786 
fxus65 kslc 182148 
afdslc 


Area forecast discussion 
National Weather Service Salt Lake City Utah 
348 PM MDT Friday Jul 18 2008 


Synopsis...high pressure will remain over the Great Basin through 
Saturday. This will allow drier air to move into much of the area 
tonight and Saturday. By the end of the weekend the upper high shifts to 
the east allowing deep moisture to return to much Utah through the 
early portion of next week. 






&& 


Discussion...while dry air has moved into western 
Utah over the last 12 hours...lingering moisture in eastern Utah has 
allowed afternoon thunderstorms to form along The Spine of Utah 
and eastward. These storms have been relatively small and 
weak...with the more organized storms producing much more 
lightning in Colorado. High pressure will continue building across 
the area tonight...resulting in mostly clear skies across the 
entire state. Combined with primarily light winds...this will 
likely lead to much cooler minimum temperatures than last night in 
many locations. 


High pressure will continue to strengthen over the area 
tomorrow...making afternoon thunderstorm activity even more 
isolated and terrain based than today. The upper level ridge will 
shift eastward on Saturday night...becoming more amplified and 
centering itself over the Rocky Mountains. This will create 
stronger southwest flow across Utah and southwest 
Wyoming...bringing increased moisture into the area again from the 
south. By Sunday afternoon both the GFS and the NAM bring in 
precipitable water values of about 0.8 to 1.00 inch across the 
entire State of Utah...with the most recent runs bringing the 
moisture up to the Utah-Idaho border even faster than previously 
forecast. Accordingly...have increased probability of precipitation across the northern 
part of the forecast area on on Sunday...with a mention of 
thunderstorms in all locations. 


Confidence in the temperature forecast is low beyond the 
weekend. The European model (ecmwf) keeps temperatures below climatology for most 
of the upcoming work week...likely due to greatly increased cloud 
cover in the model. Meanwhile...the GFS is often as much as six 
degrees celsius warmer at both 700mb temperatures and surface 
temperatures. For now have mostly kept temperatures just below the 
GFS solution...which is much closer to seasonal normals. 


&& 


Aviation...northerly winds will shift to the southeast between 
03-04z tonight. Otherwise...VFR conditions will continue in mostly 
clear skies. 


&& 


Fire weather...short wave disturbance ejecting across far eastern 
Utah and upper high moving across the western Great Basin. Behind 
this first system very low humidity is observed across northwest 
Utah and breezy conditions in the far north with isolated critical 
conditions just south of the Idaho border. Across the eastern and 
southern areas widely scattered thunderstorms have developed and 
continue to ride down The East Slope. Drier air and subsidence 
spread east should end convection early this evening. 


Upper ridge will position itself over southeast Utah on Saturday for 
hot and dry conditions...but light terrain driven wind. Light 
southerly flow and lingering moisture will allow for isolated 
thunderstorms over the southern Utah higher terrain. Slightly 
stronger southerly flow on Sunday is forecast to draw deep moisture 
into the southern half of the district and up to the northwest 
deserts and southern Wasatch front by late in the day. The leading 
surge would have high based convection and possible wind gusts for 
the north and widely scattered wetting storms in central and southern 
Utah. Nocturnal thunderstorms also possible Sunday night as a 
potentially very deep moisture surge lifts into northern Utah with 
embedded disturbances lifting north and tracking into Idaho through 
Monday. Models appear to be converging on deep moisture on Monday 
which will linger at least into middle week if not the entire week with 
only slight changes near the Nevada and Idaho borders. This rich 
cooler moist southerly flow/monsoon also depicted on the 12z European model (ecmwf) 
and not uncommon for this time of the year. Scattered wetting rains 
in the south and even widely scattered wetting rain for the north 
with notably higher humidity. 


&& 


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


&& 


$$ 


Public...schoening 
fire weather...tardy 
aviation...Kruse 


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