801 
fxus63 kapx 042057 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
357 PM EST Thursday Dec 4 2008 


Synopsis.../issued at 357 PM/ 


An Alberta clipper will drop across the western Great Lakes 
Saturday...resulting in a transition from lake effect to more 
widespread snowfall Friday night into Saturday...with locally 
heavier amounts in southwest flow off Lake Michigan. A fresh shot 
of cold air will move in behind the system for Sunday...keeping the 
threat for snow showers going in areas favored by mainly northerly 
flow. 


Jpb 


&& 


Short term.../issued at 357 PM/...tonight 


Lake effect will rule supreme tonight as the coldest air (850mb 
temperatures of -18c) of this Young winter season (i know...it 
already seems like an eternity for some) overspreads the comparative 
Bath-like waters of the western Great Lakes tonight. However...as 
what has been observed today...it takes more than just over-water 
instability to induce heavy snowfall. Ascertaining this other 
critical elements...placement and amount of additional snowfall... 
and...of course...headline management remain forefront and center 
of the forecast concerns tonight. 


First...a brief description of the big picture. Real-time 
observational data shows rather impressive northern Wisconsin 
shortwave making steady southeast progress this afternoon... 
setting its sights on the Northwoods later today. Upstream acars 
soundings (the few that there are) support model projections of a 
rapid uptick in inversion heights as this feature overspreads the 
area. Closer inspection does show the latest NAM-WRF...which shows 
inversion depths growing to 11kft this evening...is much too 
aggressive...with much more support for the less extreme GFS 
scenario of inversion heights of 5kft to 7kft. Otherwise...upstream 
observational guidance and model projections support somewhat 
better moisture profiles associated with this wave...especially 
later this afternoon and evening...as 850mb- 700mb relative humidity values 
increase to >80 percent. Some manifestation of these features 
already becoming evident on local radars this afternoon...with a 
general increase in lake effect activity this early afternoon. 
Now...focusing on the all important mesoscale lake effect details: 


For Northern Lake Michigan...quasi-stationary 280-290 degree flow 
expected to lock in later this afternoon and continue into the early 
morning hours...before backing more westerly towards Friday morning. 
Utilizing boundary layer wind streamline analysis...this flow looks 
to really target areas bounded by M-72 and M-68 and along and west 
of I-75...with greater emphasis perhaps along the M-32 corridor 
where streamlines suggest greatest Green Bay connection will exist... 
and in enhanced convergence zone downwind of Little Traverse Bay. 
Given parameters outlined above and a consistent Omega signal in 
the favorable dgz...solidly expect another 4...to perhaps 7 inches... 
will fall in this region...with lesser amounts surrounding this 
area. Still some concern for our advisories along the M-55 
corridor...with short fetch length possibly limiting accumulations. 
Still...with some earlier heavier snow showers in that area...and 
a recent spotter report of just over 2 inches of new snow...will 
play it safe and leave the advisory as is. Otherwise...all ongoing 
warning and advisories will remain...ending at 4 am Friday morning. 
Very possible some of these warning and advisories may need to 
eventually be extended for a few hours Friday morning...but given 
general lack of snowfall from this event already and no warning 
verification reports...will let overnight crew see how things 
unfold and punt the decision to them. Towards Friday morning... 
flow backs almost due westerly...pushing the better banding 
farther north. Loss of synoptic moisture and lowering inversion 
heights should also begin to take their toll...at least reducing 
snowfall rates. Per the usual...away from these favored lake snow 
areas...expect mostly cloudy sky tonight with occasionally snow 
shower and flurries and minimal accumulation. 


For Lake Superior...much more complicated picture for the eastern 
part of The Big Lake as flow has been very stubborn to back more 
westerly...preventing persistent banding structures from affecting 
northern Chippewa County. Both Montreal River Canada and MQT radars 
suggest this is about ready to change...with strong Luce County 
band already showing evidence of making the pivot into far western 
Chippewa County. Expect this trend to continue for the remainder of 
this afternoon and evening...with periods of heavy snow overspreading 
areas along and north of M-28. Excellent Lake Superior fetch 
length (200+ miles) and evidence of growing convergence signature 
from possible interior land breeze sets the stage for inch per 
hours snowfall rates under the better banding...with accumulations 
on the order of 3 to 8 inches north of the M-28... highest amounts 
near the point. Rapid drop-off expected south of M-28...with 
nothing more than some scattered light snow showers. Some concern 
that snow showers could get pushed entirely offshore late tonight 
as flow backs more westerly and land breeze intensifies (strong 
signal in both the GFS/NAM-wrf). Have trended towards this 
scenario...pushing accumulating snows farther north after 
midnight...with better snows focused near the point and along 
Whitefish Bay. Evening crew will have to closely monitor trends... 
with the full possibility much...if not all...of Chippewa County 
will be snow free towards Friday morning. 


Msb 


&& 


Long term.../issued at 357 PM/...Friday and beyond 


Friday...westerly flow lake effect will be ongoing Friday morning... 
with winds expected to back southwest as clipper low moves into the 
upper Midwest. Shifting snow bands and lowering inversion heights 
along with some drying should limit potential accumulations... 
heaviest probably in The Straits/tip of the mitt were 2-3 inches may 
occur. Forcing and deeper moisture will spread across the forecast 
area from the northwest Friday night...synoptic amounts should 
generally be on the light side (1-3 inches)...but southwest flow 
enhancement expected to increase snow intensity overnight around The 
Straits and down toward Grand Traverse Bay. Inversion heights climb 
toward 700mb by Saturday morning...along with strong low level 
convergence which should result in a band of heavy snow developing 
over far Northern Lake Michigan. 


Saturday...periods of snow will continue Saturday as surface low 
crosses the state...initial middle level wave forecast to bypass lower 
Michigan but a secondary piece of energy drops in during the afternoon. 
This second wave has some focused f-general forcing to help things along 
as well. Band of heavy snow expected along the Lake Michigan 
shoreline and into The Straits area Saturday morning...should push 
inland as the surface front advances east...and may bring a couple 
hour period of more intense snowfall to much of northern lower. 
Will probably need another round of watches/warnings at least along 
the northwest lower shoreline into Mackinac County for Friday 
night/Saturday...but will let the initial lake effect event clear 
out first since "headline weariness" seems to be setting in. 


For Saturday night...northwest flow sets up as clipper passes by to 
the east...with 850mb temperatures dropping once again this time 
closer to -20c. Inversion heights start out high and drop off 
overnight...and middle levels dry out...but several more inches of snow 
possible in favored northwest flow areas expected. 


Extended range (sunday through thursday)...large scale pattern next 
week will continue to feature mean long wave troughing across 
central/eastern North America...a feature that has been slowly 
retrograding over the past week. Long range disposition of this 
trough will be coming into question heading into middle month...as 
recent stable four wave pattern showing signs of breaking down. 
Will be interesting to see if this liberates the Great Lakes from 
the recent persistent cold/snowy weather for the latter half of 
December. Just some food for thought. In the meantime...the 
extended period starts with tight cyclonic flow in the wake of 
departing clipper...with a new push of cold air (850mb temperatures 
of -15c to -20c) offset by deep layer drying and warming aloft 
implied by rising heights. So expecting these latter factors to put 
a damper on significant snowfall potential. The idea of high 
pressure building into the state Sunday night has been persistent in 
the guidance...with expected clearing inland leading to a very cold 
night with many areas expected to drop below zero. As warm air 
returns to the Great Lakes the reprieve from snowfall will be short 
lived with a chance of more widespread warm advection snows 
Monday...and will continue this into Tuesday. The midweek period 
will become more interesting with a weak split in the flow 
developing as some energy digs toward the Gulf Coast...with more 
northern stream energy crossing the northern plains. Focus on the 
midweek period has been on whether or not a storm system would spin 
up in association with either of these features. Operational GFS 
has been warming to the split flow idea and has been taking the 
southern stream energy and spinning up various storm evolutions over 
the past three runs...04/00z run west of the Appalachians...04/12z 
run back closer to the East Coast. 24/00z ggem develops strong 
systems with both pieces of energy...hitting the state Tuesday 
(similar to its idea a couple days ago). Guidance is going to 
struggle with this...so for now best bet is to try and keep 
Wednesday dry...and start Thursday out with a chance for snow. 
Needless to say...temperatures through the period will remain below 
normal. Some moderation expected Monday/Tuesday as southerly winds 
develop. 


Jpb 


&& 


Marine.../issued at 357 PM/ 


Solid Small Craft Advisory conditions all nearshore waters except nearshore zones 
along South Shore of eastern Upper Michigan tonight with strong 
over-water instability supporting frequent gusts to 25 knots or 
greater. In addition...long west-northwest flow Northern Lake Michigan fetch 
length should easily support Small Craft Advisory wave conditions along the 
northwest Michigan coastline. 


Low level flow will back around from west to southwest Friday ahead 
of next clipper low. Small Craft Advisory conditions appear likely 
by Friday afternoon/night...perhaps even some gale force gusts on 
Lake Michigan. Cold front crosses the western lakes Saturday... 
shifting winds to the northwest. Post-frontal winds expected to be 
strong given cold advection and isallobaric components...could push 
winds above gale force by Saturday night. 


Msb/jpb 


&& 


Aviation.../issued at 1238 PM/...valid for 18z tafs 


Lake effect snow showers will keep all sites alternating from VFR 
to MVFR conditions over the next 24 hours. Occasionally IFR/LIFR 
conditions are possible in the heaviest snow showers...but will 
not specifically mention in tafs owning to timing and exact 
placement issues. 


Msb 


&& 


Apx watches/warnings/advisories... 
Michigan...Winter Weather Advisory until 4 am EST Friday for miz023-029- 
031>033. 
Winter Storm Warning until 4 am EST Friday for miz016-017- 
019>022-025>028. 
Lake effect snow warning until 10 am EST Friday for miz008. 
Lm...Small Craft Advisory until 7 am EST Friday for lmz323-342- 
344>346. 
LH...Small Craft Advisory until 7 am EST Friday for lhz345-347>349. 
Ls...Small Craft Advisory until 7 am EST Friday for lsz321-322. 


&& 


$$ 

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