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fxus65 kriw 192224 
afdriw 


Area forecast discussion 
National Weather Service Riverton Wyoming 
324 PM MST Wednesday Nov 19 2008 


Short term...tonight through Saturday 
a backdoor cold front continues to move through Wyoming this 
afternoon. With limited cloud cover this afternoon over central 
Wyoming...some basin locations were able to reach into the low to 
middle 50s this afternoon ahead of the front. Precipitation 
associated with this system remains to the north of the County Warning Area this 
afternoon...but is expected to drop into northeastern Wyoming this 
evening. Shower activity will spread across the northeastern half 
of the County Warning Area during the overnight hours before tapering off between 
12 and 18z Thursday. Ridge of high pressure begins to weaken 
Thursday across the County Warning Area...as a Pacific trough begins to move 
towards the state. Temperatures will be slightly cooler on 
Thursday due to the frontal passage and cooler 700 mb temperatures. 
The Pacific trough begins to move into northwestern Wyoming 
Thursday evening...with widespread shower activity expected across 
western Wyoming after 06z Friday. Shower activity will continue 
through the day on Friday...with continued snow showers expected 
across the western mountains. This trough is expected to move 
quickly through the state...with shower activity generally 
remaining confined to the higher elevations. The NAM model turns 
this trough into closed low east of Wyoming Friday morning. Some 
continued wrap around moisture will impact northern Johnson County 
through the afternoon. Another transitory ridge slated to move 
over Wyoming Saturday limiting shower activity. However limited 
isentropic lift will cause a few isolated showers over the western 
and northern mountains during the afternoon. 




Long term...Saturday night through Wednesday 
a progressive Pacific trough will pass through the area from the 
Pacific northwest Saturday into Sunday with precipitation mainly 
focused on the western mountains. With progressive zonal 
flow...areas of clouds will pass over western and central Wyoming 
with downslope winds east of the Continental Divide. The warming 
winds and cloud cover will moderate temperatures with near normal 
to above normal temperatures in the west and above normal 
temperatures central and east. A high pressure ridge aloft will 
return to the area Sunday night through Tuesday with dry 
conditions expected. Lows may be cooler with less cloud cover at 
night but generally with rising heights...mild temperatures should 
continue with highs above to much above normal in the east. 
Southwest flow ahead of a Pacific trough will bring some moisture 
and lift into the west Tuesday night and Wednesday with some 
showers developing in the western mountains. Breezy to windy 
conditions and mild temperatures are expected east of the 
Continental Divide. Models in fair agreement through the extended 
with the main pattern. Timing of clouds and strength of the wind 
will likely have the most significant impact on the forecast 
through the extended. 


&& 


Aviation... 
a backdoor cold front will spread local MVFR conditions due to light 
snowfall and lowering ceilings behind it across areas east of the 
Continental Divide tonight. Winds will veer and strengthen from the 
north and northeast along and behind the front. These Post frontal 
winds will arrive as an east wind and increase to to speeds of of 18 
to 28 knots by 12z Thursday in krks. The Post frontal winds will 
arrive as a south southeast winds at kbpi and kpna by late tonight 
as the winds get channeled up through the Upper Green river basin. 




&& 


Fire weather... 
a cold front will continue to move through northeastern Wyoming 
this afternoon...pushing additional cloud cover and cooler 
temperatures through the majority of the forecast area tonight. 
Any associated shower activity should remain east of The Divide 
tonight. Cooler temperatures and elevated humidities will be 
present Thursday. The approach of a separate upper level 
disturbance will bring additional isolated snow showers across the 
western mountains Thursday afternoon. Winds will generally be less 
than 15 kts through Friday. Winds will increase Friday afternoon 
across the area...especially the wind corridor between krks and 
kcpr. Shower activity across the western mountains and valleys 
will become more widespread on Friday...though should move 
quickly...ending by Friday evening. Another transitory ridge of 
high pressure will be found over the area for Saturday...though 
dynamics may introduce a few snow showers over the nothern 
mountains. 


&& 


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


$$ 


Short term...branham 
long term...c.Baker 
aviation...lipson 
fire weather...branham