342 
fxus65 kcys 200924 
afdcys 


Area forecast discussion 
National Weather Service Cheyenne Wyoming 
325 am MDT sun Jul 20 2008 


Short term...today through Monday night... 
fog is a good possibility between 10z and 14z mainly at elevations 
below 4500 feet mean sea level. In those areas the low level moisture remains 
high with surface dew points between 60 and 65 and the winds are 
light. As of 09z...fog and low clouds have formed at ktif. Middle 
and upper level moisture mainly above 550 mb has continued to move 
north and had spread into southwest Wyoming early this morning. 
Some showers and thunderstorms continue at 09z over portions of 
Utah. The center of the upper level high currently over the 
central rockies will move slowly east through Monday night. That 
movement will allow the monsoonal moisture to be located over much of 
the County Warning Area this afternoon through Monday night. Some generally high 
based thunderstorms will develop over mainly the west and north 
parts of the County Warning Area early this afternoon from the daytime heating and 
surface forcing. Have increased probability of precipitation this afternoon and evening 
over those areas and with the boundary layer still on the dry side 
most of the activity will produce wind gusts to 45 miles per hour. Storm Prediction Center has 
the slight risk area into the northern Panhandle this afternoon and 
evening and that is where the models have the best instability and 
moisture. Another round of storms will develop over much of the 
County Warning Area Monday afternoon and continue through Monday evening. Some 
of the activity will linger even after 06z over the East Part of 
the County Warning Area. More significant rainfall should fall Monday afternoon 
and evening as the precipitable water values increase to an inch or 
more over the East Part of the County Warning Area. Main model differences seem to 
be with the low level moisture and the quantitative precipitation forecast over the County Warning Area. The GFS 
has lower suface dew points and less quantitative precipitation forecast than the NAM even though 
forecast precipitable water values are similar. Will lean toward 
the NAM in those regards based on current surface dew points. The 
temperatures will be very warm again today and then a bit cooler 
for Monday based on more cloud cover. 


Long term...Tuesday through Saturday 
the upper ridge axis will be over the County Warning Area on Tuesday...with a 
disturbance moving across the area during the afternoon and 
evening. Edge of monsoonal plume will also be over the area at this 
time. Will go with a slight chance of thunderstorms across the 
forecast area with more numerous storms over the mountains and 
northern Panhandle. A slight chance of late day thunderstorms can 
also be expected across the County Warning Area from Wednesday through Sat...as the edge 
of the monsoonal moisture remains over the area and the atmosphere 
destabilizes during day time heating. The flow aloft will become 
SW Wednesday as the upper ridge axis moves to the east. The upper ridge 
will rebuild over The Rockies Thursday and extend into Canada. The upper 
ridge axis will move over the County Warning Area Friday as an upper trough begins to 
move into the Pacific northwest. The flow aloft will become SW once again on 
Sat as the ridge axis moves east. A disturbance in the flow will 
also move across the area which will aid in the thunderstorm 
development. High temperatures will be from 3 to 6 degrees above 
normal each day. 


&& 


Aviation...expect some areas of MVFR visibilities in fog through 
14z at elevations below 4500 feet mean sea level. Could also be IFR ceilings 
in that area during that time...but moisture depth is shallow 
making fog more common. Some thunderstorms will be over the County Warning Area 
this afternoon and evening and even though ceilings and visibilities 
will not drop into the MVFR category...erratic wind gusts to 45 miles per hour 
can be expected. More thunderstorms will develop over the County Warning Area on 
Monday afternoon and evening and during that period...some MVFR 
ceilings and visibilities are possible with the storms. 


&& 


Cys watches/warnings/advisories... 
Wyoming...none. 
NE...none. 


&& 


$$ 


Msw/kmd