Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 282115

Area Forecast Discussion
National Weather Service Salt Lake City UT
315 PM MDT Sun May 28 2017

.SYNOPSIS...High pressure will slowly build across the region
through the remainder of the holiday weekend, resulting in a
warming trend extending into the middle of the week.


.SHORT TERM (Through 00Z Wednesday)...Just a few flat looking cumulus
clouds forming over the higher terrain of Utah this afternoon but
with a few more hours of heating there is a slight chance that these
cumulus could become somewhat more developed and produce a shower or
even a thunderstorm. The GFS shows some negative Lifted Indices over
the spine of the central and southern Utah mountains as well as the
Uinta Mountains into early evening. Most local models are
forecasting only speckles of reflectivity activity this evening so
not very confident much will occur.

Under clear skies expecting temperatures to cool off to within a few
degrees of last night`s lows.

The ridge builds more overhead Monday resulting in a warmer day with
very light winds. The local models reduce the amount of forecast
reflectivity for Monday afternoon and evening while the SPC guidance
is showing somewhat higher probability of thunderstorms over the
mountains. Have leaned towards the average of the local models
that show very little reflectivity activity for Monday.

By late Tuesday the GFS and EC show some moisture at mid levels
being tapped as a trough moves onto the West Coast. This should add
a little more instability with a greater chance for showers and
thunderstorms, although low levels remain rather dry so if storms do
develop they will be more wind producers than rain makers,
especially for the valleys. Temperatures will be nearing 5-10
degrees above normal by Tuesday.

.LONG TERM (After 00Z Wednesday)...High pressure remains over Utah
and southwest Wyoming Tuesday night into Wednesday. Southerly flow
increases through Wednesday ahead of an approaching Pacific
trough, which should help to draw up some additional mid-level
moisture and increase the coverage of showers/thunderstorms a bit.
That said, low levels look to remain fairly dry, so Wednesday
will probably be another day where any storms that manage to drift
into valleys will be more likely to produce gusty winds than
decent rainfall.

Wednesday could also be the warmest day of the week for some
locations, particularly across northern Utah; this includes a
chance for the first 90 degree day in Salt Lake City. For now,
have kept the forecast just below that threshold, with some
concern that increasing mid and high level cloud cover through the
day could trim off a couple degrees.

The trough slides across the Great Basin on Thursday, though there
is still some uncertainty about the strength of the system as it
traverses the region. The most likely scenario is still that the
trough splits as it moves through Nevada, with the bulk of the
trough and cooler low level air remaining north of the Utah/Idaho
border. However, the GFS continues to promote a more consolidated
solution than the ECMWF/Canadian, with decent low level cold
advection for Utah late Thursday and cooler air lingering into
Friday. For now, have kept the forecast toward the warmer
EC/Canadian solution, but have maintained some slight chance POPs
across most of the area, as the additional moisture from Wednesday
could still help produce convection, even without well-organized
synoptic forcing. These POPs are trimmed farther north on Friday
as a drier airmass potentially works back in, and may eventually
be taken out of the valleys completely if the more stable ECMWF
comes to pass.

Heading into the weekend, Saturday currently looks to be warm and
dry across the forecast area, but models start to diverge sharply
Saturday night into Sunday, as they try to figure out what to do
with various troughs and cut-off lows trying to move inland from
the Pacific.


.HYDROLOGY...The ridge building over the area will bring with it
temperatures 10-15 degrees above normal which will increase the
snow melt across the high elevations. Rivers across northern Utah
will run fast and cold this week. Several rivers will approach or
go above bankfull by midweek, specifically the headwaters of the Weber
and Provo. Meanwhile, the Logan River is projected to go above
flood stage by Tuesday. See the latest Flood Watch statement
concerning the Logan River.


.AVIATION...VFR conditions continue tonight and tomorrow at the SLC
terminal. Light northwest winds will switch to southeast between 03Z
and 05Z this evening.


.FIRE WEATHER...Very warm and mainly dry conditions will prevail
over the next few days with only a slight chance of afternoon
thunderstorms over the higher terrain. The minimum relative
humidities in the valleys will lower into the teens and single
digits helping to accelerate fuel drying. Winds will not be of any
consequence unless a nearby high based shower or thunderstorm causes
a local outflow gust during the late afternoon or evening.

A weak trough moves onto the West Coast by late Tuesday which looks
to tap a little additional moisture for a better chance of showers
and thunderstorms. However, low levels are still expected to remain
rather dry so any showers or thunderstorms could be more high based
and produce more wind then rain Wednesday into Thursday. Rain
amounts are not expected to be more than a few one hundredths.
Temperatures will run 5-15 degrees above normal through Saturday.


UT...Flood Watch from Tuesday morning through Saturday evening for



LONG TERM...Schoening
AVIATION...Van Cleave

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