445 
fxus63 koax 232033 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
333 PM CDT Wednesday Jul 23 2008 


Discussion... 
forecast challenges continue to be thunderstorm chances in moist 
flow through the period. 


The latest surface analysis had a trough of low pressure from the western Dakotas 
into western Nebraska with low pressure centered from SW Nebraska into eastern Colorado. Rich 
moisture with dewpoints in the 70s have worked back into the County Warning Area 
with a surface ridge over Iowa and some of those drier lower 60s 
dewpoints over parts of western Iowa with 50s dewpoints farther east. 
These higher dewpoints are pooled north of a surface fnt that 
stretches from around mck to S of sln and near ict. South of the fnt 
in the warm sector temperatures are in the 90s with 102 noted at iml. 


Clouds with showers and -tsra have held temperatures down from South Dakota into 
central and NE Nebraska and have kept instability to around 500 j/kg. 
Meanwhile...instability to the west of the trough and S of the fnt 
has climbed to 3000-4000 j/kg. A slow moving shortwave trough has 
been moving across the northern plains...however the storms had shown a 
weakening trend. Out west...the storms are beginning to fire near 
Rapid City where the instability is greater and there is a 
boundary to focus on along with another shortwave trough in the 
westerly flow. Tonight as the low leve jet strengthens along with 
Theta-E advection...thunderstorms and rain should increase over central Nebraska and move 
into NE Nebraska where the atmosphere is less capped. Overnight...the 
850 mb flow veers and should lift the storms north and 
east. With the instability axis shifting into the County Warning Area...think that 
some storms will build back into the instability axis...although 
they will have a tough time where warm middle level temperatures reside. The 
weakest cap appears to be on the periphery of the County Warning Area...thus have 
highest probability of precipitation north and east. Depending on where the boundary 
is...Thu...there should be another round of late afternoon and 
evening thunderstorms. With a lot of moisture available any of the 
storms could produce heavy rainfall. Instability will reduce 
the severe threat...although drier layers could produce some gusty 
thunderstorms winds. Thunderstorms and rain should be southeast of the area Friday 
am...however that is short-lived as the boundary hangs up in northern 
Kansas and another boundary drops in from the north by later afternoon. 


In the long term...the pattern remains unsettled with higher than 
normal chances of thunderstorms for this time of year and near normal 
temperatures. 


Saturday night the middle level ridge is around 110 west longitude 
with a trough from the upper Great Lakes into Canada. The County Warning Area is under the 
influence of northwest flow with abundant moisture still in place. There 
is a surface front to the south with relatively weak flow over the 
fnt...however a shortwave is prognosticated to drop southeast overnight 
and Theta-E advection continues Sunday. With clouds and thunderstorms and rain in the 
area...SW zones should see the warmer temperatures and NE zones with more 
of an easterly surface flow should be closer to normal. Sunday 
night...the Theta-E advection is stronger over the SW part of the 
County Warning Area and a shortwave is prognosticated to temporarily break down the ridge 
and move across the northern plains through Monday night with a risk 
for isolated storms and more scattered storms for the north and 
northeast parts of the County Warning Area where the cap will be weaker. Tuesday...the 
middle level ridge is building back up and there could be some 
residual storms north and east although it appears the deeper 
moisture has shifted out of the County Warning Area and warm middle level temperatures will 
be in place. Cooler temperatures aloft moving in to the S Tuesday night and 
Wednesday...so this may allow storms to develop. 


&& 


Aviation... 
for taf sites koma/klnk/kofk. 


Fairly widespread MVFR ceilings occurred from late morning into 
early afternoon. Highest low level moisture was to our west...but 
will likely move east overnight. This will bring potential for 
lows clouds and fog...potentially IFR. Thunderstorm chances seem better 
at kofk and koma...so did include mention at those spots. Did not 
put anything in at klnk for now. Will ammend tafs as needed. The 
chance for thunderstorms seems best before 12z. Low clouds and fog should 
lift somewhat in the 15-17z range. 


&& 


Oax watches/warnings/advisories... 
NE...none. 
Iowa...none. 
&& 


$$ 


Zapotocny/Miller