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Area forecast discussion 
National Weather Service Grand Forks ND 
332 am CST Sat Nov 21 2009 


Short term (sat-mon)...main concern will be wind potential today 
and then precipitation chances on Monday. Temperatures will also be a 
challenge. 00z models initialized with minimal errors. NAM is 
slightly slower and more amplified than other guidance with the 
boundary today...and will lean away from its solution. For later 
in the period...models (gem...ECMWF...GFS...nam) are in better 
agreement but still enough differences to keep things uncertain. 
Will follow a blend. 


Today...GFS soundings indicate mixing to around 850mb 
possible...while NAM indicates around 925mb. The deeper mixing 
depth of the GFS is likely due to cooling 850mb temperatures through the 
afternoon as 850mb thermal ridge propagates to the east. The 
slower NAM keeps the 850mb thermal ridge over the forecast area through much 
of the afternoon...keeping the inversion intact above 925mb. 
Without cooling at 850mb...think that with a south/southeast surface 
wind and late November sun angle that it will be hard to heat 
enough at the surface to mix much above 925mb. If the preferred 
quicker solution is correct and we do mix to 850mb...winds aloft 
by late morning and into the afternoon hours will be weakening. 
So...the slower solution will not allow mixing to the very strong 
winds aloft...and the quicker solution will allow deeper mixing 
but to weaker winds aloft. Still windy today...but should be 
below advisory criteria. The only reason to worry and have such a 
long discussion is because the 850mb winds will be around 55knts 
at 18z (just that the NAM hangs on to these stronger winds aloft 
through the afternoon). Given either solution...maximum temperatures in the 
low 50s a good bet. 


Tonight-Sun night...approaching upper trough will move across the 
region. This feature will lack moisture until the forcing is east 
of the forecast area. Removed the 20 probability of precipitation across the east forecast area for sun. Min temperatures 
Sun morning should be warmest across the east where best surface 
moisture return ahead of approaching system will be. Airmass cools 
a bit compared with Sat...but westerly surface flow should allow temperatures 
to rise into the mid-40s. Lighter winds Sun night should allow 
temperatures to fall to near dew points values (low-middle 20s). Clouds 
approaching from the south could keep min temperature values in the 30s 
across the far southern forecast area. 


Monday-Monday night...forming 500mb low south of the forecast area with inverted 
surface trough into the forecast area should lead to increasing precipitation chances. 
At this time thinking mostly a rain threat given model 925mb 
temperatures. 


Long term (tue-fri)...main challenge will be how long clouds and 
precipitation lingers across the eastern forecast area and then temperatures. Models 
coming into some agreement...but still enough differences to keep 
confidence toward the low end. Current forecast reasonable and no 
changes planned. 


&& 


Aviation...southerly winds will increase today with gusts from 
30-35kt possible at all sites. VFR conditions are expected with 
just some very high cirrus at times. 


&& 


Fgf watches/warnings/advisories... 
ND...none. 
Minnesota...none. 
&& 


$$ 
Tg