Weather

241 
fxus63 koax 071125 aaa 
afdoax 


Area forecast discussion...updated 
National Weather Service Omaha/valley NE 
625 am CDT sun Sep 7 2008 


Update... 
updated to include more counties in dense fog advisory. 


&& 


Discussion... 
dense fog has spread over more of the area thus expanded dense fog 
advisory to include Oma/lnk areas. However...visibilities continue quite 
variable due to a pre-existing low cloud deck. Nonetheless...when 
the visibility drops...it GOES down quickly and then to near zero. 


&& 


Previous discussion... /issued 324 am CDT sun Sep 7 2008/ 


Discussion... 


Weak surface flow this morning combined with partial clearing has 
again allowed areas of dense fog to form. However widespread 
cloud southeastern nebr or a bit better downslope blyr winds plus a few middle 
clouds far north has limited densest through 0730z to west-central zones and Iowa 
counties. Issued a dense fog advisory again through 14z from SW of lnk 
to ofk/nlg area then east into western Iowa. May expand areal coverage if 
low clouds S fail to keep holding visibilities up. Otherwise expect some 
sunshine into this afternoon after fog/low clouds burn/move off before 
middle clouds increase ahead of a well advertised shortwv energy digs 
southeastward in broad upper trough. Little change to temperatures...most areas 
should reach upper 60s/lower 70s. Isentropic lift forecast to increase 
ahead of trough tonight...focused in two main areas...again well 
advertised by models with decent agreement. One area should develop 
over western nebr/southwestern South Dakota with second area north of 850 mb front over Kansas. Precipitation 
should spread toward County Warning Area by 12z Monday and then set up from SW to NE over 
central zones in 12z-18z period Monday as strong frontogenesis sets up in 
850-600 mb layer. Spread categorical probability of precipitation from far western zones late tonight 
across the lnk/Oma areas Monday morning and lowered most highs into 
upper 50s. GFS quickly shifts forcing and quantitative precipitation forecast into far southeastern zones 
Monday afternoon which was supported by 00z European model (ecmwf) so started cutting 
back/dropping probability of precipitation western zones Monday afternoon. NAM/sref lingered precipitation 
longer but felt quicker GFS/European model (ecmwf) looked more reasonable given 
speed of jet on east side of trough. 


NAM/GFS/ECMWF quickly bring surface ridge over County Warning Area Monday night which will 
provide light winds and probably additional fog development 
again. With most highs only in the 50s Monday and with a cooler 
airmass expected by Tuesday am...see no reason...other than not 
forecasted lingering clouds...why some of the normally colder 
areas won't drop into upper 30s. Especially since some locations have 
fallen into lower 40s past few morning. Temperatures should rebound/mix 
nicely Tuesday with GFS ensemble mean/NAM/ECMWF 850 mb temperatures suggesting 
upper 60s north to lower 70s S. 


Warm advection still on track Tuesday night/Wednesday although GFS and even 00z 
European model (ecmwf) have downplayed shortwv energy lifting across the County Warning Area. GFS 
generates minimal quantitative precipitation forecast and then only across f north on Wednesday and European model (ecmwf) 
has trended downward last several runs with its quantitative precipitation forecast generation. 
Although probability of precipitation were continued...trimmed back a bit because appears 
coverage would be limited...especially southeast zones...even if it occurs. No 
changes to Thu-Sat. Next trough/front appears it will Cross County warning area Thursday 
with increased precipitation chances. However...models have flipped with forecast 
in Friday/Sat period with another trough swinging through possibly 
cooling Sat down from previous runs. That could still change as 00z 
GFS/European model (ecmwf) were faster than latest GFS ensemble mean and may revert 
back in later forecasts. 


Aviation... 


For taf sites koma/klnk/kofk. Valid through 08/06z. 


Light winds and clearing skies will result in occasional IFR/LIFR 
visibility/vv001-vv005 all sites until 14z. After 14z...outlook is conditions 
improving to VFR all taf sites through the period. Surface cold front the 
pushes through eastern Nebraska by the way 00z-06z with deteriorating conditions after 
08/06z all sites. 


&& 


Oax watches/warnings/advisories... 
NE...dense fog advisory until 9 am CDT this morning for nez015>018- 
030>034-042>045-050>053-065>068-078-088. 


Iowa...dense fog advisory until 9 am CDT this morning for iaz043-055- 
056-069-079-080-090-091. 


&& 


$$ 


Chermok/Dee