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fxus63 kiwx 210525 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
1225 am EST Friday Nov 21 2008 


Aviation... 
band of lake effect snow along Eastern Shore of lm moving due south into 
sbn at this time is expected to be persistent overnight as there will be 
little change in wind fields. Thus expect moderate-heavy snow to continue at 
sbn until around daybreak with predominantly LIFR visibilities. The northerly 
flow should keep lake effect shsn west of FWA through early Friday 
morning. After daybreak low level drying and backing winds should 
diminish band of snow showers with remnants drifting eastward during 
the day possibly briefly impacting FWA... for now just continued with 
vcsh but may need to add tempo MVFR group with 12z tafs. At sbn 
with lake effect ending conditions should improve to VFR by afternoon 
and continue through Friday night. 


&& 


Previous discussion... /issued 844 PM EST Thursday Nov 20 2008/ 


Update... 


Have updated forecast to include Cass County Michigan in warning. 
Latest radar trends showed this area under a strong band since late 
afternoon and phone calls indicated 3 inches had fallen in just a 
couple hours. Upstream reports to the north also indicated close to 
6 inches. Remainder of headlines remain unchanged at this time but 
some growing concern for northern Elkhart County later tonight. 


Latest ruc13 paints and interesting picture for lake band evolution 
tonight. Shore parallel single band beginning to get more organized 
per regional radar mosaic and is currently aligning itself right 
along eastern Lakeshore North of Benton Harbor. Water vapor showing 
short wave passing through the region and this is disrupting bands 
slightly over our area but veering winds behind it is helping set up 
the single band. We are also beginning to see a strong streamer 
connection to Lake Superior which should help fuel this band 
overnight. Ruc13 925mb Omega has this handled well with its 
depiction of a wave of strong lift moving south overnight from 
Superior and phasing with current developing band. Thus going 
forecast on track for now and more intense bands expected after 
midnight and into Friday morning. 


Of some concern is where the heaviest snow will fall. Model Omega 
fields have been displaced a bit too far west...which we have noted 
as a bias at times in the models. However this was not the case 
earlier this week. Radar trends suggest that at least through the 
next several hours...eastern Berrien and western Cass counties in 
Michigan along with St. Joseph and western Elkhart counties in 
Indiana will be in the bullseye of this developing band. Therefore 
Cass was upgraded to the warning and we are monitoring trends for 
possibly upgrading Elkhart. Secondary band coming onshore into 
southern Berrien and LaPorte counties has been rather efficient with 
estimated reports of 3 to 4 inches. 


Outside of headline areas...bands have been very efficient and 
producing narrow and brief bands of intense snowfall. Kfwa reported 
heavy snow for a few minutes and this band has intensified last half 
hour. Added scattered snow showers to eastern areas with up to an 
inch possible given the heavy but brief nature. Further updates may 
be needed as this band becomes more north south oriented. 


Short term...(tonight through Friday night)... 
lake effect snow event in its infancy ongoing across Northwest Indiana and 
SW Michigan this afternoon. Mainly disorganized multiple bands with 
low quantitative precipitation forecast and lite snow amounts thus far. Nevertheless...setup is 
underway and comparison of NAM bufr sounding with ascent sounding 
from 16z out of ksbn matches up well. 850 mb temperatures around -10c 
producing low end Delta-T of 16 degree with basically unidirectional 
winds between 310-330 degree at around 20kt. Sounding also confirms 
significant cooling further aloft at 700 mb underway with temperatures ahead of 
12z model forecasts having fallen to -20c by 16z. Followed nam12 with 
forecast details with its good handle on vertical profile and 
consistency with 12z run. 


Winds veer a little more northerly as instability increases this 
evening and peaks overnight with more cooling aloft increasing Delta 
T values to 20c with high eql peaking near 15kft and excellent lake 
induced cape throughout the growth zone. Nam12/RUC depiction of 
lake effect plume consistent with pvs runs and with inherited 
forecast with all signs continuing to point to the formation of a 
dominant band overnight with heaviest impact along NE 
LaPorte...Berrien...and St Joseph counties with advisory further 
south along forecast best uvm into Fulton County. 


Lake induced cape begins to collapse after 12z as warmer air starts 
to move in aloft however eql levels remain at or below low end of growth zone 
with some lake induced cape through 21z per NAM before soundings. 
However fetch is sharply cut beyond 18z as ll winds back to west-northwest. 
Accumulating snow slackens as it shifts north with backing winds and 
comes to and end abruptly beyond 18z as setup falls apart. 


With continued cloud cover highs Friday peak only near 30. Lows 
Saturday morning could be problematic as areas with fresh snow cover 
that clear out before morning could cool more than guidance would 
indicate. Surface ridge to the south now looks to be a bit further away 
and with light gradient winds a possibility will ride guidance for 
low temperatures primarily in the upper teens. 


Long term...(saturday through thursday)... 
surface high pressure centered over the Tennessee Valley will bring a 
quiet start to the extended period. Northwest flow aloft will bring weak 
upper level disturbance into the region Saturday afternoon. With 
surface high underneath...little moisture and forcing to work with 
so nothing more than an increase in clouds for now. Surface high 
moves to Carolina coast Sunday and next system takes shape in the 
plains setting up brisk SW flow for our area. Front approaches 
Sunday night bringing next chance for precipitation. Decent amount of warm air advection 
ahead of the front will bring precipitation type into question. Dprog/dt 
indicating GFS fairly consistent past few runs with our area being 
close to rain/snow threshold. BUFKIT sounding also showing shallow 
1200ft surface based warm layer so will continue with mix of rain/snow 
Sunday night...then all snow Monday after frontal passage. Cyclonic northwest flow 
in the wake of this system will bring another round of les Monday 
and Tuesday. High pressure again settles into Tennessee Valley by 
Wednesday bringing dry forecast through Thanksgiving day. Expect temperatures 
to generally remain at or below normal through the period. 


&& 


Iwx watches/warnings/advisories... 
in...lake effect snow warning until 1 PM EST /12 PM CST/ this 
afternoon for inz003-004. 


Lake effect Snow Advisory until 1 PM EST /12 PM CST/ this 
afternoon for inz005-012-014>016. 


Michigan...Lake effect snow warning until 1 PM EST this afternoon for 
miz077-078. 


Ohio...none. 
Lm...Gale Warning until 4 am EST early this morning for lmz043-046. 


&& 


$$ 


Short term...Ludington 
long term...logsdon 
aviation...Taylor 
update...Lashley 

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