605 
fxus63 koax 080911 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
311 am CST Thursday Jan 8 2009 


Discussion... 
baroclinic zone is across the area...with chances of weather at 
least close to the County Warning Area bringing an end to a quiet period. 
Subjective 00z upper air analysis indicates broad upper low now 
centered in WI/mi/wrn ont...with wave coming ashore in the Pacific 
northwest/western Canada. 500mb heat falls were as strong as 290m ahead of the 
Great Lakes upper low in western Virginia...and up to 60m along the Pacific coast 
with the signature of the wave coming ashore. Strongest upper level 
jet was ahead of the Great Lakes low...with impressive 180kt in eastern 
New York...but strong jet still existed behind the trough...with 155kt in 
eastern Montana. Middle-level saturation had increased over the region...with 
ribbons of stratus across South Dakota/NE/KS and with 850mb dewpoint 
depressions approaching saturation. 850mb ridge was noted from high 
in SW California through Utah/WY/ern Montana/western ND. Northwest-southeast oriented baroclinic 
zone was rather tight from British Columbia through Mt/SD/neb/KS/MO...with 16c 
difference between kddc and koma. Coldest 850mb temperatures were still 
confined to Yukon/northern British Columbia...with readings -30c or colder. Elongated 
surface high at 08z was located from eastern ND through eastern South Dakota into eastern 
Nebraska/western Iowa. 


Main forecast concerns lie in temperature swings and near-miss 
precipitation events. Temperatures today will be slow to recover given cold start 
and ridge axis/weak winds overhead for much of the day...but warm 
air advection should eventually start to push temperatures up above 
freezing by late afternoon/early evening across all but the northestern 
County Warning Area. May see a small temperature dropoff between around 00-05z...with 
temperatures becoming steady and then increasing through the night. With 
ridge axis progressing more slowly across County Warning Area than earlier 
forecasts...have leaned toward slower forecasts for frontal passage 
Friday...closer to 00z European model (ecmwf)/NAM and slower than 00z GFS. Cold front 
is fairly strong...with a push of northwesterly winds in its wake and strong 
baroclinity. Best upper level forcing does remain north of the 
County Warning Area...in South Dakota...but there is still some q-vector convergence on Friday 
during frontal passage. Frontogenetic forcing never really gets going in the 
County Warning Area though...and ageostrophic winds indicate mainly downward 
motion. Have kept schc probability of precipitation on Friday in all but sernmost County Warning Area...but 
was not confident enough to increase much. Also added flurry 
mention on Friday nt as middle-level cold air advection allows low-level 
lapse rates to increase...with moisture lingering in a fairly deep 
layer. Precipitation type on Friday is somewhat problematic...but do think 
transition will be predominantly from rain to snow with little ice 
between as cold air moves in at middle-levels faster than at the surface. 
Have kept non-diurnal temperatures today through Friday...with a late maximum temperature 
in the late afternoon...a brief drop-off in the evening...then steady or 
rising tonight and tomorrow ahead of the cold front and falling 
temperatures behind. 


Toned down the warm-up on Saturday given cold start...with strong 
northwesterly winds giving way to calming winds as surface ridge passes through. 
Kept temperatures closer to met guidance and below mex. 00z European model (ecmwf) 
indicates 850mb temperatures -12 to -16 in the County Warning Area by 12z Sat...with GFS 
slightly warmer at around -10 to -12c. 850mb temperatures are prognosticated to 
recover some on Saturday...but think recovery will struggle to 
translate to the surface. Temperatures Sat nt should moderate closer to climatology 
as winds briefly back to southwesterly before next reinforcing shot of cold 
air pushes into the area. Made no changes to grids for Sat nt and 
beyond as features are subtle and fast-moving and therefore lower 
confidence...and wanted to avoid flip-flops in the forecast for 
temperatures and precipitation potential. 


&& 


Aviation... 
for taf sites kofk/koma/klnk through 09/06z. 


Latest model time sections showing a variable moisture profile through 
the period. GFS appears to have best handle on the current low level 
moisture pattern with trend toward IFR ceilings at kofk becoming scattered by 
12z with an increase in middle level moisture. A period of MVFR ceilings 
possible at kofk around 18z associated with warm air advection as flow shifts to 
the SW then becoming VFR 20z-23z through 06z at all three sites as 
drier westerly flow moves into the area. 


&& 


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


$$ 


Mayes/fobert