Weather

986 
fxus63 kdmx 080820 
afddmx 


Area forecast discussion 
National Weather Service Des Moines Iowa 
320 am CDT Monday Sep 8 2008 


Short term /today/... 
surface cold front still progressing through southeastern Iowa early 
this morning...with cooler and drier filtering in on light northwest winds 
behind it. Cold front drapes westward into developing surface low over 
eastern Colorado. 06z surface pressure falls analysis confirms models desire 
to take the surface low almost due east through central MO today. So we 
will stay safely in the cold sector of this system. 
However...rainfall will be overspreading the area this morning. 
There are two distinct areas to watch. Rain is falling as a result 
of 700-500mb frontogenetical forcing under right entrance region of 
upper level jet across northeast Nebraska into northwest Iowa currently. The GFS 
seems to have the best handle on this feature and does not weaken it 
like the NAM...as it translates east this morning. Farther 
south...frontogenetical forcing lower in the atmosphere is maximized 
across central and southern Iowa this morning into early afternoon. 
Good moisture transport and strong isentropic lift also noted over 
this same region...with a strong transition to subsidence as the 
wave passes during the midday hours. So rain is a certainty this 
morning...ending from west to east during the afternoon. Thunder 
chances appear minimal...but will keep isolated mention in across 
the south...closest to strongest forcing. It appears a soaking rain 
is in store for much of the area...but amounts do not appear to be 
excessive...generally one half to a little over an inch south of 
Highway 20. Temperatures today will be tricky and may end up being 
close to this mornings lows...especially where rain starts around or 
shortly after 12z. Regardless...the day will be 15 to 20 degrees 
below normal for this date. 


Long term /tonight through Sunday/... 
the back edge of todays rain may still be moving out of the 
southeast this evening...otherwise it will be dry and cold with high 
pressure building in from the southwest. With clear skies...light 
and variable or dead calm winds...and falling dewpoints expect 
temperatures to bottom out at least 15 degrees below normal into the 
upper 30s across much of the area. While there is a possibility of 
patchy frost in low lying areas...do not have enough confidence in 
this to include in the forecast at this time. Widespread fog appears 
likely especially southern 2/3rds of County Warning Area where most rainfall is 
expected today...and dense fog is a distinct possibility in the 
early morning hours Tuesday. 


Surface high will begin moving away to the east Tuesday 
night...placing region in gradually increasing sserly flow. Longwave 
trough passage still expected to bring storms toward 
midweek...although timing now appears later with highest probability of precipitation 
Wednesday night and Thursday. Despite good moisture return flow 
ahead of this system the severe threat appears quite low...however 
there is a possibility of heavy rain. 


Aviation...08/06z 
isolated showers tonight should produced VFR conditions with middle deck 
and visibilities above 5sm at the surface. Widespread rain and isolated thunderstorms 
south looks very likely for Monday with unseasonably strong dynamics 
over taf/S. Best forcing and precipitation appears to be over southern Iowa. Onset 
of -ra should saturate initial dry low-levels resulting in IFR 
conditions by late morning. Conditions should improve as precipitation area 
and associated forcing move east. Surface high over taf points Monday 
night with large scale subsidence and weak boundary winds should result in 
fog late Monday night beyond the taf forecast period. 


&& 


Dmx watches/warnings/advisories...none. 


$$ 


Short term...Moyer 
long term...Lee 
aviation...Johnson