250 
fxus65 kslc 282127 
afdslc 


Area forecast discussion 
National Weather Service Salt Lake City Utah 
327 PM MDT Thursday Aug 28 2008 


Synopsis...a generally dry northwest flow aloft will reside 
across the region through the remainder of the week. A moist and 
unseasonably cool storm system will impact the region during the 
upcoming Holiday weekend. 






&& 


Discussion...skies are clear across the forecast area this 
afternoon and the tranquil conditions will persist through 
tomorrow under a light northwest flow aloft. Temperatures are 
pretty similar to what they were at this time yesterday...but 
should be slightly warmer tomorrow. 


More significant warming is expected Saturday as the flow aloft 
turns to the southwest and increases ahead of a strong trough 
moving onshore along the Pacific northwest coast. The models 
remain in very good agreement that this system will move through 
the state Sunday and Monday. Convection should begin over southern 
Utah by Saturday afternoon as monsoonal moisture gets pushed up 
ahead of the trough before becoming more widespread on Sunday. 
Good dynamics combined by forecast precipitable waters  over one inch across the 
forecast area is expected to result in areas of heavy rain. See 
the hydrology section for more details. 


In addition to moisture...the trough will be accompanied by a 
very strong cold front that models currently predict will drop 700 
mb temperatures over northern Utah from around +14c on Saturday to 
between 0 and +4c by Sunday night/Monday morning. This would 
result in temperatures around 10f below climatology over southern Utah 
and up to 20f below climatology over northern Utah on Monday. Snow 
levels could drop as low as 8000 feet with the front...resulting in 
the first snow of the season for the mountains. Excellent model 
run-to-run consistency and relatively low ensemble spread are 
resulting in higher than usual forecaster confidence in the 
evolution of this system. 


The trough is expected to exit the forecast area by Tuesday 
afternoon...allowing for subsidence to develop rapidly behind it. 
Even with northwest flow...temperatures should be fairly quick to 
recover as conditions remain dry. 


&& 


Hydrology...monsoonal moisture is expected to get drawn into the 
state beginning Saturday ahead of an approaching strong Pacific 
trough that should move across the state Sunday and Monday. Precipitable waters  
over an inch could be common across the forecast area by Sunday 
afternoon...and with good dynamics in place...areas of heavy rain 
are expected. Thus...flash flooding is a concern over the 
weekend. Areas of greatest concern are the flood prone areas of 
southern Utah...where precipitation is expected to begin 
first...and recent burn scars over northern Utah. 


&& 


Aviation...northwest winds at kslc terminal will continue into this 
evening with winds shifting to the southeast between 03-04z. VFR 
conditions expected through Friday. 


&& 


Fire weather...high pressure aloft centered along the Utah/Arizona 
border will maintain and dry/stable airmass over the fire districts 
through Friday. This high will also serve to keep the deep-layer 
moisture pinned south of the state until weekend. 


A cold/energetic Pacific trough will hit the Pacific northwest coast 
Saturday...then settle into the western Great Basin late Sunday. The 
deep-layer moisture over Arizona will be drawn rapidly north ahead 
of the trough...and will be in place when the main portion of the 
storm arrives in Utah early in the week. Much colder temperatures 
are expected statewide...with widespread precipitation for the northern 
half of the state. 


&& 


Slc watches/warnings/advisories... 
Utah...none. 
Wyoming...none. 


&& 


$$ 


Public...traphagan 
fire weather...Conger 
aviation...Myrick 


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