821 
fxus63 kdvn 201956 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
256 PM CDT Sat Mar 20 2010 


Synopsis... 
morning analysis had the upper trough over the Front Range of The 
Rockies into West Texas. Weak 800 mb low was located over southern OK with a 
stationary 800 mb front and strong baroclinic zone extending NE through 
southeast Iowa into southern lm. Latest surface analysis had the surface front 
near the Ohio River into the East Texas with a surface low over western 
OK. A wide range of conditions currently exist across the County warning forecast area. Dry 
NE flow over the upper MS valley and western Great Lakes has shut down 
most of the snow over the northwest third of the County warning forecast area with the northwest corner 
probably seeing some sun and temperatures approaching 40 degrees. Over the 
southeastern 2/3rds though low level convergence near the 800 mb boundary and 
fgen continue to support bands of -sn/snow with temperatures holding in the 
low to middle 30s. 


&& 


Short term...tonight and Sunday... 
short range models support snow continuing over the southeastern half to two 
thirds of the County warning forecast area into this evening as the Texas upper low heads into 
the MS valley and upper diffluence slides east across northern MO and western 
Illinois and low level convergence is maintained near the stationary 800 mb 
boundary. Area of -sn/snow currently moving NE through northwest MO should 
hold together as it moves across the southeastern half of the County warning forecast area late this 
afternoon and this evening. Expect additional snow fall amounts of 
1 to possibly 3 inches by midnight with the higher amounts over the 
far southern County warning forecast area. The northwest third should remain precipitation free as northeasterly flow 
continues to feed dry air into the region. Will continue the 
advisory with this issuance. Impacts are expected to be minor but 
with the potential for a few more rounds of moderate snow...especially 
after sunset...and with Road surfaces cooling off with the snow 
earlier today...feel there is still potential for some lesser 
travelled roads...bridges and overpasses to become slippery. 


By midnight we should see precipitation winding down as better forcing 
moves east of the area. Kept tonights temperature close to the lower MOS 
numbers with diminishing winds ahead of surface ridge building 
into northwest Iowa and high clouds thinning. Clouds and precipitation should keep 
temperatures from dropping much over the southeastern half of the County warning forecast area. 


For Sunday the southeastern County Warning Area will be on the fringe of the cyclonic flow 
around the surface low moving through the lower Ohio Valley so expect 
clouds to linger there through much of the day. Will also keep some 
low chance probability of precipitation going. Precipitation by then should be mainly -ra as warmer 
air wraps in from the NE. The northwest though should see mostly sunny 
skies. The sun should help temperatures in the northwest recover into the 
middle/upper 40s while the clouds in the southeast will keep temperatures from rising 
much above the low 40s. ..dlf.. 




Long term...Sunday night through next Saturday... 
weather to be generally quiet Sunday night/Monday as the last remnants of 
the weekend storm exits the area. Wet ground...clearing skies...and 
decreasing winds could result in some fog development Sunday 
night/Monday. For now will only go with patchy fog Sun night as 
models are still somewhat mixed regarding fog potential. Quiet weather is 
expected Monday night/Tuesday as high pressure moves across the 
region. 


Tuesday night/Wednesday a weak front moves through the area. 
Moisture is extremely limited but models indicate some forcing with 
condensation pressure deficits lowering. Therefore...will go with 
schc probability of precipitation with the idea that sprinkles are the more probable outcome. 


Wednesday night through Thursday night is somewhat in question. Phasing 
issues with the respective energies and smoothing of model solutions 
are contributing to diverging model solutions. GFS/UKMET would 
suggest most of the time period being dry while the Gem/European model (ecmwf) brush 
the south with the next system. Extrapolation of the WRF beyond f84 
suggests it could go either way. Therefore...will continue with the 
schc probability of precipitation through the period but confine them to the southern half 
to third of the County warning forecast area. 


Friday on...generally dry weather looks to be in store for the area. 
Solutions differ on timing but the GFS/European model (ecmwf) suggest another system 
possibly affecting or passing very close to the area the second half 
of next weekend. 
... 




&& 


Aviation... 
another round of snow lifting NE out of MO should return/keep MVFR 
to IFR conditoins at kbrl/kmli. Kdbq/kcid expected to be just 
north of the significant precipitation through the evening...but a period 
of MVFR ceilings/visibility in -sn is possible. After midnight expect 
any lingering low clouds to move southeast of kdbq/kcid. Some light fog is 
possible by sunrise though as skies clear and winds diminish 
otherwise expect VFR conditions through 18z Sunday. 06z-12z kmli/kbrl 
to remain under an MVFR cloud deck with visibilities of 3-5sm at times 
in -sn. Conditions are expected to improve to VFR at kmli after 
15z but kbrl will be on the fringe of cyclonic flow around Ohio 
Valley low pressure...so MVFR conditions may hang on through middle 
day Sunday. ..dlf.. 


&& 


Dvn watches/warnings/advisories... 
Iowa...Winter Weather Advisory until midnight CDT tonight for Des 
Moines-Henry Iowa-Lee-Louisa-Muscatine-Scott-Van Buren. 


Illinois...Winter Weather Advisory until midnight CDT tonight for Hancock- 
Henderson-McDonough-Mercer-Rock Island-Warren. 


MO...Winter Weather Advisory until midnight CDT tonight for Clark- 
Scotland. 


&& 


$$ 


Dlf/08