343 
fxus63 kmqt 061730 aab 
afdmqt 


Area forecast discussion...updated for 18z taf issuance 
National Weather Service Marquette Michigan 
130 PM EDT Sat Sep 6 2008 


Updated aviation discussion for 18z taf issuance 


Discussion... 
upper air pattern consists of a 500 mb ridge off the East Coast and 
west coasts and a longwave trough across the central U.S. With 
numerous shortwaves embedded in the trough. On shortwave is across 
northern WI and this has kicked off some showers. This shortwave 
moves through this morning and the trough stays across the area 
through this weekend into early next week. 


NAM taking 850-500 mb q-vector convergence and some moisture and 
moves them out tonight before returning them both sun evening and 
returning both again Monday night. GFS shows about the same thing and 
will use a blend of the European model (ecmwf)/GFS and NAM for this forecast. Looks 
unsettled for a while and there will be chances of rain through most 
of this weekend...however a widespread and heavy rainfall does not 
look likely at this time. Overall...did not make too many changes to 
the going forecast. Did remove thunder though from the forecast as 
instability is marginal enough for it at this time. Temperatures 
looked good and made very few changes. Abundant and deep moisture do 
not look likely either...so kept chance probability of precipitation in there. 


&& 


Aviation (for the 18z taf issuance)... 


Expect MVFR ceilings to persist at least occasionally at both sites the 
rest of this afternoon with lingering low level moisture shown on recent tamdar 
sdngs/small surface dewpoint depressions in the presence of diurnal heating. But 
the trend should be for a gradual improvement with this surface heating lifting 
the ceiling base. MVFR ceilings will likely redvlp at cmx tonight with expected 
upslope westerly flow and diurnal cooling before the arrival of drier air 
now in western Minnesota tends to break up any low cloud. Saw will be more sheltered 
from this flow...so radiation fog is a possibility there. Then VFR 
conditions will be the rule after any morning fog Burns off at saw on sun 
through 18z. 


&& 


Marine (for the 4 am Lake Superior forecast issuance)... 


Low pressure over northwest WI will be moving across Lake Superior today 
and tonight. Winds up to 20 knots are possible today...mainly around 
the low over west and Central Lake Superior. However...there could 
be a period tonight over Southern Lake Superior of up to 25 knots west 
winds on the south side of the low. Winds will diminish below 20 knots 
for sun as the next trough approaches from the northwest. In the wake of 
this trough for Sun night into Monday morning...cold air is expected to 
flow in...resulting in a period of northwest 15 to 25 knots...possibly even 30 
knots winds. The strongest winds should occur on north central and 
Eastern Lake Superior Monday morning. Expect winds to diminish Monday afternoon 
with wind speed below 20 knots for after midnight Monday night into Tuesday as 
a ridge of high pressure moves across. Southerly winds will attempt 
to pick up Tuesday night as the ridge heads off to the east...but 
thinking is that stronger winds...up to 25 knots will hold off until 
Wednesday evening. That is when a trough of low pressure approaches from 
the plains. 


&& 


MQT watches/warnings/advisories... 
Upper Michigan...none. 
Lake Superior...none. 
Lake Michigan...none. 


&& 


$$ 


Discussion...gjm 
aviation...kc 
marine...aj