Area forecast discussion 
National Weather Service Omaha/valley NE 
611 PM CDT sun Aug 30 2015 

Short term...(tonight through wednesday) 
issued at 318 PM CDT sun Aug 30 2015 

Potential for one more morning of fog...then warmer temperatures and 
a couple small rain chances through Wednesday are the primary 
forecast concerns. 

Once again this morning we saw areas of fog and stratus across a 
good portion of eastern Nebraska and southwest Iowa with light flow 
and trapped moisture under strong inversion. Fog had lifted but 
clouds were slower to clear at early afternoon...but stronger 
southerly flow should scour those out a little more efficiently than 
Saturday. Stronger low level flow in response to shortwave moving 
across the northern plains will make fog less of an issue especially 
west of our area...but weak surface winds tonight/Monday morning 
suggest much of southeast Nebraska and western Iowa will again 
see at least patchy areas of fog. 

Overall middle level pattern will begin amplification process 
through the middle of the week. Low/trough in Alaska/British 
Columbia is expected to settle south along the Pacific northwest 
coast as downstream ridge begins to pump up across the eastern 
two-thirds of the country. During this transition...modest 
southwest flow over the plains will provide a couple of rain 
possibilities as shortwaves eject through our area. 

The first will come Monday night into Tuesday morning. This appears 
weaker than previous model runs...but will still induce area of 
isentropic upglide across northeast Nebraska. No strong consensus 
among models or their ensemble will maintain a slight 
chance for convection there Monday night. 

The next shortwave is scheduled into our area Tuesday night into 
Wednesday. Again this is not a strong impulse by any means...but low 
level jet and thus Theta-E advection is stronger. And again there is 
no real consensus between models as far as quantitative precipitation forecast is concerned. However 
we will see decent isentropic upglide spreading from central into 
eastern Nebraska overnight...leading to modest elevated instability. 
And a smattering of model output converts this into thunderstorms 
over a good part of eastern Nebraska and southwest Iowa late Tuesday 
night and Wednesday. Thus am inclined to retain a small chance for 
thunderstorms during both of those periods...though coverage is not 
expected to be widespread. 

Otherwise a general increase in temperatures is forecast Monday 
through Wednesday as lower atmosphere warms due to persistent 
southerly flow and better afternoon mixing regime. Have highs into 
the upper 80s for the most part each day...with some areas seeing 
lower 90s. Higher dew point temperatures should also 
hold...suggesting overnight lows will remain well into the 60s if 
not lower 70s. 

Long term...(wednesday night through sunday) 
issued at 318 PM CDT sun Aug 30 2015 

A slow progression of longwave pattern is expected during the longer 
term period. GFS/European model (ecmwf) and their ensemble means are fairly similar 
in showing this...with a few smaller scale details still needing to 
be worked out with time. We will start out the longer term with 
western trough axis extending from British Columbia into northern 
California...with an eastward shift to a Saskatchewan to Nevada line 
by Sunday afternoon. Meanwhile...broad ridge from the plains to the 
East Coast will initially amplify from our area into the Great Lakes 
before stronger middle level flow on front side of trough works into 
the plains for the weekend. Thus a mainly dry and warm pattern is 
forecast through the end of the week...with increasing rain chances 
for the weekend. 

GFS differs from European model (ecmwf) this weekend in that it shows a much more 
pronounced sub-tropical moisture plume extending from off the 
northern Baja California coast into the plains. Thus it is much more bullish on 
precipitation both Saturday and Sunday. There is still a lot of 
uncertainty on how moisture profiles will pan out...but with a 
majority of model output suggesting decidedly higher rain 
chances...feel fairly confident we will see scattered storms 
Saturday and Sunday. Otherwise look for highs close to 90 before 
clouds/precipitation keep temperatures in the 80s for the weekend. 


Aviation...(00z tafs for kofk...klnk and koma.) 
Issued at 610 PM CDT sun Aug 30 2015 

VFR conditions early in the period. MVFR fog could redevelop at 
all sites 10-14z. Could be temporarily IFR at koma during this 
time. South southeasterly winds increase to 12 to 20 knots at 
kofk by 16z. 


Oax watches/warnings/advisories... 


Short term...dergan 
long term...dergan 

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