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Area forecast discussion 
National Weather Service Salt Lake City Utah
449 am MDT Wednesday Sep 17 2014

Synopsis...high pressure aloft over Utah will shift east of the
state later today. Moisture will increase ahead of an eastern
Pacific trough which will settle into the western Great Basin
late in the week.


Short term (through 06z sunday)...high pressure aloft squarely
over Utah this morning will shift east of the state later today.
This shift will allow the moisture pooled across Arizona to shift
north ahead of the advancing eastern Pacific trough currently near
130w. This trough will serve to generate increasing convection as
it settles into the western Great Basin Thursday night/Friday.

Tropical Storm Odile...currently positioned over the northern
Gulf of California...will remain a major player across the Desert
Southwest the next couple of days. The tropical storm...though
expected to weaken...will maintain a fairly well-defined
circulation center through Thursday. The deep easterly flow to the
north of the center will serve to keep the bulk of the tropical
moisture south of Utah as the remnant of the storm moves east into
the southern rockies.

Though the deep tropical moisture is no longer expected to reach
Utah...a significant amount of moisture still remains in place
across Arizona...and is poised to surge north ahead of the eastern
Pacific trough nearing 130w this morning. For today a broad area
of /.60/ to /.80/ inch precipitable water is in place across the entire forecast
area. Will likely see another round of scattered convection
forming across the higher terrain with afternoon thunderstorms
primarily across the southern/central mountains. Will have to keep
an eye on the southern border region late this afternoon and this
evening for the potential for isolated heavy rainfall with a few
of the stronger convective elements. The latest NAM does show a
bit of a southerly component developing late in the day which
could signal higher precipitable waters fueling the slow-moving convection. For
now not planning on a Flash Flood Watch...though can not rule out
some issues in the most flood prone areas through the southern
tier of Utah.

Focus for significant weather will shift into northern Utah as the
eastern Pacific trough settles into the western Great Basin for
late Thursday/Friday. The associated near 700mb baroclinic zone
will reach northwest Utah Thursday afternoon where it will meet up
with moisture working north through western Utah. A situation
could develop where strong convection will form along this
baroclinic zone late Thursday. Good surface heating across western
Utah will enhance low-level instability at the same time cooling
aloft increases with the approaching middle-level trough. A brief
period of enhanced jet-induced upper divergence could form across
northwest Utah late Thursday afternoon/evening. The combination of
these elements along with the likelihood of shortwave energy
ejecting northeast ahead of the main trough could produce strong
thunderstorms across west-central and northern Utah through
Thursday evening.

The splitting of the trough over the western Great Basin Friday
will likely Stem any eastward advance of precipitation through the state
and lead to a gradual weaken of the precipitation that does develop
across northern/central Utah. Will maintain an area of light to
moderate rain in the moist southwest flow ahead of the splitting
trough through Friday morning. Precipitation may briefly focus along the
northern portion of the split trough as it cross the region late
Friday. Otherwise lingering convection should wind down Friday

The closed low that forms out of the southern end of the split
trough over southern/central California will become the feature
to focus on late in the weekend. For Saturday the diffluent
southerly flow in the northeast flank of the upper low could
support some convection Saturday afternoon/evening. Not looking
for significant activity at this time as the low remains too far
removed from even southwest Utah.


Long term (after 06z sunday) models continue to reflect
similar thinking of the closed low over socal/Nevada at the
beginning of this forecast period...and its evolution thereafter
through early next week. Namely it will slowly churn northeast
through the area Sunday through Monday tapping moisture from the
southeast as it does so. Model to model and run to run consistency
allowed for a further increase to probability of precipitation across the state Sunday
through Monday as trajectories ahead of the closed low support a net
moistening trend with precipitable waters approaching 1 inch most areas. Combining
this with dynamic lift associated with the pre trough environment
and actual upper low passage...scattered showers and storms now look
likely. A drying near westerly flow will allow for this convection
to taper west to east Tuesday owing to a cool but dry transition
thereafter into the midweek period.


Aviation...operational weather concerns will remain minimal at the
kslc terminal through the valid taf period. Southeast surface are
expected to switch to the northwest between 19-20z and VFR
conditions will hold under mostly clear skies.


Fire weather...high pressure overhead will continue to yield light
winds and very warm temperatures today. Tropical moisture currently over
Arizona will attempt to move into the far south late today and
combined with maximum heating will allow for increased buildups and
scattered storms...especially over the mountains. An approaching
trough will pull this moisture north tomorrow allowing for more
widespread shower and storm potential Thursday afternoon through
Friday...focusing across northern and central portions of the
district. A drying trend will start the weekend but a low pressure
system will increase wetting rain potential again Sunday and Monday.


Slc watches/warnings/advisories...



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