186 
fxus63 kdvn 230910 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
325 am CST sun Nov 23 2008 


Synopsis... 
south winds today should bring milder air into the region before 
colder air returns. Upper trough swinging out of the northern 
rockies will become more amplified as it tracks into the Midwest and 
Great Lakes tonight and Monday. Colder weather expected early in the 
week and then a return to near normal temperatures as we get towards 
Thanksgiving as ridge builds into the area. European model (ecmwf) model suggesting 
storm system tracking into the middle Mississippi Valley Friday night 
and Saturday may impact portions of the dvn County Warning Area. However GFS is 
somewhat farther south and colder so exact path and intensity still 
needs to be resolved...and what affect if any this has on the dvn 
County Warning Area. 


&& 


Short term...today and tonight... 
warmer temperatures today with south winds and mainly thin cirrus 
clouds allowing for sunshine. Operational models similar in bringing 
at least +4c 850 mb temperatures as far north as Interstate 80. Will 
forecast maximum readings ranging from the middle 40s north to lower 
50s south. Changes occur tonight as upper trough swings out of The 
Rockies and amplifies as it pushes into the Midwest and Great Lakes. 
Qg frontogenetical forcing develops in northwest portions of the dvn 
County Warning Area this evening so will increase probability of precipitation to likely category. Forecast 
soundings and time height sections suggest deeper moisture and 
synoptic lift to arrive tonight. The better moisture and timing of 
the cold front suggest highest probability of precipitation across the northern and eastern 
portions of the County Warning Area. In the meantime colder air will be plunging 
into the region so rain will be changing to snow from northwest to 
southeast. Will forecast snow accumulations of around an inch near 
the Highway 20 corridor. Areas south of Highway 34 should see mainly 
rain from this system. 


.Haase.. 


Long term...Monday through Saturday... 
by 12z Monday upper trough axis should be over the Mississippi River 
valley with the cold front extending from a low over lm south 
through the lower Mississippi Valley. Strong cold air advection behind the front 
and high low level relative humidity extending west through central Iowa support 20 
probability of precipitation and mention of flurries Monday. Models were showing potential 
for some light precipitation lingering over the far east Monday morning...so 
included low chance probability of precipitation there through 18z. Brisk northwest winds 
and low clouds will keep temperatures from recovering much on 
Monday...especially over the northeast third of the County Warning Area which should 
be close to the axis of stronger cold air advection. Held maximum temperatures in middle 30s 
in the north which is below most of the MOS guidance. In the south 
kept maximum temperatures in the lower 40s which is close to the MOS numbers. 
This area stands a better chance of seeing some sun Monday afternoon 
which will help boost temperatures. A small but vigorous upper low drops 
southeast through WI and southern Michigan Monday afternoon and evening. Middle 
level forcing suggested by the qvector convergence and area of middle 
level saturation supports keeping low probability of precipitation in place over the northestern 
counties Monday evening. Active flow pattern will settle down some 
then for Tuesday and Wednesday as surface and upper ridging move 
into the central U.S. Expect temperatures to stay below normal through 
midweek due to continued low level cold air advection on Tuesday and then shallow 
mixing near the surface ridge on Wednesday. The dry weather will 
continue into Thanksgiving day as well as moderating temperatures as 
central U.S. Upper ridge moves into the MS valley ahead of a 
developing West Coast trough. No changes are planned to the mainly dry 
forecast for Friday and Saturday with very low confidence in any one 
model solution. Both the European model (ecmwf) and GFS continue to show wide run to 
run swings in their late week solutions...especially concerning the 
evolution of the northeastern U.S./Eastern Canada trough/upper low and 
its impact on the short wave energy ejecting out of the western U.S. Trough. 
The 00z runs are trending a little furhter north with the ejecting 
short wave...which brings precipitation into the southern County Warning Area now. Current forecast 
includes slight chance wording for a mix south of Highway 34 Friday 
and Friday night which looks reasonable based on the 00z run. 


.Dlf.. 


&& 


Aviation... 
VFR conditions today and into early tonight with south winds 10 to 
15 knots with occasional gusts to near 20 knots. Cold front will be 
sweeping across eastern Iowa after 06z switching winds to the 
northwest. Light rain will accompany the front. The rain will be 
changing to some snow from northwest to southeast as the colder air 
plunges southeastward across the region. Snow accumulations of 
around an inch can be expected tonight along the Highway 20 corridor 
including kdbq. Occasional MVFR ceilings with local IFR conditions can be 
expected tonight. 


.Haase.. 


&& 


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


&& 


$$