212 
fxus63 kabr 050855 
afdabr 


Area forecast discussion 
National Weather Service Aberdeen South Dakota 
355 am CDT Sat Jul 5 2008 


Short term...today through Monday... 
fairly active pattern setting up for this weekend with the potential 
for a couple of rounds of thunderstorms. Models were in general 
agreement with large-scale features with some discrepancies on a 
smaller-scale. Generally used a blend of model solutions with 
exceptions noted below. 


Today and tonight...wave pushing through northern Montana 
currently will move across the Dakotas later today and tonight 
breaking down amplified upper ridge. Ahead of wave southerly flow 
will continue to increase advecting much warmer air and moisture 
into the area. Middle-level clouds drifting across area from 
thunderstorm complex in Montana have kept allowed temperatures to 
level off in the middle 60s to around 70...and warmer start should 
allow temperatures to climb into the 90s across much of the area. A 
location or two in southwest forecast area could reach triple 
digits. Current surface dew points seem to be handled better by 
more aggressive NAM which brings 70+ dew points into the area by 
afternoon. Given this and fact that cap around 850 mb will keep 
boundary layer shallow think that 70 dew points will be attainable 
and have bumped up forecast accordingly. Even with increasing 
surface moisture appears that area should stay capped through the 
afternoon as surface trough moving into Missouri River area will 
likely not be strong enough to break cap. However...will need to 
keep an eye on thunderstorms pushing into western forecast area 
this morning as this activity could create an area where cap is 
weakened. Above the cap atmosphere will become extremely unstable 
along and ahead of trough and this instability lasts through the 
night. As thermal ridge is broken down by wave moving across 
Dakotas thunderstorm chances should increase...with best chances 
across northern portions of the forecast area where cap is weakest 
and eastern areas as low level jet noses in. Still not confident 
on amount of thunderstorm coverage so for now will keep probability of precipitation 
fairly low. Given instability and decent shear any thunderstorms 
that do develop will have a good chance of becoming severe and 
will add mention to forecast. 


Sunday through Monday...will likely see some lingering activity in 
the east Monday morning as wave and surface boundary push east and 
south. At some point during Sunday surface boundary will stall as 
it becomes parallel to flow aloft. Where this boundary stalls will 
have impact on thunderstorm development as instability should be 
mainly along and south of boundary. At this time it appears 
boundary will be south of forecast area Sunday afternoon into 
Sunday night so have kept area dry. Not much of a cool down behind 
the boundary with highs still in the 80s to lower 90s. Sunday 
night into Monday boundary expected to lift north as shortwave 
pushes toward the area. This will allow for increasing low-level 
moisture once again with increasing instability...especially into 
Monday. With much cooler temperatures aloft cap should not be much of an 
issue and will likely see thunderstorm development as broad scale 
lift increases ahead of wave. For now biggest change to this 
period was to dry out northeast corner some Sunday night as 
surface high nosing not area should preclude any thunderstorm 
development. Otherwise just adjusted precipitation chances a bit for 
timing issues. 






Long term...Monday night through Friday 
models are in pretty good agreement with the overall weather 
pattern through the extended forecast this morning. Period starts 
off with northwest flow aloft with the region sitting between high 
pressure in the Pacific and low pressure in Canada. May see some 
lingering precipitation in the east very early in the period in 
wake of system from the short term...but by late Monday 
night...pattern looking like a dry one. A shortwave traverses the 
international border toward the northern Great Lakes region by 
Tuesday. This allows high pressure to build into the area behind 
it for Tuesday through early Wednesday. Cooler air associated with 
the shortwave to the northeast backs in so cooler temperatures 
than thought a few days ago look right on track. With models in 
good agreement with this slightly cooler air aloft...dropped temperatures 
a few more degrees...especially in the northeast. 


Some differences between the models later Wednesday into Thursday 
morning. The European model (ecmwf) has been hinting at a shortwave passing through 
for a couple of runs while the GFS is dry. General pattern with 
possibility of shortwaves passing through the upper level flow a 
tricky one. Since pattern is favorable for shortwave 
passages...will leave some low probability of precipitation in the forecast for now and 
continue to monitor model runs. 


For the rest of the period...a trough of low pressure begins to 
take shape over the northwestern United States...which pushes the 
ridge to the east and into the area. Some very warm temperatures 
begin to build in from the west Thursday and Friday ahead of a 
cold front associated with the main low in the northwester United 
States. Will be hot and dry ahead of the front with the potential 
for the warmest temperatures of the Summer so far... 




&& 


Aviation... 
VFR conditions still anticipated for the taf sites through this 
afternoon. Some high clouds streaming into the area from system 
moving through Montana this morning. Ceilings are at 15k or 
higher. Winds will remain out of the south at 10 to 20 kts. Other 
area to note this morning in northwest South Dakota where some 
isolated thunderstorms have developed. These storms will creep 
into the northwest part of the forecast area early this morning. 
Expect activity to stay out of kmbg thus not Worth a mention in 
the taf...but will watch carefully over the next few hours. 


Expect scattered thunderstorms to develop later this evening. 
Kpir and kmbg would see thunderstorm activity first between 00z 
and 01z...then shifting to kabr after 01z...and finally Katy 
after 03z. Heavy rain...possible large hail and possible strong 
wind gusts may occur in the vicinity of any thunderstorms that 
develop. If a scattered storm does impact any of the taf 
sites...MVFR conditions will be possible. 




&& 


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


$$ 
Short term...zeltwanger 
long term...zeltwanger 
aviation...zeltwanger 


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