729 
fxus63 koax 072028 
afdoax 


Area forecast discussion 
National Weather Service Omaha/valley NE 
228 PM CST Wednesday Jan 7 2009 


Short term...tonight through Saturday. 


Temperatures through the period...and small precipitation chances tonight 
and Friday...are the main forecast concerns. 


Abundant middle level cloud cover was noted across the County Warning Area this 
afternoon...a result of warm advection ahead of well defined 
shortwave dropping south into Iowa this afternoon. Radar showed and 
observers reported areas of light snow or flurries/sprinkles under 
some of those clouds...with the strongest radar returns noted in 
southwest Iowa nearer upper shortwave. This system and associated 
light precipitation should be exiting the area early this evening...helping 
to clear skies over our northeast County Warning Area. 


High pressure will settle into the Missouri River valley tonight... 
setting up decent radiational cooling scenario where clouds can 
clear...most likely in our northeast County Warning Area. Southerly flow returns to 
central Nebraska late this evening...and our western County Warning Area late 
tonight. This warm advection regime will increase clouds...and 
could produce more flurries...but only weak isentropic upglide is 
forecast by NAM and GFS. Thus any mention of accumulating precipitation 
has been removed from the forecast. Models are slightly slower in 
moving clouds/precipitation to the east of our area Thursday...so 
maintained a mention of flurries in the north for the morning. 


South winds on Thursday will give way to southwest flow Thursday 
night. Decreasing clouds and warming low levels should push temperatures 
into the 40s in our southwest County Warning Area...tapering to 30s in western Iowa 
where clouds will be slower to lift northeast and better low level 
mixing holds off until evening. Thursday night should remain 
relatively mild given southwest flow ahead of approaching cold 
front. Have lows in the 30s south with 20s elsewhere...expecting an 
evening low with steady or rising temperatures after midnight. 


A strong cold front is forecast to sweep through the area on Friday. 
Models have diverged on timing of frontal passage...with the GFS now 
more aggressive in showing wind shift through most of the County Warning Area by 12z 
Friday. The NAM is more consistent from its earlier runs...pushing 
front to the Interstate 80 corridor by 18z...then through the 
southeast County Warning Area before 00z. This timing difference makes for a tricky 
temperature forecast Friday. Both models suggest low to middle 30s will just 
about cover it in the north. A mild start in the south should allow 
temperatures to climb into the 40s there...but could reach the 50s if 
slower frontal passage of the NAM is realized. Have trended temperatures 
down a category there for now...but still have highs in the upper 
40s. 


Models are also more bullish on precipitation with Friday cold 
front. Sharp upper trough will be rotating through the area in the 
afternoon...and forecast soundings show sufficient moisture for at 
least a mention of precipitation. So have inserted a slight chance 
for precipitation...transitioning from rain/snow in the north in the 
morning...to light snow in the afternoon/evening in the south as the 
cold air marches into that area. 


Northwest low level flow will continue into Saturday...but 850 temperatures 
try to warm a degree or two during the day. Plenty of sunshine is 
also expected...so we should see a moderate rebound of temperatures 
from the teens Saturday morning to the upper 20s or lower 30s 
Saturday afternoon. 


Long term...Saturday night through Wednesday. 


Latest ecm/GFS/UKMET are in good agreement showing gradual 
amplification of eastern Pacific Ridge through day 7...resulting in reinforcing 
shots of cold air eventually penetrating southward into the lower 48. This 
scenario further supported per remop high predictability of 
strengthening western Continental U.S. Ridge during this time. Late 
Sunday...clipper type low descends into the Dakotas and eventually 
to the Great Lakes region early Monday morning. Attendant cold front 
quickly sweeps southward and is prognosticated to be in the southern tier states by 
12z Monday. Near meridional flow over the northern plains by Monday afternoon 
will allow colder secondary airmass to sink southward...eventually 
encompassing the majority of the central/eastern Continental U.S.. fortunately the 
brunt of the cold air will generally remain along and east of the MS 
valley region through midweek. However...enough cold air advection will penetrate westward 
into the County Warning Area for temperature drops below normal mainly Tuesday and Wednesday time 
frame. Also...have introduced small token probability of precipitation for -sn Monday night as 
well as Tuesday night into Wednesday related to elongated vorticity channels and 
moist Pacific airmass moving into the plains. 


&& 


Aviation... 
for taf sites kofk/koma/klnk through 08/18z. 


A push of cold air moved in this morning and combined with an upper 
level jet shifting into the region and northwest flow...there are 
quite a few middle clouds and some MVFR ceilings. The ceilings have lifted... 
however...there are quite a few echoes aloft with flurries and 
sprinkles where it is warm enough. Continue with VFR ceilings this 
afternoon and tonight with some patchy MVFR ceilings with any 
snowshowers or sprinkles. Later tonight and Thursday morning strong warm air advection 
will increase clouds with flurries. The pressure gradient weakend 
after the frontal passage this morning...however should increase again this 
afternoon and then decrease again later tonight as surface high pressure 
builds in. Northwest winds will vary mostly from 5 to 14kts...then becoming 
light and variable late tonight...switching around to the southeast 
Thursday morning. 


&& 


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


$$ 


Short term...dergan 
long term...Dee 
aviation...zapotocny 

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