989 
fxus63 kiwx 201346 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
946 am EDT sun Jul 20 2008 


Update... 
will now proceed with grids update to remove probability of precipitation as instability 
axis across the southeast gave more more quick round of scattered showers. Axis 
now shifting east of the area with area of clearing for most 
locations at this time. Concern then turns towards previously mentioned 
expanding low cloud deck now coming onshore from Lake Michigan. No signs 
of erosion or mixing yet with weak circulation noted on Sat over 
the lake. Will adjust cloud trends in the northwest to account for this 
but still remain optimistic on will erode or mix out. This same 
feature could help set the stage for increased convective 
potential as differential heating on the edge of it could be 
sufficient to overcome lack of good trigger/focus. Will need to 
monitor this as temperatures continue to warm. For now no changes to 
afternoon grids. 


&& 


Previous discussion... /issued 740 am EDT sun Jul 20 2008/ 


Aviation/update... 
complex of storms will be clear of the County Warning Area in next 15 to 20 
minutes leaving behind areas of low clouds but little or no precipitation 
through the morning as atmosphere begins to recover. Decent 
velocity signatures in the 50 to 60 knots range shows wind potential 
but strong eml seems to have kept things in check. Will be doing 
an update to grids shortly to remove scattered morning mention and go to 
either chance or maybe isolated at best but leave afternoon intact as 
we await destabilization again later today and tonight to possibly 
spark off some activity. It remains possible that we could remain 
capped enough today to see nothing until tonight when next complex 
expected to form over Iowa/WI moves in. 


In terms of tafs...layer just below 1000 feet has shown up at kfwa 
and based on Sat trends should stick around through at least 14z 
so have went predominate with lower 400 feet ceiling based on other 
upstream observation. Ksbn is bouncing around scattered-broken at the 400 feet level. 
Sat shows back edge should be leaving the area but upstream observation 
still show the clouds remaining so have went predominate 400 feet 
ceilings for a few hours and monitor trends. As for the remainder of 
the day will leave tafs dry for the moment for above reasoning. 


Previous discussion... /issued 329 am EDT sun Jul 20 2008/ 


Short term... 
today through Monday night... 
kiwx radar showing leading edge of convective complex moving across 
Southern Lake Michigan at this time. With ongoing convection will bump up 
pre-first period to likely in the western County Warning Area. Still some 
uncertainty as to how far east precipitation will get as storms move into 
more stable airmass...so will keep probability of precipitation in chance range 12-18z but 
reword to scattered. Surface boundary to remain in the area through 
Monday keeping chances for sh/thunderstorms and rain in the forecast...but given model 
tendency to perform poorly in the wake of nocturnal convective 
complexes and the lack of any one particular significant frontal 
wave but rather a series of weak impulses...will keep probability of precipitation in chance 
range for now. Models in reasonable agreement with pushing boundary 
south of the forecast area by 06z Tuesday so will keep with current 
grids bringing in dry forecast at this time frame. Expect warm and 
muggy conditions today and tonight...while highs most areas expected 
to generally be in middle 80s...Lima reaching 89f yesterday a good 
indication that any location receiving some sun during the afternoon 
could easily approach 90f. Not quite as warm Monday and drier 
airmass beginning to move in Monday night as boundary sinks 
southward. 


Long term... 
Tuesday through Saturday 


Mean northwest flow will prevail as a rather deep upper low will again 
persist over southern Quebec...with mean upper ridgeing over The 
Rockies and plains. Have followed the mean gefs forecasts through the 
period once again...as it has been the most persistent of late and 
continues to agree well with this Summer/S pattern of rockies 
ridgeing with a slow progression east...flattening in the process. 
The ecwmf continues to forecast an anomalously strong longwave 500 mb ridge 
well into Canada by middle week...which seems much too aggressive given 
the active northern stream flow of late. Pattern will feature dry NE 
flow...which will prevail through much of Thursday. Latest guidance does 
support a small precipitation chance on Tuesday with the passage of a 
secondary front under a second short wave impulse. However...best 
instability and forcing looks to remain well south of the County Warning Area and 
have retained dry forecast. The GFS as well as the mean gefs has 
been pretty persistent with a shortwave trough advancing through the 
Great Lakes in the Thursday night/Friday time frame. Felt a small chance 
pop mention was warranted given this observation and mex trends. 
Otherwise...the only other change in the period was to lower highs 
given prognosticated 850 mb temperatures down to 11c by Wednesday...prognosticated mixing 
heights...and a continued persistent mex highs at or around normal. 
Feel more conformable staying close to climatology days 6 and 7 given 
building ensemble spread and model bias of trying advance large 
scale ridging east to fast this Summer. 


Overall...look for a less humid week with high pressure in control 
for the majority of the period. Temperatures are expected to remain right 
around seasonal values...save near Lake Michigan where long fetch 
northerly flow Tuesday and Wednesday may limit highs the 70s. 


&& 


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


$$ 


Aviation/update...Fisher 
short term...logsdon 
long term...Chamberlain