Weather

398 
fxus65 kslc 292200 
afdslc 


Area forecast discussion 
National Weather Service Salt Lake City Utah 
400 PM MDT Friday Aug 29 2008 


Synopsis...weather will get increasingly active this weekend as a 
strong storm system dives into the Great Basin Sunday and then slowly 
tracks across Utah on Monday and Tuesday. Southerly winds ahead 
of the system tomorrow will bring hot temperatures to the forecast 
area. 


&& 


Discussion...a weak upper level ridge covers the southwestern 
U.S. This afternoon. Tomorrow...light flow aloft will gradually 
shift to the southwest and increase in response to energy 
currently off the British Columbia coast moving southward. The shift 
in the flow will encourage deep moisture over Arizona and Southern 
California to move into southern and central Utah by tomorrow 
afternoon. This combined with ample instability will generate 
scattered thunderstorms. Precipitable water values will still be a 
bit modest for southern Utah...but weak storm motions could 
produce some heavy rainers. Situation is a little more serious on 
Sunday as moisture continues to increase from the south and 
forcing from the approaching upper trough generates widespread 
lift. 


12z European model (ecmwf) has come around to the GFS solution in slowing down the 
movement of the storm on Monday. The upper level system closes off 
into a low and moves over Utah during this time. The core of the 
cool air at the surface arrives at this time with precipitation 
decreasing in intensity though perhaps not duration. NAM is 
bolder in introducing a dry slot on the south side of the low 
Monday. This would result in a pleasant day across the southern 
third of Utah Monday and have nudged the previous forecast this 
way. System pulls out quickly Tuesday and temperatures will recover 
towards normal by mid-week. Uncertainty in the forecast for 
Thursday and Friday as GFS is delivering an unseasonably cool air 
mass out of Canada by the end of week while the European model (ecmwf) is weaker 
and earlier with this feature. 


&& 


Hydrology...monsoonal moisture will be drawn north into the 
state beginning Saturday...ahead of an approaching strong Pacific 
storm system. Precipitable water values in excess of one inch are 
expected to be common across Utah by Sunday afternoon...with areas 
of heavy rainfall expected. As a result...an elevated risk of flash 
flooding will exist throughout the Holiday weekend. Locations of 
greatest concern are the flood prone areas of southern Utah... 
where precipitation is expected to begin by Saturday afternoon... 
as well as recent burn scars across northern Utah...most notably the 
Corner Canyon area near Draper. 


&& 


Aviation...Northwest Lake breeze now established and will last 
through about 03z. Southeast drainage winds will be enhanced after 
06z by a southeasterly pressure gradient developing. Aww weather 
warnings for wind will likely be needed at times through the weekend 
for strong and gusty southerly winds at the kslc terminal. 


&& 


Fire weather...the strong/cold Pacific storm system scheduled to 
move into the Pacific northwest on Saturday will bring increasing 
southerly flow aloft and moisture into Utah beginning Saturday. 
Northwest Utah will remain on the dry and windy side ahead of the 
moisture Saturday afternoon/evening. A Fire Weather Watch will 
remain in effect for zones 420-423 Saturday afternoon/evening. 


Deep layer moisture will cover the fire districts by Sunday. 
Showers/storms are expected most areas of the state Sunday...with 
the areal coverage increasing rapidly across northern/central Utah Sunday 
night as the upper trough moves east into Nevada. Monday will be 
much colder with widespread precipitation expected...especially 
across the northern half of Utah. 


&& 


Slc watches/warnings/advisories... 
Utah...Fire Weather Watch from 1 PM to 10 PM Saturday for 
Utah fire weather zones 420 and 423. 


Wyoming...none. 


&& 


$$ 


Public...Pomeroy 
fire weather...Conger 
aviation...Gibson 
hydrology...traphagan 


For more information from National oceanic and atmospheric administration/S National Weather Service visit... 
http://weather.Gov/saltlakecity (all lower case)