Weather

293 
fxus63 kdvn 101953 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
250 PM CDT Friday Oct 10 2008 


Synopsis... 
region was in the warm sector of low pressure developing over the 
central rockies and High Plains. The warm front extended from the 
low northeast through NE then east through southern Minnesota and central WI. High 
pressure over lower Michigan was helping maintain southeasterly surface flow over the 
middle MS valley this afternoon. Airmass remains dry with dewpoints 
still in the upper 30s to low 40s. Low 50 dewpoints were over the 
MO valley feeding into the warm front while low 60s dewpoints were 
still over the central Gulf Coast and southeastern U.S. 


&& 


Short term...tonight and Saturday... 
little change from the past couple of days is expected over the middle 
Mississippi Valley through Saturday. Upper trough continues to dig 
over the western U.S. Which should keep the surface system to our west 
from moving much through Saturday. The surface pressure gradient 
should be strong enough to maintain light southeast winds tonight. This 
combined with slightly higher dewpoints will keep temperatures about a 
category warmer than this morning. Saturday should be another mild 
early fall day. Expect mostly sunny skies with only some cirrus moving 
over the County warning forecast area and temperatures a few degrees warmer than today. ... 


&& 


Long term...Saturday night through next Friday... 
medium range models continue to differ on eventual movement of western 
trough and attendant surface front early next week. Dprog/dt of the GFS 
past few runs shows model trending slower and stronger... and also 
ejects the energy out from southwest in one chunk which is not supported 
by the recent runs of European model (ecmwf)...Gem and UKMET. Given this and the amount 
of energy in the southwest along with the extent of amplification to the 
Pacific northwest ridge believe more energy will hang back with it coming out 
in pieces... more typical in this scenario. European model (ecmwf) has been a bit more 
consistent especially with holding energy back for midweek... which is 
in more agreement with latest Gem and UK model runs... thus have 
leaned toward its solution for forecast. Latest European model (ecmwf) in fact supports the 
main event or surge of precipitation delayed until Tuesday-Wednesday with second slug of 
energy ejecting out of the southwest... which seems reasonable given 
strength of eastern ridge deflecting initial chunk of energy North/East 
with dynamics shifting away from main moisture transport. 


Front to remain west of County Warning Area through 12z Monday...with bulk of precipitation Post frontal 
with dynamics and elevated moist conveyor from plains into upper Midwest. 
Can/T totally rule out some precipitation sneaking into northwest... but believe 
closer to 12z Monday and have opted to remove Sun night and begin mention of precipitation 
Monday am. Southerly flow and increase in moisture support going at or just 
above warmest guidance on mins. Precipitation chances then migrate eastward across the 
County Warning Area Monday-Tuesday with passage of strong frontal zone and linger into Wednesday as 
energy ejects out from the southwest. Have increased probability of precipitation Tuesday-Tuesday night and 
introduced slight chances for now on Wednesday... as timing still yet to be resolved 
but suggestions are slowing down arrival of main surge of precipitation... which 
would necessitate adjustments to precipitation chances (upward) and intensity for these 
periods by later shifts. Still quite evident is deep monsoonal type fetch 
Post frontal with remnants of Hurricane Norbert getting drawn up to lead to 
potential for widespread heavy rains. 00z gefs still depicts extreme moisture 
with precipitable water/S 1 to 2 Standard deviations above normal with models advertising 
strong 850 mb moisture advection with dewpoints of 10-14c. After brief respite 
precipitation chances look to return later Thursday and may need adding into Friday with next 
trough in active regime. 


Temperatures challenging Monday with strong front moving in and have expanded the 
gradient from northwest (coolest) to southwest (warmest) on order of 15 
degrees. Lowered maxes Tuesday... but suggestions that temperatures still too warm by 
2-5 degrees with clouds and rain. ... 


&& 


Aviation... 
VFR conditions are expected through midday Saturday. Southeast 
winds at 5 to 10 miles per hour tonight will veer to the south at 10 to 15 
miles per hour around 15z Saturday. Some wind gusts around 20 miles per hour will be 
possible by noon in the kcid vicinity. 


&& 


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


&& 


$$ 


Dlf/m^2