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fxus63 kabr 200835 
afdabr 


Area forecast discussion 
National Weather Service Aberdeen South Dakota 
335 am CDT sun Jul 20 2008 


Short term...today through Tuesday 
challenges in the short term centers around isolated thunderstorms 
early this morning and the potential of severe weather late this 
afternoon over southern South Dakota. 


Currently have a weak area of low pressure over McPherson County 
with a warm front extending east-southeast into southern Minnesota. Southerly 
winds with dew points in the middle 60s are south of the warm front. 
A middle level trough axis over North Dakota has helped in the 
development of isolated convection north of the County Warning Area. A few storms 
earlier this evening did move into McPherson County. As 
such...have left in a slight probability of precipitation across the east this morning for 
a stray shower. Extending south-southwest of the low is a cold front...with 
northerly winds reported at kmbg. Further west of the front...dew 
point temperatures are in the low to middle 50s. Except the cold front to pass 
through the area dry...with little instability to work with. Most 
of today will be dry...with attention turning towards this 
evening. A weak low level jet develops over the central plain states...with 
moisture advection northward. A narrow ribbon of boundary layer 
dew points of near 70 degrees...leads to ml convective available potential energy of over 5000 
j/kg across northern Nebraska. There is a slight risk for our 
southwestern counties...with the northern half of the County Warning Area seeing 
dry conditions with a surface high pressure over top. Have keep just 
a slight probability of precipitation across the southern County Warning Area in the event the convergence 
boundary lifts slightly northward. Certainly looks to be a 
significant weather event just south of the County Warning Area. The rest of the 
short term looks dry with an upper level ridge building into the 
northern plains. 


Long term...Tuesday night through Saturday 
biggest challenge facing the long term deals with precipitation chances middle 
week along with temperature trends. 


Extended starts off with both the GFS and ec showing 500 mb/7h ridges 
in place across the Midwest with low level flow coming off of dry 
high located in Minnesota. However...during the day Wednesday strong 500 mb 
and 7h waves crash into ridge...resulting in in quick zonal flow 
aloft at 500 mb...with longwave 7h trough moving into the upper Midwest. 
There is a bit of concern about middle-level temperatures...as the GFS is 
showing temperatures +12c or warmer during the day Wednesday...with the 
ec being a touch cooler. Given strength of ridge and time of 
year..am apt to buy into the warmer GFS solution. The chance probability of precipitation 
inherited Wednesday afternoon may end up being closer to 00z...simply 
based on timing of surface front/low combo that is prognosticated to move 
into central South Dakota in the models. Have left timing along however due to 
low confidence in timing the models are presenting. 


The models are showing a good 850 mb jet setting up Wednesday night 
with east-west warmfront draped across northern South Dakota. This is usually a good 
combo for heavy rain/severe threat across the County Warning Area. 7h/850 mb Theta-E 
forcing is also impressive...along with lift at the 310/315k 
layers. With spec humidities running 8+ g/kg...should be an 
efficient rain making process if it verifies. Chance probability of precipitation seem 
reasonable at this time. Did break the Wednesday night weather grid into a couple of 
6 hourly chunks and time ending of precipitation better. Generally followed 
the 850 mb-7h q-vector convergence as it moved east out of the County Warning Area 
Wednesday night. 


Temperature wise...inherited maximum/min grids seemed in fine shape...and 
only needed some cosmetic tweaking here/there. Early part of the 
extended should be the warmest part...as weak cold air advection moves in behind 
exiting system Thursday. 




&& 


Aviation... 
VFR conds expected for all terminal sites through 06z Monday. 
Widely scattered -tsra is possible after 00z Monday south of the 
kpir terminal. 




&& 


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


$$ 
Short term...South Dakota 
long term...Hintz 
aviation...Hintz 


Weather.Gov/Aberdeen