Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
343 PM MST sun Jan 25 2015
Synopsis...strong high pressure will build into the western
states through tomorrow. The next storm system approaching from
the southwest will impact the area Monday night through Wednesday.
Short term (through 00z thursday)...a high amplitude ridge has
shifted over the Great Basin this afternoon...leading to much
warmer than typical temperatures and sunny skies across most of
Utah and southwest Wyoming. Only areas right along the Utah/Idaho
border are still experiencing dense stratus as of 22z...with some
passing clouds moving through portions of eastern Utah. Tonight
will likely be cooler than last night across much of the
north...as there should be much less cloud cover...but sunny skies
and a warm airmass will likely allow mondays daytime temperatures
to climb in a somewhat similar fashion to today. In other
words...another unseasonably warm day across much of the area
After the ridge shifts over Colorado through Monday afternoon...a
Pacific low brings tropical moisture into the Great Basin from the
south on Monday night. The best forcing with this initial wave
will primarily move through Southern California and Nevada...but
southwestern Utah still has a high chance of seeing at least some
precipitation on Monday night and Tuesday morning. Showers begin
to migrate into northern Nevada and northern Utah through the day
Tuesday...but could be hit-or-miss across Utah if the models trend
any further westward with this wave.
The low opens up considerably as it moves through Nevada...then
slides through northern Utah as a fairly weak shortwave on Tuesday
night and Wednesday. However...with a moist airmass in
place...early Wednesday could be the most productive period of
precipitation across the northern third of the County Warning Area. By this
time...snow levels are expected to drop to about 6000 feet...and
this period Wednesday morning would probably be the best chance
for steady moderate snowfall in the higher terrain. Precipitation will
likely begin tapering off Wednesday afternoon as the trough axis
progresses to the Utah/Colorado border.
Long term (after 00z thu)...it appears precipitation shuts down fairly
quickly Wednesday night in the wake of the departing short wave trough and
weak short wave ridging moves overhead.
The next weak low ejecting out of the eastern Pacific brings another round
of tropical moisture into the western states and differences in the
models on the placement of the low create disagreement on the northward
extent of the precipitation forecast to accompany this feature. The 12z ec
moved farther north with the circulation center by 12z Friday and
spreads precipitation across much of the County Warning Area that retreats slowly south
through Sat night as the low sinks S. The GFS remains farther south
initially and keeps precipitation out of the far north...then shifts it southward
Both models do end up with the low far enough south for the threat
of precipitation to end across the County Warning Area by 00z Monday with dry and warmer
conditions forecast for the first part of next week.
Expect these subtle differences will not be resolved until we get a
few days closer to this time frame so have kept probability of precipitation on the low side
and hedged the difference between the two solutions through sun. If the
ec is right there might be fairly significant water amounts across
the County Warning Area from this event.
The other element in the forecast would be the potential for a
locally strong downslope east wind event along the Wasatch front Sat
morning. Magnitude depending on how far south the closed low is by
12z Sat with the farther north ec depicting the stronger event.
Aviation...north to northwest winds will continue at the slc
terminal...shifting to the southeast between 02-04z.
Otherwise...occasional reduced visibilities in haze will be possible
through the evening.
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)