191 
fxus63 kgrr 041818 
afdgrr 


Area forecast discussion 
National Weather Service Grand Rapids Michigan 
118 PM EST Thursday Dec 4 2008 


Latest update...short term... 


Synopsis...(412 am EST Thursday Dec 4 2008) 
colder air will continue moving in over the Great Lakes into the day 
on Friday. This will allow for lake effect snow showers to be 
expected right on through the remainder of the week. Significant 
amounts of lake effect are not expected...however some areas will 
see the snowpack gradually build. An area of low pressure will move 
in across the region late Friday night and during the day on 
Saturday. This system will bring some snow to most of the 
area...with lake enhancement increasing amounts a bit along most of 
the Lakeshore. 


&& 


Short term...(118 PM EST Thursday Dec 4 2008) 
(rest of today through saturday) 


I have issued a lake effect Snow Advisory for out southwest six most 
counties from late this afternoon through noon Friday. More details 
on this will follow shortly. 


The shortwave heading our way from WI will increase inversion height 
to near 10000 feet and with the dgz in the maximum lift zone.... and 
reports of around 1 inch in Grandville already... it makes sense 
that a significant snowfall event is immanent. The heaviest 
snowfall will be from late this afternoon into middle morning Friday. 


The next system will likely produce adviosry snowfall amounts 
Saturday but more on that later too. 




&& 


Long term...(412 am EST Thursday Dec 4 2008) 
(saturday night through wednesday) 
main story in the long term will be snow and cold. Surges of cold 
air will push into southwest lower Michigan during weekend and into 
the middle of next week. The first surge will rush in Saturday night 
in the wake of a clipper system moving off to the east. 850mb temperatures 
are forecast to plunge into the middle teens c below Zero. Lake 
effect will continue into Sunday...before ridging ends much of the 
activity into Sunday night. 


Another clipper will move through the region Monday and Monday 
night. The associated cold front pushes through the area Tuesday 
morning. Arctic air pours into the Great Lakes region into middle 
week...with 850mb temperatures plunging well into the 20s below zero c. 


Some synoptic scale snow can be expected Monday and Monday night as 
the system moves through...followed by good chances for lake effect 
Tuesday into Wednesday. 


Tried to nudge down temperatures in the extended...given what has been a 
persistent signal by the GFS to forecast a cold period. Temperatures 
for the middle of next week may very well be deep winter type 
numbers with highs in the teens and lows dipping toward zero. Did 
not go that cold yet...but have begun the trend in that direction. 


&& 


Marine...(1040 am EST Thursday Dec 4 2008) 
I extended the Small Craft Advisory until 00z Saturday since the winds and waves are 
more than strong and or large enough. We may end up with a Gale 
Warning for late Friday night on later forecasts due the strong 
system coming in from the northwest for Saturday. Freezing spray 
potential will increase at that time with colder air moving in. 


&& 


Aviation...(1243 PM EST Thursday Dec 4 2008) 
lake effect snow showers persist early this afternoon. Temperature 
inversion heights climb toward evening and lift increases as an 
upper level disturbance will further enhance the snow showers. It 
appears the lake effect should get fairly intense between 22z and 
06z with LIFR likely within the heavier snow showers. Beyond 06z 
the short wave will be through and the lake effect is expected to 
diminish slightly. There could be a diurnal component to this 
activity also with some intensification possible toward sunrise on 
Friday. At this point it appears the snow showers should diminish 
then by middle/late Friday morning. Wind flow through the next 24 
hours will be west-northwest which will favor azo and GRR getting more frequent 
snow showers...however the remaining taf sites will also see 
occasional snow showers with IFR conditions. 


&& 


Hydrology...(412 am EST Thursday Dec 4 2008) 
with temperatures expected to generally be below freezing through 
the next week...little to no runoff can be expected into area 
streams and rivers. It does appear that we will build a snowpack 
with lake effect snow showers expected most days and a few systems 
moving through. 


&& 


GRR watches/warnings/advisories... 
Michigan...Lake effect Snow Advisory for Ottawa...Kent...Allegan... 
Barry...Van Buren and Kalamazoo counties from 5 PM this evening 
until noon on Friday. 
Lm...Small Craft Advisory in effect through 00z Saturday. 


&& 


$$ 


Synopsis: njj 
short term: wdm 
long term: Duke 
marine: njj / wdm 
aviation: jk 
hydrology: njj