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fxus65 kfgz 210408 
afdfgz 


Area forecast discussion 
National Weather Service Flagstaff Arizona 
915 PM MST Thursday Nov 20 2008 


Synopsis...dry and stable conditions will persist through the 
weekend. Expect mild daytime temperatures and light winds with high 
cirrus clouds moving across the Northland. Forecast models indicate 
a low pressure system could move into the southwest by the middle of 
next week with chances for precipitation starting next Tuesday 
extending into the Thanksgiving Holiday. 


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Discussion...satellite this evening shows some high clouds 
streaking east across northern Arizona. Winds remain rather 
light and the weather continues to be quiet across the Northland. 
Grids look okay except for the low temperature grid this evening. We 
went ahead and lowered a few sites as current trends depict cooler 
overnight lows. Will be getting those out shortly. Otherwise the 
grid package tonight looks a-okay. 


Previous discussion (315 PM mst)...expect continued dry conditions 
with winds on the lighter side...mild temperatures...and periods of 
high cirrus clouds moving across the region through Monday. 


Monday through Thursday...the upper level polar front jet will split 
across the eastern Pacific and colder air will push southward 
..causing a low pressure center to move in off the California 
coast. There appears to be enough moisture ahead of this next system 
to give US chances for measurable precipitation starting on Tuesday. 
However this far out in the forecast confidence is only fair at this 
stage. 


The latest forecast grids trends towards the 12z European model run 
which brings this next low pressure system into Arizona by the 
middle of next week with chances for rain and snow extending into 
the Thanksgiving Holiday. However split flow patterns are 
notoriously challenging forecasts...especially in the extended 
periods. Another issue to further complicate the long term solution 
is that the latest 12z GFS operational model run is keeping the low 
center off the California coast and all the moisture well west of 
Arizona. The good news is the 12z GFS solution represents a 
significant departure from previous GFS runs...the latest GFS 
ensemble run and the latest 12z European model run. This means at 
this point we feel the 12z GFS operational run may be in error and 
are therefore keeping our long term Holiday forecast more in line 
with the European model. Due to the complexities of this pattern 
updates to the long term forecast are likely and as the timing gets 
closer we will be able to provide a more detailed forecast solution. 


Update...an early look at the new 18z GFS model run through 96 hours 
is showing a trend back towards the 12z European solution. This 
change in the GFS model lends more confidence to the European 
solution and our current long term forecast grid package. 


&& 


Aviation...for the 06z package...expect VFR conditions with a 
persistent layer of cirrus throughout the forecast period. Aviation 
discussion not updated for amendments. 




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Fgz watches/warnings/advisories...none. 


&& 


$$ 


Public.........Tc/42 
aviation.......tc 


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