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fxus63 kiwx 192125 cca 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana...corrected 
344 PM EST Wednesday Nov 19 2008 


Short term... 


..lake snows to impact the region once again... 


Tonight through Friday morning 


Another in a series of fast moving clippers continues to March fast 
into the Great Lakes region this afternoon. Warm air advection induced cloud cover 
has finally shifted east and will continue to do so. Clouds will 
then make a comeback as the Post frontal cold air advection airmass settles into 
the region. Perhaps the bigger story is what is approaching the 
region...currently over over southeast Saskatchewan poised to enter North 
Dakota...a secondary robust middle level impulse supporting another 
strong cold front into the region by Thursday evening. The combination 
of strong cold air advection under veering ll winds and upper level height 
falls/middle level cooling will support yet another intense lake effect 
event for the Michiana region. Forecast models and ensembles are in 
very good agreement with the synoptic details as well as the 
potential for many mesoscale interactions. Have favored the 
NAM/arw/GFS and sref for details regarding the forecast. 


Tonight...primary wave and cold front will push through the region 
and allow an increase in cloud cover coupled with cold air advection. Have cut probability of precipitation 
in line with neighboring offices. Precipitation production is expected to 
be entirely the result of lake effect process. Hence have pushed 
weather closer to the lake. Secondly...bufr forecasts indicate lake induced 
cape per veering ll flow will not be ample enough until after 
09z...at which point vertical motion fields support upward motion 
into the dgz. Middle level cooling will continue through the day per 
crashing 500 mb temperatures...as ll flow veers northerly supporting longer 
parcel residence times. Forecast models agree on placing increased 
vertical motion through the day period over Berrien County with lake 
convective available potential energy growing in excess of 500 j/kg by Thursday afternoon...supporting 
moderate to heavy lake snow showers. Continued snow shower activity 
will allow snowfall to begin to add up quickly as surface temperatures hover 
near 32 f...with 3 to 6 inches possible in Berrien County by 
evening. Forecast models depict snow showers to remain organized as 
parallel bands through the day...with a transition to longer fetch 
dominate parallel bands by Thursday afternoon as Lake Superior aggregate 
effects increase...and eventually to a single intense shoreline band 
by evening. Organization into the shoreline band will be highly 
influenced by 1)a secondary trough passing through the Great Lake 
Thursday afternoon with Mobile trough characteristics...2)mesoscale and 
microscale interactions...which at this point are still 
undetermined...3)and the evolution of the lake induced cape field 
including the balance of shear vs convective organizational 
influences. Increased large scale ascent per the secondary upper 
impulse will only add gas to the fire...allowing inversion heights 
to rapidly raise to nearly 16kft with cloud top heights approaching 
20kft Thursday evening. Given a more westerly component than Monday/S 
event...expecting the heaviest and most intense snows to remain 
farther east. However...with the potential for the development of 1 
or 2 mesolows...thinking heavier snows could fall a little farther 
west than where h925 Omega fields currently forecast things. So have 
included Starke and marshal in a lake snow watch. Given lake induced 
convective available potential energy of 600 to 800 j/kg and very high inversion heights with Omega 
centered in the dgz. Snowfall rates of 2-5 inches per hour are very 
well possible...especially Thursday evening when the core of 500 mb temperature 
minimum /down to -40c/ will be collocated over Lake Michigan. Things will 
then begin to wind down Friday morning with lowering inversion heights 
and backing ll flow. In addition to heavy snows...areas /possibly 
widespread/ of blowing snow will be likely given expected strong surface 
winds per 25 to 35 knots of flow just off the surface at h95 coupled 
with a strong pressure gradient in place. Have issued a warning for 
Berrien County where the longest duration of snow fall/heaviest 
bands are expected. Left the watch as is due to some uncertainty 
where th best banding will setup given questions on the true ll 
h925-h95 flow...with a warning likely needed for another tier of 
counties once the west or east bias is trend is established. Watch 
outlined counties are at expected to be in an advection at the 
least....with a potential advection needed another tier to the southeast. Total 
snowfall expected to range from 6 to 12 in Berrien with an extension 
of this snowfall maximum possible into either La Porte or St. Joe 
counties. 


&& 


Long term... 
pattern remains active in the extended with lake effect ongoing to 
begin the period Friday followed by another shot of cold air behind 
frontal passage Sunday night with yet another lake effect event potentially in 
the cards for early next week. 


Followed nam12 early in the period which is in general agreement with op 
GFS in regards to lake effect snow ongoing in earnest Friday 
morning. Activity slowly wanes through the day as ll flow backs to 
northwesterly significantly reducing fetch and eql level falls 
through the day with lake induced cape placed entirely below growth 
zone by Friday night. Expecting setup to fall apart by 00z Sat with 
lingering snow flurries downwind of the lake. Low temperatures Saturday 
morning could end up undercutting current guidance by several 
degrees with strong ridging centered just to our south and skies 
clearing Post-Lake effect and have conservatively trended temperatures 
lower. 


Weak middle level wave scoots through the Ohio Valley Sat as surface low 
shears out to our west with only some lingering clouds moving 
through. Upper low then sags into the eastern Great Lakes along with 
associated surface low. Ll SW flow kicks into high gear ahead of surface front 
with 40kt h92 winds per 12z GFS/European model (ecmwf) in advance of frontal passage Sunday 
night. Medium range models disagree on quantitative precipitation forecast potential ahead of frontal passage so 
have kept blanket low chance probability of precipitation with rain or snow as temperatures initially 
begin above fz through 850 mb. Cold air follows with a return to north/northwest 
flow hinting at possibility of More Lake effect. A bit early to get 
into specifics but overall agreement on a more borderline Delta-T 
with 850 mb temperatures only falling to -7c per 12z European model (ecmwf). One difference 
with this system is upper low itself prognosticated to drop through the 
Great Lakes with -35c 500 mb cold pool sliding overhead late 
Monday/early Tuesday resulting in chance probability of precipitation County Warning Area wide through Tuesday 
afternoon. 


&& 


Aviation.../18z tafs/ 
overcast conditions will give way to a period of clear skies this 
afternoon with VFR conditions expected until a cold front arrives. 
Lake effect snow showers are expected to develop tonight in the northwest 
increasing in coverage and intensity through Thursday. Expecting MVFR 
conditions in the northwest with periods of IFR and LIFR likely 
in moderate to heavy snow showers. Otherwise...MVFR cloud deck is 
expected across the remainder of the forecast area in a cold air advection regime. 




&& 


Iwx watches/warnings/advisories... 
in...lake effect snow watch from Thursday morning through Friday 
evening for inz003>005-012-014. 


Michigan...Lake effect snow watch from Thursday morning through Friday 
evening for miz078. 


Lake effect snow warning from 7 am Thursday to 1 PM EST Friday 
for miz077. 


Ohio...none. 
Lm...Gale Warning from 7 PM this evening to 7 PM EST Thursday for 
lmz043-046. 


&& 


$$ 


Short term...Chamberlain 
long term...Ludington 
aviation...Chamberlain 

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