377 
fxus63 kdvn 211949 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
245 PM CST sun Mar 21 2010 


Synopsis... 
stacked system was located over eastern Arkansas this afternoon with upper 
ridge over the southern rockies...tipping into the middle/upper MS valley. 
Zonal flow was in place along the Canadian border. A surface ridge 
was centered from north central Kansas NE through southeastern Minnesota and center WI. Clouds 
are still hanging on along the northwestern fringe of the cyclonic flow 
around the Arkansas system. The clouds were being cutoff to the northwest though 
in the strongly diffluent and subsident flow southeast of the upper ridge. 


&& 


Short term...tonight and Monday... 
models in good agreement moving the Arkansas system east tonight and 
Monday ahead of another southern stream trough moving into the Pacific northwest late 
tonight and Monday. Radar composites were still showing some weak 
returns moving northwest through central Illinois towards the County warning forecast area however have 
yet to see any surface reports of precipitation with the returns. Also with 
the subsidence over the are the returns have been fading away as 
they enter our west-central Illinois counties. With upper system moving away 
from the region will go with a dry forecast and decreasing clouds southeast. 
Mostly clear skies are expected over the rest of the area tonight. 
Have gone below guidance again tonight for min temperatures in the northwest. The 
surface ridge should be centered over north central/central Iowa so winds in 
the northwest are expected to decouple this evening. Also afternoon 
dewpoints are around 20 supporting mins in the low 20s. Kept mins 
around 30 in the southeast where winds should remain in the 5 to 10 miles per hour 
range overnight. Have also maintained a mention of patchy fog late 
tonight in the west. Weak convergent flow tonight in the west 
indicated by the models...the cool temperatures and wet ground may be 
enough for some shallow fog. 


For Monday high clouds should spread over the region ahead of the 
western U.S. Trough. With the filtered sun and light winds near the 
surface ridge kept highs in the low to middle 50s...close to the cooler 
met numbers. ..dlf.. 


Long term...Monday night through next Sunday... 
generally quiet weather is expected through Friday. Models have a front 
moving through Tuesday/Tuesday night but moisture is limited. Models 
do show some respectable Post frontal forcing but condensation 
pressure deficits decrease only slightly. At best there may be some 
sprinkles so will go dry Tuesday night/Wednesday. 


Another system passes just south of the County warning forecast area late Wednesday night through 
Thursday night. Forcing/condensation pressure deficits indicate most 
of the precipitation will remain south of the County warning forecast area. However...will include 
schc probability of precipitation south of Highway 34 in case models start trending the 
system a bit further north. 


On Friday all models develop an Alberta clipper system which moves 
southeast into the plains by Saturday morning. Model smoothing and 
phasing issues are the main reasons for the various model solutions. 
However...it does appear that precipitation will be in store for at least 
part of next weekend. Based on forcing it appears that Saturday will 
be dry with precipitation moving in Saturday night and continuing Sunday. 
Thermal profiles suggest that the event would be rain but a rain/snow mix 
might occur prior to ending Sunday night. ..08.. 


&& 


Aviation... 
VFR conditions expected at all tafs sites through this evening. 
However there is potential for brief period of MVFR ceilings at kbrl through 
early this evening. Widespread MVFR ceilings in cyclonic flow around Arkansas 
low pressure were just southeast of kbrl at 19z. It/S possible that some of 
these clouds could back to northwest into kbrl. But with Arkansas low moving east 
any MVFR ceilings that develop shouldn/T last long. 


Have included some MVFR visibilities late tonight due fog at 
kcid/kdbq/kmli. There is some uncertainty that the fog will develop 
at all...but there are enough factors including wet ground...cold 
temperatures and light winds to give it some mention in the tafs. ..dlf.. 


&& 




Dvn watches/warnings/advisories... 
Iowa...none. 
Illinois...none. 
MO...none. 


&& 


$$ 


Dlf/08