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fxus63 kdvn 210820 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
220 am CST Sat Nov 21 2009 


Synopsis... 
high pressure ridge over the region with clear skies...calm winds 
and temperature/dewpoint spreads very close. Radiational fog/stratus 
increasing over the County Warning Area. Warm air advection returning to the plains 
on the backside of the high producing veil of high level clouds from 
Nebraska to ND. ..haase.. 


&& 


Short term...today and tonight... 
forecast focus is the fog this morning then warm advection clouds 
tonight...and its impact on temperatures. Will continue with dense 
fog advisory until 16z or 10 am this morning. Fog product shows 
fog/stratus increasing over the County Warning Area with several locations in 
eastern Iowa already down to 1/4 mile or less. With clear skies... 
calm winds and temperature/dewpoints spread very close dense fog should be 
widespread across the County Warning Area before sunrise. After the fog dissipates 
around middle morning expect plenty of sunshine to boost temperatures into the 
50s... somewhat similar to yesterday. Believe met/mav guidance may 
be a tad too high considering the foggy start to the day. 


Clouds should be on the increase tonight as warm air advection 
spreads into the region from the west. European model (ecmwf)/GFS/Gem bring light quantitative precipitation forecast 
into our northwest County Warning Area late tonight. The UKMET/NAM are dry so the end 
result is I will maintain the patchy drizzle. With the cloud cover 
temperatures will be warmer...with much of the County Warning Area having min temperatures near 
to above 40. 


.Haase.. 


Long term...Sunday through Friday... 
the long term once again will focus its attention on the storm which 
continues to be forecast for the periods surrounding Tuesday. 
Tonight...all models have slowed the system slightly...and 
strengthened it as well. Other than that...the tendencies of the GFS 
being fastest and weakest...with the European model (ecmwf) slower...and the UKMET 
strongest and slowest are holding true once again. All have shifted 
slightly south...with the UKMET once again the most southern...and 
the GFS the farthest north. This model spread at 00z Tuesday mslp 
forecasts has the GFS in southwest Minnesota...ec in central Kansas...and the 
UKMET in southwest OK. That is a pretty wide spread in a 72 hour 
forecast period. Our forecast will continue to reflect a blend of 
the ec and UK runs...slower and stronger which matches the trends of 
other models. 


Prior to the storm...warm advection continues Sunday and 
Monday...with forcing remaining mainly west of the County Warning Area. The 
questions for our area will be cloud cover and any brushing glance 
of precipitation chances. Other than the GFS...models show the forcing to 
remain well west...and will limit slight chance probability of precipitation and drizzle 
threats to the northwestern County Warning Area Sunday and Monday. Temperatures 
continue to look mild Sunday through Monday...with southerly winds 
continuing to pump increasing moisture into the region...and keeping 
the boundary layer mixed and mild. This once again supports 
widespread lower to middle 50s Sunday and Monday...especially in the 
southeast 2/3rds where dry conditions are a strong bet. Sunday night 
and Monday night...we should remain mixed as winds stay up above 8 
kts...possibly higher...this should keep lows from dipping much 
lower than the lower 40s. With the slower solutions preferred...I 
raised tuesdays highs up as few degrees as well since cold advection 
looks to be delayed until Tuesday night. Probability of precipitation have been brought up 
to high chance Tuesday and moderate chance Tuesday night. 


A transition to a mixed rain and snow or all snow is still 
possible...but these details are of little confidence at this 
time...thus our low probability of precipitation for a mix will be maintained into Wednesday 
night. Further out...the trend toward rapid modification has been 
maintained on the European model (ecmwf) run...and similar trends are shown for late 
week in the GFS. No changes made...but a warmup looks possible. 
... 


&& 


Aviation... 
widespread dense fog with IFR/LIFR conditions through 16z then rapid 
improvment to VFR conditions thereafter. MVFR ceilings develop this 
evening and continue overnight...especially for kcid/kdbq. Believe 
that kmli/kbrl will have ceilings above 3k feet but this will need to be 
monitored for potential for MVFR ceilings. 


.Haase.. 


&& 


Dvn watches/warnings/advisories... 
Iowa...dense fog advisory until 10 am CST this morning for Benton- 
Buchanan-Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry Iowa- 
Iowa-Jackson-Jefferson-Johnson-Jones-Keokuk-Lee-Linn-Louisa- 
Muscatine-Scott-Van Buren-Washington. 


Illinois...dense fog advisory until 10 am CST this morning for Bureau- 
Carroll-Hancock-Henderson-Henry Illinois-Jo Daviess-McDonough- 
Mercer-Putnam-Rock Island-Stephenson-Warren-Whiteside. 


MO...dense fog advisory until 10 am CST this morning for Clark- 
Scotland. 


&& 


$$ 


Haase/Ervin