976 
fxus65 kriw 192055 
afdriw 


Area forecast discussion 
National Weather Service Riverton Wyoming 
255 PM MDT Tuesday Aug 19 2008 


Short term...tonight through Friday 
first shortwave lifting northeast over northern Idaho and western 
Montana this afternoon. Some convection firing ahead of it...even 
some over northwest Wyo. Absarokas seeing the bulk of the cumulus field but so 
far no lightning as of 2030z. Southwest flow over the area as the 
ridge has been pushed to the east by the incoming troughs. Limited 
middle level moisture working its way in with the aforementioned 
convection the result. Very dry and warm low levels with rh's 
dipping into the lower to middle teens. Winds haven't been much of a 
concern up to this point so do not anticipate needing fire weather 
highlights this evening. Next wave to clip the northwest around 
12z Wednesday with southwest flow increasing. The lower levels 
remain very dry and warm tomorrow...and with the high likelihood of 
stronger winds moving in have issued Fire Weather Watch for noon 
until 9 PM...for the absarokas...Cody foothills...S Lincoln Colorado...Sweetwater 
Colorado...East Slope wind rivers and Green Mountains best chance for these 
conditions will be the absarokas and Cody foothills. Southwest winds 
will become windy over these areas...though the rh's may be 
marginal. Main trough moves on shore Wednesday night and moves 
across southern Canada and Montana Thursday and Thursday night. 
Front moves across the area Thursday night. Winds to be especially 
windy Thursday as the jet moves across Montana. Higher humidities 
will limit need of fire weather highlights. Much cooler 
temperatures will move behind the trough. Maximum temperatures Friday across 
the north will be in the low to middle 70s. 


Long term...Friday night through Tuesday southern Canada shortwave 
should be exiting the area just at the start of the medium range 
period allowing for heights to rebuild through the weekend and 
into early next week. Both the European model (ecmwf) and the GFS are trying to 
show the left behind frontal boundary across the far south being 
energized slightly as it lifts northward Saturday allowing for a few 
storms to fire across the south. We have seen this for two nights 
now but moisture and instability is still rather limited along 
with flow that may still be west to even northwest aloft. Will watch this 
one more night before adding isolated thunderstorm coverage if need be. If 
this moisture does become a player then isolated storms may also 
move northward and affect more of the area on Sunday. For now...the dry 
forecast will remain as this scenario is far from certain yet. A 
series of shortwaves are then poised to impact the pacnw and northern 
rockies early next week in much faster flow. Details vary 
significantly but depending on the strength of these systems we 
may Need More than isolated coverage across the far north by 
Monday night or Tuesday. 


&& 


Aviation... 
winds in the west will increase this afternoon and evening in 
response to an approaching trough of low pressure. Taf sites should 
remain under 15 kts. Isolated thunderstorms will occur this 
afternoon and evening...particularly in the northwest mountains and 
western Big Horn basin. Kcod will be impacted by the storms. 
Primary threats will be localized gusty outflow winds and occasional 
lightning. Wednesday will see gusty southwest winds and isolated 
afternoon thunderstorms in the west. 


&& 


Fire weather... 
southwest flow will continue to increase over the area tonight and 
Wednesday. Very warm and very dry conditions will persist. This 
combined with the increase in winds...this will lead to the high 
likelihood of extreme fire danger Wednesday afternoon and evening. 
Therefore...have issued Fire Weather Watch for fire zones 276 
through 279...286...288 and 289 from noon until 9 PM. Will also 
have the threat of dry lightning in mainly the higher terrain of 
the west. Southwest winds of 15 to 25 miles per hour with gusts to 35 miles per hour are 
likely in the west. Winds increase further Thursday...but will 
likely see the humidity increase. Trough moves across southern 
Canada Thursday night with a front moving across northern Wyoming 
with much cooler temperatures expected for Friday. 


&& 


Riw watches/warnings/advisories... 
Fire Weather Watch from Wednesday afternoon through Wednesday 
evening for wyz276>279-286-288-289. 


&& 


$$ 


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