Weather

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Area forecast discussion 
National Weather Service Grand Rapids Michigan 
1145 PM EST Monday Jan 5 2009 


Latest update...aviation... 


Synopsis...(407 PM EST Monday Jan 5 2009) 
high pressure over Ohio will produce mostly clear skies across 
southwest lower Michigan tonight. Clouds will return toward 
daybreak Tuesday across far Southern Lower Michigan and spread 
northward to central lower Michigan by middle day Tuesday. These 
clouds will be ahead of a developing low pressure that will move 
over the area late Tuesday night into Wednesday. This system will 
bring a prolong period of light snow Tuesday night through Wednesday 
night. Many areas will see three to six inches of snow over this 36 
hour time frame. 


&& 


Short term...(407 PM EST Monday Jan 5 2009) 
(tonight through Wednesday night) 
main focus continues to be on the middle week snow potential. The 
models continue to show the southern and northern stream systems 
merging over Michigan late Tuesday night or early Wednesday. This 
will keep the best moisture and energy to the east of the area. 
What will result will be a long period of light snow. As the 
systems merge the upper level open trough closes off as an upper 
low. This will slow the entire system down...resulting in the 
lengthy snowfall. The steadier snow will move in Tuesday 
night...spreading from south to north. The snow will persist in 
most areas through Wednesday night. Expecting that most areas will 
see three to six inches of snow over this 36 hour period. 


Tonight will be mostly clear resulting in a chilly night. Min temperatures 
in the 10 to 15 degree will be common...although lows will be in the 
single digits across the interior north. 


Have delayed the onset of the precipitation until Tuesday night for most 
locations. Tuesday morning will start out partly sunny...then 
clouds will thicken from south to north through middle day. With the 
slower merging of the northern and southern stream systems the 
deeper moisture does not arrive until close to 00z Wednesday. Will 
leave low probability of precipitation along the I-94 corridor for Tuesday afternoon... 
elsewhere it should remain dry through 00z. 


The snow will then spread from south to north Tuesday night. The 
snow will become enhanced by Lake Michigan Wednesday afternoon and 
Wednesday night as colder air wraps in on the back side of the low. 
This may very well be the period that the western County Warning Area sees the bulk 
of its snow and have trended probability of precipitation higher there. Winds will become 
rather brisk Wednesday night leading to drifting of the newly fallen 
snow. 


&& 


Long term...(407 PM EST Monday Jan 5 2009) 
(thursday through monday) 
Middle Range models showing good continuity with previous runs and with 
each other through the weekend. The European model (ecmwf) has under gone a large 
shift for next week. Forecasters across the area are going with the 
GFS solution. Made only small changes to keep our grids consistent 
with surrounding offices. 


As the long term begins on Thursday... lake effect snow will be 
ongoing as a low pressure system moves away to the east. The snow 
should diminish and end Thursday night. 


A northern stream low pressure system will approach from the west on 
Friday... bringing snow back into the forecast. The surface low is 
forecast to pass between upper and lower Michigan Friday night. 
Expect strong... cold northwest winds in it/S wake. Lake effect snow 
and wind chills below zero are both likely Saturday night into 
Sunday. Sunday afternoon and evening may see clearing skies... highs 
in the teens and lows falling into the single digits above zero. 


The 12z GFS run has another northern stream low approach the area 
Monday. Meanwhile... the European model (ecmwf) 00z run has high pressure lodged over 
the region. Went with the GFS and snow for Monday. 
&& 


Marine...(407 PM EST Monday Jan 5 2009) 
will cancel the southern portion of the Small Craft Advisory as 
winds have become more southwest...limiting the fetch over the 
southern portion of the lake. Winds will continue to pivot to the 
southeast by daybreak Tuesday...allowing waves to diminish elsewhere 
over the nearshore by middle day. So have shorten the time frame of 
the advisory across the north. Winds remain easterly Tuesday 
night...keeping waves lower. Another period of stronger winds will 
develop from the west on Wednesday on the back side of the low. 
Waves will be building through the day. 


&& 


Aviation...(1145 PM EST Monday Jan 5 2009) 
VFR weather to prevail through 00z Wednesday. Middle level clouds will 
arrive during Wednesday morning from the south. A lower VFR deck should 
also arrive from the south later Tuesday afternoon. Light winds tonight 
will become east southeast on Tuesday. Some snow could develop from 
south to north after 02z Wednesday. 


&& 


Hydrology...(407 PM EST Monday Jan 5 2009) 
area rivers continue to return closer to normal as the heavy rain 
and snowmelt from a week ago has now made its way through the water 
system. The warning that was in effect for Robinson township and 
Maple Rapids was cancelled this morning as the river stages dropped 
below flood stage. 


As for the upcoming week...we are not expecting any significant 
melting of snowpack on the ground...or any heavy rainfall. 
Temperatures are expected to trend colder with accumulating snow 
expected through much of the week. This could end up causing some 
ice jams to form at typical locations. 


&& 


GRR watches/warnings/advisories... 
Michigan...none 
lm...Small Craft Advisory in effect through Tuesday morning Holland 
to Manistee. 
&& 


$$ 


Synopsis: jk 
short term: jk 
long term: iod 
marine: jk 
aviation: mjs 
hydrology: jk