288 
fxus65 kcys 190316 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
916 PM MDT Thursday Mar 18 2010 


Update... 
area webcams depict snow and low clouds increasing over the past 
hour or two across southeast Wyoming. This trend will continue 
through the overnight hours. 


Initial look at the 00z NAM would suggest a bit tempered snowfall 
accumulations across the area...with perhaps 1 to 3 north of a 
kdgw to kbff line. South of this line accumulations may reach 3 to 
7 inches. Will keep current hilite package going for now...and 
await the 00z GFS for confirmation. Hahn 


&& 


Previous discussion... /issued 255 PM MDT Thursday Mar 18 2010/ 


Short term...tonight through Friday... 


Certainly not an easy forecast for tonight. Have a surface low 
centered over western Wyoming this afternoon with a trailing cold 
front extending southwestward into central Utah and southern 
Nevada. Starting to see an increase in aerial coverage of snow 
across rivertons County Warning Area this afternoon. Temperatures were fairly warm 
this afternoon with upper 40s/low 50s across the Nebraska 
Panhandle and extreme southeast Wyoming...while south central 
Wyoming is seeing current temperatures in the middle 40s. 


Precipitation really begins picking up this evening after 6 PM across our 
western zones as the cold front progresses east. Best isentropic 
lift looks to occur around the 9 PM through 9 am time period 
across southern Wyoming and Nebraska Panhandle. Went ahead and 
issued winter storm warnings for most of our southern Wyoming and 
southern Nebraska Panhandle counties. For our Nebraska counties 
back to Laramie County...models really hit winds pretty hard as 
well. Have snow accumulations of 5 to 8 inches in these 
areas...but do believe we will be impacted equally as bad by 
blowing snow/drifting snow as well. By noon time or so...the storm 
should be coming to an end from west to east...though GFS is 
showing a secondary upper vorticity system moving through the area that 
could keep light snow/flurries going for most of the afternoon. 


Long term...Friday night through Thursday... 
the European model (ecmwf) is the model of choice for the extended period. Snow will 
end from north to south Friday night as the upper trough axis moves 
to the east of the County Warning Area. A large amplitude upper ridge will move 
over the western U.S. On Sat with north to northwest flow aloft over the 
forecast area and downslope wind at the surface. This will result 
in dry conditions for the area from Sat through Monday. Sat will still 
be cold but temperatures will warm quite a bit on sun and Monday. The 
upper ridge axis will move east of the County Warning Area by Monday night with another 
deepening upper trough moving inland from the West Coast. The flow 
aloft will become SW over the forecast area by Monday night. A chance 
of snow can be expected west of the Laramie range Monday night and Tuesday 
morning...with snow changing to rain at the lower elevations Tuesday 
afternoon. An upper low will form over the Great Basin on Tuesday and 
a cold front will move across the area during the day. The 
upper low will move into western Colorado Tuesday night. North to northeast 
winds will occur at the surface at this time and with moist low and 
middle layers...will go with a chance of snow showers across the entire 
County Warning Area Tuesday night. Rain and snow showers will continue through the day 
Wednesday as the upper low moves across the central rockies and out onto 
the Central Plains. Dry conditions will occur Wednesday night and Thursday as 
the upper trough moves to the east and the upper ridge rebuilds over 
the western U.S. High temperatures will be up to 15 degrees below 
normal on Sat...around normal sun...4 to 6 degrees above normal on 
Monday...and around normal Tuesday through Thursday. 


&& 


Aviation... 
conditions expected to deteriorate this evening as snow begins to 
fall from west to east...impacting our western airports around the 
00z timeframe. Further east...impacts expected to be snow and 
blowing snow across the Nebraska Panhandle. LIFR/IFR conditions 
expected to continue across southeast Wyoming and Nebraska 
Panhandle through Friday afternoon. 


&& 


Fire weather... 
no concerns through Friday with much cooler temperatures and 
snowfall. 


&& 


Cys watches/warnings/advisories... 
Wyoming...Winter Storm Warning until 3 PM Friday for wyz103. 
Winter Storm Warning until 3 PM Friday for wyz105-wyz106-wyz107- 
wyz110-wyz112-wyz114-wyz115-wyz116-wyz117-wyz118-wyz119. 
Winter Weather Advisory until 3 PM Friday for wyz101-wyz102- 
wyz104-wyz108-wyz113. 
NE...Winter Weather Advisory until 3 PM Friday for nez002-nez003- 
nez019-nez021-nez095-nez096. 
Winter Storm Warning until 3 PM Friday for nez020-nez054-nez055. 


&& 


$$ 


Short term/aviation...claycomb 
long term...kmd