Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Salt Lake City Utah
315 am MDT Sat Apr 19 2014

Synopsis...a weak system will remain across the region through
the weekend. A stronger storm will impact the area during the
middle of next week.


Short term (through 12z tuesday)...
water vapor loop shows a closed low nearing western Arizona. A
ridge is located over the Pacific northwest with the next storm
system approaching the coast. Amdar 400-250mb wind observations
reveal a 85- 115kt cyclonically curved jet over the northern
rockies. GOES/GPS/rap/00z radiosonde observation indicate the precipitable water
value ranges between 0.25" and 0.65".

Deformation zone associated with the Arizona system will present the
best opportunity for convection east of Interstate 15 today. Morning
showers across southeast Utah are forecast to expand due to daytime
instability this afternoon.

Meanwhile second area of convection likely to occur in the higher
terrain along the Nevada border late this afternoon considering
ridging aloft building into place with significant remnant
moisture in place. High resolution local WRF guidance indicates
that this convection makes it east across northern Utah
tonight...which seems plausible ahead of the next cool front.
Greatest probability of precipitation for the wastach front are therefore this evening.

Next northern rockies wave Saturday night will prompt a shallow cold
front across northern and into central Utah Sunday. With remnant
moisture in place...kept mention of convection along and ahead of
this feature...with plenty of drying expected across the north.
Downslope winds will likely be somewhat enhanced Sunday afternoon
and night across favored locations of east central and southern

Return flow sets up quickly Monday with a broad significant storm
developing over the eastern Pacific. Guidance remains iffy regarding
convective potential across the north associated with the approach
of the warm front. Kept isolated probability of precipitation for the northern terrain.

Otherwise warm south winds develop Monday afternoon and increase
Monday night. Could see our first 80 degree day at slc Monday.
Raised temperatures above guidance Monday night ahead of a sharp
cold front...which are likely still too cool.


Long term (after 12z tuesday)...
southwest flow over the forecast area is prognosticated to increase
dramatically during the day Tuesday as the next Pacific storm
system approaches with GFS and European model (ecmwf) indicating 700 mb flow in
excess of 50 kts just ahead of the frontal boundary. These
conditions look to come during peak daytime heating...which is
quite favorable for a high wind event over much of the state.

The front is expected to go through northern Utah Tuesday evening
and through the rest of the state Tuesday night/Wednesday
morning...resulting in a dramatic cooldown. Models show 700 mb temperatures
dropping from the +7c to +9c range ahead of the boundary to -8c to
-10c behind it. The trough brings good dynamics over northern and
central Utah along and behind the front. However...moisture
appears to be the limiting factor with respect to significant
precipitation. Still...have increased probability of precipitation with increased confidence of
the track and timing of the initial trough.

By Wednesday night...the trough is expected to exit the area and
this is when guidance begins to diverge. GFS is showing a trailing
trough moving through that brings a reinforcing shot of cold air and
some additional precipitation. Meanwhile...the European model (ecmwf) indicates
ridging moving back in during this time. By Friday...high pressure
is in place in all solutions. After that...there are some
indications that unsettled weather will return for next weekend.


Aviation...VFR conditions are expected at the slc terminal
throughout the day with mostly cloudy skies. Light southeast winds
are expected to shift to the northwest between 17z and 19z. There is
a 30 percent chance that showers in the vicinity of the terminal
will result in periods of gusty and/or erratic winds this
afternoon and evening.


Slc watches/warnings/advisories...


Short term...rogowski
long term/aviation...traphagan

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