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fxus65 kriw 192018 
afdriw 


Area forecast discussion 
National Weather Service Riverton Wyoming 
218 PM MDT Friday Mar 19 2010 


Short term...tonight through Monday 
storm system working out about as expected except in the southwest 
where the second shortwave we talked about yesterday moved west of 
The Divide and gave the Big Piney and La Barge area between 6 and 
8 inches of snow so far. The most interesting part of this storm 
is that more heavy snow may be on the way into the evening hours. 
The flow between the surface and at least 700 mb is veering around to 
the southeast and increasing upslope is expected. A middle level low over 
Uinta County and the surface high dropping slowly towards NE 
Wyoming will produce this moist southeast flow. Both the GFS and the NAM 
produce another .3 to .5 inches of liquid and a pretty strong 
Omega signature centered on 00z. Earlier we issued an advisory for 
the southwestern zones for another 3 to 6 inches by midnight. 


Further NE over the central zones...snow showers are developing as 
expected especially between riw and lnd in the NE middle level flow. 
These snow showers will likely continue through the evening hours 
and I have bumped up the probability of precipitation to likely for this area through 06z. 
Some of these snow showers are producing some decent snowfall 
already and I wouldn't be surprised to see some additional 
accumulation under the heavier snow bands into the evening hours. 
Since snow continues around Lander and South Pass and over to the 
Green Mountains...I will keep those highlights going until 6 PM and let 
the evening crew look at those once again. 


This storm system should release its grip later tonight and a Dry 
Ridge aloft should dominate the weather over the weekend for 
warming temperatures and lowering min rh's. We could see some morning fog 
with the fresh snow cover but we're still under the coldest air 
aloft until very late in the night. Next storm system will edge 
towards the northwest late Monday with rain and snow showers developing 
and possibly an isolated thunderstorm or two as lifted indice's are forecast to 
drop below zero. I trimmed back the probability of precipitation from 12-18z Monday quite 
a bit and even a little in the afternoon. It's just a timing issue 
though as another significant storm system looks to be in the 
offing just beyond the short term period. 


Long term...Monday night through Friday 
the next weather system will slice into the Rocky Mountain region 
Monday and Monday night. A cold front will drop south Monday and 
another round of upslope will develop east of The Divide Monday 
night. On Tuesday the GFS/ECMWF/Canadian models form an upper low 
around northern Utah and then move this upper low to The Four 
Corners Tuesday night. Have increased precipitation chance all areas from 
Monday afternoon through Tuesday. Precipitation will linger into Tuesday 
evening then decrease late Tuesday night. The upper system heads into 
New Mexico on Wednesday with weak ridge over the area Wednesday. Have reduced 
precipitation to isolated over the mountains and across the south zones 
Wednesday. Dry Wednesday night. A west northwest flow on Thursday with 
possible light snow over the northwest mts Thursday PM. Otherwise dry on 
Thursday. On Thursday night a cold front is forecast to drop south 
into northern Wyoming as a shortwave moves across eastern Montana and 
into the plains states. This front will likely ease into the 
central zones Friday. May see some light precipitation across the north 
and NE zones Thursday night and Friday. The rest of the region looks 
dry next Friday. As for temperatures...mild on Monday with cooler highs 
over the north and northwest where colder air will be first to arrive. 
Then cooler highs Tuesday followed by warming highs Wednesday and Thursday. 
Little cooler east of The Divide next Friday if timing is correct 
with little change west of The Divide. 


Aviation... 
areas of IFR visibilities and ceilings in light to moderate snow will return to 
the Upper Green river basin this evening and continue until 
approximately 06z Saturday...likely impacting kbpi and kpna. The 
areal coverage of the snow will gradually diminish after midnight. 
Elsewhere...scattered snow showers will continue to move southward 
through central Wyoming at approximately 10 miles per hour until several hours 
after sunset. Scattered MVFR with isolated IFR conditions are 
expected with these instability showers through about 03z. Clouds 
associated with the showers will gradually dissipate after 
midnight. 


Fire weather... 
our storm system will gradually move south of the area overnight 
but snow showers will continue across much of the area through 
this evening...especially Fremont...Natrona and Sublette counties. 
A ridge of high pressure will build in for the weekend with lowering 
min rh's into the higher teens and 20s and no precipitation. The 
next storm system will move in Monday night and Tuesday for another 
round of potentially significant snow similar to the current system. 


&& 


Riw watches/warnings/advisories... 
Winter Weather Advisory until 6 PM MDT this evening wyz019. 


Winter Storm Warning until 6 PM MDT this evening wyz015-018. 


Winter Weather Advisory until midnight MDT tonight 
wyz024-026-027. 


&& 


$$ 


Short term...skrbac 
long term...Arkansas 
aviation...church 
fire weather...skrbac