917 
fxus65 kcys 072200 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
259 PM MST Wednesday Jan 7 2009 


Short term...tonight through Friday afternoon... 


Tonight...satellite imagery...radar trends...snotel data and webcams 
indicate snow is decreasing in areal coverage and intensity across 
the Snowy Range...thus will allow the Winter Storm Warning to expire 
at 6 PM. Winds still gusting over 60 miles per hour at several locations across 
the High Wind Warning area. Surface through 700 mb gradients will 
relax through the evening with winds diminishing. Suspect...as 
briefed by the midnight shift short term forecaster...that the High 
Wind Warning may be cancelled earlier this evening than midnight. 
Will still remain windy after midnight across much of southeast 
Wyoming but well below High Wind Warning criteria. Expect scattered 
to numerous orographic snow showers to continue across the Snowy 
Range in moist northwest flow aloft. 


Thursday...the flow aloft becomes westerly as the next shortwave 
trough moves across Idaho and western Wyoming. Right front quadrant 
of an 80 knot 500 mb jet moves across southeast Wyoming with a 40-50 
knot jetlet streaking across southeast Wyoming. Fortunately...this 
event will be less widespread with strong winds than those of today. 
Typically wind prone locations such as Arlington and Bordeaux look 
to have possible high winds thus will issue a high wind watch for 
northern Carbon County...the Snowy Range and Platte County. Warm 
downslope winds...minimal cloud cover and 1000-500 mb thicknesses 
near 5580 meters will produce high temperatures in the 50s east of 
Interstate 25 with 30s to lower 40s further west. 


Thursday night...strong cold frontal passage will occur as next 
sharp shortwave trough passage aloft occurs across Wyoming. Isolated 
to scattered snow showers will occur with the baroclinic band 
passage across Carbon...Converse...Albany and Niobrara counties with 
more widespread orographic snow showers across the Snowy Range. 


Friday...deep unidirectional north northwest flow from the surface 
to 500 mb will prevail. NAM shows a 40-55 knot jetlet at 700 mb 
across western Nebraska and far eastern Wyoming in the afternoon 
with 850 mb winds of 30 to 40 miles per hour projected. Have seen these types 
of situations in the past and NAM and GFS many times underforecast 
the winds on the NAM and GFS MOS guidance products. Believe winds 
may approach or exceed high wind criteria...thus have issued a high 
wind watch for far eastern Wyoming and the western Nebraska 
Panhandle. Isolated to scattered snow showers...mainly along and 
west of Interstate 25. Rubin 


Long term...Friday night through Wednesday... 
fast flow aloft will continue for the long term portion of the 
forecast. Energetic northwesterly flow Friday night will increase 
Saturday and will be quite strong Sunday through Wednesday. Surface based 
leeside troughing Friday night and Saturday will act in conjunction 
with mixing of the strong middle level flow to produce windy areas with 
a few orographically assisted areas of light snow Friday night in the 
highest mountains. Saturday will be dry with somewhat above normal 
temperatures. Continued downslope flow will produce a dry and even 
milder day sun. A backdoor type cold front will bring colder temperatures 
Monday along with a chance of light snow in the highest mountains as 
well as over northern portions of the forecast area. Tuesday looks to be 
dry with approximately normal temperatures and areas of brisk winds. Models 
remain inconsistent regarding Wednesday...with the European model (ecmwf) depicting a 
midcontinental Arctic outbreak while the GFS is much weaker with the 
southward transport of cold air. For now...will forecast 
conservatively for Wednesday and will forecast for maximum consistency 
with neighboring offices. 


&& 


Aviation...tonight...strong winds decreasing this evening with 
lessening mountain wave turbulence and Lee eddy effects. Localized 
IFR and MVFR in snow showers across the Snowy Range...otherwise VFR. 


Thursday and Thursday night...VFR. Locally strong west winds across 
northern Carbon County...the Snowy Range and Platte County producing 
mountain wave turbulence and Lee eddy effects. Strong cold frontal 
passage Thursday night with winds becoming northwest and increasing. 
Snow showers producing MVFR and IFR along and west of Interstate 
25. Rubin 


&& 


Cys watches/warnings/advisories... 
Wyoming...Winter Storm Warning until 6 PM Wednesday for wyz063. High 
wind watch from 6 am Thursday to midnight Friday for wyz062- 
wyz063-wyz067. 
High Wind Warning until midnight Thursday for wyz061-wyz062- 
wyz064-wyz065-wyz066-wyz067-wyz069-wyz070. 
High wind watch from 8 am Friday to 6 PM Friday for wyz060- 
wyz068-wyz069-wyz070. 
NE...high wind watch from 8 am Friday to 6 PM Friday for nez001- 
nez002-nez003-nez019-nez020-nez021-nez054-nez055. 
Wind Advisory until 6 PM Wednesday for nez001-nez002-nez003- 
nez019-nez021-nez055. 
High Wind Warning until midnight Thursday for nez020-nez054. 


&& 


$$ 


Short term/aviation...Rubin 
long term...Jr