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fxus63 koax 090931 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
331 am CST Friday Jan 9 2009 


Discussion... 
primary concerns in the short term are precipitation...temperatures and wind. 
Surface analysis early this morning showed a fairly complex pattern. 
Wedge of warm air was in place ahead of frontal system that will be 
moving through the area today. By early evening...low pressure and 
the front should stretch from northestern MO down into North Texas and high pressure 
will be building down from eastern Montana and western ND. Latest water vapor 
loop showed a fairly decent shortwave trough moving toward our area. 
500 mb chart from 00z showed 12 hour height falls up to 140 meters 
at kboi (boise id). Although the system is positively tilted...it 
appears there will be enough forcing and moisture for precipitation across 
our area today and early tonight. Generally raised probability of precipitation from the 
previous forecast. 00z runs of the GFS and European model (ecmwf) were in decent 
agreement with quantitative precipitation forecast (mainly a tenth of an inch or less). Middle level 
frontogenesis increases after 12z and weakens after 00z according 
to cross sections Cut Through the forecast area. The previously 
mentioned wedge of warm air will be a complicating factor for highs 
today...and for precipitation type. Generally stayed with previous forecast 
of morning highs in the north and highs around 18z south...then 
temperatures should be steady or falling. As for precipitation type...would 
expect a mix of rain and snow initially...then changing to snow... 
but it appears that a mix of sleet or maybe light freezing rain may 
occur for a few hours. At least for now...it would be tough to pin 
down anything for an advisory. Next shift will have to monitor that. 
North/northwest winds behind the front should be strong...but might 
be a little marginal for a Wind Advisory. Kept winds in the grids 
just below advisory criteria. 


There is a chance that some light snow could linger through the 
evening hours...so raised probability of precipitation to 25 to 40 percent across the eastern 
half of the forecast area from 00z to 06z tonight. Some flurries 
may occur after that. Expect lows in the single digits north and 
10 to 15 south. Models shift cold high pressure off to the east/ 
southeast fairly fast on Saturday. Warm air will return aloft... 
but not sure how much this will translate down to the surface. So 
stayed fairly close to previous forecast highs Saturday...in the 
lower 30s in our western zones ranging to middle or upper 20s in western Iowa. 


Next shot of cold air will be Sunday night into Monday...and some 
light snow is possible. Best shot at snow should be to our north 
and east...but raised probability of precipitation Sunday night into the chance category 
northestern 1/3 of our area. 


Other than some minor smoothing...did not make many changes beyond 
Monday. Previously advertised high amplitude pattern with a strong 
middle level ridge around 120-130w and troughing over the Great Lakes 
region should bring a series of cold fronts through the area next 
week with below normal temperatures. It appears that we may be on 
the edge of a wet/snowy pattern that will be in place from the northern 
plains into the Great Lakes and Ohio Valley. 


&& 


Aviation... 
for taf sites kofk/koma/klnk through 10/12z. 


Surface low pressure over eastern Nebraska will track southeast...dragging a 
cold front through this morning. Meanwhile...an elongated middle level 
trough will approach with increasing upward vertical velocity...an area of middle level 
frontogenesis and support from the right entrance region of the upper 
jet. Forecast soundings saturate late this morning/this afternoon with 
steepening lapse rates. Initially there is some warm air aloft and 
this would contribute to a mix in precipitation...however expect primary 
precipitation type to be snow once column is saturated. Expect MVFR 
conditions with IFR ceilings and visibilities with the low level saturation and 
snow especially from late morning through evening (15z-06z). Low level wind shear for 
koma/klnk this morning as fby/koax profilers have 50-60kts at 500m 
above ground level will shift southeast of the tafs sites around the 12z issuance 
so will not include...however...northwest winds will pick up with 
the frontal passage and should strengthen to 18 to 28kts sustained this 
afternoon with gusts 25 to 35kt with favorable mixing...and a 
period of strong pressure rises at kofk and klnk and slightly less at 
koma. The winds gradually decrease after 06z. 


&& 


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


$$ 


Discussion...Miller 
aviation...zapotocny