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fxus63 kiwx 210907 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
407 am EST Sat Nov 21 2009 


Short term... 


..today through Sunday night... 


High pressure was across most of area early this morning while an 
upper level trough was moving through. Little surface reflection 
from the trough but clouds were hanging in across the far north and 
northeast ahead of this feature. Meanwhile...area of stratocumulus 
clouds that formed last night in Illinois and persisted through the day 
have drifted into our southwest counties. Satellite fog product 
shows this area slowly expanding and drifting east. Forecast 
challenges continue to be cloud cover...temperatures and fog possibility in 
the short term period. 


With weak high pressure and subsidence today expect a gradual 
decrease in overall cloudiness through the day. Clouds across north 
and northeast should gradually dissipate/exit our area behind the 
departing trough this afternoon. A little concerned with the clouds 
in the southwest though as they persisted yesterday and did not mix 
out. It is possible a similar situation could occur again today. 
Will be optimistic with a gradual eroding of these clouds. 
Temperatures should be very similar to Friday readings with similar 
airmass. 


Drying continues tonight with continued subsidence as middle level 
ridge noses into the area. Should see mostly clear skies and light 
winds early which should set the stage for fog formation late. Setup 
looks a little better than this morning as ridge will be building in 
and dense fog already forming to our west near this ridging this 
morning. 


Fog may take some time to burn off Sunday morning but once it does 
should be another nice late November day with highs into the 50s. 
Continued to be a little conservative with possible fog and stratus 
in the morning hours inhibiting temperature rise. Feel fog could 
form yet again Sunday night as high slides east but there may be 
enough gradient wind to preclude widespread fog. Will likely hold 
off on any mention in this period. 


&& 


Long term /Monday through Friday/... 


Moisture will be working north at the start of the period...but relative humidity 
profiles suggest skies should still generally be partly to mostly 
sunny with some high clouds. This will result in highs likely being 
a few degrees warmer than previously thought so have brought up a 
bit but holding shy of ensemble and met guidance in the middle 
50s...which is still entirely possible with slower solutions for the 
system to the west. 


A bit of agreement on timing of the initial low approaching the area 
is attempting to occur. At this point...increasing chances that 
Monday night and maybe even the first part of Tuesday may end up 
dry. Enough confidence in trends to remove probability of precipitation Monday evening but leave 
untouched late Monday night through much of the remainder of the period. 
More than likely probability of precipitation will be removed entirely for remainder of 
Monday night in future forecasts. Where the challenges remain is how 
much cold air arrives and how long it sticks around. 00z oper GFS 
continues to bring shot of -3 to -5 c 850 mb temperatures in by Wednesday but 
has now backed off on the much colder scenario with next push of 
coldest air...still only as low as -6 c...passing by to the SW. This 
would result in the potential for rain or snow mixed. 00z European model (ecmwf) 
paints a different picture with the low moving to the northwest slower than 
the GFS and the coldest air not arriving till mainly Thursday. GFS 
ensemble seems to be middle of the Road with progress of system with 
most favorable time frame still in the Wednesday/Wednesday night period followed 
by a push of cooler air. With so many questions in terms of thermal 
fields and timing...will leave temperatures and precipitation types alone through 
the remainder of the period with any changes made now likely having 
to be modified once again...potential flip flopping. If models are 
to be believed after this system moves by...a quick moderation could 
occur with 00z European model (ecmwf) showing surge of well above zero 850 mb temperatures 
for the Holiday weekend and GFS not too far off. 


&& 


Aviation... 


Continued challenges with fog forecasts overnight as patch of 3-4kft 
clouds are drifting across the area. Upper short wave nearing ksbn 
at issuance time and will traverse the area overnight. Lift ahead of 
this feature enough to generate small area of clouds in addition to 
clouds from today across Illinois that have drifted east and refuse to 
dissipate. These VFR ceilings about to move into ksbn and will slowly 
work toward kfwa next several hours. With these clouds do not 
expected IFR visible due to fog but MVFR still possible and stayed the 
course with those for now. If clouds begin to dissipate in wake of 
short wave passage...could see visible drop late. Will monitor for these 
trends. Otherwise expect weak mixing to leave behind scattered clouds on 
Saturday with light winds. 


&& 


Iwx watches/warnings/advisories... 
in...none. 
Michigan...none. 
Ohio...none. 
Lm...none. 
&& 


$$ 


Short term...Lashley 
long term...Fisher 
aviation...Lashley