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fxus65 kriw 220910 
afdriw 


Area forecast discussion 
National Weather Service Riverton Wyoming 
310 am MDT Monday Mar 22 2010 


Short term...today through Wednesday night 
strong wind developed over the eastern slopes of the Absaroka 
Mountains last evening...with increased wind continuing this 
morning. Otherwise light radar reflectivity noted over the western 
mountains as the approaching shortwave pushes moisture across the 
state. Models continue to indicate an unstable atmosphere this 
morning and afternoon...and with the potential for periods of 
moderate to heavy convective snowfall...the decision was made to 
issue a Winter Weather Advisory for the northwestern mountains 
through this evening. Additionally...instability may create isolated 
showers and thunderstorms for areas east of The Divide through the 
daylight hours. 


An area of low pressure moving along western Wyoming tonight will 
bringing increased snowfall and cooler temperatures east of the 
Continental Divide. Models demonstrating the increased presence of 
upslope across the central and northern basins overnight and into 
Tuesday morning with showers converting to snowfall this evening. 
Some concern for needed highlights for the favored locations in the 
Wind River basin...though with warmer temperatures lingering into 
this afternoon...the snowfall may be quick melting with a lessened 
impact. Regardless...did increase probability of precipitation to account for potential 
upslope. The Big Horn Mountains are also an area of concern in the 
snowfall tonight and into Tuesday morning. Model quantitative precipitation forecast not as 
intriguing with this area. The GFS is the most progressive with 
higher snowfall amounts over the area. Instability will be a larger 
factor in developing this snowfall. Current forecast maintains the 3 
to 5 inches of snowfall from previous forecast...though these totals 
may be on the modest side if convective snow bands develop. 


This area of low pressure will continue to move south Tuesday night 
and into Wednesday with snowfall tapering off across the County Warning Area late 
Tuesday night. Dry conditions then expected Wednesday as a ridge of 
high pressure builds over the area. Temperatures will begin to 
rebound on Wednesday. 




Long term...Thursday through Monday 
ridge axis is expected to weaken Thursday allowing a shortwave to 
skirt the northwestern zones during the afternoon and evening. The bigger 
weather change will occur in the west Friday and spreading east of 
The Divide late in the day or by Friday evening. Rain will quickly 
change over to snow across the central and southeastern zones Friday 
evening with significant accumulations possible depending on the 
exact track and strength. Have increased probability of precipitation east of The Divide 
Friday night into the middle chance to low likely category for 
starters. Will see what the trends look like tonight. This system 
is currently over Kamchatka and should have plenty of cold air 
with it so the changeover to snow should not be a problem Friday 
night. Still a chance this system could dig too far S and impact 
more of Colorado and southeastern Wyoming but even with that track...the strength of 
this low would likely result in at least some light precipitation this far 
north. Gradual improvement from northwest to southeast Saturday as a ridge aloft 
slowly builds into the inter-mountain west for the second half of 
the weekend. Temperatures should rebound nicely on Sunday. Next 
system is expected to move into the pacnw early next week with the 
ridge axis shifting across Wyoming on Monday. Keeping Monday dry 
for now unless the timing speeds up. Mild lows could be quite 
possible Monday morning with west to SW breezes and some high clouds. 
Monday still looks mild in most areas with only Lee enhanced 
clouds possibly hampering some Lee Side Mountain areas. 


&& 


Aviation... 
a Pacific storm system and associated cold front will move across 
Wyoming today. Snow showers will become more numerous across the 
northwest this morning...vicinity and west of a kcod-kpna line...with 
the heaviest snow showers and widespread IFR conditions and mountain 
obscurations expected vicinity kjac and Yellowstone National Park 
through 18z. The showers will spread into north central Wyoming 
during the afternoon. Expect isolated thunderstorms primarily in 
the afternoon vicinity and north of a kcpr-klnd line. A Canadian cold 
front will push south across central and southern Wyoming overnight 
Monday with numerous MVFR/IFR snow showers along with local 
persistent heavy snow bands and IFR/LIFR conditions. Conditions 
will improve in west after 06z Monday. 


&& 


Fire weather... 
an upper level disturbance will bring shower activity across western 
and northern Wyoming today. Snowfall will be present over the 
western mountains with snowfall accumulations of 6 to 9 inches 
possible by late tonight. Northern Wyoming will see the potential 
for isolated thunderstorms this afternoon with lightning and gusty 
wind being the primary threats. Later...areas east of The Divide 
will see shower activity convert to snowfall tonight and increase in 
coverage. This increased coverage will be noted over the central 
basins into Tuesday afternoon. Meanwhile...increased wind over 
favored locations...such as the eastern mountains slopes and wind 
corridor will see increased smoke dispersal today. 


&& 


Riw watches/warnings/advisories... 
Winter Weather Advisory until midnight MDT tonight wyz001-012. 


&& 


$$ 


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