Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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125
FXUS65 KSLC 231310 AAA
AFDSLC

Area Forecast Discussion...UPDATED
National Weather Service Salt Lake City UT
610 AM MST Mon Jan 23 2017

.UPDATE...
Quick update to change weather to convective wording and add
mention of thunder from I-70 southward. Had a strike earlier in
Iron county, and based on upstream radar trends and HRRR simulated
reflectivity, looks like the threat will build through the early
afternoon.

&&

.SYNOPSIS...The active weather pattern will continue across the
region, with a series of weather systems crossing the area through
the first half of the week.

&&

.SHORT TERM (THROUGH 00Z THURSDAY)...
Water Vapor Satellite shows a gradually filling closed low off the
Oregon coast beginning to ease southeast. 400-200mb MDCARS wind
observations place a 160-190kt anticyclonic jet from central
California into northern Utah and southwest Wyoming. GOES/SLC 00Z
RAOB/HRRR indicate that precipitable water values vary from
0.15"-0.25" mountains to 0.40"-0.60" valleys. Blended
Precipitable Water products shows an Atmospheric River from near
Hawaii into the Southwest CONUS.

As the Atmospheric River advances east of the southern California
mountains, radar trends show an uptick in precipitation in and
near southern Utah. This area of precipitation should continue
through the morning before shifting off toward the east. SREF
indicate there may be just enough instability for thunder, but SPC
calibrated thunder probabilities were too low to include in the
forecast at this time.

850-700mb Thickness/Saturated Equivalent Potential
Temperature/Streamlines bring the cold front (currently over
central Nevada) into the Interstate 15 corridor midday, before
continuing through the remainder of the forecast area this
evening. Ahead of this feature, 700mb wind field, pressure falls
and pressure gradient will continue to support gusty winds
particularly across southern Utah. Wind Advisory gusts are
dovetailed into the Winter Weather Advisory for southwest Utah
this morning. Meanwhile south central Utah, along with the San
Rafael Swell, and Lake Powell area look to near wind advisory
criteria with infrequent gusts 45 mph gusts.

Strong height falls followed by the arrival of the cold pool
aloft this afternoon into tonight along with continued 700mb cold
advection and northwesterly upslope flow should bring another
round of decent QPF to the region.

A cyclonic unstable airmass will remain in place late tonight
through tomorrow. Models continue to have a difficult time
resolving weak shortwaves as they pivot back south on the approach of
the upper level trough axis. Bumped up PoPs and QPF across the
north during this time period. Later shifts may need to extend
some of the northern headlines to account for this portion of the
system should the models come into line. Its worth noting given
the cold airmass (-15C at 700mb and -30C at 500mb), need much less
QPF to fluff up snow totals given a high snow ratio.

Another wave will reinforce the cyclonic unstable and cold
airmass Wednesday, though it looks to pass to our northeast.

.LONG TERM (AFTER 00Z THURSDAY)...
A few snow showers are expected to hang around over the higher
terrain of northern Utah Wednesday night/Thursday morning with
lingering moisture and shortwave instability on the back side of
the exiting trough. Otherwise, looking at a rather cold airmass
over the forecast area during this time with 700 mb temps progged
to be in the -15C to -17C range.

EC/GFS indicate one last trough rotating into the Great Basin during
the day Thursday before continuing south into SoCal and Arizona
Friday into Saturday. This will allow for increasing covering of
precip on Thursday, primarily over northern and central Utah.
However, the system is relatively weak and instability is not overly
impressive, so expect coverage to be on the low side.

As the system continues out of the area by Friday, a drier and more
stable northerly flow is progged to rapidly develop over the
forecast area on the front side of a strong ridge along the
California coast. The airmass should warm rapidly over the upcoming
weekend as this ridge builds, with global models showing 700 mb
temps as high as 0C by Sunday afternoon. However, with valley
inversions developing, many locations will remain on the cold side
through day seven.


&&

.AVIATION...
A few snow showers are expected to hang around over the higher
terrain of northern Utah Wednesday night/Thursday morning with
lingering moisture and shortwave instability on the back side of
the exiting trough. Otherwise, looking at a rather cold airmass
over the forecast area during this time with 700 mb temps progged
to be in the -15C to -17C range.

EC/GFS indicate one last trough rotating into the Great Basin during
the day Thursday before continuing south into SoCal and Arizona
Friday into Saturday. This will allow for increasing covering of
precip on Thursday, primarily over northern and central Utah.
However, the system is relatively weak and instability is not overly
&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Warning until 10 PM MST this evening for UTZ006-012-
     020.

     Winter Storm Warning until 4 AM MST Tuesday for UTZ007>010-517-
     518.

     Winter Weather Advisory until 10 PM MST this evening for UTZ001-
     002-004-005-011-016.

WY...Winter Weather Advisory until 10 PM MST this evening for WYZ021.

&&

$$

SHORT TERM...Rogowski
LONG TERM/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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