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Area forecast discussion 
National Weather Service Salt Lake City Utah
442 am MDT Tuesday may 5 2015

Synopsis...a low pressure system over northern Arizona will move
east into the southern and central rockies later today. A cold
Pacific weather disturbance will move south out of the Pacific
northwest and impact much of the Great Basin Friday and through
the weekend.


Short term (through 06z saturday)...the upper low just to the
south of The Four Corners region early this morning will continue
east-northeast and gradually weaken over Colorado today. The
rather moist air mass already in place working in concert with the
synoptic-scale lift generated by the upper low will produce a
broad area of light to moderate precipitation north and west of the low
center over southern and central Utah today. Across northern and
western a similar scenario exists from yesterday where good early
heating will destabilized the air mass leading to scattered
convection again by this afternoon. This convection may develop
rather quickly early this afternoon as the various model guidance
suggest a weak shortwave may trial the exiting upper
some organization to the convection during the afternoon. A
shortwave ridge moving into Utah this evening should bring an end
to all but a few light showers during the overnight hours.

The cold core upper low moving into the Pacific northwest from
the eastern Gulf of Alaska tonight will track due south and reform
a closed low over central California on Thursday. Ahead of this
upper low an increasingly dry southerly flow will develop across
the western portion of Utah and eastern Nevada. This entrained dry
air will either significantly reduce or eliminate most of the
convection by Wednesday night/Thursday.

The central California upper low will take a turn to the east
beginning Thursday evening. Both the latest versions of the GFS
and European model (ecmwf) show this turn...with the European model (ecmwf) taking the center of the
low into southwest Utah Friday while the GFS remains further south
over central Arizona. Both solutions would indicate a significant
and widespread precipitation event for Utah heading into the weekend...
with the European model (ecmwf) placing heavier precipitation a bit further north than
the GFS. Inclined at this point to follow the European model (ecmwf) more closely
on the track of the low...though the difference between the two
models is not all that significant. Precipitation should expand in both
intensity and areal coverage late Friday...and remain widespread
with areas of heavier precipitation beyond the short term forecast period.

Long term (after 06z saturday)...the upper level trough will be
crossing the southern Great Basin to start the long term forecast
period. The main part of the trough will eject into the southern
rockies later Saturday into Sunday...with the back edge of the
trough expected to slowly move across the state through Sunday

Expect convection to be ongoing at the start of the forecast period
after a fairly active day Friday. With the main portion of the
trough crossing the state overnight Friday into Saturday...held on
to fairly robust probability of precipitation through the overnight period. Though the best
jet dynamics will remain east of the County Warning Area Saturday
afternoon/evening...expect another round of convection for much of
the state.

As to the evolution of the pattern after the main portion of the
trough ejects into the southern rockies...significant differences
exist between the 00z GFS and 00z ec...with the ec featuring a
stronger ridge developing across the west. The GFS has several
additional developing/strengthening shortwaves across the west.
Leaned heavily toward the more logical ec solution...though kept
probability of precipitation a bit above climatology Sunday through Tuesday given the lack of run
to run and model to model consistency and the lack of model skill in
the evolution of such patterns.


Aviation...southerly winds will continue at the slc terminal this
morning before switching to the northwest between 18-20z. Another
day of unsettled weather will bring the threat of gusty outflow
winds impacting the terminal between 19-23z.


Slc watches/warnings/advisories...


Short term...Conger
long term/aviation...Kruse

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