Scientific Forecaster Discussion
fxus65 kslc 221037
Area forecast discussion
National Weather Service Salt Lake City Utah
337 am MST sun Jan 22 2017
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 wednesday)...
water vapor satellite shows a cold closed low along the Pacific
northwest coast. Meanwhile a shortwave ridge is over Utah.
400-200mb mdcars wind observations place a 150-175kt
anticyclonic jet from California into southwest Utah and Arizona.
GOES/slc 00z radiosonde observation/hrrr indicate that precipitable water values
vary from 0.05"-0.15" mountains to 0.20"-0.35" valleys. Blended
precipitable water products shows an atmospheric river from near
Hawaii into the southwest Continental U.S..
Jet buckles to our west today and tonight shifting the ridge to
our east. This next storm system has a nice atmospheric river,
thus expecting precipitation to continue to expand in the warm
advective flow. Southwest winds will be gusty as wind field
continues to accelerate with the buckling jet arriving. 700mb
winds in excess of 50 kts, building southeasterly pressure
gradient and pressure falls will support gusty winds across the
western valleys and southwest Wyoming.
Precipitation will begin as snow everywhere except Dixie today.
Then snow levels rise to between 5000-5500 feet in response to
the approach of the the storm system tonight into early tomorrow
morning. This will change precipitation to either a rain snow mix
or snow across many valleys. This is expected to lower snow
totals from south of Ogden through the Salt Lake valleys.
Across Dixie, am concerned about a heavy rain threat this
afternoon and tonight, coincident with the arrival of the exit
region of the strong jet and atmospheric river, enhancing
integrated vapor transport. BUFKIT forecast soundings though show
little to no warm cloud layer. Decided to make a mention of heavy
rain in the forecast but held off on a Flash Flood Watch. There is
also an outside shot of lightning near Dixie Monday afternoon per
calibrated thunder output from the sref. Probabilities were not
high enough to include mention in the forecast at this time.
Cold front quickly crosses Utah Monday. Strong height falls
followed by the arrival of the cold pool aloft Monday night along
with continued cold advection and northwesterly upslope flow
should bring another round of decent quantitative precipitation forecast to the region.
A cyclonic unstable flow remains Tuesday. Models bring a remnant
closed circulation into northern Utah. This may enhance snow
chances again after falling off later Monday night.
This is the kind of slow churning multifaceted event that tend to
get folks a bit too excited going into it. The mountains do look
like they will see another 1-2 feet of snowfall. And east-
southeast upslope should enhance snowfall across the western Uinta
Basin and Castle country, similarly affecting south central Utah
as well. The Wasatch back also is looking good for significant
snowfall thanks to the higher elevation. But many valleys will
struggle at times to maintain consistent winter driving conditions
as features of this storm translate overhead. Also affecting snow
totals is a period of rainfall tonight and tomorrow morning.
Long term (after 00z wednesday)...
some showers are expected to continue, primarily over the higher
terrain of northern and central Utah, Tuesday night into Wednesday
morning in lingering cold pool instability from the trough. Ec/GFS
show the back end of the trough scooting across the forecast area
Wednesday afternoon/evening, with coverage of showers diminishing
as it does so. The airmass will be quite cold in the wake of this
trough, with 700mb temps in the -14c to -17c range.
Global models show one last weak wave digging into the Great Basin
Thursday before sliding south into Arizona on Friday. With
unimpressive instability and little in the way of moisture to work
with, additional precip should be limited and have left only some
token pops in.
The forecast area finds itself under a dry and stable northerly flow
beginning Friday night on the front end of a ridge centered over
California. The airmass is progged to warm significantly as the
ridge builds over the weekend, but these temperatures will not be
realized in the valleys as inversion conditions redevelop and
continue past day seven.
VFR conditions are expected at the slc terminal through the
morning. Conditions are then expected to deteriorate to MVFR or
IFR between 20z and 22z with snow or a mix of rain and snow
developing at the terminal. Southerly winds are expected to
continue through the daytime hours, becoming gusty by this
Utah...Winter Storm Warning from 10 am this morning to 10 PM MST Monday
Winter Storm Warning from 10 am this morning to 4 am MST Tuesday
Winter Weather Advisory from 10 am this morning to 10 PM MST
Monday for utz001-002-004-005-011-016.
Wyoming...Winter Weather Advisory from 10 am this morning to 10 PM MST
Monday for wyz021.
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