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Area forecast discussion 
National Weather Service Riverton Wyoming 
232 am MDT Sat Aug 30 2008 


Short term...today through Monday night 
ridge heading off to the east this morning with backing southwest 
flow increasing over the area. This as large scale trough along 
the British Columbia and Pacific northwest coast begins to move onshore. Busy next several 
days with fire weather concerns today and significant 
precipitation event shaping up for late Sunday into Monday. For 
today...very warm and dry air will combine with increasing 
southwest winds many locations across the central and west 
producing red flag conditions. Southwest winds of 15 to 25 miles per hour 
with gusts to 35 miles per hour will be common in these areas as Lee trough 
deepens over southeast Montana and NE Wyoming. Red flag warnings are in effect from 9 
am to 9 PM for fire zones 279>281-285-286-288-289 and from 12pm 
through 9 PM for fire zones 140-277-278-416. 


The flow backs further to the south southwest this evening allowing 
moisture from over the southern Great Basin to advect in beginning 
this evening...quickly overspreading the area with dewpoints in 
the 3os to middle 40s. This will quickly alleviate the red flag 
conditions. Winds will accompany this however...especially over 
eastern Sweetwater through Natrona and Johnson County. First batch 
of showers move into the southwest after 12z Sunday and spread 
north into the remainder of west through the morning and afternoon 
hours with shortwave lifting over the area providing lift. Should 
be mostly showers...though some lightning is possible. Instability 
not very impressive...though could get some boomers going if any 
insolation occurs...ie break in the cloud cover. This first batch 
spreads across the north and central Sunday evening and Monday 
morning. The next...main batch of moisture moves into the west 
central and northwest Sunday night and Monday as the trough digs 
south into the SW Great Basin. This will allow another batch of 
subtropical moisture move into this area. Good difluence with this 
as well..so could see a good baroclinic Leaf form. Temperatures 
continue to remain too warm for snow...except for the highest 
peaks. Trough lifts northeast Monday afternoon into the eastern 
Great Basin and finally across Wyoming Monday night. The northwest 
and even the north could see an inch or two of precipitation out of this. 
With that said...will need to watch the burn scars very carefully 
especially around The Gunbarrel fire as the the terrain is very 
steep with very loose rock/soil. 


Long term...Tuesday through Saturday 
upper low lifts out of NE Wyoming into northern plains Tuesday 
with cold wraparound precipitation likewise lifting NE out of area. 
Snow levels early Tuesday morning will be near 7000 feet across 
north central Wyoming. Clearing skies and warm air advection will 
allow valley and basin temperatures to rise into the 60s Tuesday 
afternoon. Medium-range operational models trending toward NCEP 
ensemble mean of flatter flow Wednesday through Friday with 
downstream trough flattening ridge over the eastern U.S. Wednesday 
with upstream kicker trough out of the Gulf of Alaska moving into 
south central Canada Wednesday as more of a clipper system...into 
the northern plains Thursday. European model (ecmwf) still hanging on to a further 
west solution similar to what older GFS runs were advertising. 
Clipper will drive a backdoor cold front south across north and 
central Wyoming Thursday. Expect if flatter trend continues...GFS 
700 mb temperatures of 0c to -4c dipping down east of The Divide Thursday 
night will continue to moderate over the next few runs along with 
amount of quantitative precipitation forecast generated by front. Upper ridge builds in Friday and 
Saturday along with a warming trend into next weekend. 


&& 


Aviation... 
VFR conditions will occur today and this evening. Areas of smoke 
from wildfires may impact visibility in the morning hours in the 
valleys. Then afternoon and evening smoke plumes will impact the 
north and central basins one again with reduced visibility. 
Expect breezy areas from Casper to Rock Springs and over parts of 
the western mountains. 


&& 


Fire weather... 
very active pattern shaping up for the next several days as a 
major trough approaches and moves through. Ridge breaks down this 
morning with southwest winds increasing most areas today. These 
winds will combine with very low humidities and critical fuels to 
produce red flag conditions. Red flag warnings are in effect from 
9 am to 9 PM for fire zones 279>281-285-286-288-289 and from 12pm 
through 9 PM for fire zones 140-277-278-416. Most other areas will 
see increased winds and very low humidities as well but should 
stay below criteria. Much more humid air will move in tonight with 
winds becoming more south southwest. Showers will work into the 
southwest by late Sunday morning...spreading north across the west 
through the morning and afternoon. Some of the showers could 
spread east of The Divide as well. Some thunderstorms are 
possible. More persistent rains will move into the northwest and 
north Sunday night and continue through Monday...and a good 
potential to move into the central as well. Precipitation amounts of an 
inch or two are possible...creating a high potential for ash/mud 
slides in recently burned areas. 


&& 


Riw watches/warnings/advisories... 
red flag warning from 9 am this morning to 9 PM MDT this evening 
for wyz279>281-285-286-288-289. 


Red flag warning from noon today to 9 PM MDT this evening for 
wyz140-277-278-416. 


&& 


$$ 


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