Weather

290 
fxus63 kapx 211139 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
639 am EST Friday Nov 21 2008 


Synopsis.../issued at 401 am/ 


Midnight surface analysis shows a tight pressure gradient across the 
western Great Lakes...to the east of an elongated 1040+mb area of 
high pressure over the plains states. Small scale trough axis lies 
northwest-southeast across Lake Superior and the St. Mary's River... 
with some weak ridging to the north of Lake Superior within the cold 
air over northern Ontario. North flow lake snow bands continue to 
impact parts of eastern upper and most of northwest lower...with a 
narrow strip of clearing along the I-75 corridor in northern 
lower. 


Elongated surface high will build into the western Great Lakes over 
the next 24 hours...with warmer air returning for the latter half of 
the weekend as southerly return flow develops ahead of short wave 
energy digging into the upper Midwest. This feature will set the 
stage for more unsettled weather to return by Monday. 


Jpb 


&& 


Short term.../issued at 401 am/...today 


Lake effect snow showers will continue to be the main issue today... 
with shifting winds becoming the complicating factor. Instability 
parameters remain impressive as deep layer cold advection has pushed 
inversion heights above 600mb...with 850mb temperatures around -15c 
per 00z apx radiosonde observation. Forecast lake induced cape values above 1100j/kg 
through this afternoon. Infrared imagery shows a good bit of low/middle 
level moisture north of Lake Superior poised to drop across the lake 
today...along with a middle level speed maximum which should help maintain 
a deep mixed layer through the afternoon. As mentioned above... 
backing low level flow is going to complicate matters today as winds 
become more northwest or even west-northwest over Northern Lake 
Michigan by later this afternoon. Radar trends off the kmqt 88d and 
Montreal River radars show winds are already beginning to shift more 
northwest over Lake Superior. This wind shift will gradually 
shorten the effective fetch over Northern Lake Michigan...though 
decent trajectories will continue into far northwest lower through 
the afternoon. Another possible concern for northwest lower is that 
weakening low level flow may also disrupt better organization during 
the afternoon...especially given tremendous instability in place. 
Can't be totally sure about that...but it is something to consider 
especially with loss of effective fetch and "monster" banding 
emanating from Central Lake Superior. Current thinking is that best 
accumulations will be during the first part of the day in the 
M-37/US-131 corridor given potential for best organization. Off 
Lake Superior...there may be a period of focused convergence in the 
vicinity of Whitefish Bay through the day...which may result in 
persistent heavier snow accumulations there. 


As far as the current headlines go...not planning to make any changes. 
Advisory for Emmet/Otsego/Crawford starts at zone issuance...and 
given uncertain evolution with changing wind fields...hard to 
justify making any changes at this point. Headlines for Benzie and 
M-55 counties around midday and that looks fine...once heavy 
banding shifts east of this area accumulation potential should 
diminish. Accumulations across the remaining advisory area a 
general 3-6 inches. Across eastern upper...considered putting 
Chippewa in a warning but will just keep the advisory for both 
Chippewa/Mackinac in place. 


Jpb 


&& 


Long term.../issued at 401 am/...tonight and beyond 


Tonight...lake effect intensity expected to wind down as low/middle 
level warm advection and increasing anticyclonic flow help bring 
inversion heights down...and drier air begins to work into the 
area. Expect drainage flow out of Ontario to become predominant 
across eastern upper overnight...and will probably push remaining 
snow shower activity out of the area as low level flow takes on an 
easterly component. Snow showers will probably stick around much of 
the night across northwest lower...may also see a remnant Lake 
Superior/eastern upper band get pushed out into Lake Huron by 
developing land breeze...and possibly into the US-23 corridor 
between slh-apn overnight. 


Saturday...other than perhaps some residual snow showers across 
northwest lower during the morning hours...finally looking at a 
quiet period across the forecast area with a mix of clouds and sun 
anticipated. Deep layer warm advection continues Saturday night... 
ahead of a developing warm frontal structure forecast to set up west 
of the forecast area overnight. An increase in low clouds is 
probably in the offing...moisture may be too shallow to support 
measurable precipitation but could result in some freezing drizzle 
(which we'll leave out of the forecast for the time being). 


No changes made to Sunday and beyond. 


Jpb 


&& 


Marine.../issued at 401 am/ 


Gusty northwest winds to continue today...resulting in a 
continuation of small craft advisories for all nearshore zones 
through today. Will probably allow most advisories to expire 
tonight as surface ridge axis builds into the western lakes and 
pressure gradient weakens...exceptions may be northwest lower 
nearshore zones and straits to Presque Isle light Lake Huron zone 
(mainly due to residual wave issues). Headline conditions not 
expected Saturday as flow shifts to the southwest. 


Jpb 


&& 


Aviation.../issued at 637 am/...valid for 12z tafs 


Lake effect snow showers to continue...bringing occasional IFR 
conditions to pln/tvc through this afternoon. Lake convection 
expected to diminish in coverage and intensity tonight. 


&& 


Apx watches/warnings/advisories... 
Michigan...Lake effect Snow Advisory until 1 PM EST this afternoon for 
miz033. 
Lake effect snow warning until 7 PM EST this evening for 
miz019>021-026-027. 
Lake effect Snow Advisory until 7 PM EST this evening for miz008- 
015-016-022-028. 
Lake effect snow warning until 1 PM EST this afternoon for 
miz025-031-032. 
Lm...Small Craft Advisory until 7 PM EST this evening for lmz323-341- 
342. 
Small Craft Advisory until 5 am EST Saturday for lmz344>346. 
Gale Warning until 7 am EST this morning for lmz344>346. 
LH...Small Craft Advisory until 7 PM EST this evening for lhz345>349. 
Ls...Small Craft Advisory until 7 PM EST this evening for lsz321-322. 


&& 


$$ 

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