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fxus65 kcys 200338 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
938 PM MDT Friday Mar 19 2010 


Update... 
kcys 88d continues to depict a downward trend to snowfall across 
the area...which is confirmed by surface observations. Just have 
occasional flurries here at kcys...minimally reducing 
visibilities at times. So...have removed accumulating snow chances 
from lower elevations...keeping them only in the mountains and 
just through midnight. Will keep occasional flurries in lower 
elevations through midnight as well. A much drier air mass will 
move in after midnight. Decreased overnight lows some...especially 
for areas west of the Laramie range. Hahn 


&& 


Aviation... 
conditions will continue to improve at area terminals overnight. 
So expect VFR conditions to prevail. A few pockets of fog may 
develop overnight...but do not anticipate much...if any impact at 
area terminals. Much drier conditions can be expected through the 
weekend as high pressure builds in. 


&& 


Previous discussion... /issued 211 PM MDT Friday Mar 19 2010/ 


Short term...tonight through Saturday night... 


Forecast challenges turn to temperatures as our winter storm has 
ended. Another system Tuesday into Wednesday will be the challenge 
in the long term. 


Currently...water vapor imagery showing upper shortwave across 
central Colorado this afternoon moving eastward. Infrared imagery 
showing remaining cloud tops warming across southeast Wyoming and 
western Nebraska. Wrap around clouds over western Wyoming continue 
to warm as well. Mosaic radar showing most echo returns have pushed 
off to the southeast of the County warning forecast area as well. Secondary disturbance 
over west central Wyoming will need to be watched this 
afternoon...but with continuing warming of clouds...this may fall 
apart late this afternoon/early evening before it makes its way 
into the western County warning forecast area. 


For tonight...high pressure over Montana forecast to move into the 
state overnight. Cloud coverage should help temper lows somewhat. 
Morning observed lows this morning over Montana were also in the 
upper teens and low 20s in the vicinity of this high. So went a 
few degrees above MOS guidance for lows Saturday morning. Evening 
shift will need to monitor temperatures as any breaks in clouds 
could see US dropping into the single digits as winds become light. 


Saturday looks fairly cool for the most part for areas that 
received significant snowfall today. Have tempered lows to try to 
reflect this with coldest temperatures over southern Wyoming in 
the low 30s...further north where very little snow 
fell...temperatures may be significantly warmer and have gone with 
middle and upper 30s up that way. Upper ridging begins to build into 
the area Saturday afternoon with surface winds becoming more 
westerly as the afternoon wears on. 


Long term...Sunday through Friday... 
an upper level ridge will be over The Rockies Sunday and Sunday night 
before being pushed east. The thermal ridge axis at 700 mb will be 
over the County Warning Area Sunday night and Monday morning. A surface low pressure 
trough develops along the eastern Wyoming border Sunday afternoon and 
continue for Monday. As a result...the surface pressure gradient 
tightens some and the low level height differences across the region 
increase. The 12z NAM actually has the largest difference between 
kcag and kcpr centered around 12z Sunday with the 12z GFS centered 
more around 12z Monday. The 700 mb winds increase over the County Warning Area to 
between 30 and 40 knots Sunday night and Monday morning. Have 
increased the wind speeds over the County Warning Area during that time...especially 
along and west of the Laramie range. Temperatures will return to 
above normal on Sunday and then another 4 to 8 degrees warmer for 
Monday. 


Another storm system looks to be headed for the central and southern 
rockies Tuesday through Wednesday night. Recent model runs continue 
to close off a middle and upper low over southern Idaho and northern 
Utah Tuesday morning. The feature then digs southeast before heading 
east across northern New Mexico on Wednesday. The 12z European model (ecmwf) is now 
very similar in timing with the 12z GFS but is slightly further to 
the north. A Pacific cold front initially moves across the County Warning Area 
Monday night with cyclogenesis setting up along the front in central 
Colorado by 18z Tuesday. The boundary layer upslope remains 
favorable through perhaps Wednesday morning before surface high 
pressure builds over the area. Snow looks to be fairly widespread 
over the County Warning Area Tuesday night and Wednesday morning...especially in 
the southern portions. There could be significant snowfall during 
that time...with the County Warning Area again generally on the northern fringe of 
the storm. For now have increased probability of precipitation over the area and lowered 
temperatures. Precipitation could be showery and in the form of 
rain or snow Tuesday afternoon and evening. As the storm system 
departs...drier and generally warmer air will slowly return to the 
County Warning Area. Models do suggest a shallow cold front backing into the East 
Part of the County Warning Area Thursday morning before being pushed back east 
Thursday afternoon and Thursday night. The frontal boundary may 
have an impact on temperatures on Thursday over the East Part of 
the County Warning Area. 


&& 


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...none. 
NE...none. 


&& 


$$ 


Short term/aviation...claycomb 
long term...Weiland