Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 281449
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
849 AM MDT Wed Sep 28 2016

.SYNOPSIS...High pressure stretching north into the northern
Rockies region will weaken today, aided by northeastward
translation of shearing wave currently over SoCal. Moisture
associated with this feature will spread into far southern Utah
this morning, then will reach northern Utah by later this evening
This moisture will in large remain in place through late week. A
stronger trough will impact the region this weekend into early
next week.

&&

.DISCUSSION...
Water Vapor loop shows ridging over the Rockies, while a closed
low was spinning over southern California. MDCARS winds
observations show a 90KT-130KT southwesterly jet across western
Canada. GOES/HRRR/12Z KSLC ROAB indicate precipitable water
values range from 0.15"-0.30" mountains to 0.60"-0.90" southern
valleys.

SREF indicates dry stable conditions across the north while
increasing mid level moisture is expected to destabilize the south
by afternoon. With the aforementioned closed low circulating
moisture northward expecting scattered showers and thunderstorms
by afternoon across the south.

Dewpoints are in the upper 40s with dry low levels in the BUFKIT
forecast soundings and relatively thin warm cloud layer, so even
with training of deeper convection flash flood risk should be low
but worth monitoring this afternoon and evening.

During the evening could see gusty winds emanating from the
southern Utah precipitation northward given the dry conditions
across Central Utah.

&&

.PREVIOUS DISCUSSION...
Early morning water vapor and H5 analysis indicate mean ridging
from northern Utah north into the northern Rockies region, with a
weakening closed low over SoCal. This low is in the initial stages
of shearing within an increasing southwesterly flow aloft
stretching north from there into the PacNW. Modest moisture
currently being infused into this low is ever so gradually
advecting north into extreme southern Utah at this time, and
moving forward will continue to spread north across the area over
the next 24 hours as this low further shears with remnants
tracking northeast through the area.

Bufr soundings portray rather benign vertical profiles over the
next 24 plus hours as this moisture advects north, with sub par
lapse rates and limited buoyancy potential. This said,
combination of above average moisture and weak forcing should
still aid isolated to widely scattered convection largely south of
I-70 this afternoon, and all areas into the overnight hours on
through tomorrow. Not much change to note relating to this feature
as previous forecasts handle this well.

The aforementioned southwesterly flow aloft will continue to
increase late week as the pacific trough driving it amplifies over
the Pacnw region. Globals continue to depict a short wave rounding
the base of the trough Saturday will then begin to eject inland
during the day, though details in timing and track of this feature
remain fairly limited between various solutions. Do expect this
short wave to at least graze far northern Utah as it lifts
northeast bringing an increased threat of precip over the north,
and initial stages of cooling trend heading into the long term
periods.

Medium range period begins with an upper level trough moving into
the western U.S. Both the GFS and the ECMWF indicate that a
leading wave will eject up the east side of the trough axis
Saturday night or Sunday, but differ on the timing and strength of
this feature. Both the ECMWF and the GFS indicate that Sunday
could potentially be a windy day ahead of a cold front poised west
of Utah. Both models swing the strong cold front through the state
Sunday Night and Monday bringing considerably cooler air back to
the area. After this point in time the models begin to diverge.

Both the ECMWF and GEFS ensembles indicate a good deal of
uncertainty with both the the depth of the trough and the how
quickly it moves east of the area. The ECMWF, CMC, and UKMET
ensemble means are all slower and deeper than the GEFS mean and
have trended forecast toward this solution. In all Monday through
Wednesday this will be an unsettled period especially across
northern and, perhaps, central Utah. At this time the system does
not look like it is likely to be a prolific producer although some
mountain snowfall can be expected in northern Utah. Temperatures
will be well below normal through the period.

&&

.AVIATION...
Southeast winds this morning are expected to become northwest
between 18-20Z. There is a 10 percent chance that the switch to
northwest winds will be delayed until after 20Z.

&&

.FIRE WEATHER...
Yesterday`s ERC values were below the 50th percentile across the
state.

Convection with little rainfall today across southern Utah. Gusty
microburst winds will likely emanate from this this precipitation
northward into central Utah this evening.

Scattered showers and storms will spread northward to include all
of Utah tomorrow and Friday. Profiles look to moisten in the lower
levels across southeast Utah, where wetting rain chances are
maximized.

Significant storm system develops along the west coast this
weekend, expecting to see an increase in southwest winds and
lowering RH values.

The storm system crosses Utah early next week, bringing a cooling
and moistening trend with a good shot of wetting rain/high
elevation snow across northern and portions of central Utah.

&&

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

$$

PUBLIC...Rogowski/Merrill/Graham
AVIATION...Kruse
FIRE WEATHER...Rogowski

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php


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