Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Salt Lake City Utah
418 PM MDT Monday Oct 20 2014

Synopsis...a dry and mild southwesterly flow will give way to a
Pacific cold front on Tuesday. Dry and mild southwest flow will
return for Thursday and Friday.


Short term (thru 00z fri)...southerly flow is over the County Warning Area this
afternoon to the east of an elongated upper trough moving on to the West
Coast. A little tropical moisture is in place and some afternoon
convection has developed over mainly the higher terrain. This
should last into the evening and could persist later tonight
across the north and east as dynamics increase ahead of the West
Coast trough. Only expect light precipitation from this and no thunder.

The Pacific trough lifts northeastward tonight through Tuesday as an upstream trough
forces it to weaken and eject into the northern rockies. The trailing
cold front maintains enough integrity that combined with the
moisture in place to produce an organized band of precipitation for the
northern County Warning Area Tuesday morning extending southward into west central Utah. This band
shifts to northestern to central Utah along the stalling front in the
afternoon and starts to weaken.

The ejecting nature of this trough prevents much cold air from
reaching the County Warning Area and it appears the bulk of the precipitation for northern Utah
occurs before it gets cod enough for any real high elevation snow
accumulation. So impacts look negligible from snowfall.

As the front does not make it through the County Warning Area...lingering moisture
across the south lifts northward Wednesday as the stalled boundary lifts northward
as a weak warm front. Models do not generate any quantitative precipitation forecast from this
however. Increasing southwesterly flow Thursday returns dry and mild weather to the
County Warning Area.


Long term (after 00z friday)...confidence in a late weekend trough
impacting the eastern Great Basin continues to increase. Though
details differ on a variety of levels regarding timing...
amplification...and now per 12z European model (ecmwf) breadth of cold air...Sunday
is expected to be a much cooler and wetter day across much of the
forecast area.

Details...12z European model (ecmwf) a little sharper with the splitting nature of
the trough as it comes on shore Saturday/Saturday night. Though the
southern split continues to take aim on the area Sunday...said run
closes the upper low off over southern Nevada before entering the
state... moderating as it loses connection to coldest air. 700 mb temperatures
only drop to around zero at kslc during peak of cold air advection which is a
modest 5 to 6 degree increase from previous runs and that of the the
last several GFS solutions. Can see this as a potential due to a
decent wavelength to yet another trailing trough near 150w at this time with
ridging between...but chances of it closing off more sharply to our
west slowing progression down further appear minimal due to said
upstream trough. Minimal changes run to run in GFS though
progressive nature appears to be about as fast as it can get. Thus
increased probability of precipitation significantly for the period that falls
between...Sunday...and took a blended approach to other details in
latest forecast expecting these to change over time as model to
model consistency trends more positive. Increased probability of precipitation on both sides
of that period as well...but again...quite blended due to
differences in speed of track. Regardless of these differences an
all dry but cool forecast remains for Monday beneath building


Aviation...the lake breeze is currently stalled on the far northern
end of the kslc terminal after making an earlier surge. Seeing an
additional surge north of the terminal so will maintain latest taf
timing of 2230-23z for a switch to northwest winds. This said...a 40
percent chance exists that winds will remain southerly through

A cold front will move through the terminal between 14-16z Tuesday
bringing gusty northwest winds...light rain and ceilings at or below
6000ft above ground level through midday.


Slc watches/warnings/advisories...


Short term...wilensky
long term/aviation...Merrill

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)

National Weather Service Glossary of Abbreviations