602 
fxus63 kfgf 182020 
afdfgf 


Area forecast discussion 
National Weather Service Grand Forks ND 
320 PM CDT Friday Jul 18 2008 


Short term tonight through Monday... 


Main forecast challenges include precipitation chances and the 
potential for severe thunderstorms Saturday night and Sunday. 12 
UTC GFS and NAM show similar evolution of next system through 
tomorrow afternoon...diverging thereafter in storm track and 
strength. Since both models initialized well...decided to use a 
model blend for this forecast. 


Current water vapor imagery shows strong short wave across British 
Columbia/Saskatchewan border. GFS and NAM depict this feature moving 
eastward across southern Canada...centered over Regina Saskatchewan 
tomorrow night. A northwest to southeast oriented 850 to 700 hpa 
trough axis/wind shift boundary extends from the short wave...moving 
out ahead of the parent low. 


Model quantitative precipitation forecast shows convective bulls-eye indicative of a mesoscale convective system moving 
along 925 hpa Theta-E gradient and across South Dakota overnight. 
NAM quantitative precipitation forecast shows this feature along the eastern North Dakota/South 
Dakota border between 12 and 18 UTC tomorrow...whereas the GFS 
paints the same feature a bit farther south. As such...did 
introduce 40 percent probability of precipitation across the southern Red River valley and 
west central Minnesota tomorrow. 


Main trough axis/wind shift boundary prognosticated to enter forecast 
area between 00 and 06 UTC tomorrow night...with the potential for 
isolated severe storms mainly across and south of the Devils Lake 
basin. Daytime heating and middle-level warm air advection along the 
trough axis...combined with ml cape values from 800 to 1000 j/kg 
and showalter index values approaching minus four should produce 
enough instability and lift for convective initiation. Main 
threats will be large hail and strong winds. 


There appears to be a better chance for severe convection Sunday... 
mainly along and east of the Red River valley as short wave and 
associated 300 hpa 90 knots jet dives southeast across the Minnesota 
arrowhead. As the middle-level trough axis moves through Sunday 
afternoon...the NAM paints ml cape values approaching 2000 j/kg. 
This fits well with current Storm Prediction Center day three slight risk convective 
outlook. Much of Sunday will depend on the exact track of the 
storm system. At 06 UTC Sunday...NAM closes off a 144 dm secondary 
850 hpa circulation across eastern Minnesota/western Wisconsin... 
whereas the GFS is weaker and farther south with this feature over 
northeast Iowa. A southern track could limit moisture influx and 
keep most of the convective activity out of the forecast area. 


Monday expected to be dry as upper level short wave moves east of 
the region. 


Long term Monday night through Friday... 


Long term period opens with guidance in agreement showing h50 
ridge over the northern plains. GFS and European model (ecmwf) solutions diverge by 
Wednesday with the former holding the ridge in place while the 
latter carves a shortwave into the forecast area. Siding with 
continuity at this time keeping 20-30 thunder pop in place. 
Protective ridge likely to set up again to end the week so removed 
any lingering probability of precipitation from forecast for Thursday and Friday. 


&& 


Aviation... 


VFR conditions and light wind regime through early Saturday 
afternoon. Introduced 5000 feet ceilings to kfar late in period as next 
system approaches but held off thunderstorms and rain mention at this time. 


&& 


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


$$ 
Rogers/wjb