observed Saturday. A more
substantial warming trend will be realized across the higher
terrain, as well as across far southern Utah.

The models continue to suggest a weak shortwave trough will dig
east of the forecast area Monday, as the mid level ridge amplifies
to the west. Some discrepancies are apparent between the models
with respect to how amplified this trough remains, as well as the
degree of moisture advection across northern Utah. Have generally
leaned toward the EC solution as an amplifying ridge and rising
heights would seem to favor a weaker trough. As such have only
retained chance PoPs across the valleys north of I-80 as well as
the Wasatch and western Uintas.

The upstream ridge is forecast to build eastward during the
midweek period resulting in continued warming aloft. Given cloud
cover is likely Monday night and possibly Tuesday night as well,
this should weaken the valley cold pools, and likely allow for a
more substantial warming trend Tuesday into Wednesday across the
northern and central valleys.

.LONG TERM (After 00Z Thursday)...Global models are in very good
agreement with respect to the large-scale pattern through Thursday,
but then the GFS Ensemble mean has the 500mb heights across the
northern Great Basin lower by 20 meters or so for Thursday night as
a weak trough barely flattens the ridge. The airmass behind this
trough is not as cold as earlier forecasts. The forecast from 24 hrs
ago showed 700mb temperatures lowering to near -3C to the Idaho
border. Latest guidance shows the 700mb temps down to +2C degrees on
the GFS and 0C degrees on the EC. This shows that the overall trend
is weaker and weaker with this feature. Did not want to completely
remove PoPs due to the Ensemble mean, so left some chance PoPs in
the extreme northern mountains while lowered or removed them from
about Ogden southward.

The ridge strengthens for the weekend with southwest winds at 700mb
increasing to 20-30 kts according to the EC but increases to 50 kts
over the west central portions of the CWA Saturday morning according
to the new 06Z GFS which shows a spurious shortwave flying by
Saturday morning. Not likely this feature will be there but the
overall idea that southwest winds will increase Saturday has led me
to lean toward the WPC guidance which has temps a few degrees warmer
than the SuperBlend. Record at SLC for November 24 is 65F while the
forecast is 63F. If the air mass gets well mixed the potential of
the 700mb temps would support readings in the lower 70s at SLC.
However, with the EC ensemble members showing a weaker trough to the
west of Utah this weekend, didn`t want to lean too heavily on the
operational runs of the GFS and EC. Have kept the temperatures mild
through Sunday as well, but the 700mb temps are not quite as warm so
took a couple of degrees off. Removed PoPs across northern Utah for
Sunday into Monday.

&&

.AVIATION...No operational weather concerns at the SLC terminal.
Light SE winds this morning will shift to NW about 20-21Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Seaman/Struthwolf

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