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fxus63 kiwx 172320 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
720 PM EDT Wednesday Mar 17 2010 


Aviation... 
surface ridge will move across the area tonight providing light winds 
with only a few cirrus for clouds. Cold front over the northern plains will 
move east-southeast to the upper Great Lakes by 00z Friday. Low levels will remain 
relatively dry as the front approaches, so just expecting an 
increase in cirrus, with moderate SW-west surface winds during the day Thursday. 


&& 


Previous discussion... /issued 355 PM EDT Wednesday Mar 17 2010/ 


Short term...tonight through Thursday night... 


Mostly clear skies and relatively light winds for the next 36 hours as 
surface to upper ridging continues to dominate weather in the Midwest. A 
few high clouds and a little tighter pressure gradient...bringing 
slightly stronger winds...in store for Thursday as an area of low 
pressure brushes the US/can border. 


Kept colder lows tonight at kbeh given how much they tanked last 
night into the low 20s but with a bit of onshore flow will not get 
overly aggressive and will leave lows tonight near 30. Lowered highs 
a touch near the lake in northern Berrien County Thursday which undercuts 
guidance immensely but afternoon temperatures today in middle to upper 40s give 
little reason to believe these areas will see middle or upper 50s with a 
wswrly surface wind. Did raise temperatures substantially in northern LaPorte County 
as 10-12kt gradient wind from west-southwest should keep lake breeze out of 
LaPorte County Thursday. This should provide a much more pleasant 
day than today in areas like Michigan City where temperatures are currently 
riding in the middle 40s at 19z. Unfortunately for those on the Gold 
coast in Michigan...a drive inland will probably be necessary to 
enjoy the middle 60s we will all enjoy Thursday. Highs well above guidance 
outside lake breeze influence tmrw looking good as mix down 
techniques from h82-850 mb that are working today show a few degree 
increase for Thursday. Very large diurnals still in store tonight as 
dewpoints have fallen into the teens this afternoon. 


Long term... 


.Friday through Wednesday... 


Long term focus remains on strong storm system in the Midwest this 
weekend...its impact on our area and the strong cold air advection 
in its wake. 


Latest 12z guidance has simply lowered forecaster confidence in 
details with timing/strength of weekend system and associated 
precipitation. 12z GFS has come in much faster than previous run 
which is directly opposite of previous shifts thoughts and changes 
which were made to forecast grids. Given the large spread in models 
and lack of any run to run continuity will not make large changes to 
grids. However...will remove some of the timing details as new model 
guidance is significantly different by 12 to 18 hours now from 
previous runs. The overall idea remains that a strong upper low and 
associated cold front will track across the forecast area from 
sometime between Saturday afternoon and Sunday afternoon. Most of 
area should see rain within this period but timing and amounts still 
very much in doubt given solution differences. Faster and less 
phasing offered by most recent GFS and previous trend of European model (ecmwf) would 
mean less rainfall and faster arrival of colder air. Still think a 
slower solution with southern wave development along surface 
boundary is still plausible and not ready to give up on some phasing 
and thus stronger and slower solution. A quick look at new 12z European model (ecmwf) 
supports this idea and is similar to its previous run. Hence The 
Hedging and attempts to keep forecast positioned in the middle of 
all solutions but closer to latest European model (ecmwf). 


Less phasing of waves would likely mean more of a glancing blow of 
cold air Sunday into Monday but we still should see a day or two of 
well below normal temperatures. This will feel especially cold given 
this weeks warm spell and potential windy conditions with strong 
pressure gradient and winds off of Lake Michigan. Sunday temperatures 
remain tricky with new GFS now pushing cold front well through the 
area by 12z Sunday with cold air advection during the day followed 
by secondary front Sunday night and much colder air on Monday. Have 
lowered temperatures a bit more on Monday with strong cold air 
advection and northwest flow. Medium range models look too dry in relative humidity 
and moisture fields but this likely due to synoptic drying and 
subsidence. Delta T values of over 13c should easily yield lake 
clouds and at least flurries. Measurable snowfall still very 
questionable given the degree of synoptic drying being shown so will 
not add any probability of precipitation to forecast for now but will add flurries. Expect 
mostly cloudy conditions with steep low level lapse rates through 
Monday afternoon. 


Indications in models of a warm up by Tuesday into Wednesday. Remain 
skeptical with low confidence given the lack of ability to properly 
model the strong dynamic system between now and then. Stayed near 
HPC numbers with trend of warming. 


&& 


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


$$ 


Short term...Simpson 
long term...Lashley 
aviation...jt