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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
1243 PM EST Thursday Dec 4 2008 


Latest update...aviation... 


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...(1040 am EST Thursday Dec 4 2008) 
(rest of today through saturday) 
I have updated the forecast to increase the area of conditional pop 
through this afternoon. I also increased the forecast snowfall 
amounts for today to 1 to 2 inches centered on US-131. That was 
based on radar trends and the infrared and water vapor images confirming 
what the 12z RUC suggests.... that is core of the polar jet has 
passed east of the southwest Michigan. With the VAD wind suggests 
the inversion height has increased about 1000 feet from 5000 feet prior 
to 14z to about 6000 feet at 15z. Tamdar soundings shows similar 
trends. 850 mb temperature continues to fall from around -13c at 12z over 
Lake Michigan to near -15c by 18z. Surface observation show 1to mile visible at GRR 
lan azo rqb at 15z. Also the RUC shows the dgz has become saturated 
and will remain so the rest of the day. The best lift is between now 
and 20z. The mean boundary layer wind is 270 degrees around 25 
knots. Thus I believe we will see snow all day over most of the County Warning Area 
down wind of Lake Michigan between Route 10 and I-94. South of I-94 
winds are not over the Lake Long enough to really do much in terms 
of snowfall. 


Next speed maximum/short wave trough is now diving southeast over the 
Dakotas and Minnesota. This system will be enough to send the polar jet 
south of the area tonight. With the approach of the upper 
systems....inversion heights are expected to increase to around 8-9k feet. 
Low level flow is expected to remain mainly west-northwest through the night. 
The synoptic forcing in addition to the favorable over-lake 
instability will increase the intensity of the snow showers. Models 
are indicating that a good deal of low level convergence will 
develop late this evening and last into the overnight hours. The 
favored areas will be roughly south of a line from Grand Haven to 
Charlotte. The limited inversion heights should keep this pickup in lake 
effect from getting too out of hand. We do not have the confidence 
any location will see warning criteria accums...however we do 
believe there is a good chance that an advisory may be needed. We 
have trended amounts up...and enough time exists that the day shift 
can take another look at possible headlines. 


Inversion heights will fall a bit as the short wave moves away from the 
area on Friday morning. Winds are expected to shift from the west-northwest to 
more SW by late Friday afternoon. This will help to keep any one area 
from seeing much snow. The focus of better snow accums will 
transition from the SW corner of the County warning forecast area to the northwest corner. 


The next couple of short waves will then dive southeast toward the area 
late Friday night and during the day on Sat. It will be the second 
short wave that will bring a clipper type surface low across the northern 
portion of the state. The system itself will be potent...and would 
bring a couple of inches of snow by itself. H850 temperatures do not warm 
all that much ahead of it...leaving Delta T/S at least in the middle 
teens across the area. The SW flow combined with almost a 
non-existent inversion and the over-lake instability will set up 
what looks to be a potentially significant lake enhancement event 
for the northwest portion of the County warning forecast area. Some details will need to be worked 
out...but there is potential for some warning criteria snows. This 
will be late 4th period/5th period...so we will hold off on any 
watch for now. 


&& 


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...none. 
Lm...Small Craft Advisory in effect through 00z Saturday. 


&& 


$$ 


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

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