798 
fxus63 kmqt 042049 
afdmqt 


Area forecast discussion 
National Weather Service Marquette Michigan 
350 PM EST Thursday Dec 4 2008 


Synopsis... 


Upper air pattern consists of a 500 mb ridge off the West Coast and 
East Coast and a broad 500 mb trough across the rest of the U.S. 
With some shortwaves embedded in this trough. One strong wave in 
this trough is across central Ontario and this is dropping south 
today and will affect the area tonight. 


Short term through 00z Sat... 


Upper level trough remains across the region. NAM showing 850-500 mb 
q-vector convergence moving out by this evening. A clipper type 
system will affect the area Friday night. NAM showing weak isentropic 
lift on i270k-i285k and some moisture across the County Warning Area tonight and 
this is mostly across the northern and eastern County Warning Area. This lift and 
moisture remain across the north and east in the low levels on Friday 
as well on i270k-i275k surfaces. Did not make too many changes to 
the going forecast as previous forecast had things well in Hand. 
Lake effect snow looks to continue as the wind slowly backs to the 
west and west-southwest late tonight and also for Friday. 850 mb temperatures warm 
up a bit and inversion heights fall before the clipper system 
arrives for Friday night...so combo of winds and lowering inversion 
heights should keep lake effect snow in check late tonight and also 
for late Friday afternoon. Overall...did not change much. 


Long term...00z Sat - 00z Monday 


Guidance remains in strong agreement through day 4. GFS still looks 
favorable through day 6. Models showing considerable divergence 
there after contributing to lower confidence in the models. 
Therefore, will follow HPC recommendation of going with GFS through 
day 6 and a blend of the ensemble means day 7. 


A weak shortwave trough rotating through the base of the middle level 
low over Hudson Bay will sweep through Upper Michigan Friday night 
and Saturday. The surface low over southern Manitoba will also sweep 
across Upper Michigan and reach Lake Huron by Saturday evening. A 
ridge developing over central Canada will dive into south central 
Canada and the northern plains by Saturday evening. Q-vector 
convergence and isentropic ascent associated with this system will 
produce system snow over the area. 


The shortwave will deepen into a longwave trough and push east into 
southwest Quebec. A weak ridge and a pronounced surface ridge will 
push into Wisconsin and Western Lake Superior by Sunday evening. The 
system snows will weaken as the northerly winds bring an 850mb 
thermal trough into the area increasing the Delta-t's to around 23c 
and increasing the potential for les over the area. The areas most 
likely to receive the heavy les will be those most affected by 
northwest winds flows. Strong winds coming off of Lake Superior 
along with snowfall potential of 4 to 6 inches. Thus plan to go with 
a Winter Storm Watch for the Keweenaw peninsula. Limiting factors 
of les will be the strong winds and the duration before the dry air 
moves into the area. 


As the longwave trough lifts northeast into the Canadian 
maritime...another longwave trough will develop over the Central 
Plains on Sunday night and Monday into Monday night. The surface 
ridge will shift east as cold front tracks into the u.P. On Monday 
and progress on to lower Michigan Monday night. Winds will veer 
northwest following the frontal passage. This will produce a lake-850mb 
Delta-T of around 18c. This will lead to a les production across 
much of the northern part of the area. As dry air descend on the 
area and winds back southwest ending the chances of les. 


A middle level low will shift out of northern Manitoba into northern 
Ontario...in association with a longwave trough tracking through the 
upper Mississippi River valley. The longwave trough will sweep 
through the forecast area Tuesday night and Wednesday while 
deepening. Meanwhile...another ridge will settle south out of 
central Canada cold air advection ahead of the ridge will continue 
to produce Delta-t's of 23c to 27c over Lake Superior. This is 
plenty unstable at the low levels to keep the chances of lake effect 
snow showers going. This will also produce very cold temperatures 
across the area. Tuesday night low temperatures will dip to near 
zero over the western u.P. 


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


Conditions remain favorable for lake effect -shsn off Lake Superior 
under nwrly flow. Under nwrly flow...ksaw won't see any significant 
-shsn. Conditions there should generally be VFR...though with cool 
temperatures aloft/afternoon heating...there could be MVFR -shsn this afternoon. At 
kcmx...conditions should generally stay IFR...though some breaks of 
MVFR conditions are certainly possible during lulls in the snow 
showers. More concentrated/persistent LIFR conditions are expected 
by evening as winds back wrly which will increase low-level 
convergence and set up a longer fetch for lake effect into kcmx. As 
winds go SW Friday morning...conditions will slowly improve at kcmx. 


&& 


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


Gales possible on Sat and Saturday night...otherwise winds look to 
stay below 30 knots through the period with a couple other periods 
close to gales though. Winds diminish by Sunday as high pressure 
moves across the Great Lakes. Srly gales possible on Monday...mainly 
eastern sections of Lake Superior...ahead of low pressure system dropping 
into the region from central Canada. 


&& 


MQT watches/warnings/advisories... 
Upper Michigan... 
lake effect snow warning until 10 am EST Friday for miz006-007. 


Winter Storm Watch from Saturday afternoon through Sunday 
afternoon for miz006-007-085. 


Lake effect Snow Advisory until 7 PM EST this evening for miz004. 


Lake effect snow warning until 7 PM EST this evening for miz002- 
084. 


Winter Storm Watch from Saturday morning through Sunday morning 
for miz001>003. 


Lake effect snow warning until 7 PM EST Friday for miz003. 


Lake effect Snow Advisory until 7 PM EST Friday for miz001. 


Lake effect Snow Advisory until 1 am EST Friday for miz085. 


Lake Superior...none. 
Lake Michigan...none. 


&& 


$$ 


Synopsis/short term...GM 
long term...dlg 
aviation/marine...GM 

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