Weather

454 
fxus63 kdvn 130759 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
255 am CDT Monday Oct 13 2008 




Synopsis... 
a strong cold front will move across the region today and tonight 
bringing a chance of rain to the area. The passage of the front 
signals a change in the flow aloft which will bring below normal 
temperatures for the remainder of the week. 


&& 


Short term...today and tonight... 
weather starts out quiet this morning as lower atmosphere continues to 
saturate. Cold front starts arriving in the far northwest County warning forecast area by 
late afternoon. Forcing indicates precipitation to be mainly Post frontal. 
However...if enough differential heating can take place during the 
day...some isolated rain showers might pop up ahead of the front. Cloud cover 
and time of year should result in lower temperatures compared to 
yesterday but still above normal. 


Tonight cold front to slowly move across the County warning forecast area. Forcing remains 
fairly strong so plenty of Post frontal precipitation should be seen. Cold 
air moving in behind the front is quite impressive. So... 
temperatures should drop in spite of clouds. Coldest temperatures 
will be in the west and the warmest in the east. ..08.. 






Long term...Tuesday through next Sunday... 
..disturbances along slow moving cool front to produce clouds and 
periods of rain Tuesday and especially Wednesday along with much 
cooler temperatures... 


Models initialize well with only NAM-WRF experiencing convective 
feedback issues. Verification at 06z supports use of hi-res European model (ecmwf) 
and GFS solutions through period. All solutions trending toward 
decent rain event late Tuesday into Wednesday with moderate to 
possibly locally heavy rain amounts over much of area. 


Tuesday and Wednesday...cool front to slide south of area with much 
cooler conditions and lots of clouds. Upglide from disturbances 
ejecting out ahead of main SW upper low to produce areas of light 
rain and sprinkles. Kept chance probability of precipitation but likely probability of precipitation may be needed 
though amounts Tuesday should be light. Highs upper 50s northwest with middle 
60s southeast sections expected under a cloudy sky. Tuesday night...lots of 
rain to move NE from Southern Plains and have upped probability of precipitation to high 
chance which later shifts may be able to raise to likely. Appears 
best forcing and most precipitation to occur between 09z and 21z 
Wednesday and with evaporative cooling highs may need further 
lowering into lower to middle 50s. Local tools with precipitable water/S at or above 1.25 and 
850 mb dew point/S of 10-12c suggest large areas of .25 to .75 inches or 
more with some training to allow localized 1 plus inch amounts. 
Forcing tools suggest heaviest amounts greater than 1 inch along and 
south of Highway 34. Low dewpoints and saturated conditions to 
result in very stable conditions for rain with areas of fog possible 
for later shifts to consider. Nwp techniques suggest quantitative precipitation forecast fields of 
solutions to more accurately reflect higher quantitative precipitation forecast totals which already 
have risen quite a bit on 00z runs in the next 12-24 hours. Wednesday 
night...have skies clearing and kept dry though some risk if system 
is slower which is common with ejecting SW upper disturbances... 
lingering probability of precipitation may need to be added into the evening hours. Kept 
with northwest winds of 5 to 10 plus miles per hour and late clearing lows in upper 30s 
and lower 40s with limited frost potential at this time. 


Thursday...clearing and cool with below normal temperatures. Low 
level thermal fields suggest highs may need trimming down a few more 
degrees for a brisk change. 


Thursday night and Friday...disturbance from northwest to produce some rain 
and have 20 to 30 probability of precipitation with best forcing north 1/2. Mins with clouds 
a challenge and kept mainly in lower 40s but if clouds come in late 
will need lowering. Friday...highs in at least north 2/3 per cold 
850 mb temperatures may need trimming by another 2 to 5 degrees for later 
shifts to consider. Friday night...850 mb temperatures to fall to 
near to below zero supporting areas of frost and freeze and will add 
this to morning severe weather potential statement product as end of growing season. Most or all the 
region. No changes made after Friday night. ..Nichols.. 


&& 


Aviation... 
clouds of 4-5kft rapidly developing in response to broad synoptic 
lift. VFR weather is still expected through 00z. Isolated rain showers may develop 
ahead of the front if differential heating is strong enough but will 
not include in 12z. Thunderstorms and rain threat appears near zero. Ceilings to lower to 
2kft once cold front passage occurs tonight at each taf site with -ra. Based on 
current trends...ceilings around 1kft and visibilities of 3-5sm are possible 
around/after 06z. Will monitor trends up to taf issuance and make a 
decision on whether to include in 12z tafs. ..08.. 


&& 


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


&& 


$$ 


08/Nichols