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Area forecast discussion 
National Weather Service Aberdeen South Dakota 
255 PM CDT Sat Jul 5 2008 


Short term...tonight through Monday night 
forecast challenges include precipitation chances and temperatures 
through the period. 


Currently...a dry-line/pre-frontal surface trough is slowly nudging 
into the Missouri River valley...while a surface cold front is 
analyzed in the 19z msas analysis over northwestern North 
Dakota...tailing down into eastern Montana. Plentiful Gulf 
moisture has found its way north into the Dakotas on strong 
southerly winds...with dewpoints noted ahead of the surface trough 
in the middle 60s to lower 70s. While middle-level capping inversion 
temperatures at 700hpa are still holding over the majority of the County Warning Area at 
+13c to +14c...some slight cooling is noted working into the far 
western Dakotas at this time in association with middle/upper level height 
falls working through the northern plains. Laps surface-based cape 
at 19z out across the western third of zones has increased to an 
astounding 4000-5000 j/kg. Conversely...cinh has only lowered to -60 
to -120 j/kg. Severe met watch marches on. 


Tonight...little change in the forecast grids. Still expecting 
enough middle-level cooling to see organized convection fire up 
across North Dakota by middle-evening this evening...with shear 
vectors supporting potential to see scattered supercellular 
convection organize into an mesoscale convective system overnight...tapping into 30+ knots 
of low level jet winds over the eastern Dakotas and highly 
unstable/moist low level environment. Could still see some of this 
mesoscale convective system activity spill over into the northeastern forecast zones later 
tonight with large hail and damaging winds the severe weather 
threat. The surface trough over this County Warning Area this evening does not look 
to serve as a focusing mechanism for thunderstorm development with 
too strong of a capping inversion in place...and all the pertinent 
synoptic scale lift staying pretty much bottled up in North Dakota 
overnight. 


Latest caveat to consider in the model data...though...is better 
refinement/agreement in the short term between the NAM/GFS/ec with respect to 
this aforementioned cold front. Now the models push the pre-frontal 
trough south and east pretty much out of this County Warning Area on Sunday...but 
only drag the cold front southward into northestern South Dakota and 
central Minnesota before stalling it out over said area Sunday 
night into Monday. The surface winds Sunday and Sunday night will 
be a bit of a pickle what with a surface trough across the northern 
tier of counties and another trough stalled out south of this County Warning Area. 
The thing to watch will be if this pre-frontal trough does in 
fact take all the high-octane Gulf moisture south and east of 
this area on Sunday. The middle-level cap is eradicated by Sunday 
evening...so if there is more available moisture /instability/ to 
work with along this stationary cold front sagged south into the 
County Warning Area...there would be better convective potential than what the 
models are currently suggesting. 


Sunday night into the first half of Monday still bodes a decent 
shot at precipitation as the next chunk of upper level energy 
works east out of The Rockies onto the northern plains. But...once 
that energy works east into Minnesota by Monday 
evening...stabilizing high pressure begins to work into the County Warning Area 
Monday night. 


Without a bonafide surface cold frontal passage in the short term...Max/min 
temperatures will remain fairly warm/mild at or slightly above 
normal for early July. 




Long term...Tuesday through Saturday 
00z operational runs of the GFS/European model (ecmwf) and latest 12z GFS ensemble 
mean were all pretty close and mostly followed by NCEP...and this 
forecaster. Decent looking middle level trough is still prognosticated to 
dive toward the Great Lakes on Tuesday/Tuesday night. Subsidence 
behind this trough will drive a Canadian cold front south through 
the region...delivering another dry and mild Continental airmass 
to the area for Tuesday into Wednesday. Looking out further...middle 
level heights begin to rebound ahead of energy expected to dig 
into the Pacific northwest. Currently the models indicate a wealth 
of middle level warmth spreading out across the northern plains ahead 
of this trough. So...despite expectations of a surface boundary 
slowly heading east into the region by Friday/Saturday...will keep 
forecast mostly dry until middle level warmth abates. Temperatures 
were an amalgam of HPC guidance and mex MOS. 




&& 


Aviation... 
isolated storms may occur in the vicinity of a frontal boundary as 
it pushes east over the region this evening. A few severe storms 
will be possible. Meanwhile outside of thunderstorms you can 
expect VFR conditions with unrestricted visibilities and little if any 
cloud cover below 5k feet through tonight. 




&& 


Abr watches/warnings/advisories... 
South Dakota...none. 
Minnesota...none. 
&& 


$$ 
Short term...dorn 
long term...tdk 
aviation...tdk 


Weather.Gov/Aberdeen