657 
fxus65 kcys 191526 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
926 am MDT Friday Mar 19 2010 


Update... 


Looking at recent infrared satellite imagery...looks like coldest tops 
on clouds over extreme southeast Wyoming and southern Nebraska 
Panhandle as system continues to push southeast. Area webcams to 
north of Cheyenne showing good conditions. Have therefore went 
ahead and dropped headlines for advisories north of Laramie 
County. Will let the warnings ride another couple hours to see if 
winds pick up. Update out shortly. 


Claycomb 


&& 


Previous discussion... /issued 430 am MDT Friday Mar 19 2010/ 


Short term...today through Saturday night... 
main forecast concern tonight continues to be the ongoing winter 
weather event across the area. 


Northern zones...and all but the southern Nebraska Panhandle...have 
continued to have much less precipitation than previously expected 
overnight. With the main dynamic support for accumulating snowfall 
pushing south...will cancel advisories for those locations at this 
time. Will also now have just a Winter Weather Advisory for snow and 
blowing snow across the Shirley Basin... central Laramie range and 
eastern Platte County. Snotel data in the northern Laramie range 
indicate limited accumulations...and therefore have decreased 
expected accumulations there and decreased this area to a Winter 
Weather Advisory for snow and blowing snow. 


Snowfall has picked up on the Snowy Range ski area live cameras 
overnight...but only Sage Creek Basin snotel reporting significant 
accumulations through the evening and early hours of today. Sage 
Creek Basin reported accumulations overnight around 8 to 12 
inches. Will keep the Winter Storm Warning in effect for these 
mountain areas through 300 PM MDT today. Winds have not been 
strong across the mountain areas thus far...but breezy conditions 
are expected to add blowing snow to the hazardous weather 
potential through the morning hours today. 


Satellite imagery this morning continues to show support for the 
Winter Storm Warning in place along the Interstate 80 corridor. In 
particular...short-wave energy aloft is deepening the base of the 
upper trough and another short-wave is moving into northwest Wyoming 
early this morning. The short-wave energy moving across western 
Wyoming this morning is due to the left exit region of the jet 
streak on the west side of the upper trough. Areas beneath this 
region will see enhanced upward motion and snow production. The 
Interstate 80 corridor in Albany...Laramie...Kimball and Cheyenne 
counties will see the greatest impact from the favorable dynamics as 
up-slope low level winds will continue to enhance precipitation. The 
MM5 and RUC models are supporting this idea well and have therefore 
adjusted accumulations across the southern zones to show increased 
snowfall during the morning hours today. Winds will also be a bit 
stronger across the southern Nebraska Panhandle creating increased 
blowing and drifting snow...so this area will remain in the Winter 
Storm Warning even though storm total accumulations may only be 4 to 
6 inches. Southern Albany County and Laramie County can expect 5 to 
7 inches of storm total snowfall by middle-afternoon today when 
precipitation chances decrease. 


Precipitation is expected to move out of the area completely 
tonight...with dry conditions expected Saturday and Saturday night. 
Surface high pressure will be in place Saturday...with 500mb heights 
increasing due to the upper level ridge axis located over the Great 
Basin. Temperatures Saturday will still be around 15 degrees cooler 
than normal...but warmer than today. Overnight lows tonight will 
generally be around ten degrees below normal...with single digits 
across the west and teens in the east. 


Long term...Sunday through Thursday... 
NAM...GFS and European model (ecmwf) in decent agreement on synoptic features at 
500 mb...thus moderate to high confidence in their solutions. 


Sunday...dry and mild with ridge aloft. High temperatures in the 40s 
and 50s with plenty of sunshine...1000-500 mb thicknesses near 5540 
meters and 700 mb temperatures near 0 celsius. 


Monday...flow aloft becomes zonal inducing even more warming. 
Maximum temperatures in the 50s to lower 60s with 1000-500 mb 
thicknesses near 5550 meters and down-slope warming from west winds. 


Tuesday...cooler in the wake of a cold frontal passage. High 
temperatures in the 40s with 1000-500 mb thicknesses near 5430 
meters. Shortwave trough moving south across western Wyoming and 
Utah will produce a chance of precipitation across our western and 
central counties along and west of the Laramie range. 


Wednesday...shortwave trough moves across Colorado and New Mexico 
with the northern fringes of the precipitation shield skirting our 
southern and central counties. Maximum temperatures in the 40s to 
lower 50s with 1000-500 mb thicknesses near 5460 meters. 


Thursday...dry and mild with northwest flow aloft. High temperatures 
in the 40s to lower 50s with 1000-500 mb thicknesses near 5550 
meters. 


Aviation... 
widespread LIFR and IFR today in snow and fog south of a 
Rawlins to Scottsbluff line with VFR and MVFR to the north of the 
line. Widespread mountain obscuration. 


Ceilings and visibilities improving to VFR tonight with VFR 
continuing on Saturday. 


Fire weather... 
no significant fire weather concerns are present today or tonight as 
the current storm system will continue to produce widespread 
snowfall and much cooler than normal temperatures. 


&& 


Cys watches/warnings/advisories... 
Wyoming...Winter Storm Warning until 3 PM Friday for wyz110-wyz112-wyz114- 
wyz115-wyz116-wyz117-wyz118-wyz119. 
Winter Weather Advisory until 3 PM Friday for wyz113. 
NE...Winter Storm Warning until 3 PM Friday for nez020-nez054-nez055. 


&& 


$$ 


Short term/aviation...claycomb 
long term...Rubin