Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 211215
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
515 AM MST Tue Feb 21 2017

.SYNOPSIS...A mild and strong southwest flow will prevail today.
A cold front tonight will usher in a period of cold unsettled
weather lasting through the end of the week.

&&

.SHORT TERM (Thru 12z Friday)...A broad upper trof continues in
the ern Pac early this morning with a strong and mild swly flow on
the downstream side over the Great Basin.

South winds have increased across our CWA overnight and expect
them to remain solidly in advisory criteria thru the aftn across
the wrn valleys with stronger gusts in the most favored locations.
Current Wind Advisory will remain in effect.

Moisture has shifted north of the CWA overnight but expect it to
increase this aftn as the ern Pac trof edges inland and a frontal
boundary enters the nwrn CWA. Models indicate an organized band of
precip develops along the cold front as it moves south across nrn
UT tonight. Snow levels will lower to the valley floors north of
about SLC overnight but do not expect much accumulation. Snow will
impact mtn passes overnight into Wed from Parleys Summit north
and the existing Winter Weather Advisory will also remain in
effect.

The front stalls on Wed waiting for the main upper trof axis to
move into the Great Basin and precip will taper off for a time.
The upper trof approaches Wed aftn with the increasing dynamics
tightening up the cold front and making precip more widespread
again late Wed into Wed night.

The main focus should be across central portions of the CWA but
most of the I-15 corridor will be involved. Snow levels drop to
the valleys swd thru central UT with accumulation becoming likely
Wed night into Thu morning, and heavy amounts possible in the
mtns.

A cold unstable northwest flow sets up on Thu and lasts into Thu
night. This will bring additional accumulation to the nrn and
central mtns along with snow showers bringing local accumulation
in the western valleys.

.LONG TERM (After 12z Friday)...Subtle short wave ridging will
build north across the area Friday within the mean long wave
trough across the western CONUS, this as a trailing short wave
trough amplifies off coastal Cali. As such, anticipating a
relative break from the active period beneath rising heights and
subtle subsidence across the eastern Great Basin into Saturday.
Have lowered PoPs locally through the period.

Focus turns to the upstream trough amplifying and eventually
closing off along the coast (per Globals) heading into Saturday,
and the net evolution of inland progression thereafter. GFS/EC
continue to maintain model to model differences in detail
regarding sensible weather locally, with the GFS roughly 12 hours
faster bringing in another round of precip across the area by 18z
Sunday due to more progressive inland penetration.

What is known is that the trough`s amplification off the west
coast will support continued WAA locally, and onset of precip
will predominantly retain valley rain and mountain snow,
regardless of timing differences. Have hedged slightly towards the
faster GFS as moisture typically advects in sooner than
anticipated in similar large scale patterns, especially with
modest flow at the mid/upper levels. Hedged to bump up PoPs
roughly 10 percent as such.

Decent model to model agreement exists in globals thereafter
depicting a net inland track of the closed low southeast of the
area. Although not a direct hit...upper diffluence and continued
modest moisture advection/convergence to the NW looks likely to
produce fairly widespread precip across the area through Monday.
H7 temps look to continue to support valley rain/mountain snow
(above 6kft) through the bulk of the period, though mid level axis
passage will bring enough CAA to support snow down to valley
floors overnight Monday into Tuesday with any lingering precip.
These details will continue to fall out with subsequent model
runs, and more confidence in detail.

&&

.AVIATION...Gusty southerly winds will remain the primary
operational weather concern at the KSLC terminal through the valid
TAF period. Anticipate gusts into the 30-40 mph range to prevail
well into the afternoon. Rain showers will likely fill in this
evening lowering cigs to or below the 6000ft agl level with
passage of a cold front. Winds with this will switch to a gusty
northwest...most likely between 00-02z this eve.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until 9 PM MST this evening for UTZ003-005-015-016.

     Winter Weather Advisory from 2 PM this afternoon to 11 AM MST
     Wednesday for UTZ007>009.

WY...None.

&&

$$

SHORT TERM...Wilensky
LONG TERM/AVIATION...Merrill

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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