990 
fxus63 kiwx 070526 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
126 am EDT Tuesday Oct 7 2008 


Aviation... 
a large ridge of high pressure will move from west Quebec province 
to New England by the end of the taf period. Conditions should 
remain VFR through the period with except possibly some MVFR or 
IFR arriving close to 06z. Winds should remain east and may be 
gusty this morning given the anticipated pressure gradient. The 
winds may veer a little toward the southeast. Kept the taf 
VFR...but may need to add MVFR/IFR conditions just before 06z. 


&& 


Previous discussion... /issued 215 PM EDT Monday Oct 6 2008/ 


Short term... 
tonight through Tuesday night 


Rather impressive baroclinic zone now in place over the 
region...with 50s in Southeast Michigan to the lower 70s in west central in. 
Quasi-stationary upper level ridge over the Midwest has stalled at 
the moment due to ll cold air advection now ongoing across the southern Great 
Lakes...indicated by cross isotherm flow highlighted in short term 
mesoscale models. Rather potent SW trough now pushing across the NE Continental U.S. 
Supported a rather strong push of cold air into the NE Continental U.S....some 
of which has been incorporated into the widespread southeast flow now 
ongoing across the forecast area per traversing low pressure over the western 
Midwest. Two other important features will affect the weather during 
the period...a nearly closed upper low over Kansas/OK and an advancing 
upper trough over the Dakotas. Both of these upper waves will push 
east and partially phase...supporting intensification of the ll 
veered southerly flow into the region and eventual rain chances...as 
ample moisture is in place across the Southern Plains and lower 
Mississippi Valley...evidenced by 60s-70s surface dewpoints there. 


Forecast model and ensembles are in rather good agreement on 
forecast details in the short term. Have tailored the majority of 
the forecast to the NAM with help from the GFS/ECMWF/sref/and UKMET 
in sorting timing of precipitation through dynamical forecasts aloft. 


Tonight...middle level height rises will continue as ll winds /h925 
forecasts/ veer allowing warm air advection to commence. This will support a diminish in 
cloud cover across the region with perhaps a few middle and cirrus 
hanging on in the NE. Have adjusted temperatures to guidance forecasts...which 
retain warmer 50s in the west. Turbulent mixing downward per 
stronger flow just off the surface combined with a tightening surface 
pressure gradient should hold surface winds up similar to last night and 
allow temperatures to remain mild. Eastern areas will see better potential 
for cooler temperatures with weaker flow prognosticated. 


Tuesday...upper ridge axis will shift east across the region under 
well mixed fast ll flow. Given cloud forecasts by cras and middle level relative humidity 
forecasts by the GFS and NAM...the majority of the forecast area will see mostly 
sunny skies for a good part of the day. Hence...the Prospect for 
warm temperatures looks good. Have opted for a mix to h875 based on buffer 
forecasts...cooling the NE a couples degrees per ongoing warm air advection. This sends 
highs slightly above guidance. There will be an increase in middle and 
cirrus clouds by afternoon west to east with the approach of the 
plains upper vorticies. Q-vector fields clearly display widespread 
large scale ascent will begin to push into the western forecast area by late 
afternoon and expand east and increase overnight. Meanwhile...ll 
momentum forecasts favor the development of a rather potent ll jet with 
up to 40 knots veer flow indicated at h925. This will support 
robust moisture advection into the region...a feature that is highlighted 
on 305k isentropic charts...where 40-50 knots of cross isobaric flow 
is present on the NAM and GFS during the overnight period...under 
aforementioned large scale ascent from the approaching nearly phased 
upper troughs. Have raised pop for these concerns which is in line 
with MOS trends. Have not added timing detail at this time Tuesday 
night...due to concerns on precipitation arrival and favored regions of 
lift...preferring a 12 hour pop. Best forcing and lift look to favor 
the west at this time. Also added thunder for forecast negative 
showalter indices and buffer sounding indications of elevated cape. 


Long term... 
Wednesday through Monday 


Main focus for this package on the first 24 hours or so of the long 
term with the handling of the ejecting upper low and frontal 
boundary which will be sliding through. Showers and possibly a few 
storms will likely be scattered around the area with the main focus 
appearing to be in the eastern areas. As a result of this and also 
give a better blend to late Tuesday night probability of precipitation have increases probability of precipitation to 
likely in east for Wednesday am...but will leave in chance category for the 
afternoon as best lift and dynamics will be pulling away but could 
be some lingering precipitation. Another weak wave looks to move through 
Wednesday night so will maintain chance probability of precipitation but by Thursday things should be 
moving out. While not real confident on how fast the system leaves 
on Thursday will go ahead and drop probability of precipitation for Thursday afternoon. 


In terms of temperatures...trend of being above normal through the period 
appear to be on track yet with highs generally in the 70s. In the 
wake of the above system...mex guidance is showing highs into the 
upper 70s or close to 80...which is not out of the question...but 
will hold with a more conservative approach for now. 


&& 


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


$$ 


Short term...Chamberlain 
long term...Fisher 
aviation...skipper