051 
fxus63 kdvn 151930 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
230 PM CDT Wednesday Oct 15 2008 


Synopsis... 
low pressure moves quickly off to the east by early this evening 
while high pressure builds into the region overnight and Thursday. 
Weak disturbance moves through the Midwest on Friday followed by 
potential for widespread frost/freeze early Saturday morning. 
Another cold front arrives early next week accompanied by a chance 
of showers. 


&& 


Short term...tonight and Thursday... 
low pressure that brought the widespread 1/4 to 3/4 inch of rain to 
the dvn County Warning Area today was quickly moving off to the east. AWIPS speed 
tool shows back edge of the rain should exit our Illinois counties by 22z. 
Surge of drier air on gusty northwest winds occurring in the Dakotas 
and Nebraska with dewpoints in the 20s. Clearing skies noted on visible 
satellite already into northern Iowa and this trend to continue 
southeast across the County Warning Area as the evening progresses. Clear skies 
expected overnight with minimum temperatures in the 30s...but around 
40 in our southeast County Warning Area. Somewhat concerned about widespread frost 
formation late tonight. However believe winds will stay up much of 
the night as the center of the high is prognosticated in the eastern 
plains. Towards morning winds may die down some in our northwest County Warning Area 
to allow temperatures to fall into the middle 30s so have thrown in 
mention of patchy frost. 


Thursday should be a rather nice middle October day with high pressure 
over the region. Maximum temperatures should top out in the middle 50s 
to around 60 with plenty of sunshine. 


.Haase.. 


Long term...Thursday night through next Wednesday...the extended 
forecast will generally reflect slightly cooler than normal 
weather...but otherwise pleasant Fall weather. The main impacts 
during the next 7 days will be nearly nightly potential for frost or 
freeze conditions. As said in past days...we are beyond seasonal 
normals for the first date of frost and freeze...and given our 
current airmass entering the Midwest...we will be at risk most any 
night winds can drop below 5 miles per hour and skies will be clear. 


The potential for frost is greater over Illinois Thursday night...as 
skies should stay clearer longer. An approaching short wave over the 
Dakotas should spread middle and high clouds over the entire area after 
midnight. Ending the threat for frost as they move east. Still lows 
in the middle 30s should be widespread. After a partly to mostly 
cloudy Friday...and cool highs under them in the middle to upper 
50s...subsidence behind the short wave should erode the clouds 
Friday evening. This will set the stage for a strong chance of 
frost or freeze Friday night as high pressure should provide calm 
winds after dark. Lows around 32 north to 34 south can be expected 
of skies do remain clear. 


Beyond...the 00z European model (ecmwf) model will be used primarily due to good 
consistency. A strong short wave in southern Canada should bring a 
day of deep mixing and warm advection to the area Sunday and Sunday 
night. Highs should reach the middle to upper 60s...and may need to be 
raised farther in future updates. Highs around 70 are not out of 
the question. However...behind this warmup will come a re enforcing 
shot of cool high pressure for early next week. This should keep 
temperatures cool again through Wednesday as the upper flow becomes 
amplified much like over the last 7 days. A warm up should precede 
the chance of rain...but at this time...the rain and warmer air look 
to hold off until later in the week. All this said...models are 
very inconsistent with the progression of this trough...with the 12z 
GFS and European model (ecmwf) both inconsistent with their 00z counterparts. The 
12z European model (ecmwf) much farther east with the upper trough by Tuesday. 
... 


&& 


Aviation... 
rain will have ended by late afternoon in eastern Iowa with VFR 
conditions returning as skies clear this evening from northwest 
to southeast. Overnight sky clear with northwest winds around 10 knots. 
VFR conditions on Thursday as high pressure moves across the region. 
Expect sky clear in the morning with sct050 in the afternoon with 
northwest to north winds about 5 to 10 knots. 


.Haase.. 


&& 


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


&& 


$$ 


Haase/Ervin