683 
fxus63 kgrr 071734 
afdgrr 


Area forecast discussion 
National Weather Service Grand Rapids Michigan 
1234 PM EST Wednesday Jan 7 2009 


Latest update...aviation.. 


Synopsis...(440 am EST Wednesday Jan 7 2009) 
an area of low pressure extending from Ohio to West Virginia this 
morning...will gradually move northeast through the day on Thursday. 
This system will remain close enough to the area through Wednesday 
night to continue to bring light snow to the area. Snow 
accumulations from today through Thursday will generally range from 
2 to 4 inches across the area. Some locally higher amounts are 
likely toward the Ludington...South Haven...Kalamazoo...and Hart 
areas where snow will be enhanced a bit from Lake Michigan. 


Another system will then approach the area during the day on Friday. 
This system is expected to spread snow across the area by Friday 
afternoon and continue into early Saturday. Temperatures will trend 
down through the period. 


&& 


Short term...(757 am EST Wednesday Jan 7 2009) 
(today through friday) 


Allowed the Winter Weather Advisory for freezing drizzle to expire 
now that all the precipitation has changed over to snow. Previous 
discussion follows. 


Surface lows as of 09z this morning extend from WV...to Northern Ohio...with a 
trough hanging back across lower Michigan and WI. Area of light snow 
associated with the deformation band extending from just south of 
James Bay through MO is now moving spreading across the entire County warning forecast area. 
This feature moving overhead is bringing deeper moisture across the 
area...which is helping transition any fzdz over the southeast counties to 
-sn as the dgz is saturated. Generally speaking...the forcing 
associated with the deformation band is fairly weak. Even with 
deeper moisture moving in...only light snow is expected across the 
area with an inch or two expected for most areas today. Another inch 
or two will be possible tonight as the trough sinks south. 


Some enhancement of the snow is still expected over the northwest corner of 
the County warning forecast area and a good portion of the I-94 corridor. This occurs as the 
flow becomes west-northwest and the trough on the backside of the low sinks 
south through the area later this afternoon and tonight. Models are 
showing a pretty good band of convergence...especially extending 
from Holland to the Battle Creek area. This forcing and deep 
moisture in place is initially a little concerning. Delta T/S only 
around 13c or so...expected snow ratios in the lower teens...and 
main forcing below the dgz are factors that should limit snow accums 
from getting too out of hand. We considered issuing an advisory for 
the snow...but the confidence of reaching advection criteria is just not 
there at this time to pull the trigger. 


Some lake effect will linger into Thursday morning...however inversion 
heights will be falling rapidly as the flow aloft will be 
transitioning more anti-cyclonic in the afternoon. An inch or so of 
additional accumulation will be possible across the northwest and SW...with 
little inland. 


The next feature then is the Alberta clipper poised to move through 
the County warning forecast area from Friday into early Sat. Energy supporting this expected 
low is still over the northern Pacific just south of the Gulf of Alaska. 
Models are in decent agreement in taking the low somewhere across 
lower Michigan. Accumulating snow looks likely...especially further north 
closer to the low. It does not look like much lake enhancement 
potential ahead of the system with southeast flow and h850 temperatures warming to 
the lower negative single digits. 


&& 


Long term...(440 am EST Wednesday Jan 7 2009) 
(friday night through tuesday) 
long term period continues to feature chances for snow...with cold 
air forecasted at the very end of the period (tuesday and beyond). Long 
term will begin on Friday night with a northern stream shortwave 
swinging through the region...with accumulating snow. Both the 
European and GFS keep things cold enough for all snow. The NAM 
appears to be too warm at 850mb/S a result of a low that is likely 
too deep. A push of colder air filters in behind the departing wave 
on Saturday...with 850mb temperatures falling into the -10 to -15 c range. 
These temperatures are not all that cold for this time of year...but cold 
enough for some lake effect. Moisture depth decreases on Saturday... 
which will likely keep the lake effect in check...as will Delta T/S 
that are not very impressive. 


Kept Sunday and Sunday night dry at this point...but models seem to 
be trending toward bringing a low through the Great Lakes in this 
time frame. Decided to hold off for now in introducing snow...but we 
may need to add snow to these periods...the only dry periods at this 
point in the long term. 


Snow is in the forecast again Monday through Tuesday. Its cold 
enough for lake effect on Monday...with even colder air poised to 
surge into the area on Monday night. It appears a very cold period 
is on tap for Tuesday stretching into much of next week. The cold 
snap beginning Monday night occurs with a surge of air that has 
origins in the Arctic from the North Slope of Alaska and the Yukon 
territory and points north even. The models have been pretty 
consistent up to this point forecasting this cold snap...but that 
said we are still talking about 150hrs into the forecast and beyond. 
Plenty of Arctic air outbreaks are forecast by the models this far 
out that do not verify. This has both the GFS and European on board 
though...with the GFS being the colder of the two models at this 
point. Both bring -20c air into the region by Tuesday evening...with 
the GFS wrapping -30 c air around Lake Michigan into Indiana by Wednesday 
at 00z. It will be interesting to see if the models continue this 
cold...or will they warm with time...which is the usual tendency. 


&& 


Marine...(440 am EST Wednesday Jan 7 2009) 
easterly flow across the nearshore waters early this morning will 
transition to a west/northwest flow as the surface low pulls further 
east today. This will allow somewhat colder air to move in on the 
west/northwest flow and help to increase the winds and waves. Models 
have trended down a notch with wind speeds over the waters. It now 
seems like this event will stay within Small Craft Advisory criteria 
and is expected to run through the day on Thursday. 


Next marine event and set of headlines looks to come ahead of the 
next system poised to move across the area late Friday and into 
Saturday 


&& 


Aviation...(1234 PM EST Wednesday Jan 7 2009) 
light snow is expected to continue during the next 24 hours. Expect 
visibilities generally in the 2-4sm range and ceilings around 1.5k feet. 




&& 


Hydrology...(440 am EST Wednesday Jan 7 2009) 
no immediate Hydro concerns for the next couple of days as all 
precipitation will be in the form of snowfall. The biggest concern 
will be the colder weather pattern shaping up over the course of the 
next week. This colder weather will likely produce some ice jams at 
the normally favored locations. This will be something that will be 
monitored. 


&& 


GRR watches/warnings/advisories... 
Michigan...none. 
Lm...Small Craft Advisory Wednesday afternoon through Thursday from 
St. Joe through Manistee. 


&& 


$$ 


Synopsis: njj 
short term: njj/Duke 
long term: Duke 
marine: njj 
aviation: 93 
hydrology: njj 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)