363 
fxus63 kapx 041741 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
1241 PM EST Thursday Dec 4 2008 


Synopsis.../issued at 413 am/ 


Cold air flowing across the relatively warm waters of the Great 
Lakes will produce lake effect and lake enhanced snowfall through 
the upcoming weekend. Lake effect snow showers will intensify this 
afternoon and tonight as an upper level disturbance pushes across 
the region. A clipper system is forecast to cross the state 
Saturday...which will bring more widespread snowfall to northern 
Michigan...as well as a period of heavier enhanced snowfall off of 
Lake Michigan Friday night into Saturday. 


Kas 


&& 


Short term.../issued at 1026 am/...today 


Much anticipated lake effect snow event trying to gets it act 
together this morning...with local radar showing somewhat better 
banding structures becoming evident in west-northwest flow 
regime...with pockets of inch per hour snowfall rates 
(although...these are still highly transitory). However...despite 
great over-water instability (pushing 20c)...low inversion levels 
(12z kgrb sounding inversion of only 860mb)...no Lake Superior 
connection...and lack of synoptic support are keeping things 
relatively in-check over northwest lower. A little different story 
north of the mighty Mac...with enhanced convergence along southwest 
intruding remnant Ontario cold air drainage flow leading to a rather 
healthy Eastern Lake Superior band pivoting into Luce County...all 
the while keeping just scattered lighter snow shower activity over 
much of eastern upper. Additional snowfall amounts and headline 
management remain forefront for the rest of the day...especially as 
rather impressive upstream wave begins to flex its muscle over the 
lake waters. 


For Lake Michigan...upstream acars and radiosonde observation soundings confirm latest 
model guidance of a rapid increase in inversion levels this 
afternoon (pushing 11kft by evening) and maximum Omega in favorable dgz. 
This should allow the lake machine to increase in intensity through 
the afternoon...with persistent west-northwest flow (290ish) targeting the 
traditional snowbelts north of M-72 and along and west of I-75. 
Therefore...will leave inherited snowfall amounts of an additional 3 
to 4 inches in this area untouched. As always...locally heavier 
amounts are certainly possible...especially with the belief banding 
structures should remain through the afternoon with deep northwest 
lower Michigan snowpack and low sun angle preventing much diurnal 
disruption. Have some concern along the M-55 corridor counties with 
limited fetch length (~60 miles) possibly hindering snowfall 
accumulations. Still...would like to see how everything transpires 
with passage of aforementioned wave this afternoon before cutting 
accumulations in this area. In a nutshell...will leave current 
headline and snow amounts as is for northwest lower Michigan. 


For Lake Superior...much like Lake Michigan...a rapid increase in 
inversion levels is expected this afternoon...with maximum Omega pegged 
in the fluff producing dgz. Would also expect a quick backing of 
winds to the west-northwest as drainage flow ceases with diurnal response. 
850mb-700mb streamline analysis continues to point to areas north of 
M-28 as under the gun...including the Soo by later this afternoon. 
With excellent upstream fetch length...expect an inch per hour 
snowfall rates to easily be attained at times...with additional 
snowfall amounts approaching 6 inches near the point and 2 to 3 
inches at the Soo. Thus...current warning will remain in 
effect. 


As northern michiganders are used to...away from the favored lake 
areas expect just scattered snow showers with light accumulations. 
Quick peek at tonight continues to show excellent lake snow 
parameters through about 9z in areas favored by 280 to 290 degree 
flow...with several additional inches expected. 


Msb 


&& 


Long term.../issued at 413 am/...tonight and beyond 


Models are certainly in decent agreement heading into the upcoming 
weekend...so will take a blended approach. 


Flow remains 280-290 through tonight...with enhanced snowfall 
continuing in the snowbelts. The best snow accumulations will occur 
tonight with an additional 4 to 7 inches expected north of M-72 in 
the warning area and near Whitefish Bay in eastern upper. 


Flow will begin to back around to the southwest on Friday with 
dry air again invading the middle levels...pushing inversion heights 
down to around 5kft. Still plenty cold enough for lake effect 
snow...but we should see a significant reduction in intensity with 
relatively minor snow accumulations. 


As the clipper pushes in the western lakes Friday night...we will 
likely see an enhanced band of snowfall develop across the long axis 
of Lake Michigan...pointed into Mackinac and Chippewa counties. At 
this time...it does not appear the band will set up long enough to 
produce warning criteria snowfall...but will likely be a solid 
advisory event. However...not planning to hoist any additional 
headlines at this time...so we can remain more focused on the 
ongoing headlines. As the Alberta clipper drags a surface trough 
across the area...the band of enhanced snowfall will likely be 
dragged onshore into northwest lower Michigan on Saturday... 
producing a period of low visibilities and heavy snowfall during 
the morning to early afternoon hours across northwest lower 
Michigan. Regardless...all of northern Michigan will see a period 
of snowfall with the large scale ascent provided by the clipper 
system. Finally as the system departs Saturday evening...we will 
transition to lake effect snow in the north-northwest flow favored snowbelts. 


All in all...much below normal temperatures and snowy conditions 
will continue trough the upcoming weekend and likely beyond the 
weekend. 


No changes made were made to the forecast beyond Saturday night. 


Kas 


&& 


Marine.../issued at 413 am/ 


West-northwest winds continue to gust up over 20 knots occasionally in the 
nearshore areas. However...winds have weakened enough across the 
Southern Shores of Mackinac County to allow the Small Craft Advisory to be cancelled 
for these zones...including The Straits. Also...went ahead and 
cancelled the Sturgeon Point to Alabaster zone. All other zones 
will continue to see wind gusts up to 25 knots through Thursday 
night and extended the Small Craft Advisory accordingly. 


Will need to continue to monitor the potential for gales Friday 
night into Saturday as the gradient tightens up ahead of our next 
low pressure disturbance. However...preferring to wait at least one 
more forecast package before any headlines are issued. 


Kas 


&& 


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 lhz347-348. 
Ls...Small Craft Advisory until 7 am EST Friday for lsz321-322. 


&& 


$$ 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)