216 
fxus63 kind 212038 
afdind 


Area forecast discussion 
National Weather Service Indianapolis in 
335 PM EST Sat Nov 21 2009 


Discussion... 
quiet weather was the rule as high pressure was centered over the 
eastern Great Lakes and Ohio. Visible satellite showed patchy low 
clouds across our far northeast. Otherwise skies were mostly clear 
across our region. Water vapor infrared showed a weak upper trough over 
the St. Lawrence Valley and upper low over East Texas and an upper 
ridge from the Central Plains to Lake Superior. 


Main forecast challenges are whether to mention any patchy fog late 
tonight. Rain chances early to middle of next week and precipitation 
chances and type around Thanksgiving. 


Concerning fog tonight...dewpoints are presently higher than 
foretasted lows. On the other hand models bring some slightly drier 
air in later tonight. NAM shows a weak east-southeast gradient developing 
overnight especially across our south and this should be enough to 
limit any fog there. Across our north and NE winds should remain 
light and will mention patchy fog that area late tonight. Also with 
clear skies temperatures dropped a little cooler than met/mav blend 
in the areas with light or no winds. 


Mild and uneventful weather will be the rule Sunday. Most models 
still keep precipitation south of our region as the upper low moves east 
along the Gulf Coast states. We will probably see increasing middle 
and high clouds late Sunday into Monday. 


The NAM/GFS/Gem and European bring the next cold front to the 
Illinois border by 00z Wednesday and then across our area Tuesday 
evening. Will drop mention of any rain chances across our eastern 
half Tuesday morning as models keep all precipitation closer to front. 


Light precipitation still looks possible Wednesday and Thursday as the 
upper low deepens over the upper Midwest and then moves east across 
the southern Great Lakes on Thursday. There are still minor 
disagreements between models on cold it will get. Most models Show 
Low level thickness cold enough for at least mixed rain and snow by 
Thursday. So will continue low chances of rain and snow showers. 


Dry weather will be the rule Friday and Saturday as the upper low 
continues moving east. Models build a weak upper ridge into the 
Mississippi Valley by Saturday. 


As far as temperatures are concerned went a little lower than 
mav/met blend as skies will be clear and winds will be light 
especially across our north and northeast. Did not make any 
significant changes to most other periods. But I went a little 
cooler than HPC around Thanksgiving day as the upper low moves by 
and most models indicate this period is when the coldest air will be 
moving across our region. 


&& 


Aviation...discussion for 21/18z tafs 


High pressure will provide a dry easterly flow which should keep 
most clouds at Bay during the first half of the period...with mainly 
high clouds increasing on Sunday. 


Problem is potential for more fog tonight. Forecasted lows are below 
afternoon dewpoints...but slightly drier air will be working in 
overnight. With light winds overnight though...feel that odds for 
fog development are high enough to put MVFR fog in at most sites 
near Sunrise. East winds should prohibit fog formation at ind due to 
influence of city. Any fog will burn off quickly Sun morning. 


&& 


Ind watches/warnings/advisories...none. 


&& 


$$ 


Public...jh 
aviation...cs