Weather

936 
fxus63 kdmx 061135 
afddmx 


Area forecast discussion 
National Weather Service Des Moines Iowa 
634 am CDT Monday Oct 6 2008 


Short term.../today/ 
situation looks to change little until later this afternoon with 
onset of precipitation biggest question. Middle/high clouds should continue 
to stream northward ahead of High Plains trough. Stronger short 
wave now maturing over Texas is expected to reach Kansas/OK by 00z with 
deeper moisture and forcing ahead of it reaching southwestern Iowa after 
20z. Nearly all deterministic models and suggestions from 
ensembles support this scenario as 300-310k isent layer saturates. 
Thus have slight and eventually low chance wording creeping slowly 
eastward this morning into early afternoon followed by slights to 
likelies from east to SW late. 


Raised high temperatures several degrees based on relatively warm current 
observation and sun highs. Much like yesterday...warmer NAM soundings seem 
to have a better handle on reality and support this as well. Clouds 
may hold things back somewhat...but winds/mixing and a few breaks 
should be enough to reach forecast highs. 


Long term.../tonight...Sunday/ 
with deepening trough to the west and strong southerly flow in 
place...very Summer like air mass to continue over the area prior to 
the trough passage on Tuesday night/Wed. GFS/NAM similar in timing 
with low arriving by tonight...though GFS a bit faster in bringing 
system in north into Iowa. Both models also hinting at upper level 
boundary with northern stream kicker wave helping to push the 
southern stream wave farther east Tuesday...resulting in a marked shift 
with the best moisture transport during the night time hours tonight. 
Thus...two favored areas of precipitation develop. One northwest along the 
surface/upper level cold front across the west/central and another 
farther southeast and east of the forecast area by Tuesday. Though 
pop still looks high at all locations...quantitative precipitation forecast looks more variable with 
the bulk of it northwest and west with another area east. Might be 
some lesser amounts central when all said and done. Generally still 
looking at .50 to 1.5 totals over the region. Temperatures continue on the 
mild side tonight with warm southerly flow ahead of the front. By early 
tomorrow morning...GFS shows northwest flow will take over with cold air advection 
following passage of front. With the GFS...decent subsidence and 
clearing behind the boundary will promote mixing with northwest 15-25 miles per hour 
while NAM is still slower in system exiting the region...similar to 
yesterdays models. Other than the NAM...models have leaned toward 
speeding up departure of first system. With break on schedule for 
part of Wed/thurs...will see slightly warmer air on Wednesday afternoon. 
Next upstream wave poses some challenges again...for both timing and 
placement issues. So far the Euro model has been more consistent 
with the overall development and timing of the strong weeks end 
system compared to the Gem or GFS. GFS continues to have differing 
solutions with each run. For now am leaning toward the Euro which has 
system arriving later...with warm air advection rainfall by late Friday or Sat and 
increasing chances for more widespread rain and/or thunder late sun 
with strong h500 wave tracking farther northwest. Uncertainty 
remains rather large to make too many changes to extended portion 
for now...with pattern change and models lack of consistent handling 
to consider. But one thing is certain. Looking at the large scale 
h500 flow...active weather pattern to remain for a while beyond 
Sunday. 


&& 


Aviation...06/12z 
primary concern will be onset of precipitation. Trends look to be a 
bit slower so have pushed back beginning in many locations. Now 
starting near fod/dsm during the late afternoon or early evening and 
working eastward ever so slowly. Mention still included at alo/otm 
before 12z but confidence has decreased somewhat. Thunder could 
occur with any period of precipitation...but have only included cumulonimbus wording 
for now rather than prolonged mention. Later issuances will be able 
to fine tune thunder as timing confidence increases. 


&& 


Dmx watches/warnings/advisories...none. 


&& 


$$ 


Rev/bss