261 
fxus63 kdmx 202011 
afddmx 


Area forecast discussion 
National Weather Service Des Moines Iowa 
300 PM CDT Sat Mar 20 2010 


Short term /tonight/... 
low pressure consolidating over Arkansas will lift northeastward tonight. Bulk of the 
energy expected to remain the south of the County Warning Area. -Sn will brush the 
southeastern zones and went for an inch or less through the night with most of it 
before 06z. Clouds will linger through the night and that will keep temperatures 
from dropping much more than 5-7 degree. Nwia will be clear and went 
at or below MOS across most of the area. Winds will keep the bottom from 
falling out though. 


Long term /Sunday through Saturday/... 
high pressure to build into the area over the next couple of days. 
Along with that...foehn warming will take place across the northern 
plains as downslope winds commence there on Sunday. Looking at h850 
temperatures warm nicely into Monday and Tuesday. Despite that...little 
mixing taking place on Monday so rise in temperatures may be limited 
compared to a fully mixed scenario. For Sunday...will have to melt 
off the recent snow cover to fully appreciate the warmer temperatures aloft 
on Monday. This should be no problem for most of the region except 
for a few instances where the highest totals from fridays event 
occurred. By Tuesday...models all suggest Lee side troughing over 
the northern plains. This will slightly enhance mixing across the 
region and allow for highs to reach the upper 50s to lower 60s. 
Moisture return with the midweek system is rather limited...so am 
not looking at high probability of precipitation to return anytime soon. Weak convergence 
and some light Post frontal precipitation is possible for Tuesday 
night as the northern stream low tracks to the east. High pressure 
and a slightly cooler airmass will follow for Wednesday afternoon. For 
now...southern stream continues to be favored over the north as for 
storm development. As another low develops over the Southern Plains 
on Thursday...both Euro/GFS/Gem suggest that the system and its best 
forcing will pass south of the region with only a slight chance for 
some measurable precipitation across the south. Though the timing 
will be slower...a system arrives by late Saturday which may bring 
some light precipitation to the region as well. Likely timing will be on 
day 7 or beyond...so have left probability of precipitation under slight chance Cat for now 
and will let evaluate over a few more days. With southern storm 
track currently move favored...it is possible that the frontal 
boundary and forcing may become too sheared/weak to support any Post 
frontal precipitation later on Saturday or Sat night of next 
weekend. 


&& 


Aviation... 
20/18z...storm system to the S will brush Iowa this afternoon and evening. Only 
taf site affected will be kotm..though middle and hi clouds will sweep 
over kdsm and Kalo. With the exeption of kotm and some scattered-broken SC 
over northwestern Iowa...gud VFR conds will prevail. 


&& 


Hydrology... 
widespread flood event nearing its Climax across our County Warning Area...with 
rivers having either cresting or expected to crest over the next 
couple of days. Our latest snowfall will melt quickly through 
Monday. This snow melt however is not expected to impact river 
crests though may briefly delay their retreat. 


The most important news...and good news...is that the Des Moines 
River north of Saylorville Reservoir has crested and the inflow into 
Saylorville will continue to diminish. As a result...less inflow is 
expected into the Reservoir which will result in a lower crest of 
its pool. 


Many locations that have not yet seen the river crests will see 
crests lasting longer than normal. In addition...it will take longer 
than normal for the rivers to fall to flood stage. In some 
cases...it may take as much as 2 to 3 weeks for some streams to fall 
back to flood stage. Any heavy rainfall would either slow the falls 
further...or would result in secondary crests. 


We are not out of the Woods yet...however for this Spring. Now that 
the river rises from the snow melt have either peaked or will do so 
within the next several days...our attention will then move toward 
the rest of this Spring season. Soil moisture will likely remain 
high through the end of this Spring season...making US more 
susceptible than normal to flooding from heavy rainfall events. 


&& 


Dmx watches/warnings/advisories...none 


$$ 


Short term...MS March 10 
long term...rev 
aviation...MS March 10 
hydrology...zogg/donavon