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fxus63 kiwx 041759 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
1259 PM EST Thursday Dec 4 2008 


Aviation... 
lake effect/Post frontal cloudiness has been diminishing from west-east across 
northern Indiana this morning with west edge extending from mcy to 
just west of FWA at 17z. Appears there is sufficient northwest component 
to the winds to keep the clearing line from progressing much 
farther east so left both terminals with predominantly MVFR ceilings. A 
weak trough moving east across the MS river at this time should move across northern 
Indiana this evening causing -shsn with MVFR visibility at both terminals. 
Although 280-300deg flow not favorable for significant snow showers at 
sbn... there may be a few periods of MVFR visibilities...especially overnight 
as winds veer slightly behind trough passage this evening. 


&& 


Short term... 
today through Friday...the main challenges this 
period include the location and amount of lake effect snow. Much 
colder air was spreading into the region behind a cold front. 850 
mb temperatures should fall close to -18c by Friday morning...with Delta 
T values well over 20. However...very dry air...unconditioned by 
upstream lakes and without cyclonic flow...will continue to spread 
over Wisconsin and then across Lake Michigan. This limited fetch 
will also limit heavy lake effect snow. Went with amounts through 
Friday morning of 1 to a little over 2 inches over far SW lower 
Michigan. Kept highs in the 20s both days. 


Long term... 


.Friday night through Wednesday... 


Few changes to long term package. Well below normal temperatures and 
numerous clippers with periods of snow expected. Things 
looking interesting toward end of period as medium range models have 
been hinting at possible stronger storm system by middle of next 
week somewhere across the Ohio or Tennessee Valley 
regions...possibly followed by coldest air of the season. 


In the shorter term...another clipper system will approach late 
Friday night into Saturday. Best timing of lift and moisture looks 
to be from middle day Saturday into late Saturday afternoon and early 
evening. Have removed probability of precipitation across southeast areas Friday night but 
left low chance pop northwest for continuity. Increased probability of precipitation during 
the day Saturday to likely. As with last several systems...model quantitative precipitation forecast 
looks overdone and will go with lesser amounts. System exiting the 
area this morning generally produced one to two tenths of an inch of 
liquid. Expect similar or even less amounts Saturday but with colder 
air in place expect a higher liquid to snow ratio. Basically 
expecting up to 2 inches with highest amounts currently expected in 
the far north. 


Period of lake enhanced snow Saturday evening transitioning to 
scattered lake effect snow showers. Inversion heights look to remain 
around 6kft or less with moisture depth below this level as well. 
Could get a couple inches out of lake effect if moisture is 
sufficient. Delta T values will certainly be sufficient with values 
in upper teens. This will certainly be watched. 


Models remain inconsistent for next week with phasing and possible 
development of a strong winter storm system in the Ohio or Tennessee 
Valley regions. Several runs of European model (ecmwf) and GFS have shown a rapidly 
deepening system moving up the eastern Continental U.S.. system would look to 
be developing a negative tilt as it deepens and current research 
here at iwx suggest track of system will be farther northwest if it 
indeed occurs. How far northwest is still a question...along with 
whether this system will even materialize. Will therefore not make 
any changes to current grids which have a chance of rain or snow. 
Both GFS and European model (ecmwf) indicating possibility of much colder air 
invading central and eastern Continental U.S. Middle to late next 
week...especially if deep system does develop to aid polar 
intrusion. GFS ensembles remain divided so again few changes to 
temperatures at this point and will monitor. 


&& 


Iwx watches/warnings/advisories... 
in...none. 
Michigan...none. 
Ohio...none. 
Lm...Small Craft Advisory until 7 am EST Saturday for lmz043-046. 


&& 


$$ 


Short term...skipper 
long term...Lashley 
aviation...Taylor