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Area forecast discussion...updated 
National Weather Service Grand Forks ND 
1039 am CST Sat Nov 21 2009 


Discussion... 
the main forecast challenges are temperatures and winds. When looking at 
the latest surface analysis...an area of low pressure is centered in 
Saskatchewan...with a trough extending along the Montana/ND line. When looking at 
the models...they remain similar in keeping east ND...northwest and wc Minnesota in S 
flow today with a tightening surface pressure gradient creating 
windy conditions. Thus...pretty much kept forecast continuity for 
this update. 


Temperatures not warming as quickly as earlier expected...especially in the 
dvl area...so did need to make a slight downward adjustment for 
today's maximum in some areas. With winds still anticipated to mix to 
about 925 mb...which could result in gusts up to 40 miles per hour. However... 
since this is still below advisory criteria and with temperatures not 
warming as fast as previously expected...will hold off on issuing 
any wind headlines at this time. Rest of forecast in good 
shape...with only minor changes needed. 


&& 


Aviation... 
VFR sky and visibility to continue today with southeast-S winds increasing by 
21z with gusts to around 30 kts possible. 


&& 


Previous discussion... /issued 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 S/southeast surface wind and late Nov 
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 55 kts 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. Air mass 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 S 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 east 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. 


&& 


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


$$ 
Ng