Weather

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afdriw 


Area forecast discussion 
National Weather Service Riverton Wyoming 
333 am MDT Thursday Aug 28 2008 


Short term...today through Saturday night 
northwest flow over the County Warning Area this morning behind departing trough. 
Will see some northwest breezes across the area today. Humidities 
will be higher today over yesterday so dont expect any critical 
fire weather conditions. Temperatures today to be near normal. Flow on 
Friday becomes more westerly with some breezes...though less than 
Thursday. Will see temperatures warm by a few degrees Friday under 
warm air advection. Ridge axis moves across the state Friday evening with 
southwest flow building in ahead of the next major trough. Will 
start to see winds increase and humidities and dewpoints crash. 
Looks to be a high potential for the need of fire weather 
highlights for Saturday across much of the forecast area. Will see 
very warm temperatures Saturday with 700 mb temperatures climbing to nearly 
+19c. The trough itself will move onshore Saturday. The flow 
continues to back Saturday night as the trough digs over the West 
Coast. Winds will continue over the mountains Saturday night. 


Long term...Sunday through Thursday 
medium-range global models in good agreement this morning digging 
a trough into the northern Great Basin Sunday and Monday with 
amplified ridge building downstream over the eastern U.S. Both GFS 
and European model (ecmwf) have 500 mb closed low over the southeast corner of Idaho by 
00z Tuesday...lifting the low NE across Wyoming Monday night and 
into the northern plains Tuesday. This upper low expected to tap 
into deep sub-tropical moisture from an upper low to the south 
over the Gulf of California. If all comes together as advertised 
by both GFS and European model (ecmwf)...this could be the first big widespread 
precipitation event for Wyoming since late Spring...and the first 
significant snow of the season for elevations above 7500 feet 
late on Labor Day/Monday night with colder -3c at 700 mb on backside 
of low. Heaviest and most widespread precipitation is expected in 
baroclinic region combined with good jet support on Labor Day with 
GFS showing a trowal over northern Wyoming. Precipitation will 
decrease Tuesday as upper low lifts into northern plains with some 
wraparound moisture lingering mainly over the Big Horn Mountains 
and NE Wyoming. Transitory ridge follows Tuesday night. Kicker 
system follows out of the Gulf of Alaska into the northern rockies 
Wednesday into Thursday. Labor Day storm system has potential to 
be much cooler system than currently forecast if widespread 
precipitation event unfolds. Temperatures have been trended 
downward tonight but within the bounds of the low end of guidance. 


&& 


Aviation... 
VFR conditions will prevail across the region today with less 
wind and only some high clouds across the northern portion of the area. 
Winds will be much less than Wednesday but afternoon west winds of 
10 to 20 miles per hour will still be noted across Red Desert and western part 
of Wyoming. 


&& 


Fire weather... 
northwest flow expected over the area today with higher humidities. 
Northwest breezes are expected today with 10 to 15 miles per hour...mainly 
over the west and southwest. The flow backs to the west Friday 
with drier air working its way back in. Temperatures warm by a few 
degrees. Will see a return to breezy to windy and very dry 
conditions Saturday...likely resulting in extreme fire weather 
conditions. A major trough approaches the area Sunday...bringing an 
increased probability for significant precipitation Sunday into 
Monday. 


&& 


Riw watches/warnings/advisories... 
none. 
&& 


$$ 


Short term...twb 
long term...aem 
aviation...skrbac 
fire weather...twb