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fxus63 kiwx 050953 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
553 am EDT Sat Jul 5 2008 


Aviation... 
infrared satellite imagery suggests ragged northern edge of strato cumulus deck over 
central Indiana just reaching FWA at 09z. Clouds have slowed 
radiational cooling at the terminal early this morning and with 
temperature still a few degrees c from the xover temperature...will go with 
persistence and keep visibilities VFR this morning. Diurnal mixing and 
advection of drier air from the NE should break up northern edge of 
strato cumulus deck further by midday with just a few cumulus developing in rather 
dry airmass this afternoon. With ridge moving into the area 
tonight...should be good radiational cooling over northern 
Indiana...likely leading to MVFR visibilities by morning. 


&& 


Short term... 
weak shortwave moving southeast across the area this morning through general weak northwest 
flow aloft. This shortwave still forecast by models to close off into an 
upper low today...hwvr...a little farther southeast than earlier 
indications. Dry airmass...weak anticyclonic low level flow...and weak 
height rises over the area in wake of this shortwave and with High 
Plains ridge building eastward into the upper Great Lakes as strong shortwave tops it 
moving from Pacific northwest/southwestern Canada to Manitoba/ND by this evening...will result 
in stable conditions across the County Warning Area today. Ridging aloft/height 
rises expected to continue over the area tonight/Sunday as 
upper low drifts east through the Ohio Valley and northern plains shortwave 
moves east to ls/upper MS valley. Models suggesting weak-moderate 
instability developing Sunday afternoon as low level flow veers from east-S in 
response to surface ridge moving east from the Great Lakes and becoming 
absorbed by Bermuda high as cold front moves east from the northern plains. 
However...bufr soundings indicate warm temperatures around 10k feet will cap 
deep convection so continued with dry forecast. 


Surface cold front expected to extend from eastern u.P. Southwestward to central Iowa by 12z 
Monday. Thunderstorms likely will develop along the front Sun afternoon/evening and be 
advected east in westerly flow aloft overnight. However airmass over 
in/WI/OH will stabilize with loss of heating Sun night and propagation 
vectors and 850-300mb thickness...and moderately unstable MUCAPES over 
the middle MS valley all suggest deep convection will turn southeast into western 
Illinois...with just some dissipating convection possibly makes a run toward 
our County Warning Area...thus kept dry forecast in tact for Sunday night. 


Highs should be a few degrees warmer today as airmass undergoes 
slow modification. Models suggest northern edge of strato cumulus deck now 
covering southeastern portion of County Warning Area will erode with dry NE flow 
today...hwvr... don't seem to be handling moisture too well at this time. 
Have blended persistence into models by 18z suggesting a slow 
clearing this area this morning...allowing for temperature recovery this 
afternoon. Good radiational cooling expected tonight as surface ridge moves 
into the area...cooler mav MOS mins preferred which is several degrees 
below previous forecast grids. Continued airmass modification combined with weak 
low level warm air advection should result in temperatures slightly above normal by Sunday 
afternoon-night with highs in the m80s and lows in the l-m60s. 


&& 


Long term... 
Monday through Friday. 


Challenge one will be with remnants of mesoscale convective system expected Sunday night 
from the west. GFS/Gem showing precipitation moving across the County Warning Area during 
the morning hours of Monday. While the complex will likely have 
weakened...several boundaries should interact with unstable 
conditions as temperatures climb into the middle 80s. GFS gives sbcapes of 
around 2k j/kg and lifted indice's -2 to -4 c with NAM little bit lower on 
values. Not overly concerned about severe threat other than risk for a 
wet microburst with strongest storms. Larger concern for Monday 
afternoon looks to be heavy rain as slower mvmt of storms and precipitable waters  
at or above 2" in many areas and warm cloud layer at or above 11,000 feet would yield 
some efficient rain producers. For now no sig changes to Monday 
until overall mesoscale setup becomes better defined. 


Cold front will begin to shift into the area Monday night into 
Tuesday night with best potential for showers and thunderstorms 
coming together. Exact timing still a bit tricky with main short wave 
energy arriving into Tuesday. Models agree on focus of low level jet to be 
over Iowa/MN/northwest Illinois Monday night and then slowly shifting east 
into Tuesday. Much like with past system...decent mesoscale convective system should develop 
and move towards the area late Monday night into Tuesday but track 
GOES anywhere from central lower Michigan to much of our County Warning Area. With that much 
uncertainty would prefer to hold off on going real high on probability of precipitation. 
Have leaned towards lower end probability of precipitation of mav in the chance range...but 
higher than past grids more towards a 50 pop in the northwest. Would not be 
surprised if next forecast or 2 will need to increase to likely but 
would like to see pattern become a bit more defined in terms of mesoscale convective system 
track. Precipitation chance continues into Tuesday night as front moves through. 
Could be some lingering precipitation early Wednesday but for now will 
leave dry. 


For remainder of Wednesday into Friday...high pressure looks to grab hold 
and bring a shot for cooler temperatures again. With general zonal flow to 
continue...having a hard time at this point buying a cooler solution 
and as a result will maintain temperatures around normal the remainder of 
the period. 


&& 


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


$$ 


Short term/aviation...jt 
long term...Fisher