279 
fxus65 kfgz 211615 
afdfgz 


Area forecast discussion 
National Weather Service Flagstaff Arizona 
915 am MST Thursday Aug 21 2008 


Synopsis...drier air will remain over the area through Friday. 
Isolated afternoon thunderstorms will continue along the New Mexico 
border...with mostly sunny to partly cloudy skies elsewhere. Over 
the weekend and into early next week...high pressure will become 
established near The Four Corners area with a gradual increase in 
thunderstorm activity. Slightly above average temperatures are 
expected to continue. 


&& 


Discussion...mainly sunny skies this morning with a dry air mass in 
place. Some moisture resides out east across the White Mountains and 
the eastern rim...and we may see a storm or two out in that 
direction. Otherwise we will continue with the dry conditions. 
Temperatures will be up maybe a degree or so this afternoon when 
compared to yesterday. No changes with the grid package. 




Previous discussion (230 am mst)...high pressure in the middle to 
upper levels was centered off the Baja California California coast during the 
early morning hours. This was placing Arizona under a warm and dry 
west to northwest flow aloft. For today...this will mean a 
continuation of mainly clear and dry conditions. Enough moisture 
will remain over the eastern Mogollon Rim and White Mountains for a 
slight chance of a thunderstorm or two during the afternoon and 
early evening hours. Overnight it will clear and with drier air in 
place...low temperatures at elevations above 7000 feet will drop 
into the 40s...somewhat chilly for middle August. 


For Friday into early next week...models continue to indicate that 
the middle to upper high pressure system off the Baja California California coast 
will migrate northeastward and become established over the southwest 
United States. This will result in a flow pattern more favorable for 
the movement of moisture into Arizona from the south. In addition... 
the middle level temperature profile should become more conducive to 
daytime thunderstorm development. As a result...a gradual increase 
in thunderstorm activity from Friday into early next week is still 
anticipated with low grade monsoon activity in order. 


&& 


Aviation...for the 18z package...expect mostly clear skies through 
the period. The exception will be over the White Mountains this 
afternoon and evening where isolated -shra/-tsra will be possible with 
cloud bases around 8-10kft above ground level. Any convection in that area will 
diminish after sunset. Aviation discussion not updated for 
amendments. 


&& 


Fire weather...see fire weather forecast (fwffgz) for discussion of 
days 1 and 2. 


Saturday through Monday...a trend toward more low level moisture is 
expected over the weekend as high pressure re-establishes near The 
Four Corners. Chances for showers and thunderstorms will gradually 
increase each day from Saturday to Monday with a possible change to 
a more wet monsoon pattern for the eastern fire weather zones on 
Monday. Minimum relative humidity values are forecast to be above 15 percent over 
most fire weather zones except on Saturday over the lowest elevation 
areas along the Utah/Arizona border. 


&& 


$$ 


Public...............42 
aviation/fire weather.....Peterson 


Visit weather.Gov/Flagstaff for northern Arizona weather information.