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fxus63 kiwx 181738 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
138 PM EDT Friday Jul 18 2008 


Aviation... 
a weak cold front to the northwest will drift toward the area 
tonight. Expect activity to remain mainly along the front northwest of 
sbn...so have kept tafs VFR with no mention of thunder. 


&& 


Previous discussion... /issued 623 am EDT Friday Jul 18 2008/ 


Short term... 


.Today through Saturday night... 


Another hot and humid day expected but upper ridge begins to weaken 
and weak surface front will sag closer to the area from the north. 
Satellite shows extensive cloud cover near the front from northern 
Michigan to Kansas. Expect some of this higher cloud cover to work 
into northwest areas later today. By late afternoon...front will be 
close enough to northwest to warrant a small chance of 
thunderstorms. 4km NAM WRF output shows some convection after 21z 
over Lake Michigan and drifting into Southern Lower Michigan after 
00z. Have included low chance probability of precipitation these areas from late afternoon 
into the evening. Front continues to sag into northern forecast area 
on Saturday with several weak short waves being prognosticated by models. 
This warrants continued probability of precipitation Saturday. Looks like strongest wave to 
come across late Saturday afternoon and Saturday night with surface 
reflection indicated along frontal boundary. Have raised probability of precipitation in the 
north to high chance category with this feature. 


Long term... 
Sunday through Thursday 


Mean westerly flow over the northern Continental U.S. Will amplify in response 
to an advancing middle level trough now entering the Pacific northwest. The break 
down of a massive ridge over the eastern US will occur in phases as 
a series of middle level speed maxima will generate 
convection...pushing a cold front slowly into the forecast area by Sunday 
morning. The deeper upper trough over the Pacific northwest will eventually 
shift east into the Great Lakes by midday Sunday...supporting a 
stronger surface wave along the frontal boundary. This will support 
convection chances throughout the forecast area given the degree of instability 
in place. The best upper level kinematics will pass to the north of 
the forecast area...along with the best precipitation chances. However...given the 
degree of instability in place per dewpoints around 70 with temperatures in 
the 80s...feel precipitation chances are warranted Sunday through Monday. 
Timing/coverage/and intensity of convection is still very much in 
question given concerns on convective evolution/location and effects 
of previous mesoscale convective system/S and associated boundaries/and strength of embedded 
middle level speed maxima and their effects on frontal location. Severe 
threat on Sunday and possibly Monday remains very questionable at 
this time...although with increasingly strong middle and upper level 
flow...a few strong rotating updrafts would be possible if 
instability is realized. Biggest threat would look to be damaging 
winds given mesoscale convective system/derecho pattern featuring a stalled frontal 
boundary/deep moisture with ample instability in place /ml cape 
around 2000 j/kg per GFS forecasts/and rather strong northwest flow supporting 
increasing deep and ll shear. This will need to be watched. 


Tuesday through Thursday...00z GFS still offering a highly anomalous 
solution...progging a 5690 closed 500 mb low over the upper Great Lakes 
by 06z Wednesday...a solution similar to the 12z European model (ecmwf)/the 12z UKMET and 
00z Gem...but a solution that does not have much support from the 
mean gefs...which makes sense given the deep nature of the 500 mb forecast 
and smoothing through averaging. Gefs perturbation forecasts do not 
display too mich deviation until near the end of the period when The 
Rockies ridge begins to shift east. Given the repeat pattern of a 
deep southeast Canadian upper lows over the past several months...will give 
the 00z GFS/12z European model (ecmwf) solutions some more credibility and continue 
to trend toward them. This offers a slightly cooler and dry solution 
as deep moisture and warmer 850 mb temperatures would be west of the forecast area. 
Overall...this spells little change from the ongoing 
forecast...basically pushing temperatures in the direction of mex trends. 


&& 


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


$$ 


Short term...Lashley 
long term...Chamberlain 
aviation...skipper