325 
fxus63 koax 230915 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
315 am CST Monday Nov 23 2009 


Discussion... 


Main forecast concern/focus remains compact upper low the models 
still forecast to close off over the plains tonight. 00z European model (ecmwf)/GFS 
forecast the upper low near the SW nebr/northwest Kansas vicinity by this 
evening and then track it near the nebr/Kansas border Tuesday before 
moving it into northestern MO by 00z Wednesday. Although there is general model 
agreement on this...the European model (ecmwf) has been the most consistent and had 
decent support from 21z sref/00z GFS and was mostly followed in 
its handling of the system/qpf. The 00z NAM...although close to 
others...was a bit S/SW with 500 mb track/quantitative precipitation forecast placement and was a 
modest outlier. 


Overnight satellite imagery showed broad trough over rockies with last 
evenings upper air indicating 100+ knots jet at 300 mb digging southeastward from Washington 
into western Utah. Modest height falls were noted...with 10 dm or more 
at 300 mb at riw/slc/Elko and boi. Moisture ahead of the 
system...although above climatology for late November...was a bit modest 
with surface dewpoints in the 40s f and 850 mb dewpoints...outside of coastal 
sites...mostly at or below 5 degree c. Although most of the forcing from this 
system won't arrive until tngt/Tue...some isentropic upglide was 
forecast...especially this afternoon...over northestern and far western zones. Kept in 
higher probability of precipitation those areas this afternoon since condensation pressure 
deficits were lower there. Tapered probability of precipitation off to slight chance far southeast 
where lift was weaker and middle level moisture more absent. Little/no 
changes made to maximum temperatures with readings ranging from upper 40s far northwest 
to middle/upper 50s southeastern 1/2 where mild start and some occasional breaks in overcast 
could prevail. Clouds have generally kept visibilities from falling too 
low this morning...although some patchy dense fog was reported west 
of lnk. At this time no advisory for fog planned but will carry patchy mention 
of it west and S this morning. 


For tngt/Tue...500/700 mb low track along northern Kansas into 
northestern Kansas by 12z Tuesday and then into northestern MO by 00z Wednesday would place 
highest precipitation band in our County Warning Area near the i80 corridor...although 
models want to continue to forecast a secondary quantitative precipitation forecast maximum farther NE Tuesday 
afternoon. Generally placed highest quantitative precipitation forecast from SW to NE through the Oma/lnk 
metros but with speed of system and subjective view of moisture 
available...amounts were placed more in a compromise of higher 
GFS/European model (ecmwf) vs. Lower sref totals. Nonetheless...storm totals over 1 
inch appear quite probable...which for a late November storm is 
decent and would then lead to what do temperature profiles look 
like. General model trends have been for thicknesses and 850 mb 
temperatures to moderate/warm a bit. Plus current forecast soundings from 
GFS/ECMWF...although European model (ecmwf) more limited in levels/time periods...also 
only modestly support a possible change to snow far western County Warning Area mostly 
on northwestern/western flank of precipitation shield toward and a little after 12z Tuesday. 
Thus limited mention of snow to far western zones with any amounts 1 
inch or less. System still bears watching though as there could be 
a narrow area where accumulations exceed this but over all precipitation 
type appears will remain liquid. Using slightly slower European model (ecmwf) would 
keep most of the overnight cold advection over western County Warning Area. So raised lows 
east a bit. With system moving into northestern MO late in the day...a 
decrease/end in precipitation and even some brightening skies western zones 
along with the slightly milder start to the day east bumped up highs 
most areas...although still kept a tight diurnal range. 


Basically made little changes to Tuesday night through Thursday period. A trailing 
upper trough/low drops quickly into Iowa by 00z Thursday aiding in 
ejecting first low and ending most precipitation early Tuesday night. Left in 
small snow chances with this trailing low far eastern zones as most of 
the forcing and quantitative precipitation forecast should remain to our east. Pretty good agreement 
between 00z European model (ecmwf)/GFS with this next system. Looks blustery and 
cool...however...with stratocu possibly lingering well into Thursday 
eastern zones. Maximum temperatures could struggle to get much above 40 eastern 
zones Wednesday/Thursday according to forecast GFS soundings. 


Moderating trend still on track Friday/Sat before next trough late 
next weekend. No changes made those periods. 


&& 


Aviation... 
taf sites kofk/koma/klnk 


06z tafs 


Weak stationary boundary located in central Nebraska on western edge 
of the forecast area this morning expcted to move very little through the day 
as low pressure develops over the Southern Plains. Most variable 
conditions expected at kofk closest to the boundary. VFR to MVFR conditions 
expected at klnk and koma until front begins to move in after 00z with 
conditions becoming IFR or LIFR ceilings and visibilities in fog and showers. 


&& 


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


$$ 


Chermok/fobert