Weather

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fxus63 kiwx 080827 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
426 am EDT Monday Sep 8 2008 


Short term... 
impressive baroclinic Leaf developing this morning back across the northern 
plains in response to strong middle level SW trough over eastern Wyoming digging southeastward 
within larger scale broad troughing extndg southward from polar vortex over 
Nunavut. Precipitation continues to expand poleward of surface frontal boundary and 
responding to intensifying low level jet over Kansas as a result of intense height 
falls spreading eastward out of the central rockies. Tight downstream ll 
Theta-E gradient extndg eastward sprtg shallow conv growth from the 
MO/IL/IA border area eastward to just north of kind and making steady 
progress northeastward. Shallow but moist saturated ascent suggests adding a 
small window of small chance probability of precipitation SW through middle morning yet concerned 
this may manifest itself moreso further north into the afternoon given 
strong middle level backed follow developing by then and fairly sig middle level based 
ascent over northwest in by 21z. Current pop gradation this afternoon looks a bit 
too tight and too far westward west/00z consensus placement of surface frontal 
boundary and have made some eastward adjustment...however surface wave position 
certainly slower as was expected and deeper middle level trough reflection 
tonight west/corresponding eastward expansion of Cat probability of precipitation warranted especially left 
of surface wave track. Ballooning 850-700mb Theta-E advection also favors 
more of a thunder threat then previously anticipated especially per look at 
NSSL 4km WRF run and will expand that chance across central/south in 
proximity to strengthening ll baroclinic zone both lt this afternoon and 
tonight. In addn...per expanding middle level cloud deck and slightly eastward 
surface boundary positioning...will shave temperatures a bit. 


Strong cold air advection lt tonight and Tuesday morning as surface wave passes and enough of 
a temperature differential in moist cyclonic wrap around to keep west/morning 
shower mention. Otherwise strong drying in the afternoon and incoming surface 
ridging will make for chilly night west low to middle 40s expected. 


&& 


Marine... 
long northerly fetch expected lt tonight in veered strong cold air advection Post frontal follow 
and no doubt will warrant a Small Craft Advisory. However surface ridging building quickly eastward 
Tuesday presents some uncertainty on how long to run it and given 
xpcn of Small Craft Advisory conds not developing until after 00z will defer call to 
dayshift. 


&& 


Long term...(wednesday trough monday)... 


Extended begins with a dry calm Wednesday as flow begins to return 
ahead of the next system with morning temperatures quickly rebounding back 
to at or above climatology by Friday morning. 


Large differences still evident between medium range models handling 
of the entire period...beginning with system for Thursday night into the 
weekend. 00z GFS/ 12z ec advertise surface ridging moving east out of 
the plains as middle level trough digs into the Central Plains. European model (ecmwf) 
elongates ridge to our north and stalls boundary along Ohio Valley 
through the weekend with unsettled weather. In contrast...GFS digs a 
much deeper trough and consequently pushes ridge into the eastern US 
with front clearing the area on Friday night leaving the County Warning Area dry for 
the weekend. Op GFS is an outlier among its ensemble members and European model (ecmwf) 
has shown some run to run consistency while the GFS has been all 
over the map. Also...the deeper GFS trough picks up Hurricane Ike and 
brings it NE through the Gulf into the Florida Panhandle. This 
is...at least for now...an outlier among model tracks for 
Ike...which reinforces reasoning to continue to discount the GFS at 
this time and side with the European model (ecmwf). 


Going by the European model (ecmwf)...probability of precipitation still need to be carried Thursday night into 
Friday as cold front passes through the County Warning Area and stalls just to the 
south. Thursday afternoon probability of precipitation are in question particularly in 
eastern portions of County Warning Area...however ec has not trended slower with 
boundary in pvs runs and have elected not to make changes yet and run 
the risk of having to reinsert probability of precipitation with the next package. After front 
passes...another wave is depicted riding along the boundary Sat 
night/sun as it attempts to return north as a warm front. With 
consecutive runs giving weight to Saturday probability of precipitation and for sake of 
collaboration have added probability of precipitation for Sat which saddles the extended 
with probability of precipitation across many periods. Will hope successive runs allow 
better insight into an appropriate window to focus upon. 


Previous runs of European model (ecmwf) built a ridge in behind this front with 
clearing weather for early week. 00z run has lulled the boundary 
slower and rushed Ike remnants along and right over the County Warning Area. Simply 
cannot bite on this after one model run so have left end of extended 
dry. Largely rode previous forecast temperatures through the week with such 
low confidence which keeps highs near guidance and lows rising late 
in expectation of moisture for the weekend. 


&& 


Aviation... 
VFR conds expected to hold through this afternoon before strong upstream SW trough 
and attendant frontal zone push eastward into the area tonight west/widespread 
MVFR conds developing this evening and an increasing potential for IFR 
conds after 06z as cold air advection ramps. Will look closer at that for 12z 
issuance. 


&& 


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


$$ 


Short term/marine...holsten 
long term...Ludington 
aviation...holsten