Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 292148
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
348 PM MDT Thu Sep 29 2016

.SYNOPSIS...A weakening weather disturbance will track north
across Utah through this evening. A cold Pacific storm system
will enter the Pacific Northwest early Saturday, then strengthen
as it settles into the Great Basin by early Monday. This storm
system will impact much of Utah during the early portion of the
upcoming week.

&&

.SHORT TERM (THROUGH 06Z SUNDAY)...
Water Vapor loop shows ridging over the Rockies, while a weakening
closed low lifting into central Nevada. MDCARS winds observations
show a 90KT-115KT southwesterly jet across western Canada.
GOES/HRRR/12Z KSLC ROAB indicate precipitable water values range
from 0.40"-0.55" mountains to 0.80"-1.20" most valleys.

Dewpoints have risen 10-15F during the past 24 hours across
southern and eastern Utah, with values rising through the 50s
currently. This along with precipitable water values indicate the
uptick in moisture across this part of the forecast area. Weak
waves will continue to shear northeast across southeast Utah this
afternoon and evening providing ascent as will the coupled upper
level jet near the four corners late day. SREF instability
parameters indicate plenty of instability. Given all this and a
warm cloud layer of around 5kft, continue to advertise a Flash
Flood Watch.

The shearing aforementioned upper low will continue to support
more tranquil convection into the middle of the night across the
west.

Maintain some form of convection across the southeast forecast
area overnight near the nose of an instability axis. Tomorrow
moisture profiles look to dry a bit. Nevertheless, enough low
level moisture to provide instability to spark another round of
lower convergence convection from the spine of the mountains
eastward during the afternoon and early evening.

Instability is meager on Saturday, though the arrival of the shear
axis of the upper level jet associated with a broad cold storm
system over the Pacific Northwest should be able to provide some
shower activity especially closer to the Idaho border. In
addition, with the storm beginning to approach, expect gusty
southwesterly winds to develop especially across west central and
southwest Utah.

.LONG TERM (AFTER 06Z SUNDAY)...
Upper level trough will approach the Pacific Coast early Sunday.
A vort max and associated jet streak rounding the west side of the
trough will help to dig and deepen the system as it crosses into
the western United States through the day Sunday. This trough is
expected to be fairly strong as it crosses Utah Monday into early
Tuesday. Global models are in fair agreement with this system
lending more confidence into a widespread precipitation event
across northern and possibly central Utah Monday into Tuesday.
Current 700mb temperatures are near -6C behind a relatively strong
cold front by Monday afternoon/evening. This would bring snow
levels as low as 6500 feet or possibly lower for a time Monday
evening into early Tuesday morning. Started lowering snow levels
in response, though not all of the model guidance is quite that
cold. Definitely looking a bit more like fall, though at this
time, significant lower elevation snow accumulations are not
expected.

Following the trough, expect northwest flow to develop across the
western CONUS for much of the remainder of the week.

&&

.AVIATION...
VFR conditions are expected at the SLC terminal through the
evening. Northerly winds are expected to shift to the southeast
between 03Z and 05Z. There is a 30 percent chance that nearby
showers will result in periods of gusty and/or erratic winds
through the early evening.

&&

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

Convection will affect mainly areas east of Interstate 15 today.
With moistening profiles, the threat for heavy rainfall will exist
through this evening. Tomorrow there is the possibility of another
round of convection for the same area, though it looks like it
will be lower in coverage and there wont be as much moisture for
the storms to work with.

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...Flash Flood Watch until 10 PM MDT this evening for UTZ012-013-
     020-021.

WY...None.
&&

$$

SHORT TERM/FIRE WEATHER...ROGOWSKI
LONG TERM...KRUSE
AVIATION...TRAPHAGAN

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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